Solder Tip Setscrew

Abstract

A setscrew comprising a rounded soft metal tip extending from a threaded shaft. The soft metal tip is adapted to contact a member against which it is forced without damaging deformation to the member or the tip. The setscrew is constructed by melting a piece of soft metal on to a recessed portion in the end of the threaded shaft.

Description

The present invention relates to a setscrew adapted to hold two members in substantially stationary relationship. The setscrew of the present invention is described in connection with preventing rotational movement of two concentric members but may be used with members of various shapes and designs.

Setscrews of the type here described generally consist of a threaded shaft adapted to be screwed into one member and to contact a second member and hold it in relative stationary relationship. In designing setscrews of this type a balance must be struck between three important considerations. First, the material at the end of the threaded shaft adapted to contact the second member must be of a type such as to cause a minimum of damage to the second member upon contact therewith and the application of compressive force. Second, the material must be of a type such as to withstand the compressive force applied upon contact with the second member without deforming to a shape in which it is no longer useful for its intended purpose. Third, the engagement between the material and the second member must be effective to hold the second member stationary.

It is a primary object of the present invention to devise a setscrew with a tip portion of a material and shape particularly suitable for continued and repeated contacts in holding relationship with a member.

It is a further object of the present invention to devise a setscrew which is easily manufactured and in which a contacting tip is automatically formed in a desired shape without the necessity of machining.

It is still a further object of the present invention to devise a setscrew with a contacting tip of a soft metallic material in which a minimum of such material is wasted during manufacture.

It is another object of the present invention to devise a setscrew utilizing a contacting tip of a material and shape such that a minimum of tip material will sustain a maximum useful life.

The setscrew of the present invention comprises a threaded shaft with a recessed portion at one end. A soft metal insert is positioned in said recess and extends beyond the end of said shaft in a rounded or convex configuration.

It has been found that conventional setscrews of the type here described which utilize nonmetallic tip inserts, such as nylon, become inoperative after they have been used only a few times to lock two members in stationary relationship. The tip in such devices tends to deform and sometimes crack in outward radial direction upon the application of the compressive force necessary to hold the two members in stationary relationship. This spreading in an outward direction tends to interfere with the insertion of the threaded shaft into the first member. Moreover, continual use of a setscrew with a tip which has been so deformed may result in a complete severance of the tip portion from the threaded shaft, the tip portion thereafter remaining jammed in its holding position. The difficulty is partially due to the conventional cylindrical shape of such tips. As is well known, a member of such shape will tend to deform radially outwardly upon the application of compressive forces at its ends. This type of deformation is aggravated if the surface of the member which contacts the cylindrical tip is rounded because in such a case the compressive force is exerted unevenly on the end surface of the cylindrical tip.

I have found that a setscrew comprising a tip of soft metal is particularly well suited for repeated compressive contact with a member adapted to be held. Moreover, I have found that such a soft metal tip when formed in a rounded or convex configuration displays a pattern of deformation, after repeated contact with the member to be held, which does not interfere with the insertion of the threaded shaft into the first member and does not weaken the tip, as by cracking.

Moreover, a soft metal tip of the type used in the present invention is more readily adapted to conform to the shape of the member it holds after repeated contact with such member. As a consequence, the tip becomes more, rather than less, effective in preventing unwanted relative movement after repeated use.

To the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to a setscrew as defined in the accompanying claims and as described in this specification, taken together with the accompanying drawings in which:

FIG. 1 is a cutaway side elevation of the setscrew of the present invention, the cutaway portion showing the tip material inserted in a conical recess of the screw shaft;

FIG. 2 is a front view of the setscrew of FIG. 1;

FIG. 3 is a cutaway side elevation of the setscrew in its operative environment;

FIG. 4A is a side elevation of a prior art setscrew with a cylindrical tip portion of a material such as nylon;

FIG. 4B is a side elevation of the setscrew of FIG. 4A showing the deformation of the tip material after repeated use; and

FIG. 5 is a side elevation of the setscrew of the present invention showing the deformation of the tip material after repeated use in the environment of FIG. 3.

As best shown in FIG. 1, the setscrew of the present invention comprises an externally threaded screw body generally designated 10 with a driving recess 12 at one end, as is conventional. In the form here shown the driving recess 12 is designed to accommodate an Allen-head wrench, but this is of course merely a matter of choice. The tip of the screw body 10 is provided with a tapered or bevelled portion 18 terminating in a flat circular end 19. A recess 14 extends axially into the screw body 10 from the tip end 19, and is provided with inwardly tapering walls, the preferred form here disclosed being substantially conical in shape. A slug 16 of soft metallic material is received within the recess 14 and extends axially out therefrom, the outwardly extending part terminating in a rounded configuration. It is preferred that the tapered screw surface 18 extend all the way to the recess 14 and that the rounded outer surface of the slug 16 extend all the way to the screw surface 18, preferably merging with the surface 18 with little or no discontinuity as illustrated in FIG. 1.

The device may advantageously be manufactured by placing a mass of appropriate soft metal in or on the recess 14 and then melting the mass so that it flows into and conforms to the shape of the recess 14. The mass of soft metallic material in its original form may take any suitable shape, as determined by the availability of the material in question. Thus, it may be in the form of individually produced spherical globules, or in the form of small cylinders cut from a rod of the material in question, or even in the form of a collection of small particles. The initial shape of the mass of soft metallic material is of little significance, since when it melts it will change its shape to conform to the particular configuration of the recess 14. The significant feature is that the amount of soft metallic material provided is appropriate to the volume of the recess 14 in order to substantially fill that recess and to project out therefrom. The mass of molten soft metal, when it cools and hardens, will inherently, by virtue of surface tension, solidify with a rounded exposed surface, the radius of curvature of which will depend upon the specific material employed, the amount of material present, and the size of the outermost perimeter of the recess 14 defined by end portion 19. Thus, it will be seen that the slug 16 may be formed to the desired shape without having to perform any machining operation, and without being limited to any specific initial shaping of the soft metallic material.

