US3398447A - Method of making a draftsman's straightedge - Google Patents

Description

A g- 1953 (37 s. DOLGORUKOV 3,398,447

METHOD OF MAKING A DRAFTSMAN'S STRAIGHTEDGE 2 Sheets-Sheet 1 Filed May 25, 1967 Luvs or CUT ING OFF INVENTOR.

United States Patent 3,398,447 METHOD OF MAKING A DRAFTSMANS STRAIGHTEDGE Gregory S. Dolgorukov, Ferndale, Mich. (407 Fisher Bldg., Detroit, Mich. 48202) Continuation-impart of abandoned application Ser. No. 307,283, Sept. 5, 1963. This application May 25, 1967, Ser. No. 586,570

7 3 Claims. (Cl. 29-407) This invention relates to geometric instruments and more particularly to improved methods of making draftsmans straightedges such as used as free straightedges or in connection with a drafting machine. The present application is a continuation-in-part of my co-pending application Ser. No. 307,283 filed Sept. 5, 1963, for Drafting Instrument, now abandoned.

The necessity of producing on a drawing relatively long straight lines approximating in their straightness a geometric straight liue presented a ditficult problem which has persisted in this art for a great many years. The straightness of such line in many instances is required to be within only several thousandths of an inch. Such precision cannot be produced by drawing a line along the edge of a wooden straightedge, which is, in effect, a wood strip of a desired length and thickness. Warpage of wood due to its natural drying or seasoning or its absorption of moisture from the surrounding air, all influenced by the heterogeneous structure of the wooden mass affected by its grain, increases with the length of such straightedges and becomes noticeable in wooden straightedges beyond 12" in length. Lining the edges of such a wooden strip with transparent plastic, such as cellulose nitrate, has been resorted to for many years. Such straightedges give the advantage of transparency for a distance such as A" adjacent the working edge. However, the structure of the straightedge, being still that mainly of wood, not only did not solve the above difficulties, but, on the contrary, under many conditions amplified them still further. The difference in expansion and shrinkage of the two materials may, in longer straightedges, aggregate to a considerable amount, causing warpage and even separation of the plastic edges from the wood. The high flammability of cellulose nitrate requires extreme care in its machining, handling and storage. In addition, attack of this material by fungi, both prior to fabrication into drafting instruments and after such instruments have already been in use for some time, has taken within the last decade very serious proportions. Such attack usually manifests itself by sweating of the surface of the cellulose nitrate material, at which stage presence of the affected material or instruments next to metal drawing instruments is exceedingly corrosive and destructive to these very delicate instruments. The next stage of the disease manifests itself by mold covering the surface of the material and mottling the interior thereof. Next comes cracking and virtual complete disintegration of the material.

This development caused virtual discontinuance of the use of cellulose nitrate as material for drafting instruments and adoption of acrylic resin plastics for this use. It has been found, however, that while possessing certain properties superior to those of cellulose nitrate, particularly resistance to attack by fungii, better fire resistance, greater transparency and better dimensional stability, acrylic resin plastics are also much harder and more brittle than cellulose nitrate, and for this and other reasons are not fully suitable for substitution with the same dimensional and constructional specifications into the designs developed over several decades by trial and error with the use of cellulose nitrate.

Particularly, it was found that While being fully acceptable for use in instruments, such as drafting triangles, acrylic plastics are not suitable for mere substitution in place of cellulose nitrate in T-squares and straightedges in the form of edge linings. Attempts to make straightedges of wood with acrylic plastic lined edges did not produce better or even satisfactory constructions. Machined to produce squared pgncil-point guiding surfaces, acrylic plastic produces sharp and brittle edges easily nicked. Several nicks on the sharp edges of a pencilpoint guiding side are so annoying in use as to make an instrument virtually unusable. Furthermore, such nicks provide places Where minute cracks originate in the process of cutting and rapidly extend into the body of the plastic, causing breakage of the instrument on impact, such as when falling off a drawing board. In addition, when plastic lining strips are split-cut at their ends for the provision of a plastic strip or key strip trying lining on both sides of the Wood strip together, such split ends break off or crum out, often even before the straightedge gets into the hands of the user, causing eventual separation of the lining strips from the Wooden strip, i.e. disintegration of the straightedge.

The difliculties in machining long plastic straightedges with requisite precision, because of very peculiar and puzzling problems, coupled with the above-explained disadvantages have been responsible for the attitude of those skilled in the art that plastic straightedges are not fully reliable. Accordingly, the use of draftsmens straightedges made of steel has been constantly growing in spite of other serious disadvantages and problems peculiar to steel straightedges. Attempts to manufacture draftsmens straightedges by molding or extruding plastic mass into a strip form has the disadvantage of lacking the requisite precision, producing Wavy or streaky surfaces distorting the image underneath and causing eye strain, as Well as rapid disintegration due to severe thermal stresses produced within the mass of such plastic due to its rapid cooling in the process of molding or extrusion.

