Drafting instrument

Abstract

A drafting instrument comprising relatively adjustable divergent arms and a resiliently flexible spring tape having spirally curved end portions selectively engaged by the arms. A curvature control lever is engageable selectively with the spring tape to control in cooperation with the arms the curvilinear shape of the spring tape for tracing the selected curvilinear shape thus effected.

Description

This invention relates to improvements in drafting instruments, and is more particularly concerned with such an instrument for providing an infinite range of curves to assist in various pattern and drafting situations.

Regular curves are fairly easily found and are provided by various fixed instruments such as the well known French curves. However, numerous situations require curvilinear variations that are either rather complex or at least are not readily found in a fixed pattern or instrument.

It is an important object of the present invention to provide a new and improved drafting instrument by which numerous and varied curves can be effected easily and quickly.

Another object of the invention is to provide a new and improved drafting instrument having a resiliently flexible strip material such as clock spring material.

A further object of the invention is to provide a new and improved drafting instrument having novel means for controlling the curvature of a flexibly resilient strip or band of material.

Other objects, features and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawing although variations and modifications may be effected without departing from the spirit and scope of the novel concepts embodied in the disclosure, and in which:

FIG. 1 is a top plan of a drafting instrument embodying features of the invention.

FIG. 2 is a detail view showing certain features of the spring tape of the invention.

FIG. 2A is an elevational view showing a portion of the tape.

FIG. 2B is a prospective view of the center member.

FIG. 3 is an elevational view of the instrument.

FIG. 4 is a perspective view of a spacer member used in the instrument.

FIG. 5 is an exploded elevational view of the curvature control lever of the instrument.

FIG. 6 is an isometric view of a coupling used with the control lever.

The present invention is adapted to be employed in various drafting situations, such as, architectonic drawing, architecture, orography, mathematics, geology, artistic drawing, statistics, engineering meterology, shoemaking, carpentry, tailoring, commercial drawing, precission mechanics, electronics, mining. There are other uses in which a variable pattern drafting instrument is valuable such as: in anatomy in order to draw the muscles or build a model in clay or paste for the medicine studies in which is necessary to distinguish a muscle from the other, under the different shapes acquired by the pattern. In engineering is the broadest field, because in all of the branches it can be used very frequently because the student helps himself to build the mathematical curves which are necessary to study the different phenomena presented in the said study.

The main principle of the present apparatus is to maintain to different shapes a spiral spring or a deflected band which normally tends to remain in straight line. In this case, there are two spirals joined as a single tape or band, with the spiral centers staying at a certain distance due to arms formed from plates, one above and one below, which by means of clamps secure the band very tight. The plates connected this way, cooperate to hold the tape rigidly in the desired form in which is is to be employed. The mechanism which will be discussed later allows the operator to release the tape totally or partially and then work with it. In mechanical engineering there is a very appropriate work concerned with oscillatory movements with softening in which is necessary a curve pattern that gives eliptic forms in order to present it graphically, and this is used for the design of some machines. In orogaphy, geology or any other science it is used to draw elevation curves. In tailoring it is employed in the designing of clothes, giving greater flexibility to such designing. The arms of the device may be as simple as two plates joined by a screw which can be clamped to a spiral tape and that accomplishes the requirements mentioned above.

A sample of variable plate is like the one presented in FIG. 1. The tape of double spiral is represented with the letter A. The locations of rectangular holes O (FIG. 2) made in the longitudinal centerline of the tape, looking from the front, are represented a1 to a7, respectively. The arm system is represented in its entirety by B. A control lever connects the holes of the tape with the arms and is identified by C2. The circle C1 can also receive the mounting for the lever C2 or another of the said levers which allows greater complexity of the curves that are desired to project. The arm system B is two pairs of plates comprising a pair of upper and lower plates, upper plate B1 and lower plate B1', and a pair of plates comprising an upper plate B2 and a lower plate B2' joined in divergent relation at one end by means of a screw T by which different angles, as well as flexible adjustments for different positions can be attained. With the screw T the arms can be variably adjusted relatively to provide an infinity of various forms of curve and greater or smaller radius of curvatures.

