Screw Manufacturing Method, Whirling Cutter, And Screw Manufacturing Machine

Abstract

A screw manufacturing method by thread whirling machining and others are provided which can solve problems due to thread rolling and cutting and which inhibits moving paths of inserts from interfering with a curved line of a desired screw upon going in and out, thereby providing the screw with a targeted curved line. In the method of manufacturing a screw, a mount angle of the screw is calculated by formulae below in case that a lead angle of the screw is different from the mount angle. mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) in case .DELTA.T>0, {(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of Japanese Patent Application No. 2009-294915 filed Dec. 25, 2009 in the Japan Patent Office, the whole disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The present invention relates to a screw manufacturing method by a thread whirling method, and a whirling cutter and a screw manufacturing machine used in the thread whirling method. Accordingly, the present invention can be applied to a field of manufacturing ordinary screws, such as medical screws, worm screws, metric screw threads, and others.

BACKGROUND ART

[0003] A conventionally known method of manufacturing ordinary screws (mechanical screws) is, for example, thread rolling. In thread rolling, thread rolling dies corresponding to a specific screw-thread shape are used. Thus, thread rolling is preferred in the case of manufacturing a mass of single products.

[0004] Other than thread rolling, a screw manufacturing method by turning is known. In the method by turning, a work piece being rotated is cut by a turning tool. Turning is preferred in the case of manufacturing a wide variety of products in small quantities.

[0005] Separately from these screw manufacturing methods, a thread whirling machining is known as a manufacturing method of medical screws such as implant screws and bone screws, for example (see Patent Document 1).

[0006] The thread whirling machining is a screw manufacturing method which uses an annular whirling cutter that is fixed to a tool spindle of a lathe and is rotatable around its rotation axis, and a main spindle that holds a rod to be machined (work piece) which is a material for manufacturing a screw and is rotatable.

[0007] In detail, the machining method uses a whirling cutter in which a plurality of inserts are radially arranged. A work piece held by the main spindle is inserted into a center through hole of the whirling cutter. Also, the whirling cutter is inclined at a predetermined angle (mount angle) with respect to a center axis of the work piece. In this state, the work piece is moved forward in an axial direction while being rotated in a predetermined direction. At the same time, the whirling cutter is rotated at a rotation speed higher than a rotation speed of the work piece, thereby cutting a thread by one or a plurality of inserts.

[0008] The mount angle set upon the above-described thread whirling machining has been generally set equal to a lead angle in a design drawing of a screw.

PRIOR ART DOCUMENT

Patent Document

[0009] Patent Document 1: U.S. Pat. No. 6,877,934

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

[0010] In case that screws are manufactured by the above-described thread rolling, thread rolling dies corresponding to a specific screw-thread shape are used. Thus, thread rolling is not adequate to manufacturing of a wide variety of products in small quantities.

[0011] Also, in case that screws are manufactured by turning, the turning is performed by a turning tool. Due to a cutting load, it is difficult to cut a screw thread in one pass. The screw thread is formed in a plurality of passes. Thus, the machining requires time. Especially in a case of manufacturing a long screw, it is difficult to do the cutting work piece at a time. It is necessary to form the screw thread in a sequential manner of, after forming several threads, forming another several threads, for example. Since the machining includes joining, there is a problem that machining accuracy at a joined part is low.

[0012] Further, in the case of medical screws, as compared to screws used in ordinary machines, there are exceptional circumstances such that a difference between a valley diameter and an outer diameter is large, a shape of the screw thread is special (cross-sectional shape is orthogonal to a direction of a series of threads), etc. Thus, upon machining of medical screws, a problem as below exists.

[0013] Particularly, as noted above, if a mount angle in thread whirling machining is set equal to a lead angle, it has been difficult to manufacture a screw of a desired shape, depending on a targeted work piece shape (screw-thread shape).

[0014] The first reason why it is difficult to obtain the targeted screw-thread shape is because medical screws have special shapes. The second reason is because, since thread whirling machining is a machining method by a milling tool in which inserts are attached toward a center of a whirling cutter and the whirling cutter rotates, moving paths (machining paths) of the inserts interfere with a curved line of a screw. That is, the inserts may shave a portion which should not be ground when going in and out of the work piece.

[0015] In other words, the problem is that shaving is performed in both inward and outward cutting (as shown in FIG. 23, there are triangular gray zones (=interfering portions) in both an outer diameter side and a valley side of a screw). That is, if interference occurs to both portions on the screw outer diameter side and the base end side (valley side), it becomes difficult to fasten the screw with good accuracy. Further, backlash of the screw may occur.

[0016] However, if the interference occurs to either of the portions on the screw outer diameter side or the screw base end side (valley side), there is not much problem in using the manufactured screw.

[0017] The problem due to the above noted interference is significantly exhibited when a screw having a special shape such as a medical screw is manufactured. The same problem may sometimes occur to other ordinary screws.

[0018] The present invention was made in view of the above problem. One object of the present invention is to provide a screw manufacturing method by thread whirling machining, and a whirling cutter and a screw manufacturing machine used in thread whirling machining, wherein the problem due to thread rolling and turning can be solved. In the present invention, moving paths of the inserts are inhibited from interfering with a desired curved line of a screw upon both going in and out. Thereby, a targeted curved line of a screw is provided in a preferred manner.

Means to Solve the Problems

[0019] A first aspect of the present invention in order to achieve the above object provides a screw manufacturing method for manufacturing a medical screw. The method uses: an annular cutter member (e.g., whirling cutter) that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a holding portion (e.g., main spindle) that holds a work piece for forming the medical screw and is rotatable. The cutter member is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle). When a lead angle of the medical screw is different from the mount angle, the mount angle is calculated by formulae (1), (2), (3), (4) and (5) below.

mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) [0020] in case .DELTA.T>0,

[0020] {(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4) [0021] in case .DELTA.T<0,

[0021] {(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5)

[0022] where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

[0023] In the screw manufacturing method of the present invention, even if a lead angle of a medical screw, for example, is designed to satisfy a formula (X) below or the medical screw has a special shape specific to medical screws, it becomes difficult for inserts to interfere with the medical screw upon rotating the work piece and the cutter member, as shown in TABLES 1 to 3 of later-explained first to third embodiments.

[0024] Particularly, if the mount angle is set smaller (shallower) than the lead angle (i.e., 0<.DELTA.T), it becomes difficult to hit especially a side face of a tip end of the screw thread. Conversely, if the mount angle is set larger (deeper) than the lead angle (i.e., 0>.DELTA.T), it becomes difficult to hit especially to a side face of a base end of the screw thread. Here, .DELTA.T indicates an adjustment range of the mount angle.

[0025] Hereinafter, the above-described respective formulae will be explained.

[0026] As shown in the above formula (3), a minimum value of D1 is the screw valley diameter, and a maximum value thereof is the screw outer diameter. As shown in the formula (2), when D1=the screw valley diameter, .DELTA.T={(screw valley diameter)-{screw valley diameter+screw outer diameter)/2}. Similarly, when D1=the screw outer diameter, .DELTA.T={(screw outer diameter)-{screw valley diameter+screw outer diameter)/2}. Accordingly, when D1 is equal to the screw valley diameter or the screw outer diameter, the fluctuation range .DELTA.T with respect to {screw valley diameter+screw outer diameter)/2} takes a maximum value (also referred to as a maximum fluctuation range).

[0027] Here in D1, explanation will be given on a value of D1 between the minimum value and a pitch diameter, and the value of D1 between the pitch diameter and the maximum value.

[0028] By setting the fluctuation to 100% when .DELTA.T=maximum fluctuation range, values of .DELTA.T in fluctuations from 0 to 100% can be calculated. Particularly, when the fluctuation is 50%, .DELTA.T=maximum fluctuation range/2. The values of .DELTA.T determined as such are given to the above formula (2) so that the value of D1 between the minimum value and the pitch diameter, and the value of D1 between the pitch diameter and the maximum value can be determined. By providing the acquired D1 to the above formula (1), the mount angle can be calculated.

[0029] Further, as shown in TABLES 1 to 3 of the later-explained first to third embodiments, by setting the range of .DELTA.T to the above formulae (4) and (5), it becomes difficult for the inserts to interfere with the medical screw.

lead angle=tan.sup.-1{n.times.pitch/(n.times.pitch diameter)} (X) [0030] where the pitch diameter={screw valley diameter+screw outer diameter)/2}, and n indicates a number of threads.

