US2298555A - Mechanical lead pencil - Google Patents

Description

c. R. FARGO MECHANICAL LEAD PENCIL Filed Sept. 25, 1939 Patented Oct. 13, 1942 UNHTED STATES earner ,FIQE

MECHANICAL LEAD PENCIL Charles R. Fargo, Beverly Hills, Calif.

Appiication September 25, 1939, Serial No. 296,383

2 Claims.

The hereinafter described invention relates to mechanical pencils, containing improvements by which the utility of pencils of this class is greatly extended; the new features and advantages of my invention permitting its entrance into a new field where the more expensive wooden pencils are now required to serve the purposes of draughtsmen, engineers, and architects.

Heretofore it has been practically impossible to meet the service demands in a mechanical bare lead pencil where the pressure in the lead is a principal factor in producing the character of line drawings required on vellum paper for blueprinting and/or duplication. The present disadvantages are a breakage of the leads when held against end movement and a slippage of the leads if held without breakage.

In the present mechanical pencils a strain is set up on the lead, the chuck arrangement being such as to cause the exertion of pressure in a cir cumferential line or small circumferential bearing around the lead which cracks it.

The primary object of my invention is to provide an improved structure of mechanical pencil wherein all of the disadvantages explained hereinabove are substantially entirely eliminated and a pencil which is superior to any known prior to my invention with regard to its resistance to the slippage of the lead and its ability to prevent breakage of same.

My invention is based on the discovery that a wedging action which will prevent breaking and slipping of the lead can be effected between the slotted tapered end of the tube holding the lead and the inner tapered surface at the end of the pencil barrel by preventing rotation of the leadcontaining tube after the respective tapered surfaces contact each other, and thereafter forcing the slotted tapered tube end around the lead so that it will flatten out and form a longitudinally extending bearing of considerable extent along the surface of the lead. My improved structure is such that all torsional strain is taken ff the lead when the tapered surface of the lead tube engages the tapered surface of the pencil end.

Now in order that my invention may be fully understood, reference is made to the illustrative embodiments shown in the accompanying drawing, and in which Fig. 1 is a View in side elevation of my improved pencil.

Fig. 2 is an enlarged sectional view taken on line 22, Fig. 1, showing the lead as secured in position by the improvements of my invention.

Fig. 3 is an enlarged fragmentary secticnal View of my invention at the lead point end showing the lead in released position.

Figs. 4, 5 and 6 are sectional end views taken on line 4-4, line 55, and line-55, respectively, of Fig. 1.

In the drawing, numeral Iil denotes the pencil barrel, and numeral II the chuck end of the barrel which in the present instance is a separate member secured thereto. Numeral I2 denotes the lead-conta-ining tube, this being a continuously extending tube completely telescoping the lead. The chuck end I I is formed with a comparatively long running tapered inner surface, while the outer surface of lead tube I2 is finished with a tapered surface complementary to the tapered surface of the end II. The tapered surfaces of the respective members H and I2 are made with a relatively small degree of angularity, to assist the wedge action therebetween.

As distinguished from pencils of prior use, the lead tube I2 of my invention is made with a relatively thin tube wall and provided with slots I 2a, which run a considerably greater distance along the tube wall than now possible to use in present pencils. My purpose is to provide a flexibility at the tapered lead gripping end of the tube I2 which will permit of its compression when forced into the inner tapered surface of the chuck end II and a flattening out so that the lead tube will present a cylindrical surface bearing against the lead. In order to force the flexibly formed end of tube I2 into its bearing engagement with the inner surface of chuck II, I have mounted the tube I 2 into a head I3 which carries it. The tube I2 is slipped through the bore of head l3 and held endwise thereagainst by the tube collars I4 and I5. Tube I2 is free to rotate in the head I3. One end of the head I3 is provided with a running thread which is adapted to engage a similar running thread formed in the upper end of pencil barrel It.

In the illustrated embodiments of my invention the pencil barrel I II is made of plastic mouldable material such as Tenite, the chuck end II being inserted in the barrel during moulding. Plastic material is also moulded around the head I3, as denoted by numeral I6, so as to form a finishing cap over the upper end of tube I 2. Numeral I1 denotes the lead as situated in lead tube I2.

Now in regard to the functioning of my invention and the new features and advantages arising therefrom. Referring to Fig. 2, which shows the lead in gripped position in the pencil. In operation the screwing in of the head I3 into the pencil barrel Ill, carries the tapered split end of lead tube [2 into contact with the tapered inner surface of chuck end l3. Immediately after the respective tapered surfaces contact each other, no further movement axially of the tube l2 takes place. Then upon continuing to screw in the head l3, the end thereof as bearing against the lead tube collar I4, is forced down and fiattened out against the lead I! in a wide bearing area as shown between arrows and denoted by f.

It will therefore be clear that all torsional strain on the lead tube 12 is relieved by reason of the head l3 being free to move around the lead tube l2 without turning the tube. It can be well understood in view of this, and as heretofore stated, that I can employ a light tube wall and secure the advantages of the extreme flexibility thereof at the lead gripping end which will permit the metal of the wall to hug in tight around the lead, and in fact without an excessive pressure between the tapered surfaces of the lead tube and chuck, which means. that an undue screwing in of the head I3 is not required to force the metal of the lead tube around the lead in securely holding it against a pressure of the hand of a draughtsman in a comparable manner to that now commonly applied in the use of the relatively hard lead wood draughting pencil in producing the same character oflines on a drawing. In fact, I have found in the practical use of my improved pencil, when the screw head I3 is slacked back in its threaded engagement with the barrel I0, that the frictional engagement and compression of the metal of the lead, tube around the lead will securely hold the lead against slippage; and although this manner of operating my pencil is not advocated, it is nevertheless desired to point out thereby the great tenacity of my structure in firmly holding the lead in tightly gripped position.

In Fig. 5 I have shown the released position of the lead in the pencil. In releasing the lead the head i3 is slacked back in its threaded engagement with the barrel ID, at which time the end of the head I3 is brought to bear against the collar l5 of lead tube l2, causing, the separation of the tapered frictionally engaging surfaces of the chuck H and tube I 2; however, without twisting the lead tube and destroying its advantages, as the separation of the lead-holding surfaces is a direct pull without rotary movement of the lead tube.

I desire it to be understood that reasonable modifications may be made by me in adapting the improvements of the structure to the trade, and the scope of same is limited only to the extent of the appended claims.

I claim:

1. In a mechanical pencil having a barrel with an internally tapered chuck end, and a running thread on its. opposite end, a lead containing unit adapted for reciprocation in said barrel comprising a continuously extending cylindrical tube substantially uniform in cross section having a compressible end beveled to a sharp knife-like edge and engageable with the inner tapered surface of the chuck, the other end of said tube having a head slipped over it, said head having a bore closely engageable with the outer cylindrical surface of the tube wall and a running thread integral therewith engageable with the threaded end of the pencil barrel, there being abutments on the tube wall and said head being rotatably confined on the tube wall by said abutments so that its ends are engageable therewith.

2. In a mechanical pencil having a barrel with an internally tapered chuck end, and a running thread on its opposite end, a lead containing unit adapted for reciprocation in said barrel compris- CHARLES R. FARGO.

Images