US2161889A - Mechanical pencil - Google Patents

Description

1 June 13, 1939. M. SCHAEFER 2,161,889

' MECHANICAL PENCIL Filed Feb. 8, 1937 INVENTOR Max Jaime er ATTORNEYS Patented June 13, 1939 UNITED STATES MECHANICAL PENCIL Max Schaefer, Bloomfield, N. J.,

assignor to Eagle Pencil Company, a corporation of Delaware Application February 8, 1937, Serial No. 124,530

4 Claims.

My present invention relates to mechanical pencils, more particularly of the'helical feed type.

As conducive to a clear understanding of the invention, it is noted that the construction would be rendered mechanically weak and subject to distortion and jamming if the feed tube were in the form of helically wound metal ribbon or the like, rotatable relative to the casing but of the I low pitch feasible in constructions in which the feed tube is rigid with the casing. If for the purpose of attaining adequate mechanical strength the feed tube ribbon is however made of a higher pitch, it would be subject to rotary slippage under writing pressure, with consequent retraction of 15 the lead.

It is among the objects of the invention to provide a pencil of the type presenting a high pitch rotatable helical feed tube, which pencil is adjustable for writing, without the looseness or 20 slippage that leads to lead recession under writing pressure, and this without appreciably adding to the cost of the pencil, either for materials or for precision of manufacture.

Another object is to provide a pencil of the 25 above type, presenting the above advantages, Without the need for modification of any of the conventional elements or of the mode of assembly thereof, but by the simple expedient of adding to the structure an element of negligible cost 30 assembled into the structure with great ease.

In the accompanying drawing in which are shown one or more of various possible embodiments of the several features of the invention:

Fig. 1 is a view in longitudinal cross-section of 35 one embodiment of the invention,

Fig. 2 is a sectional view on a greatly enlarged scale taken on line 22 of Fig. 1,

Fig. 3 is a perspective view of a preferred embodiment of brake element, and

40 Fig. 4 is a view similar to Fig. 2 of a slight modification.

Referring to the drawing, the casing shown as a metal tube It! has a ferrule II at its tapered point into which there is axially fitted and se- 45 cured against movement the lead tube [2, longitudinally slotted at I3. Telescoped into the opposite end of the casing I is a tube I4 which is frictionally held therein for facility of rotation thereof, accomplished preferably by means of the 0' conventional eraser ferrule I5 tightly fitted thereover by friction. The tube [4 has a reduced extension IG rigidly fixed, as for instance, by indentations ll, to the feed tube is, which is accordingly rotatable about the lead tube [2 upon turn- 55 ing of the eraser ferrule Ill. The feed tube I8 is illustratively shown as formed from an elongated strip of sheet metal, helically wound on a relatively high pitch, illustratively of three to four convolutions per inch. The ribbon is preferably crowned as at [9 to present a convex outer sura face.

The feed tube I8 is connected with the lead tube l2 for propulsion of the lead in any conventional manner. Preferably the propelling unit is a lead clutch tube 20 lodged within the lead tube l2. It clasps the rear end of the lead 2| and has a lateral wing or extension 22 which protrudes outward from the slot I3 into the helical feed track 23 of the feed tube. There is also illustratively shown a conventional expelling 16 mechanism comprising a pin 24, within the lead clutch tube 20, equipped with a lateral offset 25, also protruding through the slot l3 into the track 23 and trailing the wing 22 by one or more convolutions.

The relatively high pitch of helical track set forth, made necessary for mechanical strength, may be less than the critical ange of friction, so that rotary slippage of the feed tube is apt to occur under ordinary writing pressure. Brake 25 or snubber means is provided according to the invention to retain the feed tube against such slippage. This means is enclosed .in the casing and exerts resilient pressure on the feed tube to impose a load on the latter for the purpose set forth, without however interfering with rotation thereof from the eraser ferrule IS in effecting the desired lead feed.

In a preferred specific embodiment, the brake member comprises a spring-brass clasp 26, made of a unitary blank longitudinally folded along line 27 to form a pair of sides or jaws 28 and 23, each of which is symmetrically curved substantially like a pair of calipers, convex at the outside and concave at the inside. This clasp member is simply placed in straddling relation over any part of the length of the feed tube l8 and introduced therewith in the assembly of the pencil into the casing l0 thereof. As best shown in Fig. 2 and especially with a metal pencil casing of polygonal cross-section, illustratively shown in Fig. 2 as hexagonal, the hinge line 21 of the clasp naturally lodges itself in one of the di-hedral angles 30 of the casing and the length of each .jaw is such that the free edges 3| and 32 thereof are cammed toward each other by the sides 33 and 34 respectively of the casing determining the dihedral anglewhose vertex is the edge 35 diametrically opposite edge 30, thereby causing the bowed sides 55 the clasp to embrace the feed tube with substantial resilient pressure.