While manufacturing steel straightedges could be done in accordance with well worked out techniques of grinding steel to ensure the requisite precision at least in a new square edge, such steel straightedges have not solved the problem of providing a draftsman on the board with a straightedge having the requisite precision and which is convenient to use. Steel straightedges are heavy to move on the board or to carry around. They are not transparent and often mar the drawing. In addition, they often slide off inclined drawing boards and have been known to cause injuries when falling. Furthermore, unless hardened and reground, such steel straightedges are more susceptible to nicking than even plastic straightedges. While in a plastic edge a nick usually causes a piece of plastic to crum out, thus causing interruption of a drawn straight line but not affecting its straightness and precision of its location, in a soft steel straightedge a nick manifests itself not only by a depression in the edge but also by protrusion of the displaced soft steel outwardly of the edge. Such a nick occurring on an edge used against another edge, such as that of a drafting triangle, may destroy precision of the straightedge by as much as .020" or .030". On the 3 other hand, hardened steel straightedges are very expensive.

One of the important applications of straightedges is in connection with so-called drafting machines. I have found, however, that conventional straightedges used for such purpose possess a large number of disadvantages which have accumulated to the point where many draftsmen prefer to use a T-square on a small drawing board, or a strung straightedge on larger boards with a pair of triangles rather than a drafting machine with its two perpendicularly disposed straightedges or scales. I have found that much of such difliculties result from the fact that drafting machine straightedges are usually provided with various graduations or scales for the purpose of laying off distances and thus eliminating in a large measure the use of dividers and similar instruments, and presumably make drafting operations more efiicient. In order to impart stability to the scale, the straightedges provided therewith are often made of metal, Which usually is aluminum, since the use of heavy steel scales may not be practicable when such straightedges are connected to a drafting machine. However, metal straightedges are opaque and, therefore, have all the consequent disadvantages. Furthermore, aluminum rubs off on the paper leaving dirty spots exceedingly difiicult to erase without erasing drawn lines. Such spots when left on the drawing are then reproduced on the drawing copies, greatly decreasing their legibility. Furthermore, in order to make measurements possible, the guiding sides of such straightedges are beveled to approximately .040" in order to bring the graduation lines as close to the paper as possible and thus avoid parallax.

By such a construction it is attempted to have on such straightedges one or two point-guiding sides each of which is also a measuring edge. I have found, however, that because of such a construction the straightedge does not have an eflicient measuring edge or an efiicient pointguiding side surface and does not perform satisfactorily either of its two intended functions, i.e. measuring or point-guiding, and, in addition, is exceedingly harmful to draftsmens eyes.

The latter disadvantage results from the fact that the use of measuring graduations or scales in drafting operations takes approximately of the time while the remaining 90% requires the straightedge to be used merely for guiding the point of a pencil or of an ink pen along a straight line. Yet the measuring graduations remain in front of the draftsmans eyes 100% of the drafting time, causing involuntary focusing of the eyes on such graduations, producing eye strain and headache after several hours of work. At the same time, such measuring edge being reduced in its vertical extent to only .040" or .035" does not have sufiicient vertical extent to provide for a satisfactory performance of its point-guiding function or to provide sufficient bearing for the pencil point or for triangles, particularly beveled triangles turned over for the purpose of inking. It was attempted to eliminate the first of the abovementioned difficulties by omitting the scale on the drafting straightedge and providing a straightedge in the form of a piece similar to a conventional T-square blade made of Wood with plastic lined edges. However, such straightedges have all of the disadvantages of the construction explained above. Use of molded plastic straightedges made for the provision of scales thereon but with scales omitted did not provide a proper point-guiding side surface for many drafting operations, since it was made to serve also as a measuring edge heavily beveled. In addition, being of molded plastic such straightedges had additional disadvantages explained above.

Provision of measuring graduations on the point-guiding surfaces of T-squares has also been practiced for many years With equally objectionable results. I have solved the above problem with respect to the T-squares and such solution is disclosed in my US. patent No. 3,280,465.

In the construction disclosed in that patent, the measuring scale was removed from the upper point-guiding side surface of the T-square and placed upside down and in reverse on the upper surface of the lower side of the T- square blade. For use as a measuring edge, the T-square has to be turned upside down bringing the measuring edge into the upper position, in which position the scale would be disposed against the surface of the drawing and would read direct. However, such a solution could not be used in drafting machines since the straightedge is rigidly secured to the drafting machine and cannot be turned over without being disconnected from the drafting machine. Accordingly, this problem remained unsolved for the drafting machine edges for many years even after it was solved for T-squares.

One of the objects of the present invention is to provide an improved method of making a draftsmans straightedge used freely by itself or connected to a drafting machine whereby the above difficulties and disadvantages are overcome and largely eliminated without introducing new problems or increasing the costs involved.

Another object of the present invention is to provide an improved method of making a draftsmans free straightedge which combines the advantages of a steel straightedge and of a plastic straightedge but in which the disadvantages of both, explained above, are eliminated.