[0031] Here, "n.times.pitch(P)" is a value called a lead (L), which is a distance of move when the screw is rotated once. The pitch diameter (D) is defined by JIS B0101 1215, the lead angle is defined by JIS B0101 1208, and the pitch is defined by JIS B0101 1206. Other terms also indicate meanings defined by JIS, respectively. Using the pitch diameter in calculation of a lead angle is general to a person skilled in the art (the same applies to below).

[0032] According to the present invention, moving paths of the inserts are inhibited from interfering with a desired curved line of a screw upon both going in and out. Thereby, the screw provided with a targeted curved line can be manufactured in a preferred manner.

[0033] Particularly, in the present invention, the interference can be inhibited from occurring to both the portions on the outer side of the screw and the base end side (valley side) of the screw. Thus, upon fastening, etc., using the manufactured screw, the screw can be rotated without problem. That is, there is no big problem in using the manufactured screw.

[0034] Here, the interference upon going in means the interference when the insert enters the curved line of a screw, and the interference upon going out means the interference when the insert goes out of the curved line of the screw, upon machining the screw.

[0035] Also in the present invention, as compared to thread rolling, a wide variety of products in small quantities can be easily manufactured. Moreover, as compared to turning, machining time can be shortened. Also, continuous machining can be applied to one piece of work piece. Thus, a joining process is not necessary. Machining accuracy is advantageously high. [0036] A second aspect of the present invention provides a screw manufacturing method for manufacturing a worm screw. The method uses: an annular cutter member that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a holding portion that holds a work piece for forming the worm screw and is rotatable. The cutter member is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle). When a lead angle of the worm screw is different from the mount angle, the mount angle is calculated by formulae (1), (2), (3), (4) and (5) below.

[0036] mount angle=tan.sup.-1{n.times.pitch/(n.times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) [0037] in case .DELTA.T>0,

[0037] {(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4) [0038] in case .DELTA.T<0,

[0038] -{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5)

[0039] where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

[0040] The present invention is an invention of manufacturing a worm screw. The same effect as in the first aspect can be achieved.

[0041] Particularly, the screw manufacturing method of the present invention has effect such that it becomes difficult for the inserts to interfere with the worm screw, as shown in TABLES 4 and 5 for later-explained fourth and fifth embodiments, upon rotating the work piece and the cutter member, for example, in order to manufacture the worm screw of which lead angle is designed to satisfy the formula (X) above.

[0042] Specifically, in a worm screw having a large difference between a valley diameter and an outer diameter and having a special shape of the screw thread (cross-sectional shape is orthogonal to a direction of a series of threads), use of the screw manufacturing method of the present invention can shorten machining time while maintaining machining accuracy. [0043] Further, a third aspect of the present invention provides a screw manufacturing method for manufacturing a metric screw thread. The method uses: an annular cutter member that has a plurality of inserts radially arranged and is rotatable on its rotation axis, and a holding portion that holds a work piece for forming the metric screw thread and is rotatable. The cutter member is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle). When a lead angle of the metric screw thread is different from the mount angle, the mount angle is calculated by formulae (1), (2) and (3) below.

[0043] mount angle=tan.sup.-1{n.times.pitch/(n.times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3)

[0044] where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

[0045] The present invention is an invention of manufacturing a metric screw thread. The same effect as in the first aspect can be achieved.

[0046] Particularly, the screw manufacturing method of the present invention has effect such that it becomes difficult for the inserts to interfere with the metric screw thread, as shown in TABLES 7 to 12 for later-explained sixth to eleventh embodiments, upon rotating the work piece and the cutter member, for example, in order to manufacture the metric screw thread of which lead angle is designed to satisfy the formula (X) above.

[0047] Also, as is clear from the later-explained embodiments, if the lead angle in a design drawing of the metric screw thread falls below 7.degree., the interference is not necessarily heavy upon going in and going out even if the fluctuation is 0%. Depending on a level of inspection, the manufactured screw may be accepted. However, if the lead angle exceeds 7.degree., the interference becomes heavy upon going in and going out when the fluctuation is 0%. Thus, it is preferable to set the mount angle to conform to the above formulae (1), (2) and (3). [0048] In a fourth aspect of the present invention, the .DELTA.T may be set as in formulae (6) and (7) below.

[0049] in case .DELTA.T>0,

{(screw outer diameter-screw valley diameter)/2}.times.0.6.ltoreq..DELTA.T.ltoreq.{(screw outer diameter-screw valley diameter)/2} (6)

[0050] in case .DELTA.T<0,

-{(screw outer diameter-screw valley diameter)/2}.ltoreq..DELTA.T.ltoreq.{(screw outer diameter-screw valley diameter)/2}.times.0.6 (7)

[0051] By setting as above, as is clear from later-described TABLES 1 to 12, the interference upon both going in and out between the curved line of the screw and the moving paths of the inserts can be further reduced. [0052] In a fifth aspect of the present invention, D1 can be set to be the outer diameter of the screw or the valley diameter of the screw.

[0053] By setting as above, as is clear from the later-described TABLES 1 to 12, the interference upon going in or going out between the curved line of the screw and the moving paths of the inserts can be null. [0054] A sixth aspect of the present invention provides an annular whirling cutter that has a plurality of inserts radially arranged and is rotatable on its rotation axis. The whirling cutter is inclined with respect to an axial center of a work piece for manufacturing a medical screw at a predetermined angle (mount angle). In case that a lead angle of the medical screw is different from the mount angle, formulae (1), (2), (3), (4) and (5) below are satisfied.

[0054] mount angle=tan.sup.-1{n.times.pitch/(n.times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3)

[0055] in case .DELTA.T>0,

{(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4)

[0056] in case .DELTA.T<0,

-{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5)

[0057] where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

[0058] Even if a lead angle of the medical screw, for example, is designed to satisfy the formula (X) above or the medical screw has a special shape specific to medical screws, as in the first aspect, when the medical screw is manufactured using the whirling cutter of the present invention, it becomes difficult for the inserts to interfere with the medical screw upon rotating the work piece and the whirling cutter.

[0059] Particularly, if the mount angle is set smaller (shallower) than the lead angle (i.e., 0<.DELTA.T), it becomes difficult to hit especially a side face of a tip end of the screw thread. Conversely, if the mount angle is set larger (deeper) than the lead angle (i.e., 0>.DELTA.T), it becomes difficult to hit especially to a side face of a base end of the screw thread.

[0060] Accordingly, when a medical screw is manufactured using the whirling cutter of the present invention, moving paths of the inserts are inhibited from interfering with a desired curved line of the screw upon both going in and out. Thereby, the screw provided with a targeted curved line can be manufactured in a preferred manner.

[0061] Also in the present invention, as compared to thread rolling, a wide variety of products in small quantities can be easily manufactured. Moreover, as compared to turning, machining time can be shortened. Also, continuous machining can be applied to one piece of work piece. Thus, a joining process is not necessary. Machining accuracy is advantageously high. [0062] A seventh aspect of the present invention provides an annular whirling cutter that has a plurality of inserts radially arranged and is rotatable on its rotation axis. The whirling cutter is inclined with respect to an axial center of a work piece for manufacturing a worm screw at a predetermined angle (mount angle). In case that a lead angle of the worm screw is different from the mount angle, formulae (1), (2), (3), (4) and (5) below are satisfied.

[0062] mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3)

[0063] in case .DELTA.T>0,

{(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4)

[0064] in case .DELTA.T<0,

-{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5)

[0065] where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

[0066] The present invention is an invention of a whirling cutter that manufactures a worm screw. The same effect as in the sixth aspect can be achieved.

[0067] Particularly, use of the whirling cutter of the present invention has effect such that it becomes difficult for the inserts to interfere with the worm screw, upon rotating the work piece and the whirling cutter, in case that a lead angle of the worm screw, for example, is designed to satisfy the formula (X) above. [0068] An eighth aspect of the present invention provides an annular whirling cutter that has a plurality of inserts radially arranged and is rotatable on its rotation axis, wherein the whirling cutter is inclined with respect to an axial center of a work piece for manufacturing a metric screw thread at a predetermined angle (mount angle), and, in case that a lead angle of the metric screw thread is different from the mount angle, formulae (1), (2) and (3) below are satisfied.

[0068] mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3)

[0069] where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

[0070] The present invention is an invention of a whirling cutter that manufactures a metric screw thread. The same effect as in the sixth aspect can be achieved.

[0071] Particularly, use of the whirling cutter of the present invention has effect such that it becomes difficult for the inserts to interfere with the metric screw thread, upon rotating the work piece and the whirling cutter, in case that a lead angle of the metric screw thread, for example, is designed to satisfy the formula (X) above. [0072] A ninth aspect of the present invention provides a screw manufacturing machine including: an annular whirling cutter that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a main spindle that coaxially holds a base of a work piece for manufacturing a medical screw and rotates the work piece. The whirling cutter is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle). When a lead angle of the medical screw is different from the mount angle, the mount angle satisfies following formulae (1), (2), (3), (4) and (5).