It is of course essential to proper operation that the slug 16 remain attached to the screw body 10. This may be accomplished in any convenient manner, as by providing a layer of material on the surface of the recess 14 which will bond the two operative parts 10 and 16 together. Thus, where as is preferred, the slug 16 is formed of silver solder, a conventional solder flux is applied to the surface of the recess 14 before the slug 16 is melted thereon.

FIG. 3 shows the set screw of the present invention in its operative environment. By way of illustration, a member 20 is shown carrying a cylindrical shaft 22 in a cylindrical passage 24. Within member 20 is a threaded passage 26 communicating with passage 24 and adapted to receive setscrew 8. Screw 8 is shown received in passage 26 so that tip 16 contacts shaft 23 at point 28. Shaft 22 is here shown purely by way of example, as cylindrical, but it should be noted that tip 28 will initially bear against the surface of a member of any shape (other than a complementary concave surface) in point contact. After initial contact has been made, further turning of screw 8 will produce a slight deformation of the rounded tip 28 and a compressive settling of the tip material in conical recess 14. In this position screw 8 is adapted to firmly hold shaft 22 stationary with respect to member 20.

FIG. 5 shows a setscrew of the present invention after repeated use in an environment such as that shown in FIG. 3. The concave configuration of the tip 16 is due partially to deformation and partially to wear. It can be seen that the tip shape has tended to conform to the shape of the surface of shaft 24.

FIG. 4A shows a prior art construction of a setscrew of the type described. A cylindrical tip portion 30 of a synthetic material, such as nylon, is inserted in a cylindrical recess 32 in threaded shaft 34 having a tapered or bevelled surface 33. After repeated use in an environment such as that shown in FIG. 3, the tip material deforms to the shape shown in FIG. 4B. Upon the application of axial compressive force the cylindrical tip bulges outwardly, as will any cylindrical member of a deformable material. It will be readily apparent that this bulging effect once begun is self-perpetuating. Substantially all the deformation of tip 30 takes place exteriorly of the recess 30. Thus the material outside recess 30 is squeezed outwardly, weakening the material along a line separating the interior from the exterior portion. Continued use may result in complete severance of the exterior tip material from the portion within recess 32, whereby the setscrew is of no further use. Moreover, this severance is likely to occur while the screw is in use so that when the screw is loosened the severed portion may remain lodged against member 22, an obviously undesirable result.

It has been also found that the exterior material tends to develop cracks, such as 36 in FIG. 4B, emanating from the perimeter of recess 32. This effect is due to the localized compressive force exerted by the sharp edge formed at the intersection of the surface of recess 32 and bevelled surface 33. The portion extending beyond the perimeter of recess 32 may tend to sever completely from the tip material, again causing obviously undesirable results.

While the tip of a conventional set screw shown in FIG. 4A will show undesirable deformation after only a few uses, it has been found that the setscrew of the present invention can be used to lock and unlock two members over 100 times with a minimum of undesirable distortion.

Although all the reasons for the more desirable distortion pattern achieved with the setscrew of the present invention are not known, it is clear that the tip material used and its shape both contribute to the improved result. The following is offered as a partial explanation for this phenomenon.

As previously discussed, initial application of compressive force will occur by point contact at the center of tip 16. The tip, being constructed of a soft metal material, is readily adapted to flow and conform to the surface against which it is pressed. Thus, unlike a tip of a material such as nylon, the initial deformation takes place substantially solely at the point of actual contact. That is, the compressive force exerted by member 28 has very little effect on tip material beyond the point of contact. While material is squeezed outwardly, this deformation is not harmful since the material in question is initially near the central axis of the tip and is not squeezed outwardly beyond the perimeter of recess 14 defined by end portion 19. The resulting flow pattern thus exhibits substantially very little outward bulging. Any bulging that does occur does not extend radially outwardly a sufficient distance to interfere with the insertion of threaded shaft 10 into member 20.

The present invention, therefore, comprises a setscrew which is easy to manufacture with a tip the shape and material of which exhibits substantially more durability than conventional setscrew tips.

While only a single embodiment of the present invention has been herein specifically disclosed, it will be apparent that many variations may be made thereto without departure from the scope of the invention as defined in the appended claims.

Claims

I claim:

1. In a setscrew for holding a first member in substantially stationary relationship to a second member, comprising a threaded body adapted to be screwed into a threaded opening in said first member toward said second member, the improvement comprising said body having at a first end adapted to be directed toward said second member, a substantially axially extending recess, the sidewalls of which taper inwardly from said first end of said body, said recess being relatively shallow in comparison to the length of said threaded body, and a soft metal insert in said recess, fixedly secured to said body, and extending beyond the plane of said first body end, the extended portion thereof being convexly curved at least in the region of its farthest extending portion and being confined laterally within the limits of the periphery of said recess at said first end of said body, said insert substantially filling said entire recess and being bonded to said body along substantially said entire recess, whereby said soft metal insert initially engages said second member in point contact thereby eliminating radial deformation beyond the outer periphery of said recess.

2. The setscrew of claim 1, wherein said soft metal insert is silver solder.

3. The setscrew of claim 1, in which said recess is substantially conical in shape.

4. The setscrew of claim 3, wherein said soft metal insert is silver solder.

5. The setscrew of claim 1, wherein said soft metal insert is formed of a single soft metal material, said soft metal material being exposed outwardly of said recess.