A further object of the present invention is to provide an improved method of making a draftsmans free straightedge which can be made with requisite precision and retain the same, which is light to move on the drawing board and to carry around, which does not present danger in falling off the board, which does not mar the drawing, is transparent and in which the tendency of its machined sharp edges to nick is reduced to a minimum.

A further object of the present invention is to provide an improved method of making a draftsmans straightedge in which origination of minute cracks in the process of machining, common in machined plastics, particularly acrylic plastics, which cracks have a tendency to grow into the plastic mass and finally to develop into cracks causing nicking and even breakage of the edge on impact, is reduced to a minimum.

A still further object of the present invention is to provide an improved method of making a draftsmans straightedge made of harder and, therefore, usually more brittle plastic material, such as acrylic resin, the construction of the straightedge being such as to produce a more durable straightedge in which easy breakage of corners and chipping of sharp end edges and nicking of the sharp edges of the squared point-guiding surfaces are reduced to a minimum.

A still further object of the present invention is to provide an improved method of making a draftsmans free straightedge which, in effect, has guiding surfaces of three different types; namely, a plain squared side Surface, a side beveled at the top and particularly desirable for close pencil work, with the latter side becoming, when the straightedge is turned over, an edge relieved at the bottom and thus providing for safer inking, particularly for very heavy ink lines.

A still further object of the present invention is to provide an improved method of making a draftsmans free straightedge of the nature specified in the preceding paragraph, the bevel on the top surface of the straightedge along its point-guiding side surface being of such width and inclination as not to distort by refraction the image underneath.

A still further object of the present invention is to provide an improved method of making a draftsmans straightedge of the foregoing character which is convenient to use, pleasant to handle and has a long life.

A still further object of the present invention is to provide an improved method of making a draftsmans free straightedge and a packing case therefor, with the respective construction of the straightedge and of the case being so correlated that the case serves as a fully sealed package before the straightedge is sold but upon opening becomes a permanent protective case very convenient and easy to use and permitting the straightedge to be hung up while left in the case.

A further object of the present invention is to provide an improved method of making a drafting straightedge adapted to be used connected to a drafting machine, whereby the difficulties and disadvantages of conventional drafting straightedges of drafting machines are eliminated without introducing new problems or making such straightedges more expensive.

A still further object of the present invention is to provide an improved method of making a draftsmans straightedge adapted for use connected to a drafting machine, which straightedge provides an improved pointguiding side surface useable with success both for pencil work and for ink work without turning such edge over as in the use of the straightedge disclosed in FIGS. 1-9.

It is a further object of the present invention to provide an improved method of making a straightedge for use in connection with a drafting machine, which straightedge has provided thereon a side point-guiding surface particularly advantageous for such purpose and a separate measuring edge particularly advantageous for that function and in which the combined point-guiding and measuring edges usually not capable to operate properly either as a point-guiding surface or as a measuring edge for the reasons explained above are eliminated.

It is an added object of the present invention to provide an improved method of making a draftsmans straightedge of the nature specified above which is simple and rugged in construction, dependable in use and is relatively inexpensive to manufacture.

Further objects and advantages of this invention will be apparent from the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification, wherein like reference characters designate corresponding parts in the several views.

FIG. 1 is an elevational view showing an improved .draftsmans free straightedge embodying the present invention.

FIG. 2 is an elevational view on an enlarged scale of the left-hand end of the straightedge with said view showing more clearly various features of construction of the straightedge of FIG. 1.

FIG. 3 is a sectional view taken in the direction of the arrows on the section plane passing through the line 3-3 of FIG. 2.

FIG. 4 is an end view on an enlarged scale taken on the left-hand end of the edge from the line 44 of FIG. 2, with the middle portion of the edge being broken away to reduce the size of the figure.

FIG. 5 is a view on an enlarged scale taken in the direction of the arrows from the line 5-5 of FIG. 2.

FIG. 6 is a view similar in part to FIG. 5 but taken in the direction of the arrows from the line 66 of FIG 2.

FIG. 7 is a perspective view of one end of the straightedge illustrating further various features of the construction thereof.

FIG. 8 is an elevational view showing the improved free straightedge disclosed herein packaged in a transparent case for distribution, which case becomes, after the straightedge is placed in the hands of a user, a permanent protective case for continued use.

FIG. 9 is a fragmentary view showing the configuration of the end of the straightedge made with a hollow cutter and having a rounded configuration of its end surface instead of having a squared end relieved at both sides as in FIG. 6.

FIG. 10 is a view similar in part to FIG. 1 but showing the straightedge intended for use connected to a drafting machine and provided with a chuck for such purpose.

FIG. 11 is a sectional view taken in the direction of the arrows on the section plane passed through section line 1111 of FIG. 10.

FIG. 12 is a view similar in part to FIG. 11 with the indication of the preferred dimensions being omitted in order to prevent their inferefence with the numerical designation of portions of the straightedge used in said FIG. 12.