[0072] mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3)

[0073] in case .DELTA.T>0,

{(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4)

[0074] in case .DELTA.T<0,

-{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5)

[0075] where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

[0076] When a medical screw is manufactured using the screw manufacturing machine of the present invention, in the same manner as in the first aspect, for example, even if the lead angle of the medical screw is designed to satisfy a formula (X) above or the medical screw has a special shape specific to medical screws, it becomes difficult for inserts to interfere with the medical screw upon rotating the work piece and the whirling cutter.

[0077] Particularly, if the mount angle is made smaller (shallower) than the lead angle (i.e., 0<.DELTA.T), it becomes difficult to hit especially a side face of a tip end of the screw thread. Conversely, if the mount angle is made larger (deeper) than the lead angle (i.e., 0>.DELTA.T), it becomes difficult to hit especially to a side face of a base end of the screw thread.

[0078] Accordingly, when a medical screw is manufactured using the screw manufacturing machine of the present invention, moving paths of the inserts are inhibited from interfering with a desired curved line of the screw upon both going in and out. Thereby, the screw provided with a targeted curved line can be manufactured in a preferred manner.

[0079] Also in the present invention, as compared to thread rolling, a wide variety of products in small quantities can be easily manufactured. Moreover, as compared to turning, machining time can be shortened. Also, continuous machining can be applied to one piece of work piece. Thus, a joining process is not necessary. Machining accuracy is advantageously high. [0080] A tenth aspect of the present invention provides a screw manufacturing machine including: an annular whirling cutter that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a main spindle that coaxially holds a base of a work piece for manufacturing a worm screw and rotates the work piece. The whirling cutter is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle). When a lead angle of the worm screw is different from the mount angle, the mount angle satisfies following formulae (1), (2), (3), (4) and (5).

[0080] mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3)

[0081] in case .DELTA.T>0,

{(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4)

[0082] in case .DELTA.T<0,

-{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5)

[0083] where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

[0084] The present invention is an invention of a screw manufacturing machine that manufactures a worm screw. The same effect as in the ninth aspect can be achieved.

[0085] Particularly, use of the screw manufacturing machine of the present invention has effect such that it becomes difficult for the inserts to interfere with the worm screw, upon rotating the work piece and the whirling cutter, in case that a lead angle of the worm screw, for example, is designed to satisfy the formula (X) above. [0086] Further, an eleventh aspect of the present invention provides a screw manufacturing machine including: an annular whirling cutter that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a main spindle that coaxially holds a base of a work piece for manufacturing a metric screw thread and rotates the work piece. The whirling cutter is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle). When a lead angle of the metric screw thread is different from the mount angle, the mount angle satisfies following formulae (1), (2) and (3).

[0086] mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3)

[0087] where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

[0088] The present invention is an invention of a screw manufacturing machine that manufactures a metric screw thread. The same effect as in the ninth aspect can be achieved.

[0089] Particularly, use of the screw manufacturing machine of the present invention has effect such that it becomes difficult for the inserts to interfere with the metric screw thread, upon rotating the work piece and the whirling cutter, in case that a lead angle of the metric screw thread, for example, is designed to satisfy the formula (X) above.

[0090] Here, screws subject to the present invention include ordinary mechanical screws and medical screws. The present invention is a manufacturing method which is preferred to manufacture screws especially having special shapes such as medical screws.

[0091] Examples of the ordinary mechanical screws include various screws defined in JIS, e.g., metric screw threads, worm screws, unified threads, trapezoidal threads, buttress threads, and others.

[0092] The medical screws mean screws (implants) used inside bodies of humans and animals.

[0093] Examples of cases where the interference between the screw and the inserts becomes large in a medical screw include cases where: its pitch is larger than that of an ordinary mechanical screw (e.g., equal to or larger than 2.0 mm); a number of thread is larger than that of a single-threaded screw, e.g., double-threaded screw; a screw is deep threaded (a difference between an outer diameter and a valley diameter is large, e.g., equal to or larger than 2.0 mm); and a lead angle of a target screw is large (e.g., equal to or larger than 15.degree.).

BRIEF DESCRIPTION OF THE DRAWINGS

[0094] FIG. 1 is an explanatory view illustrating a manufacturing method of a medical screw by a thread whirling method.

[0095] FIG. 2 is an explanatory view illustrating a whirling cutter provided with inserts.

[0096] FIG. 3A is a front view of the screw, and FIG. 3B is an explanatory view showing part of the screw being enlarged and fractured.

[0097] FIG. 4 is a perspective view of the insert used in a first embodiment.

[0098] FIG. 5A is an explanatory view illustrating a state of interference in case that a fluctuation is set to -100% in the first embodiment, FIG. 5B is an explanatory view illustrating a state of interference in case that the fluctuation is set to -80%, FIG. 5C is an explanatory view illustrating a state of interference in case that the fluctuation is set to -60%, and FIG. 5D is an explanatory view illustrating a state of interference in case that the fluctuation is set to -40%.

[0099] FIG. 6A is an explanatory view illustrating a state of interference in case that the fluctuation is set to -20% in the first embodiment, FIG. 6B is an explanatory view illustrating a state of interference in case that the fluctuation is set to 0%, FIG. 6C is an explanatory view illustrating a state of interference in case that the fluctuation is set to +20%, and FIG. 6D is an explanatory view illustrating a state of interference in case that the fluctuation is set to +40%.

[0100] FIG. 7A is an explanatory view illustrating a state of interference in case that the fluctuation is set to +60% in the first embodiment, FIG. 7B is an explanatory view illustrating a state of interference in case that the fluctuation is set to +80%, and FIG. 7C is an explanatory view illustrating a state of interference in case that the fluctuation is set to +100%.

[0101] FIG. 8 is a perspective view showing an insert used in a second embodiment.

[0102] FIG. 9A is an explanatory view illustrating a state of interference in case that a fluctuation is set to -100% in the second embodiment, FIG. 9B is an explanatory view illustrating a state of interference in case that the fluctuation is set to -80%, FIG. 9C is an explanatory view illustrating a state of interference in case that the fluctuation is set to -60%, and FIG. 9D is an explanatory view illustrating a state of interference in case that the fluctuation is set to -40%.

[0103] FIG. 10A is an explanatory view illustrating a state of interference in case that the fluctuation is set to -20% in the second embodiment, FIG. 10B is an explanatory view illustrating a state of interference in case that the fluctuation is set to 0%, FIG. 10C is an explanatory view illustrating a state of interference in case that the fluctuation is set to +20%, and FIG. 10D is an explanatory view illustrating a state of interference in case that the fluctuation is set to +40%.

[0104] FIG. 11A is an explanatory view illustrating a state of interference in case that the fluctuation is set to +60% in the second embodiment, FIG. 11B is an explanatory view illustrating a state of interference in case that the fluctuation is set to +80%, and FIG. 11C is an explanatory view illustrating a state of interference in case that the fluctuation is set to +100%.

[0105] FIG. 12 is a cross-sectional view showing a cross section along a center axis of a medical screw according to a third embodiment.

[0106] FIG. 13A is an explanatory view illustrating a state of interference in case that a fluctuation is set to +100% in the third embodiment, FIG. 13B is an explanatory view illustrating a state of interference in case that the fluctuation is set to +60%, FIG. 13C is an explanatory view illustrating a state of interference in case that the fluctuation is set to +40%, and FIG. 13D is an explanatory view illustrating a state of interference in case that the fluctuation is set to +0%.

[0107] FIG. 14A is an explanatory view showing a worm screw according to a fourth embodiment, and FIG. 14B is a cross-sectional view showing a cross section along a center axis of the worm screw.

[0108] FIG. 15A is an explanatory view illustrating a state of interference in case that a fluctuation is set to +100% in the fourth embodiment, FIG. 15B is an explanatory view illustrating a state of interference in case that the fluctuation is set to +60%, FIG. 15C is an explanatory view illustrating a state of interference in case that the fluctuation is set to +40%, and FIG. 15D is an explanatory view illustrating a state of interference in case that the fluctuation is set to +0%.

[0109] FIG. 16 is a cross-sectional view showing a cross section along a center axis of a worm screw according to a fifth embodiment.

[0110] FIG. 17A is an explanatory view illustrating a state of interference in case that a fluctuation is set to +100% in the fifth embodiment, FIG. 17B is an explanatory view illustrating a state of interference in case that the fluctuation is set to +60%, FIG. 17C is an explanatory view illustrating a state of interference in case that the fluctuation is set to +40%, and FIG. 17D is an explanatory view illustrating a state of interference in case that the fluctuation is set to +0%.