The indicated points P1, P2, P3, and P4 are the different strategic positions in which one can put the pin 10 that represents approximately the center of any of the two ellipsi, according to the desire of the operator. This way one can achieve making greater or smaller any of the internal curves of the ellipsi moved to P2 or P3. Isolating each one of the parts of the pattern one can attain a variable curvature pattern. It will be seen that one half of the spiral shape tape A, which is made of metal with a width h exerts a force of expansion in the same way as a clock spring, is at its internal extremity rigidly joined to the pin 10 with a groove 11 that comes out to the end at the upper plate in order to be able, as desired to move the tape to contract it or expand it. The holes a1, a2, and a3, are represented in FIG. 2. In those holes will enter the head N3 of the lever C2, or C1 if it also exists, and the one left will enter in another hole. Viewing the arm plate system in FIG. 3, one can see the fastener clamps S1 and S2, arrows indicating the direction in which the plates are pressed against the tape. Layers of resistent rubber H1 and H2 are provided to give immobility to the tape, allowing it a better handling to the operator. The screw T with a hand or wingnut secures the four plates B1 and B2 simultaneously, leaving them immovable, due to the fact that there is a cylindrical spacer J which allows the said operation.

Referring to the levers C1 or C2, (FIG. 5) the two of them are equal. The screw M could be soldered to the plate B1 or B2. The screw and washer parts K, L are only used to fasten the lever bar C2. The head U of the bar C2 is slotted, as shown, and receives a neck N2 of a coupling N which has a retaining tail N1 at one end and a head N3 at the opposite end and which coincides in size with any of the holes a1, a2, etc. of the tape, and has a rotating movement, to facilitate coupling to the tape A for maintaining any desired curvature.

In use of the instrument the lower plates B1' and B2' offer an advantage to the operator, in that they maintain the tape A to a certain height over a surface on which a pencil or pen traces the curvature of the band A. The plates should be easily slidable over the flat surface of the table over which one is going to draw or make sketches. Supposing that what is being designed is a cam for a certain engine and one has the points over which a curve will be designed to coincide with them all, the device of the present invention is adjusted to dispose the tape A to the best curvature between the mentioned points trying as nearly as possible to obtain more than 50 percent of the profile of the cam, assuring perfection of the curve for the rest of the curve to follow. The levers C1 and C2 are useful in more elaborate efforts in which the curves change directions or allow a new sketch in a given position. If one would like to know the concavity of a surface in a hole in which the device may fit easily, one can take advantage of the characteristics of the spring and tighten the fasteners S1 and S2 in order to maintain the said curvature.

It will be understood that variations and modifications may be effected without departing from the spirit and scope of the novel concepts of this invention.

Claims

I claim as my invention:

1. A drafting instrument for selectively producing a large variety of traceable curves, comprising:

a resiliently flexible spring band having opposite expansile spiral end portions and each end portion having a terminal within the spiral thereof;

two pairs of elongated top and bottom clamping plates which generally coextensive in each pair and each pair providing a respective arm;

means connecting proximal end portions of the pairs of plates together with the plates of each pair spaced apart, and said connecting means including fastening structure operable for adjustably securing the arms in various divergent relative positions;

means connecting the terminal of one of said spiral end portions between the distal end portion of one of said pair of plates, and means connecting the terminal of the other of said spiral end portions between the distal end portions of the other of said pairs of plates;

at least one elongated control lever extending between one of said arms and said band intermediate said spiral portions to maintain the band in a controlled curvature;

means adjustably connecting one end portion of the control

means adjustably attaching the control lever at its opposite end portion directly to one of the plates of said one arm; and means for releasably clamping said spiral protions of said band between said plates whereby to hold the band in predetermined adjusted curvatures.

2. An instrument according to claim 1, wherein said band has a series of longitudinally spaced apertures therein, and said means connecting said one end of said lever to the band being selectively engageable in any one of said apertures in the band.

3. An instrument according to claim 1, wherein said band has a series of longitudinally spaced apertures therein, and said means connecting said one of the lever to the band comprising a coupling selectively engageable in any one of said apertures in the band.

4. An instrument according to claim 1, including resiliently compressible surfacing material carried by at least one of the plates of each of said pairs of plates on the surface of said at least one plate which faces toward the edge of the associated spiral end portion of the band, and said compressible facing means engaging said edges of the associated spiral end portion of the band and thereby positively holding the spiral end portions to assist in retaining the band in selected curve adjustments.

5. An instrument according to claim 1, wherein said pairs of plates include in each pair a lower plate to engage a supporting surface, said lower plates having bottom surfaces which are coplanar so as to lie flat in the same plane on a drawing surface, one of said lower plates having its proximal end portion offset to the thickness of the lower plate of the other pair of plates and lapping said lower plate of the other of said plates whereby to provide for the coplanar bottom surface relationship.