FIGURE 13 is a view similar in part to FIGURE 11' but showing a straightedge for use in connection with a drafting machine and having a separate point-guiding side surface and a separate measuring edge providedwith suitable graduations, each of said expedients performing properly its intended respective function without interference from the other expedient which must satisfy'different and contradictory requirements and'in which the measuring edge is used only for measuring operations without accompanying involuntary focusing of the draftsmans eyes thereon in non-measuring drafting operations.

FIGURE 14 is a side view of the straightedge of FIG- URE 13 with the observer looking on the left-hand end thereof' It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation.

In the drawings there is shown, by way of example, an improved straightedge embodying the present invention. Referring specifically to FIGS. 1-9, the free straightedge illustrated therein comprises .an elongated rectangular body, designated by the numeral 10, made perferably from a transparent plastic material, such as acrylic resin. I prefer to make such a body approximately i thick even in relatively short lengths, such as 18", to provide for easier picking up of the straightedge from the board and, in general, for a more convenient handling thereof. However, a thickness of 4:" may also be used with success but without attaining the advantages mentioned above. The width of the straightedge varies with the length in order to ensure convenient handling and requisite rigidity of the straightedge and to reduce its bending under the pressure of a pencil point or other drawing instrument. I prefer to use widths ranging from approximately 1%" in a straightedge 18" long to as much as 3" in a straightedge 40" long or longer. M

It will now be seen in view of the foregoing that a body of such form will have two longitudinal sides and two ends, each having a sharp top edge and a sharp bottom edge and, therefore, having four sharp longitudinal edges and four sharp end edges meetingin pairs at four corners. The top longitudinal edges are designated by the numerals 11 and 12 while the bottom longitudinal edges are designated by the numerals 13 and 1 4. The top end edges are designated by the numerals 15 and 16 and the bottom end edges by the numerals 17 and 18. The corners of the straightedge body are designated by the numerals 21, 22, 23, and 24.

The top longitudinal edge 11 is produced by beveling the straightedge at its top surface along one of its sides at approximately a 2025 angle to approximately onehalf of its thickness and thus producing the beveled'surface between A and 71 in width. The beveled surface of such width while being transparent does not have the tendency to double up the line underneath because of refraction, as would a narrower bevel.

It is an important improvement of the straightedge disclosed above that all four of its longitudinal sharp edges including the edge 11 are chamfered preferably at a 45 angle to give a chamfer of approximately .010" wide. I have found that with harder plastic materials,

such as acrylic resin, the action of a milling cutter produces at the sharp edge where two surfaces meet a multiplicity of minute cracks caused by pressure of the cutter. These cracks, originally invisible to the naked eye, have a tendency to grow inwardly of the plastic mass, particularly where the starightedge is subjected to stress due to mechanical loading or thermal conditions, and progress gradually further and further into the body of the straightedge. Should such straightedge be subjected to an impact, such as when falling on the floor, or to bending, it may break along one of such cracks without the user realizing the actual cause of the breakage. Furthermore, when adjacent cracks occur at a short distance form each other and proceed at angles causing their meeting in the body, the material between such cracks soon crumbs out, producing highly objectionable nick along the edge. Occurrence of such nicks along a sharp edge is greatly facilitated even without the action of the cracks described above but only because of the sharpness and resulting weakness of the edge. However, presence of such minute cracks greatly increases the tendency of the sharp edge to nicking.

Furthermore, even a perfectly sound but sharp edge has a serious disadvantage of cutting into the graphite of the pencil, producing breakage of the pencil point even with harder grades of graphite without the draftsman realizing the actual cause of such breakage and attributing it to the weakness or the hardness and brittleness of the graphite. However, this condition is not cured by using softer graphite and it adds an additional problem of having the graphite film or powder accumulating on such edge and smudging the drawing when the edge is turned over.

By providing the chamfer described above, I greatly dull the sharp edge, virtually destroying its tendency to cut into the graphite and cause the graphite to contact the edge further away from the top surface of the instrument. Therefore, when the instrument with such chamfered edge is turned over, the graphite film deposited on the edge and is disposed on the edge which is spaced from the drawing paper and is not rubbed or smudged on the drawing. Furthermore, a chamfer of such depth removes or cuts away the sharp edge in the mass of which minute cracks originated in the process of milling, and thus produces the edge which is incomparably stronger and has a much longer life without being affected by nicks, and thus increasing the life of the entire straightedge.

All four corners of the straightedge are rounded. I prefer to have such rounding to be done at a radius of approximately A in order to decrease breakage of the corners. It should be distinctly understood that such expedient is not effective by itself to reduce breakage of the corners since the condition under which it would be effective for such purpose actually never occurs. This condition would be falling of the straightedge on the floor or other hard surface while being in the plane strictly perpendicular to such hard surface. Any deviation from such a position causes the edge to fall not on its end surface but on its sharp edge, usually at the corner, producing chipping of such corner irrespective of whether such corner is rounded or not. In my improved straightedge chipping and breakage of the ends is eliminated by providing a relief or light bevel not only along the end edges of the straightedge but also around the corners as illustrated, thereby eliminating all sharp corners that could not withstand impact.