[0111] FIG. 18 is a cross-sectional view showing a cross section along a center axis of a metric screw thread according to a sixth embodiment.

[0112] FIG. 19A is an explanatory view illustrating a state of interference in case that a fluctuation is set to +100% in the sixth embodiment (pitch: 0.8), FIG. 19B is an explanatory view illustrating a state of interference in case that the fluctuation is set to +0%, FIG. 19C is an explanatory view illustrating a state of interference in case that a fluctuation is set to +100% in a seventh embodiment (pitch: 1.0), and FIG. 19D is an explanatory view illustrating a state of interference in case that the fluctuation is set to +0%.

[0113] FIG. 20A is an explanatory view illustrating a state of interference in case that a fluctuation is set to +100% in an eighth embodiment (pitch: 1.25), FIG. 20B is an explanatory view illustrating a state of interference in case that the fluctuation is set to +0%, FIG. 20C is an explanatory view illustrating a state of interference in case that a fluctuation is set to +100% in a ninth embodiment (pitch: 1.5), and FIG. 20D is an explanatory view illustrating a state of interference in case that the fluctuation is set to +0%.

[0114] FIG. 21A is an explanatory view illustrating a state of interference in case that a fluctuation is set to +100% in a tenth embodiment (pitch: 1.75), and FIG. 21B is an explanatory view illustrating a state of interference in case that the fluctuation is set to +0%.

[0115] FIG. 22A is an explanatory view illustrating a state of interference in case that a fluctuation is set to +100% in an eleventh embodiment (pitch: 2.0), FIG. 22B is an explanatory view illustrating a state of interference in case that the fluctuation is set to +60%, FIG. 22C is an explanatory view illustrating a state of interference in case that the fluctuation is set to +40%, and FIG. 22D is an explanatory view illustrating a state of interference in case that the fluctuation is set to +0%.

[0116] FIG. 23 is an explanatory view illustrating a problem in prior art.

EXPLANATION OF REFERENCE NUMERALS

[0117] 1, 31, 35, 41, 51, 53, 61 . . . screw [0118] 3 . . . work piece [0119] 5 . . . screw portion [0120] 7 . . . main spindle [0121] 9 . . . whirling cutter [0122] 10 . . . screw manufacturing machine [0123] 11 . . . cutter head [0124] 13, 21 . . . insert [0125] 17 . . . through hole

BEST MODE FOR CARRYING OUT THE INVENTION

[0126] Hereinafter, embodiments of the present invention will be described together with the accompanying drawings.

First Embodiment

[0127] a) First, an outline will be provided on a manufacturing method of a medical screw by a thread whirling method.

[0128] As shown in FIG. 1, the thread whirling method according to the present embodiment uses a main spindle 7 and a whirling cutter 9 to form a screw portion 5 on a surface of a rod material (work piece) 3 which is to be a medical screw (hereinafter, simply referred to as a screw) 1. The main spindle 7 coaxially holds a base of the work piece 3 and rotates the work piece 3. The whirling cutter 9 is arranged to incline at a mount angle .beta. (.degree.) with respect to an axial direction of the work piece 3 and rotates.

[0129] The whirling cutter 9 is an annular device which is rotated by a not shown tool spindle. As shown in FIG. 2, a plurality of, e.g., nine, inserts 13 are radially arranged on an annular cutter head 11 of the whirling cutter 9.

[0130] Each of the inserts 13 is secured to the cutter head 11 by a fixation screw 15. A machine that includes the main spindle 7 and the whirling cutter 9 and manufactures the screw 1 by the thread whirling method is referred to as a screw manufacturing machine 10.

[0131] For example, when the screw 1, as shown in FIGS. 3A and 3B, is to be prepared by thread whirling machining, the following steps are taken.

[0132] First, as shown in FIG. 1, the rod-like work piece 3 is inserted to a rotation center of the main spindle 7.

[0133] Next, the work piece 3 is inserted to a through hole 17 in a center of the whirling cutter 9. Also, the whirling cutter 9 is inclined at a predetermine angle (mount angle .beta.) with respect to a center axis of the work piece 3. In this state, the work piece 3 is forwarded at a predetermined speed to its axial direction (upward direction in FIG. 1) while being rotated to a predetermined direction (direction A in FIGS. 1 and 2). At the same time, the whirling cutter 9 is rotated to the same direction at a rotation speed higher than a rotation speed of the work piece 3, thereby to prepare a screw by the plurality of inserts 13.

[0134] In detail, as shown in FIG. 2, a rotation center of the whirling cutter 9 and an axial center of the work piece 3 are arranged such that the work piece 3 is in contact with the insert 13 (the axial center of the work piece 3 is arranged in an upward direction in the same figure). When the whirling cutter 9 rotates, the screw portion 5 is formed by the respective inserts 13 which sequentially come into contact with the work piece 3.

[0135] The medical screw 1 to be manufactured in the present embodiment is a single-threaded screw. Here, in order to prepare a single-threaded screw, the insert 13 having one-ridged cutting portion 19 as shown in FIG. 4 is used. A shape of the insert 13 is parallelogram. However, shapes such as a diamond and a triangle, for example, can be also handled. Further details of the shape will be determined according to a shape of a screw to be prepared.

[0136] b) Next, how to set the mount angle .beta. will be described.

[0137] The mount angle .beta. is determined by a shape of the screw 1 to be prepared.

[0138] Thus, first of all, as shown in FIGS. 3A and 3B, numerical values which specify the shape of the screw 1 are read from a drawing of the screw 1 (here, a single-threaded screw) to be prepared.

[0139] For example, typical data which specify the shape of the screw 1 is as below. Other than below, there are data for specifying a three-dimensional surface shape (curve) of the screw portion 5. Here, the numerical data of the screw 1 to be prepared by the inserts 13 are shown.

[0140] Whole screw length in axial direction: 50.0 mm

[0141] Screw portion length in axial direction: 30.0 mm

[0142] Screw outer diameter: .phi.6.0 mm

[0143] Screw valley diameter: .phi.4.0 mm

[0144] Pitch: 5.0 mm

[0145] Thread lead angle: 17.66.degree.

[0146] The mount angle .beta. is different from the lead angle of the screw 1. That is, D1 in the above formula (1) is different from a pitch diameter of the above formula (X).

[0147] c) Next, an example of the method of manufacturing the screw 1 using thread whirling machining will be described.

[0148] Here, a case of preparing the screw 1 having the aforementioned measurements will be described.

[0149] As shown in FIG. 1, the work piece 3 is attached and secured to the rotation center of the main spindle 7, and inserted to the through hole 17 in the center of the whirling cutter 9. Also, the whirling cutter 9 is inclined at the mount angle .beta. with respect to the center axis of the work piece 3.

[0150] The mount angle .beta. is calculated using formulae (1), (2), (3), (4) and (5) below. Here, the mount angle .beta. is an angle at which the whirling cutter 9 is inclined with respect to the center axis of the work piece 3 upon thread whirling machining.

mount angle=tan.sup.-{n.times.pitch/(.pi..times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3)

[0151] in case .DELTA.T>0,

{(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4)

[0152] in case .DELTA.T<0,

-{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5)

[0153] where D1 (mm).noteq.0, .DELTA.T (mm).noteq.0, and n indicates a number of threads.

[0154] As for the work piece 3, a cylindrical rod made of titanium alloy was used which has a length of 2.5 m.times.an outer diameter of 0.0 mm.

[0155] Then, according to machining conditions below, the screw 1 having a target shape shown in FIGS. 3A and 3B is to be prepared.

[0156] Main spindle rotation speed: 10 rpm

[0157] Work piece forward speed: 2.75 mm/rev

[0158] Tool spindle rotation speed: 2000 rpm

[0159] As shown in TABLE 1 below, the screw 1 was prepared by changing D1 to change the mount angle .beta.. At that time, presence/absence of interference (interference between a curved line of the screw 1 and moving paths of the inserts 13) was studied. In detail, a simulation was conducted by a known CAD. Also, the screw 1 was actually prepared to check a state of interference.

[0160] As for the CAD, a three-dimensional CAD USG NX4 was used.

[0161] The result is shown in the TABLE 1 and FIGS. 5A to 5D, 6A to 6D and 7A to 7C.

