US2170734A - Tip for draftsmen's mechanical pencils - Google Patents

Description

1939. H. F. SMENNER 2,170,734

TIP FOR DRAFTSMENS MECHANICAL PENCILS Filed May 1 1959 Patented Aug. 22, 1939 PATENT OFFICE TIP FOR DRAFTSMENS MECHANICAL mucus Herbert F. Smenner, Muncie, Ind.

\ Application May 1, 1939, Serial No. ZiLllZ 3 Claims.

Mechanical pencils, from which loose pieces of lead may be fed as the points of the leads are consumed, have long been in common use. More recently, however, pencils of that type have been 5 manpfactured for the purpose of utilizing leads suitable for use by mechanical and architectural draftsmen. The manner in which draftsmen employ pencils, namely by drawing the pencils along the edges of T-squares, triangles, curves, and

, the like, gives rise to problems that are not present in the use of pencils for writing or freehand work; and, since the design of the old types of pencils has been followed in the creation of the pencils containing hard leads for draftsmens use, these latter pencils have not attained any considerable popularity.

The object of the present invention is to improve mechanical pencils adapted. for use by draftsmen, so that they may beused with the same ease and facility as are ordinary pencils, while retaining over the ordinary pencil the advantages incident to mechanical pencils and especially mechanical pencils utilizing leads of small diameter.

In the ordinary mechanical pencil for draftsmen the metal tip from which the lead protrudes is usually in the shape of a frustum of a cone the large base of which registers with the small base of a frusto-conical end of the body member of the pencil; the smaller base of the tip, which is the free end thereof, being about twice as large in diameter as is the lead. In drawing such a pencil along the edge of a T-square or other guide used by drafstmen, a slight change in the angle at which the pencil is held causes a displacement of the lead toward or from the edge of the guide member, due to the bringing of a larger or smaller diameter of the frusto-conical tip into engagement with the guide. This, of course, creates an irregularity in the line which is being drawn by the pencil. Furthermore, draftsmen are accustomed to lower their pencils against the sheet upon which a line is to be drawn, by placing the point of the lead in contact with the edge of the'guide and then moving the pencil bodily in the downward direction. The common pencil, in which the wood is shaved away along with the lead so that the lead and what corresponds to the tip in the mechanical pencil provide smooth, continuous surfaces from the points of the leads upwardly along the tip of the wood body, may be brought in contact with the drawing paper in the manner just explained; but, in the case of mechanical pencils as heretofore made, when the lead is brought into engagement with the edge of a .T-square or other guide and is moved downwardly, the edge face of the metal tip strikes the top face of the T-square or other guide member and prevents the lead from reaching the surface on which a line is to be drawn. In other words, mechanical pencils as heretofore constructed, are awkward in the hands of a draftsman.

Specifically considered, the present invention may be said to have for its object to overcome no the difficulties in mechanical pencils for drafts-. mens use, just mentioned, so that they may be handled in the same way as common pencils in making drawings.

The various features of novelty whereby my in- 15 ventlon is characterized will hereinafter be pointed out with particularity in the claims; but, for a full understanding of my invention and of its objects and advantages, reference may be had to the following detailed description taken in con- 20 nection with the accompanying drawing, wherein:

Figure 1 is an elevation of the pointed end of a mechanical pencil embodying the present invention, on a scale greater than full size; Fig. 2 25 is a longitudinal central section through the pointed end of'the pencil of Fig. 1, on a magnified scale; and Fig, 3 is a view partly in elevation and partly in section, illustrating the invention in a form wherein the metal tip is secured to the body 30 member of the pencil in a different manner from that shown in Fig. 2.

Referring to Figs. 1 and 2 of the drawing, 1 represents the body member of a. mechanical 'pencil of any usual or suitable construction, hav- 35 ing one end in the form of a frustum of a cone. Beyond and in contact therewith is a frustoconical tip 3 which may be a continuation cone of which the section 2 is a part. The small end of the tip 3 merges into a long, slender, thin- 40 walled sleeve 4 from which the lead 5 protrudes. The sleeve 5 is substantially cylindrical and its wall is so thin that the extreme end thereof does not constitute a shoulder which can catch on top of a T-square when a pencil point is slid down- 4 ward in contact with'the edge of the latter. By making the part 4 comparatively long, the wall thereof may be gradually thickened from the free end toward the base, so as to provide the necessary rigidity even though the wall at the free end presents almost a feather edge; the slight departure from the cylindrical form being insuflicient to cause any appreciable variation from the ideal form of a line which is being drawn if the 55 altered pencil is tilted while b ing gu ded along the edge Y of one of the usual relatively t guiding members employed by drai'tsmen.

A typical pencil is one hi which the l 5 has a dleter slightly less tliian Your one-hundredths of an inch in which case the part t may be approximately a quarter of! an inch long and have well thicknesses of somewhat less than one two-hundredths or an inch and approximately one one-hundredth of an inch at the free end and lease end, respectively.

The manner oi. fastening the tip to the body of the pencil and the mechanism lor extruding the leads forms no part of the present invention.

"In the arrangement shown, the tip 3 is screwed upon a post it projecting from the end of the part 2 oi the pencil. Extending through this post there may be the usual lead-holding sleeve l and the plunger e. In the drawing the lead is shown as having been pushed completely beyond the end of the sleeve I, while the plunger may still travel throughout the length of the part i of the tip.

Fig. 3 may be regarded as an elevation 01 that portion of the tip 3 in Fig. 2 which is normally exposed; the further Purpose oi this view being to show a common modified means for attaching the tip to the pencil. In this construction the tip carries a rearwardly-projectlng, externally screw-threaded stem 9 which is screwed into the internally screw-threaded bore It in the end of the irusto-conical part 2 of the body portion of the pencil.

It will thus be seen that by employing a mechanical pencil embodying one of my improved tips, a draftsman is able to secure all of the advantages of the ordinary mechanical pencil, including those advantages resulting particularly from the small diameters of the leads, without making it necessary to unlearn old habits in pencil handling; because the manner of using a pencil during the process of making a drawing is the same, whether it be the common form 0! pencil or a mechanical pencil having thereon one of my improved tips.

While I have illustrated and described with particularity only a single preferred form of my invention, 1 do not desire to be limited to the exact structural details thus illustrated and described; but intend to cover all forms and arrangements which come within the definitions of my invention constituting the appended claims.

I claim:

1. The combination with a mechanical pencil utilizing leads of a diameter less than four onehundredths of an inch, of a tip terminating in a long, slender, almost cylindrical section whose free end has an external diameter about one one-hundredth of an inch greater than the diameter of a lead.

2. The combination with a mechanical pencil utilizing thin, round leads, of a tip terminating in a long, slender sleeve-like part adapted to be a sliding fit for a lead, the wall thickness at the free end of the sleeve-like part being not more than one twc-hundredths of an inch and the wall thickness increaslfig to about one one-hundredth of an inch at the other end of the said sleeve-like part.

3. The combination with a mechanical pencil utilizing leads of a diameter not greater than one thirty-secondth of an inch in diameter, of a tapered lead-surrounding tip about one quarter of an inch long, the external diameter of the tip being not more than' one one-hundredth of an inch greater than that of the lead at the free end.

and the external diameter at the base of the tip being about one-fiftieth of an inch greater than thatoi the lead.

HERBERT F. SMENNER.

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