I prefer to make such relief at approximately a 45 angle and .030"-.040" wide, beginning approximately A from the longitudinal edges following around the corner, proceeding along the entire end edge following around the second corner into the opposite longitudinal edge for approximately the same distance. Instead of using a chamfering cutter of a 45 angle, a rounding cutter having a radius of approximately may be used. Furthermore, the use of a hollow cutter movable in a similar manner and giving the rounded end as shown in FIG. 9 may also be used.

If shall be distinctly understood that the above-described construction is not limited in its beneficial effect to machined plastic edges but will greatly improve operation and increase the life of edges made of other materials, including steel.

The plastic straightedge constructed as above shows a surprising and unexpected convenience and comfort in use and resistance to breakage or nicking unaccustomed to in plastic instruments. Being mechined from cast acrylic plastic sheets having optically flat surfaces, it does not distort the image underneath, is fully transparent and yet provides a straight guiding surface of requisite precision. It has, in effect, guiding surfaces of three types covering all practical requirements.

I have also found that damage to straightedges results primarily because of lack of protection to its guiding surfaces and sharp edges while the straightedge is not in use, but is handled and is pushed around in its usual way of storing. Keeping the straightedge in a protective case has been considered no more practical in drafting work than keeping a triangle in a protective case. Therefore, the envelopes or cases in which such instruments are conventionally sold are intended merely as packaging and are thrown away as soon as the instrument is put 1n use. I have found that such attitude and the resulting damage to straightedges has been caused by improper construction of cases which even when made of durable material are inconvenient and impractical to use, and are discarded after only a short time of use.

In accordance with the present invention, I provide an improved protective case for the straightedge, which is not only fully effective to protect its guiding surfaces and their sharp edges but is so simple and convenient in use that a draftsman easily acquires the habit of keeping the straightedge in the case when not in use. In accordance with the invention, I provide a case made of soft plastic material not subject to drying out and falling out in flakes. I prefer to use polyethylene approximately .006" thick. The case may be made of a piece of layflat tube or may have beaded seams on one or both sides, to provide additional protection. FIG. 3 shows a case having a tubular body 30. One end 31 of the tube 30 is sealed permanently. The other end is sealed as shown at 32 and is provided with a hole 33 which substantially registers with the hole 26 provided in the straightedge when the straightedge is placed in the case and rests with its weight on the seal of the end 31. In use, the straightedge, after its insertion into the case, may be left on the board or may be hung on a nail, in which case the nail will pass through both the case and the straightedge, supporting both.

An important feature of the construction of the case is in its length which should be such as to make the case extend beyond the end of the straightedge having the hole 26 for a sufiicient distance not only to provide for sealing said end but also to fully cover said end when said sealed end is cut off. In accordance with the invention, the straightedge, after its completion in manufacturing, is put into the case with its blind end first, and is sealed in the case as shown at 32. In such condition the straightedge is distributed through commercial channels while being protected in handling from scratching or from damage to its guiding surfaces and their limiting edges. While being fully and reliably packaged, the straightedge may be examined, because of the transparency of the case, without opening the case and its identifying insignia can easily be seen. Thus, provision of a case with printing thereon is made unnecessary. I prefer to use polyethylene tube or sheet approximately .006"-.010" thick, which provides a durable case having useful life of many years. It should be noted that because of the provision of the registering holes, both in the straightedge and in the case, such straightedge may be hung in a store on a nail, and

warpage or other damage to the straightedge is thus avoided. When a draftsman purchases the straightedge, he can cut off the sealed end provided at the end of the straightedge having the hole, immediately under the seal, thus opening said end. However, because of the additional length of the case beyond said end, such opening still does not expose the straightedge to damage and, therefore, it is fully protected. The straightedge with one end open may still be hung on a nail while being left in the case. In fact, it may be so opened in a store for examination by the purchaser and yet still be properly hung and protected even if it is not purchased after opening.

FIGS. l-l2 illustrate a straightedge having all of the advantages of the straightedges disclosed in FIGS. 1-9 but adapted for use in a drafting machine by the provision of a chuck, such as the one generally designated in FIG. by the numeral 40 and providing for the connection of the straightedge to such drafting machine and for the necessary adjustments. The chuck 40 may be of any suitable construction providing for such connection and adjustments and need not be described in detail.

The straightedge illustrated in FIGS. 11 and 12 is made preferably from a cast and annealed sheet of acrylic plastic, approximately thick, having optically fiat surfaces. The point-guiding side surface 42 thereof is provided by beveling the straightedge at its top surface along one of the longitudinal sides thereof as indicated at 44 at an angle of approximately 20 to bring the thickness of the squared portion of that longitudinal side surface down to slightly less than /s or approximately .110"- .120". The bottom sharp edge of the reduced squared portion so produced is relieved at approximately 45 angle for approximately .O"-.O40 as indicated at 41 in FIG. 12 to provide for use of the straightedge for inking without affecting the usefulness thereof for guiding a pencil point, and thus to provide a straightedge for both pencil and ink work. It should be noted that provision of the chuck such as 40 does not permit the straightedge to be turned over for the purpose of inking as can be done with the straightedge of FIGS. 1-9.