TABLE-US-00001 TABLE 1 Lead L 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 4.00 4.20 4.40 4.60 4.80 5.00 5.20 5.40 5.60 5.80 6.00 Fluctuation range = .DELTA.T -1.00 -0.80 -0.60 -0.40 -0.20 0.00 +0.20 +0.40 +0.60 +0.80 +1.00 Mount angle 21.70 20.75 19.89 19.09 18.34 17.66 17.02 16.42 15.87 15.34 14.86 Determination .circleincircle. .largecircle. .largecircle. .DELTA. X X X .DELTA. .largecircle. .largecircle. .circleincircle.

[0162] In the above TABLE 1, "Fluctuation" indicates a proportion of fluctuation (in case that a maximum fluctuation range of 1.00 is set to be 100%) in D1 from an intermediate value (D1=5.00: .DELTA.T=0). "Revised fluctuation" indicates a value obtained by converting the fluctuation of 200% to 100%. "Fluctuation range" indicates a range of actual fluctuation (corresponding to the above .DELTA.T) from D1=5.00.

[0163] In the result of Determination, ".circleincircle." indicates that "interference upon either going in or out is completely avoided so that a targeted screw-thread shape can be substantially obtained". ".largecircle." indicates that "interference upon either going in or out is not completely avoided, but machining to an extent not to be called a shape defect can be performed. "A" indicates that "interference upon either going in or out is frequent, but products can be accepted depending on the inspection level". "X" indicates that "interference upon both going in and out is frequent, and only the products determined to have a shape defect can be produced".

[0164] Here, the "targeted screw-thread shape" is not only an ideal screw-thread shape which follows a screw curved line, but also a screw-thread shape in which interference can be caused only in either of portions on a screw outer diameter side or on a screw base end side (valley side).

[0165] Further, in FIGS. 5A to 5D, 6A to 6D and 7A to 7C, a white portion in the center indicates the shape of the work piece 3 before machining. Gray portions on the right and left sides indicate the shape after machining. Gray portions (inside an elliptic circle) in the central white portion of the work piece 3 indicate portions where interference occurs. The elliptic circle is omitted in FIG. 6D and the figures having a larger number than 6D.

[0166] As is clear from TABLE 1 and FIGS. 5A to 5D, 6A to 6D and 7A to 7C, a shape that evades the curved line of the screw 1 is achieved by changing D1 to adjust the mount angle .beta., more particularly, by increasing the fluctuation of D1 to increase the difference between the mount angle .beta. and the lead angle (i.e., by increasing the fluctuation). It is understood that the interference upon either going in or out can be reduced.

[0167] Particularly, for example, as shown in FIGS. 5A to 5D and 6A to 6B, if the fluctuation is increased, the shape of the interfered portions is changed from two fan-shaped sectors (see FIG. 6B, for example) expanding upward and downward to a fan-shaped sector (see FIG. 5A, for example) expanding in one of the directions (upward, for example).

[0168] Accordingly, it is understood that the screw 1 having a smaller interference (or no interference) either upon going in or out can be obtained.

[0169] Moreover, as is clear from comparison between FIGS. 5A to 5D and FIG. 6A, it is understood that, as the minus (-) fluctuation is larger than -20% fluctuation, interference on the screw base end side (valley side) can be reduced (triangular gray portion has become small). Similarly, in comparison between FIGS. 6D and 7A to 7C and FIG. 6C, it is understood that, as the plus (+) fluctuation is larger than +20% fluctuation, interference on the portion on the screw outer diameter side can be reduced (triangular gray portion becomes small).

[0170] Also, as is clear from FIG. 6B (0% fluctuation), if D1 is (screw valley diameter+screw outer diameter)/2 (i.e., .DELTA.T=0), interference occurs to both the portions on the screw outer diameter side and the screw base end side (valley side). Thus, use of the manufactured screw becomes a problem. That is, if interference occurs to both the portions on the screw outer diameter side and the screw base end side (valley side), it becomes difficult to fasten the screw with good accuracy. Furthermore, the interference may cause backlash of the screw.

[0171] e) As noted above, in the present embodiment, by setting values of the mount angle .beta. to be different from the lead angle, the screw 1 in the shape which reduces interference between the moving paths of the inserts 13 and the curved line of the screw 1 upon going in or out can be obtained in a preferred manner. Further, since interference does not necessarily occur to both the portions of the screw outer diameter side and the screw base end side (valley side), there is no problem in use of the manufactured screw 1.

[0172] That is, in the present embodiment, since interference can be avoided from occurring to both the portions on the screw outer diameter side and the screw base end side (valley side), the screw 1 can be rotated without problem when fastening, etc. is performed using the manufactured screw 1.

[0173] In detail, as is clear from the above TABLE 1, interference between the curved line of the screw 1 and the moving paths of the inserts 13 upon going in or out can be all the more reduced by setting as below.

[0174] in case .DELTA.T>0,

{(screw outer diameter-screw valley diameter)/2}.times.0.6.ltoreq..DELTA.T.ltoreq.{(screw outer diameter-screw valley diameter)/2}

[0175] in case .DELTA.T<0,

-{(screw outer diameter-screw valley diameter)/2}.DELTA.T.ltoreq.-{(screw outer diameter-screw valley diameter)/2}.times.0.6

[0176] The above "(screw outer diameter-screw valley diameter)" indicates the maximum fluctuation range. For example, if the fluctuation is +60% (revised fluctuation=+30%), .DELTA.T={(screw outer diameter-screw valley diameter).times.0.3}.

[0177] Specifically, by setting D1 upon calculating the mount angle .beta. to the screw outer diameter (+100% fluctuation) or the screw valley diameter (-100% fluctuation), no interference between the moving paths of the inserts 13 and the curved line of the screw 1 occurs upon either going in or out.

[0178] Also, even the screw 1 having a special shape such as a medical screw can be advantageously prepared by a single process, and not by processes including a plurality of passes.

Second Embodiment

[0179] Now, a second embodiment will be described. Descriptions of the same contents as those in the above first embodiment will not be repeated.

[0180] A medical screw to be manufactured in the present embodiment is a double-threaded screw. As shown in FIG. 8, an insert 21 to be used in a thread whirling method by which the medical screw is to be manufactured includes a two-ridged cutting portion 23, 25.

[0181] In the present embodiment, an example of typical data which specify the shape of the screw is as below.

[0182] Whole screw length in axial direction: 50.0 mm

[0183] Screw portion length in axial direction: 30.0 mm

[0184] Screw outer diameter: .phi.4.0 mm

[0185] Screw valley diameter: .phi.2.4 mm

[0186] Pitch: 3.42 mm

[0187] Thread lead angle: 18.79.degree.

[0188] The mount angle .beta. is calculated using the formulae (1), (2), (3), (4) and (5) in the above first embodiment.

[0189] As shown in TABLE 2 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 2 and FIGS. 9A to 9D, 10A to 10D and 11A to 11C.

TABLE-US-00002 TABLE 2 Lead L 3.42 3.42 3.42 3.42 3.42 3.42 3.42 3.42 3.42 3.42 3.42 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 2.40 2.56 2.72 2.88 3.04 3.20 3.36 3.52 3.68 3.38 4.00 Fluctuation range = .DELTA.T -0.80 -0.64 -0.48 -0.32 -0.16 0.00 +0.16 +0.32 +0.48 +0.64 +0.80 Mount angle 24.40 23.04 21.81 20.71 19.70 18.79 17.95 17.19 16.48 15.83 15.22 Determination .circleincircle. .largecircle. .largecircle. .DELTA. X X X .DELTA. .largecircle. .largecircle. .circleincircle.

[0190] Meanings of words in TABLE 2 and meanings of colors (thickness) in FIGS. 9A to 9D, 10A to 10D and 11A to 11C are the same as those in the above first embodiment.

[0191] As is clear from TABLE 2 and FIGS. 9A to 9D, 10A to 10D and 11A to 11C, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the first embodiment.

[0192] Accordingly, in the present embodiment, the same effect as in the first embodiment is achieved.

[0193] Also in the insert 21 for the double-threaded screw, its cutting surface is larger in its width direction as compared to its height direction, in order to form a double-threaded screw portion at once, than that the insert for the single-threaded screw. Since interference is easy to occur between the insert 21 and the screw portion, it is not easy to form a desired screw thread. However, the manufacturing method according to the present embodiment allows easy preparation of a screw having a desired shape.

[0194] Further, a double-threaded screw can be advantageously prepared by a single process, and not by processes including a plurality of passes.

Third Embodiment

[0195] Now, a third embodiment will be described. Descriptions of the same contents as those in the above second embodiment will not be repeated.

[0196] A screw to be manufactured in the present embodiment is a double-threaded medical screw 31, as shown in FIG. 12. Although not shown, inserts used in a thread whirling method by which the medical screw 31 is manufactured include a two-ridged cutting portion. Unit of length in FIG. 12 is mm.