The brake member set forth is of substantially negligible cost and entails no difficulty in assembly or introduction into the pencil. It exerts sufficient frictional load upon the feed tube to prevent undesired rotation of the latter under writing pressure. Yet the load imposed by the brake isnot so great as to cause slippage of the eraser ferrule IS in lead propellingor retracting operation. The added load due to the brake clasp 26 also renders the operation of propelling andretracting smoother and more uniform and enhances-the comfort of adjusting the pencil.

The helical feed tube extending substantially the length of the pencil when the pencil is charged with a. long lead, the lead propelling clutch tube with its wings orlateral offsets 22 and 25 is near the eraser end of the pencil above the extension [6 that encircles the feed tube and' well above the brake member 26. Yet in the use of the pencil, as the lead is consumed and the propelling tube is moved downward to reach and traverse the length of the brake member, there is no interference or jamming of the wings 22 and 25 with respect to the brake member. From one aspect this is due to the. fact that'the brake member engages only the crowned face, below which the ends of the wings 22 and 25 are lodged, so that the latter cannot touch'the brake even though the. concavities of the'jaws 28 and 29 thereof should extend directly over the slot of the lead tube I2. i

From another aspect the wings 22, 25 will clear the brake member in the operation of the feed tube by reason of the fact that these wings move in longitudinal slot l3. of the lead tube l2 which as shown in Fig. 1 is substantially in registry with the gap between jaw edges ,3! and 32 of the brake. The latter being fixed against rotary displacement, the wings could not reach and engage the feed 'tube clasping'. portions of the brake member, even if the feed tube were not crowned in the manner preferred.

The crowned surface of the feed tube l8-provides a smooth surface which rides in the brake memberZB, While the relatively sharpedges 3 and 32 of the latter are retained by the casing against slippage. Accordingly, thebrake member is retained against rotation within the casing V and the rotary movement during lead feed or retraction is entirely between the rotating feed tube and the fixed brake member.

It is seen that the brake member may directly engage the helical feed tube at any portion between the ends thereof and incidentally serves also to steady the latter against shifting or distor'tion.

' stantially thelengthof the pencil.

The. use of the brake in the construction set forth thus in noewiseinterfer'es with the preferred'application -of the invention to a mechaning l0 circular in cross-section in which the brake clasp '26 is frictionally engaged about the feed tube I8 in much the same way as in Fig. 2, the curvatureof the .casing contributing to the by, to preclude slippage.

camming action of approach of the jaws upon the ends 3|, 32' thereof, with resultant resilient clasping of the feed tube.

It will thus be seen that there is herein described apparatus in which the several features of this invention are embodied, and which apparatus in its action attains the various objects of the invention and is well suited to meetthe requirements of practical use.

As many changes could be made in the above construction, and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what I" claim as new and desire to secure by Letters Patent is: i I

l. A mechanical lead pencil comprising a'casing, a helical feed tube. rotatably mounted therein and extending substantially the length thereof and having a relatively steep feed track there-' along, lead'propulsion means in said'lead tube having wing means protruding into the slot thereof, said feed tube being crowned along the and having associated means at the rear end for rotating the same within the casing, a lead tube rigid with the casing and within said feed tube having a longitudinal slot, lead propeller means within said lead tube. having wing structure extending through said slot into said helical feed track, a brake clutch member, embracing .said feed tube at anintermediate part of the length thereof and also engaging the inner wall of said casing, said clutch being free from the path of movement of said propeller wingsin the'operation of the pencil. V

3. The combination recited in claim 2 in which the brake member is 'ofxsheet metal with jaws concave at their inner faces embracing the feed tube and with the hinge end'as well. as the free edges of said brake member in engagement with the inner wall of the casing, each jaw being. of

length such as to cause the jaws to be urged'inward toward each other by the concavity of the inner casing wall for frictionally clasping the tube embraced thereby. V a

4. The combination recited in claim 2 in which the casing is polygonalin cross-section and the sheet metal brake member has its hinged portion lodged in one of the edges of the casing and the 7 free edges thereof respectively engagingth'e'sides of the dihedral edge whosevertex is the opposite edge of the casing, each' jaw being of length such as to cause the jaws to be' urged inward toward each other by the concavity of the casing, thereby frictionally toclasp the tube scHAEFERf V embraced there-

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