The upper corner of the squared surface 42 is chamfered for approximately .010" at an angle of 45 as indicated at 43 of FIG. 12. The squared surface 42 forming the point-guiding and the triangle locating surface is thus brought in its vertical extent or thickness to approximately .075"-.O90", depending on the extent of the relief 41.

I have found that the point-guiding surface of such a nature provides for exceedingly eflicient point-guiding operations both for pencil and for ink work, and in addition, provides sufficient bearing for the use of square edge triangles, beveled edge triangles, lettering instruments, protractors, and the like. In fact, provision of such a surface provides for exceedingly efiicient use of a drafting machine by removing its vertical straightedge and using therewith my improved straightedge as a horizontal straightedge only, with triangles and other drafting instruments such as are commonly used with a T-square or a strung straightedge, used against such straightedge. I have found that such use of a drafting machine is more efficient than a conventional drafting machine primarily due to the fact that a conventional drafting machine has various features which, although very useful by themselves, make them interfere with each others advantages; moreover, because of the separation in a drafting machine of the horizontal and vertical straightedges by the indexing head necessitating a large gap between the inner ends of such straightedges, it is not possible to draw two lines meeting at an angle without moving the indexing head and of both straightedges connected thereto. With the frequent need to draw lines exceeding the length of the drafting machine straightedge and consequent attempt to use longer edges, constant shifting of two heavy straightedges and the indexing head becomes difiicult, and sagging of the free ends of the straightedges because of the pencil point pressure becomes excessive. With the use of my improved straightedge in the manner described above, the left hand of the draftsman rests on the straightedge instead of the indexing head and its pressure prevents sagging of the straightedge, permitting use of my straightedge in 21" and even 2 lengths. In addition, with the use of my improved straightedge, a steel scale providing for better dimensional stability and not rubbing off on the drawing as easily as do aluminum scales may be used.

I prefer to bevel only one longitudinal side of the straightedge as shown at 44 in order to have a good band hold on the squared bottom side of the straightedge. Provision of such bevel along both sides of the straightedge for the purpose of adapting the straightedge to be used as a horizontal and as a vertical straightedge, makes the hand hold on the straightedge less secure. Accordingly, I prefer to produce a vertical straightedge by providing the chuck on the right-hand end of the straightedge, instead of the left-hand end as shown in FIG. 10. It will be understood that because of the provision of the chuck on the left-hand end of the straightedge of FIG. 10, said straightedge is adapted for use as a horizontal straightedge only. I found it advantageous under some conditions to provide holes for attaching the chuck at both ends of the straightedge, but still bevel only one of its longitudinal sides. However, only one chuck is attached to such edge, with the holes provided in the other end being plugged with the use of rubber or similar plugs, preferably flush with the upper surface of the straightedge. With such expedient, the chuck may be moved from one end to the other, making the straightedge a horizontal or a vertical straightedge, with the holes at the free end being plugged. However, under certain conditions my improved straightedge may be beveled on both sides to provide for its use both as a horizontal and as a Vertical straightedge.

The straightedge such as the one illustrated in FIGS. 10-12 may be made of any convenient width and length. A straightedge of this nature made 18" long and 1 /8" wide gives very good results and shows virtually no sagging. Other features of construction of the straightedge of FIGS. 10-12 may be the same as those illustrated in FIGS. 1-9 and described above. Particularly, all other sharp longitudinal edges thereof are chamfered to approximately .010" as shown at 45 and 46.

FIGURES 13 and 14 show an improved straightedge for a drafting machine which straightedge eliminates fully the disadvantages of the straightedges or scales of the conventional drafting machines which are provided with measuring graduations at their point-guiding side surfaces and thus produce combined point-guiding and measuring edges.

In accordance with the present invention, the straightedge illustrated in FIGURES 13 and 14 is so constructed that it can be connected to a drafting machine with the aid of a chuck 40 only in such a manner that its point-guiding side surface will be situated as the upper guiding surface which is the accustomed location for such pointguiding surface and which is so universally used in drafting operations. In addition, the straightedge is so constructed that it has provided thereon a measuring edge capable of performing properly, and Without producing any parallax, measuring operations necessary in drafting operations but without being within the direct line of vision of the draftsman in non-measuring drafting operations and thus eliminating involuntary focusing of draftsmans eyes on the measuring graduations in non-measur ing drafting operations.