[0197] In the present embodiment, an example of typical data which specify the shape of the screw is as below.

[0198] Whole screw length in axial direction: 30 mm

[0199] Screw portion length in axial direction: 20 mm

[0200] Screw outer diameter: .phi.5.5 mm

[0201] Screw valley diameter: .phi.4.0 mm

[0202] Intermediate value of screw: .phi.4.75 mm

[0203] Pitch: 5.35 mm

[0204] Thread lead angle: 19.72.degree.

[0205] The mount angle .beta. is calculated using the formulae (1), (2), (3), (4) and (5) in the above first embodiment.

[0206] As shown in TABLE 3 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 3 and FIGS. 13A to 13D.

TABLE-US-00003 TABLE 3 Lead L 5.35 5.35 5.35 5.35 5.35 5.35 5.35 5.35 5.35 5.35 5.35 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 4.00 4.15 4.30 4.45 4.60 4.75 4.90 5.05 5.20 5.35 5.50 Fluctuation range = .DELTA.T -0.75 -0.60 -0.45 -0.30 -0.15 0.00 +0.15 +0.30 +0.45 +0.60 +0.75 Mount angle 23.06 22.31 21.61 20.94 20.31 19.72 19.16 18.64 18.13 17.66 17.20 Determination .circleincircle. .largecircle. .largecircle. .DELTA. X X X .DELTA. .largecircle. .largecircle. .circleincircle.

[0207] Meanings of words in TABLE 3 and meanings of colors (thickness) in FIGS. 13A to 13D are the same as those in the above first embodiment.

[0208] As is clear from TABLE 13 and FIGS. 13A to 13D, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the second embodiment.

[0209] Accordingly, in the present embodiment, the same effect as in the second embodiment is achieved. In this way, the effect of the present invention can be achieved regardless of designs such as an outer diameter/valley diameter of a screw.

Fourth Embodiment

[0210] Now, a fourth embodiment will be described. Descriptions of the same contents as those in the above first embodiment will not be repeated.

[0211] A screw to be manufactured in the present embodiment is a double-threaded worm screw (JIS B1723/3) 35, as shown in FIGS. 14A and 14B. Although not shown, inserts used in a thread whirling method by which the worm screw 35 is manufactured include a two-ridge cutting portion.

[0212] In the present embodiment, an example of typical data which specify the shape of the screw is as below. Unit of length in FIG. 14B is mm.

[0213] Whole screw length in axial direction: 11 mm

[0214] Screw portion length in axial direction: 10 mm

[0215] Screw outer diameter: .phi.6 mm

[0216] Intermediate value of screw: .phi.5.125 mm

[0217] Screw valley diameter: .phi.4.25 mm

[0218] Pitch: 2.872 mm

[0219] Thread lead angle: 10.1141.degree.

[0220] The mount angle .beta. is calculated using the formulae (1), (2), (3), (4) and (5) in the above first embodiment.

[0221] As shown in TABLE 4 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 4 and FIGS. 15A to 15D.

TABLE-US-00004 TABLE 4 Lead L 2.872 2.872 2.872 2.872 2.872 2.872 2.872 2.872 2.872 2.872 2.872 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 4.250 4.425 4.600 4.775 4.950 5.125 5.300 5.475 5.650 5.825 6.000 Fluctuation range = .DELTA.T -0.875 -0.7 -0.525 -0.35 -0.175 0.00 +0.175 +0.35 +0.525 +0.7 +0.875 Mount angle 12.14 11.67 11.24 10.84 10.46 10.11 9.79 9.48 9.19 8.92 8.66 Determination .circleincircle. .largecircle. .largecircle. .DELTA. X X X .DELTA. .largecircle. .largecircle. .circleincircle.

[0222] Meanings of words in TABLE 4 and meanings of colors (thickness) in FIGS. 15A to 15D are the same as those in the above first embodiment.

[0223] As is clear from TABLE 4 and FIGS. 15A to 15D, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the first embodiment.

[0224] Accordingly, in the present embodiment, the same effect as in the first embodiment is achieved even with the ordinary double-threaded worm screw 35.

Fifth Embodiment

[0225] Now, a fifth embodiment will be described. Descriptions of the same contents as those in the above first embodiment will not be repeated.

[0226] A screw to be manufactured in the present embodiment is a triple-threaded worm screw (JIS B1723/3) 41, as shown in FIG. 16. Although not shown, inserts used in a thread whirling method by which the worm screw 41 is manufactured include a three-ridged cutting portion.

[0227] In the present embodiment, an example of typical data which specify the shape of the screw is as below. Unit of length in FIG. 16 is mm.

[0228] Whole screw length in axial direction: 12 mm

[0229] Screw portion length in axial direction: 12 mm

[0230] Screw outer diameter: .phi.7 mm

[0231] Intermediate value of screw: 6.000 mm

[0232] Screw valley diameter: .phi.5.000 mm

[0233] Pitch: 4.867 mm

[0234] Thread lead angle: 14.degree. 28' 39''

[0235] The mount angle .beta. is calculated using the formulae (1), (2), (3), (4) and (5) in the above first embodiment.

[0236] As shown in TABLE 5 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 5 and FIGS. 17A to 17D.

TABLE-US-00005 TABLE 5 Lead L 4.867 4.867 4.867 4.867 4.867 4.867 4.867 4.867 4.867 4.867 4.867 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 5.000 5.200 5.400 5.600 5.800 6.000 6.200 6.400 6.600 6.800 7.000 Fluctuation range = .DELTA.T -1.0 -0.8 -0.6 -0.4 -0.2 0.00 +0.2 +0.4 +0.6 +0.8 +1.0 Mount angle 17.22 16.59 16.01 15.46 14.95 14.48 14.03 13.61 13.21 12.83 12.48 Determination .circleincircle. .largecircle. .largecircle. .DELTA. X X X .DELTA. .largecircle. .largecircle. .circleincircle.

[0237] Meanings of words in TABLE 5 and meanings of colors (thickness) in FIGS. 17A to 17D are the same as those in the above first embodiment.

[0238] As is clear from TABLE 5 and FIGS. 17A to 17D, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the first embodiment.

[0239] Accordingly, in the present embodiment, the same effect as in the first embodiment is achieved even with the ordinary triple-threaded worm screw 41.

Sixth Embodiment

[0240] Now, a sixth embodiment will be described. Descriptions of the same contents as those in the above first embodiment will not be repeated.

[0241] Screws to be manufactured in the present embodiment are ordinary single-threaded metric screw threads 51 and 53, as shown in FIG. 18.

[0242] The screw 51 is an external screw and the screw 53 is an internal screw. In these metric screw threads 51 and 53, a relation among its pitch (p), fundamental triangle height (H), and others in case that an outer diameter of the screws is .phi.5 mm, for example, is defined as shown in TABLE 6 below.

TABLE-US-00006 TABLE 6 Valley diameter of Pitch H H/8 (5/8)H P/4 screw 0.80 0.692820 0.086603 0.433013 0.2000 4.133975 1.00 0.866025 0.108253 0.541266 0.2500 3.917469 1.25 1.082532 0.135317 0.676583 0.3125 3.646835 1.50 1.299038 0.162380 0.811899 0.3750 3.376203 1.75 1.515544 0.189443 0.947215 0.4375 3.105570 2.00 1.732051 0.216506 1.082532 0.5000 2.834936

[0243] Although not shown, inserts used in a thread whirling method by which the metric screw threads 51 and 53 are manufactured include a one-ridged cutting portion.

[0244] In the present embodiment, an example of typical data which specify the shape of the screw (e.g., the metric screw thread 51 as an external screw) is as below.

[0245] Whole screw length in axial direction: 15 mm

[0246] Screw portion length in axial direction: 10 mm

[0247] Screw outer diameter: .phi.5 mm

[0248] Intermediate value of screw: .phi.4.567 mm

[0249] Screw valley diameter: .phi.4.134 mm

[0250] Pitch: 0.8 mm

[0251] Thread lead angle: 3.19.degree.

[0252] The mount angle .beta. is calculated using formulae (1), (2) and (3) below.

mount angle=tan.sup.-1{n.times.pitch/(n.times.D1)} (1)

D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2)

screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3)

[0253] As shown in TABLE 7 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 7 and FIGS. 19A and 19B.

TABLE-US-00007 TABLE 7 Lead L 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 4.134 4.221 4.307 4.394 4.480 4.567 4.654 4.740 4.827 4.913 5.000 Fluctuation range = .DELTA.T -0.433 -0.346 -0.26 -0.173 -0.087 0.00 +0.087 +0.173 +0.26 +0.346 +0.433 Mount angle 3.52 3.45 3.38 3.32 3.25 3.19 3.13 3.08 3.02 2.97 2.92 Determination .circleincircle. .largecircle. .largecircle. .DELTA. .DELTA. .DELTA. .DELTA. .DELTA. .largecircle. .largecircle. .circleincircle.