Referring specifically to FIGURES 13 and 14, the straightedge 50 is similar in its construction to the straightedges of FIGS. 1 and 10, except for the matter of width as discussed further below. Particularly its up per or point-guiding side surface 52 may be similar or identical in its construction to the point-guiding side surface 42 of the straightedge of FIG. 10, with its ends 55 1 1 and 56 and corners being similar in their construction to the ends and corners of the straightedge of FIGURE 1 as well as those of the straightedge of FIGURE 10. The lower side 54 of the body of the straightedge corresponding to the side 12 of the straightedge of FIGURE is heavily beveled as shown at 53 in order to bring the vertical extent of said lower side 54 of the straightedge down to only .030-.050", or even smaller, in order to avoid parallax. This particular feature is of special importance should the straightedge such as 50 be made of non-transparent material, such as metal or non-transparent plastic. The heavy bevel 53 brings the ends of the lines of measuring graduations of the scale provided along the lower side of the straightedge, very close to the paper or the surface of the drawing. It should be understood that in nontransparent straightedge the graduation lines have to be provided on the top or beveled surface of the straightedge in order to be visible, while in transparent straightedges such graduation lines should be provided on the under surface of the straightedge body in order to be as close to the drawing surface as possible, and be viewed through the transparent body of the straightedge.

Any desired scale in any desired units of measurements may be provided. However, it is of importance to note that the markings of the scale are provided in the upright position, that the zero mark of the scale is at the left-hand end of the straightedge, and that only one chuck is provided on the straightedge and it is located also at the left-hand end thereof.

By virtue of such a construction, the only way the straightedge can be connected to the drafting machine is to have the scale graduations along the lower side of the straightedge and therefore at a sufficient distance from the upper point-guiding surface 52 and also from the line of vision of the draftsman when using the pointguiding surface in non-measuring drafting operations. It may be mentioned in this connection that the width of the straightedge 50 is preferably made greater than that of the straightedges of FIGURES 1 and 10 in order to remove the graduation markings as far from the pointguiding surface 52 as practicable. While width of the straightedges of FIGURES 1 and 10, with the lengths thereof being approximately 18", may be 1%" to 2", the width of the straightedges having construction such as illustrated in FIGURES 13 and 14 may be 2" to 2% in order to give the advantage explained above, and also to prevent its bending and sagging. While in the straightedge of FIG. 1 the hole 26 may be provided at either end of the straightedge, in the straightedges of FIGS. 10 and 13 such hole, if provided, is disposed in the free or righthand end of the straightedge.

By virtue of the construction disclosed above, the edge 50 cannot be connected to a drafting machine to have its graduated side disposed as an upper side and used for point-guiding operations. In addition, the arrangement o fthe zero mark on the measuring scale, be it provided on the beveled surface 53 or the under surface 57 of the straightedge, is such that placed as an upper guiding surface the scale of the measuring side would be upside down and its numerals would read from right to left, rather than left to right as is universally used in measuring operations, thus indicating to the user that such is not the proper position of the straightedge.

For use, the straightedge is connected to a drafting machine with the aid of its chuck in a manner well known in the art. However, because of the provision of a single chuck rather than of two chucks one at each end of the straightedge as in conventional straightedges provided with measuring scales along both of their guiding sides and therefore connectable to the drafting machine with either of its two sides disposable as the upper side or the lower side, my improved straightedge can be connected to the drafting machine only to have its non-graduated or point-guiding side disposed as the upper side, while the side having a measuring scale can be disposed only as the lower side. Thus, in using the point-guiding surface, the draftsman does not have to look at multiplicity of graduations when he does not need to make any measurements. When performing a measuring operation becomes necessary, the draftsman moves the straightedge up and uses its lower measuring edge for measuring operations. Such measuring provides an additional advantage of measuring with the measuring edge being above the measured line which has a number of advantages and is often so used in tool work where measurements have to be particularly accurate.

Since the bevel on the lower side of the straightedge is much heavier and wider than on the upper side, the measuring edge is rather thin and, made of plastic, may be rather fragile. Therefore, in cases of dropping the straightedge on the floor, the ends of the lower side thereof can easily break, making the straightedge unpleasant to use. Furthermore, the very thin edge on the lower side of the straightedge provides virtually no bearing for users thumbs when it is desirable to move the straightedge up, thus making manipulation of the edge in use rather difficult. In accordance with the invention, I eliminate these disadvantages by providing the bevel 53 as illustrated at FIGS. 13 and 14 to terminate before reaching the ends of the straightedge body and thus provide thick square portions 60 and 61 and rounded portions 62 and 63 convenient to place users thumbs thereon for pushing the straightedge, together with the drafting machine head to which the straightedge is attached, upwardly. Under some conditions only one such thumb abutment, namely one provided at the right-hand end, may be sufficient.

It will be understood that my improved straightedge is particularly advantageous in use as a horizontal edge with two drafting triangles 45 and 30-6090 and with the vertical straightedge removed. The pointguiding surface of my improved straightedge has sufficient vertical extent and thus provides sufficient bearing area for the guided surfaces of drafting triangles. Such system of drafting possesses a number of important advantages and eliminates a number of serious disadvantages of drafting machines which have been holding wider use of such machines in industry. However, in some cases my improved straightedge may also be used as a vertical edge.

I claim:

1. A method of making a draftsmans straightedge to attain therein full transparency, functional effectiveness and durability, said method comprising providing a cast and annealed sheet of transparent acrylic plastic material of approximately thick with its flat top and bottom surfaces having been cast against polished glass plates to attain optical flatness, sawing an elongated rectangular piece of said material to the predetermined size of the straightedge with machining allowance, milling the sides and the ends of said piece to provide thereon two straight, smooth and squared longitudinal guiding surfaces and two squared ends meeting at four corners, rounding all four corners to eliminate sharp vertical line edges thereat resulting from the milling operation, providing a combined point-gliding and triangle-locating side surface on the piece by beveling at 2025 angle one of the longitudinal sides thereof to bring the squared portion thereof down to .100.120", smoothing the beveled surface to eliminate tool marks thereon, relieving for approximately .035" the sharp end edges of the piece at both top and bottom surfaces thereof to eliminate the sharp line edges thereat and the curved sharp line edges resulting from rounding the corners, chamfering for approximately .010" all sharp line edges formed along the squared longitudinal side surfaces of the piece by intersection of milled surfaces at 90 angles and of the side guiding surface with the top bevel surface, and polishing the beveled, relieved and chamfered surfaces to restore luster and surface tension therein.

2. The method defined in claim 1 and including a step of providing on one end of the straightedge body a chuck for connecting the straightedge to a drafting machine as a horizontal straightedge thereof and thus adapting the drafting machine to be used with only one straightedge cooperating with a drafting triangle.

3. The method defined in claim 2 and including the step of providing an identifying mark on the other end of the straightedge body to have such mark removed from the guiding surface of the straightedge and of the line of the users sight and to leave the body of the straightedge adjacent its longitudinal guiding surface free of any markings that could otherwise cause involuntary focusing of users eyes thereon.

References Cited UNITED STATES PATENTS 2,562,348 7/1951 Bowser 33107 2,958,939 11/ 1960 Turner 29407 3,051,304 8/1962 Dolgorukov 206-4533 FOREIGN PATENTS 919,388 3/1947 France. 93 6,199 2/ 1948 France.

THOMAS H. EAGER, Primary Examiner.

Claims (1)

1. A METHOD OF MAKING A DRAFTSMAN''S STRAIGHTEDGE ATTAIN THEREIN FULL TRANSPARENCY, FUNCTIONAL EFFECTIVENESS AND DURABILITY, SAID METHOD COMPRISING PROVIDING A CAST AND ANNEALED SHEET OF TRANSPARENT ACRYLIC PLASTIC MATERIAL OF APPROXIMATELY 3/16" THICK WITH ITS FLAT TOP AND BOTTOM SURFACES HAVING BEEN CAST AGAINST POLISHED GLASS PLATES TO ATTAIN OPTICAL GLATNESS, SAWING AN ELONGATED RECTANGULAR PIECE OF SAID MATERIAL TO THE PREDETERMINED SIZE OF THE STRAIGHTEDGE WITH MACHINING ALLOWANCE, MILLING THE SIDES AND THE ENDS OF SAID PIECE TO PROVIDE THEREON TWO STRAIGHT, SMOOTH AND SQUARED LONGITUDINAL GUIDING SURFACES AND TWO SQUARED ENDS MEETING AT FOUR CORNERS, ROUNDING ALL FOUR CORNERS TO ELIMINATE SHARP VERTICAL LINE EDGES THEREAT RESULTING FROM THE MILLING OPERATION, PROVIDING A COMBINED POINT-GUIDING AND TRIANGLE-LOCATING SIDE SURFACE ON THE PIECE BY BEVELING AT 20*-25* ANGLE ONE OF THE LONGITUDINAL SIDES THEREOF TO BRING THE SQUARED PORTION THEREOF DOWN TO .100"-.120", SMOOTHING THE BEVELED SURFACE TO ELIMINATE TOOL MARKS THEREON, RELIEVING FOR APPROXIMATELY .035" THE SHARP END EDGES OF THE PIECE AT BOTH TOP AND BOTTOM SURFACES THEREOF TO ELIMINATE THE SHARP LINE EDGES THEREAT AND THE CURVED SHARP LINE EDGES RESULTING FROM ROUNDING THE CORNERS, CHAMFERING FOR APPROXIMATELY .010" ALL SHARP LINE EDGES FORMED ALONG THE SQUARED LONGITUDINAL SIDES SURFACES OF THE PIECE BY INTERSECTION OF MILLED SURFACES AT 90* ANGLES AND OF THE SIDE GUIDING SURFACE WITH THE TOP BEVEL SURFACE, AND POLISHING THE BEVELED, RELIEVED AND CHAMFERED SURFACES TO RESTORE LUSTER AND SURFACE TENSION THEREIN.

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