[0254] Meanings of words in TABLE 7 and meanings of colors (thickness) in FIGS. 19A and 19B are the same as those in the above first embodiment.

[0255] As is clear from TABLE 7 and FIGS. 19A and 19B, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the first embodiment.

[0256] Accordingly, in the present embodiment, even in the ordinary metric screw thread 51, the screw 51 which is shaped to reduce the interference between the moving paths of the inserts and a curved line of the screw 51 upon going in and out can be obtained in a preferred manner by setting different values to the mount angle .beta. and the lead angle. Further, since the interference is not caused on both portions on the outer side of the screw and the base end side (valley side) of the screw, there is no problem in using the manufactured screw 51. To sum up, in the present embodiment, the interference can be inhibited from occurring to both the portions on the outer side of the screw and the base end side (valley side) of the screw. Thus, upon fastening, etc., using the manufactured screw 51, the screw 51 can be rotated without problem.

Seventh Embodiment

[0257] Now, a seventh embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.

[0258] A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw), as in the sixth embodiment, which is not shown. Especially, while its outer diameter is .phi.5 mm which is the same, its pitch is larger, i.e., 1.0 mm.

[0259] Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.

[0260] In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.

[0261] Whole screw length in axial direction: 15 mm

[0262] Screw portion length in axial direction: 10 mm

[0263] Screw outer diameter: .phi.5 mm

[0264] Intermediate value of screw: .phi.4.459 mm

[0265] Screw valley diameter: .phi.3.917 mm

[0266] Pitch: 1.0 mm

[0267] Thread lead angle: 4.08.degree.

[0268] The mount angle .beta. is calculated using the formulae (1), (2), and (3) in the above sixth embodiment.

[0269] As shown in TABLE 8 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 8 and FIGS. 19C and 19D.

TABLE-US-00008 TABLE 8 Lead L 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 3.917 4.026 4.134 4.242 4.350 4.459 4.567 4.675 4.783 4.892 5.000 Fluctuation range = .DELTA.T -0.542 -0.433 -0.325 -0.217 -0.109 0.00 +0.108 +0.216 +0.324 +0.433 +0.541 Mount angle 4.65 4.52 4.40 4.29 4.18 4.08 3.99 3.86 3.81 3.72 3.64 Determination .circleincircle. .largecircle. .largecircle. .DELTA. .DELTA. .DELTA. .DELTA. .DELTA. .largecircle. .largecircle. .circleincircle.

[0270] Meanings of words in TABLE 8 and meanings of colors (thickness) in FIGS. 19C and 19D are the same as those in the above sixth embodiment.

[0271] As is clear from TABLE 8 and FIGS. 19C and 19D, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the sixth embodiment.

[0272] Accordingly, the present embodiment achieves the same effect as the sixth embodiment.

Eighth Embodiment

[0273] Now, an eighth embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.

[0274] A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw), as in the sixth embodiment, which is not shown. Especially, while its outer diameter is .phi.5 mm which is the same, its pitch is larger, i.e., 1.25 mm.

[0275] Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.

[0276] In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.

[0277] Whole screw length in axial direction: 15 mm

[0278] Screw portion length in axial direction: 10 mm

[0279] Screw outer diameter: .phi.5 mm

[0280] Intermediate value of screw: .phi.4.323 mm

[0281] Screw valley diameter: .phi.3.647 mm

[0282] Pitch: 1.25 mm

[0283] Thread lead angle: 5.26.degree.

[0284] The mount angle .beta. is calculated using the formulae (1), (2), and (3) in the above sixth embodiment.

[0285] As shown in TABLE 9 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 9 and FIGS. 20A and 20B.

TABLE-US-00009 TABLE 9 Lead L 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 3.647 3.782 3.917 4.053 4.188 4.323 4.459 4.594 4.729 4.865 5.000 Fluctuation range = .DELTA.T -0.676 -0.541 -0.406 -0.27 -0.135 0.00 +0.136 +0.271 +0.406 +0.542 +0.677 Mount angle 6.23 6.01 5.80 5.61 5.43 5.26 5.10 4.95 4.81 4.68 4.55 Determination .circleincircle. .largecircle. .largecircle. .DELTA. .DELTA. .DELTA. .DELTA. .DELTA. .largecircle. .largecircle. .circleincircle.

[0286] Meanings of words in TABLE 9 and meanings of colors (thickness) in FIGS. 20A and 20B are the same as those in the above sixth embodiment.

[0287] As is clear from TABLE 9 and FIGS. 20A and 20B, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the sixth embodiment.

[0288] Accordingly, the present embodiment achieves the same effect as the sixth embodiment.

Ninth Embodiment

[0289] Now, a ninth embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.

[0290] A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw), as in the sixth embodiment, which is not shown. Especially, while its outer diameter is .phi.5 mm which is the same, its pitch is larger, i.e., 1.5 mm.

[0291] Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.

[0292] In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.

[0293] Whole screw length in axial direction: 15 mm

[0294] Screw portion length in axial direction: 10 mm

[0295] Screw outer diameter: .phi.5 mm

[0296] Intermediate value of screw: .phi.4.188 mm

[0297] Screw valley diameter: .phi.3.376 mm

[0298] Pitch: 1.5 mm

[0299] Thread lead angle: 6.5.degree.

[0300] The mount angle .beta. is calculated using the formulae (1), (2), and (3) in the above sixth embodiment.

[0301] As shown in TABLE 10 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 10 and FIGS. 20C and 20D.

TABLE-US-00010 TABLE 10 Lead L 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 3.376 3.539 3.701 3.863 4.026 4.188 4.350 4.513 4.675 4.838 5.000 Fluctuation range = .DELTA.T -0.812 -0.678 -0.487 -0.325 -0.162 0.00 +0.162 +0.325 +0.487 +0.65 +0.812 Mount angle 8.05 7.68 7.35 7.05 6.76 6.50 6.26 6.04 5.83 5.64 5.45 Determination .circleincircle. .largecircle. .largecircle. .DELTA. .DELTA. .DELTA. .DELTA. .DELTA. .largecircle. .largecircle. .circleincircle.

[0302] Meanings of words in TABLE 10 and meanings of colors (thickness) in FIGS. 20C and 20D are the same as those in the above first embodiment.

[0303] As is clear from TABLE 10 and FIGS. 20C and 20D, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the sixth embodiment.

[0304] Accordingly, the present embodiment achieves the same effect as the sixth embodiment.

Tenth Embodiment

[0305] Now, a tenth embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.

[0306] A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw), as in the sixth embodiment, which is not shown. Especially, while its outer diameter is .phi.5 mm which is the same, its pitch is larger, i.e., 1.75 mm.

[0307] Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.

[0308] In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.

[0309] Whole screw length in axial direction: 15 mm

[0310] Screw portion length in axial direction: 10 mm

[0311] Screw outer diameter: .phi.5 mm

[0312] Intermediate value of screw: .phi.4.053 mm

[0313] Screw valley diameter: .phi.3.105 mm

[0314] Pitch: 1.75 mm

[0315] Thread lead angle: 7.83.degree.

[0316] The mount angle .beta. is calculated using the formulae (1), (2), and (3) in the above sixth embodiment.

[0317] As shown in TABLE 11 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 11 and FIGS. 21A and 21B.

TABLE-US-00011 TABLE 11 Lead L 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.75 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 3.106 3.295 3.484 3.674 3.863 4.053 4.242 4.432 4.621 4.811 5.000 Fluctuation range = .DELTA.T -0.947 -0.758 -0.569 -0.379 -0.19 0.00 +0.189 +0.379 +0.568 +0.758 +0.947 Mount angle 10.17 9.60 9.08 8.62 8.20 7.83 7.48 7.16 6.87 6.61 6.36 Determination .circleincircle. .largecircle. .largecircle. .DELTA. .DELTA. X .DELTA. .DELTA. .largecircle. .largecircle. .circleincircle.

[0318] Meanings of words in TABLE 11 and meanings of colors (thickness) in FIGS. 21A and 21B are the same as those in the above first embodiment.

[0319] As is clear from TABLE 11 and FIGS. 21A and 21B, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the sixth embodiment.

[0320] Accordingly, the present embodiment achieves the same effect as the sixth embodiment.

Eleventh Embodiment

[0321] Now, an eleventh embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.

[0322] A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw) as in the above sixth embodiment, which is not shown. Especially, while its outer diameter is .phi.5 mm which is the same, its pitch is larger, i.e., 2 mm.

[0323] Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.

[0324] In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.

[0325] Whole screw length in axial direction: 15 mm

[0326] Screw portion length in axial direction: 10 mm

[0327] Screw outer diameter: .phi.5 mm

[0328] Intermediate value of screw: .phi.3.917 mm

[0329] Screw valley diameter: 2.835 mm

[0330] Pitch: 2 mm

[0331] Thread lead angle: 9.23.degree.

[0332] The mount angle .beta. is calculated using the formulae (1), (2), and (3) in the above first embodiment.

[0333] As shown in TABLE 12 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 12 and FIGS. 22A to 22D.

TABLE-US-00012 TABLE 12 Lead L 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Fluctuation -100% -80% -60% -40% -20% 0 +20% +40% +60% +80% +100% Revised fluctuation -50% -40% -30% -20% -10% 0 +10% +20% +30% +40% +50% D1 2.835 3.051 3.268 3.484 3.701 3.917 4.134 4.350 4.567 4.783 5.000 Fluctuation range = .DELTA.T -1.082 -0.866 -0.649 -0.433 -0.216 0.00 +0.217 +0.433 +0.65 +0.866 +1.083 Mount angle 12.66 11.78 11.02 10.35 9.76 9.23 8.75 8.33 7.94 7.58 7.26 Determination .circleincircle. .largecircle. .largecircle. .DELTA. .DELTA. X .DELTA. .DELTA. .largecircle. .largecircle. .circleincircle.

[0334] Meanings of terms in TABLE 12 and of colors (thickness) in FIGS. 22A to 22D are the same as those in the first embodiment.

[0335] As is clear from TABLE 12 and FIGS. 22A to 22D, it is understood that the interference upon going in and out can be reduced by changing D1 to adjust the mount angle .beta. in the same manner as in the sixth embodiment.

[0336] Thus, the present embodiment achieves the same effect as the sixth embodiment.

[0337] Accordingly, as is clear from the sixth to the eleventh embodiments, the same effect as in the first embodiment is achieved in ordinary metric screw threads.

[0338] The embodiments of the present invention have been described in the above. However, the present invention should not be limited to the above described embodiments, and may be practiced in various forms within the technical scope of the present invention.

Claims

1-11. (canceled)

12. A screw manufacturing method for manufacturing a medical screw, the method using: an annular cutter member that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a holding portion that holds a work piece for forming the medical screw and is rotatable, the cutter member being inclined with respect to an axial center of the work piece at a predetermined angle (mount angle), the method comprising a step of calculating the mount angle by formulae (1), (2), (3), (4) and (5) below, when a lead angle of the medical screw is different from the mount angle: mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) in case .DELTA.T>0, {(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

13. The screw manufacturing method according to claim 12, wherein the .DELTA.T is set to be within ranges of formulae (6) and (7) below: in case .DELTA.T>0, {(screw outer diameter-screw valley diameter)/2}.times.0.6.ltoreq..DELTA.T.ltoreq.{(screw outer diameter-screw valley diameter)/2} (6) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}.DELTA..ltoreq.T.ltoreq.-{(screw outer diameter-screw valley diameter)/2}.times.0.6 (7).

14. The screw manufacturing method according to claim 12, wherein the D1 is set to be the outer diameter of the screw or the valley diameter of the screw.

15. The screw manufacturing method according to claim 13, wherein the D1 is set to be the outer diameter of the screw or the valley diameter of the screw.

16. A screw manufacturing method for manufacturing a worm screw, the method using: an annular cutter member that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a holding portion that holds a work piece for forming the worm screw and is rotatable, the cutter member being inclined with respect to an axial center of the work piece at a predetermined angle (mount angle), the method comprising a step of calculating the mount angle by formulae (1), (2), (3), (4) and (5) below, when a lead angle of the worm screw is different from the mount angle: mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) {(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

17. The screw manufacturing method according to claim 16, wherein the .DELTA.T is set to be within ranges of formulae (6) and (7) below: in case .DELTA.T>0, {(screw outer diameter-screw valley diameter)/2}.times.0.6.ltoreq..DELTA.T.ltoreq.{(screw outer diameter-screw valley diameter)/2} (6) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}.ltoreq..DELTA.T.ltoreq.{(screw outer diameter-screw valley diameter)/2}.times.0.6 (7).

18. The screw manufacturing method according to claim 16, wherein the D1 is set to be the outer diameter of the screw or the valley diameter of the screw.

19. The screw manufacturing method according to claim 17, wherein the D1 is set to be the outer diameter of the screw or the valley diameter of the screw.

20. A screw manufacturing method for manufacturing a metric screw thread, the method using: an annular cutter member that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a holding portion that holds a work piece for forming the metric screw thread and is rotatable, the cutter member being inclined with respect to an axial center of the work piece at a predetermined angle (mount angle), the method comprising a step of calculating the mount angle by formulae (1), (2) and (3) below, when a lead angle of the metric screw thread is different from the mount angle: mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

21. The screw manufacturing method according to claim 20, wherein the .DELTA.T is set to be within ranges of formulae (6) and (7) below: in case .DELTA.T>0, -{(screw outer diameter-screw valley diameter)/2}.times.0.6.ltoreq..DELTA.T.ltoreq.{(screw outer diameter-screw valley diameter)/2} (6) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}.ltoreq..DELTA.T.ltoreq.{(screw outer diameter-screw valley diameter)/2}.times.0.6 (7).

22. The screw manufacturing method according to claim 20, wherein the D1 is set to be the outer diameter of the screw or the valley diameter of the screw.

23. The screw manufacturing method according to claim 21, wherein the D1 is set to be the outer diameter of the screw or the valley diameter of the screw.

24. An annular whirling cutter rotatable on its rotation axis comprising a plurality of inserts radially arranged, wherein the whirling cutter is inclined with respect to an axial center of a work piece for manufacturing a medical screw at a predetermined angle (mount angle), and, in case that a lead angle of the medical screw is different from the mount angle, formulae (1), (2), (3), (4) and (5) below are satisfied: mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) in case .DELTA.T>0, {(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

25. An annular whirling cutter rotatable on its rotation axis comprising a plurality of inserts radially arranged, wherein the whirling cutter is inclined with respect to an axial center of a work piece for manufacturing a worm screw at a predetermined angle (mount angle), and, in case that a lead angle of the worm screw is different from the mount angle, formulae (1), (2), (3), (4) and (5) below are satisfied: mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) in case .DELTA.T>0, -{(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

26. An annular whirling cutter rotatable on its rotation axis comprising a plurality of inserts radially arranged, wherein the whirling cutter is inclined with respect to an axial center of a work piece for manufacturing a metric screw thread at a predetermined angle (mount angle), and, in case that a lead angle of the metric screw thread is different from the mount angle, formulae (1), (2) and (3) below are satisfied: mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

27. A screw manufacturing machine comprising: an annular whirling cutter that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a main spindle that coaxially holds a base of a work piece for manufacturing a medical screw and rotates the work piece, wherein the whirling cutter is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle), and, in case that a lead angle of the medical screw is different from the mount angle, formulae (1), (2), (3), (4) and (5) below are satisfied: mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) in case .DELTA.T>0, {(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

28. A screw manufacturing machine comprising: an annular whirling cutter that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a main spindle that coaxially holds a base of a work piece for manufacturing a worm screw and rotates the work piece, wherein the whirling cutter is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle), and, in case that a lead angle of the worm screw is different from the mount angle, formulae (1), (2), (3), (4) and (5) below are satisfied: mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) in case .DELTA.T>0, {(screw outer diameter-screw valley diameter)/2}.times.0.2<.DELTA.T<{(screw outer diameter-screw valley diameter)/2} (4) in case .DELTA.T<0, -{(screw outer diameter-screw valley diameter)/2}<.DELTA.T<-{(screw outer diameter-screw valley diameter)/2}.times.0.2 (5) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.

29. A screw manufacturing machine comprising: an annular whirling cutter that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a main spindle that coaxially holds a base of a work piece for manufacturing a metric screw thread and rotates the work piece, wherein the whirling cutter is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle), and, in case that a lead angle of the metric screw thread is different from the mount angle, formulae (1), (2) and (3) below are satisfied: mount angle=tan.sup.-1{n.times.pitch/(.pi..times.D1)} (1) D1={(screw valley diameter+screw outer diameter)/2}+.DELTA.T (2) screw valley diameter.ltoreq.D1.ltoreq.screw outer diameter (3) where D1.noteq.0, .DELTA.T.noteq.0, and n indicates a number of threads.