US2145450A

US2145450A - Plunger for mechanical pencils and method of producing same

Info

Publication number: US2145450A
Application number: US149408A
Authority: US
Inventors: John P Lynn
Original assignee: DUR O LITE PENCIL CO
Current assignee: DUR O LITE PENCIL CO
Priority date: 1936-06-27
Filing date: 1937-06-21
Publication date: 1939-01-31
Anticipated expiration: 1956-01-31

Description

Jan. 31, 1939. J. P. LYNN 2,145,459

PLUNGER F OR MECHANICAL PENCILS AND METHOD OF PRODUCING SAME I Original Filed June 27, 1936.

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Patented Jan. 31, 1939 UNITED STATES PATENT O PLUNGER FOR MECHANICAL PENCILS AND METHOD OF PRODUCING SAME Melrose Park, 111., 2.

Original application J 87,705. Divided and corporation of Delaware nine 27, 1936, Serial No. this application June 21,

1937, Serial No. 149,408

11 Claims.

This invention relates to an improved construction for plungers of the type employed in certain mechanical pencils. The invention also re lates to a method of producing such plungers.

This invention is a division of applicants copending application Serial No. 87,705, filed June 27, 1936, and patented July 20, 1937, Patent No. 2,087,519.

In constructing certain types of mechanical pencils it is desirable in certain instances, to provide a lead guide tube formed as an open spiral which cooperates with a lead propelling plunger which is moved axially within the tube by means of a portion which projects through the open spiral slot and engages with a longitudinal slot in the body of the pencil exteriorly of the spiral tube. With such constructions, relative rotation between the body of the pencil and the spiral serves to advance or retract the plunger within the spiral tube.

For good operation, pencils of this type require a plunger which is accurately held in axial alignment within the tube without liability of tilting or jamming when the plunger is advanced against a frictionally held lead. This is usually accomplished by forming the plunger from metal stock which is of slightly less diameter than the interior of the tube whereby the plunger is free to slide axially in the tube while at the same time being held by the tube in axial alignment. Plungers of this type further have a lateral extension which is preferably formed thereon by bending the wire or stock from which the plunger is formed. It has been found in practice, that when plungers of this type are made of stock of such size as to be axially guided within the interior of the tube that then, the laterally formed portion of the plunger at the location of the bend, bulges somewhat, due to the excessive amount of metal at this location with the result that binding of the plunger in the open spiral slot frequently occurs. Such lateral extensions also usually have pitched surfaces at the top and bottom for contact with the edges of the spiral slot and a free camming and feeding action of the plunger by these pitched surfaces depends upon accurate alignment of the plunger in the tube. Thus ordinary plungers would frequently bind when made large enough to be held in alignment and would tilt and jam if made of smaller stock.

Accordingly, it is an object of the present invention to provide a new construction of plunger which is free from the above named disadvantages and which may be made by a simple and inexpensive process.

The plunger of this invention is characterized as composed of wire or red stock which is of substantially less diameter than the interior diameter of the spiral guide tube with which it is to be associated. Thus with the diminished diameter, the formation of the lateral projection for feeding the plunger does not involve the production of the unwanted bulging at the location of the bend. In order to maintain the plunger in axial alignment in the tube, the body of the plunger is deformed to provide a portion thereof with projecting bearing edges constituting means for holding and guiding the plunger in axial alignment within the tube.

This invention will be better understood by referring to the accompanying drawing in which one illustrative embodiment of this invention is given and in which,

Figure 1 is a cross sectional View of a pencil of the open spiral type embodying a plunger constructed in accordance with this invention, and

Figure 2 is an enlarged lateral view of the plunger constructed in accordance with this invention and,

Figure 3 is an end view of the plunger illustrated in Figure 2, and

Figure 4 is a fragmentary view partly in cross section taken on the lines li of Figure 2 and looking in the direction of the arrows.

By referring to the drawing it will be noted that this invention is illustrated as embodied in a pencil having a tip Ill, a body ii, and a spiral guide tube H3. The spiral guide tube is held within the body by means of a bearing it so that the same is rotatable therein while held against axial displacement. Within the spiral tube is a plunger E5, the construction of which is better shown in Figures 2 and 3. This plunger is formed with two diameters, the end diameter 22 of which is sufficiently small to project into the lead receiving opening 23 at the extreme tip of the pencil without destroying the frictional pressure provided at the pencil tip and the larger diameter 2% is of such size as to freely slide within the guide tube without undue wobbling or without liability of tilting or becoming misaligned from the axis of the tube.

This plunger is preferably formed of wire stock of diameter substantially less than the inside diameter of the tube and the body portion it thereof is preferably formed by a swedging or similar operation carried out in a punch press or equivalent machine. It is the purpose of this invention to deform an amount of material constituting the body of the plunger to provide supporting bearing edges for engagement with the larger diameter of the interior of the lead guide tube. Although any desired shape may be selected, it is preferable to form the body with a triangular cross section because this provides a three point support. While forming the body portion as above described, the head end of the plunger 25 may likewise be formed into rectangular or other cross-sectional shape such as will better prepare the plunger for the subsequent bending operation with the avoidance of the unwanted bulging at the location of the bend. Where a rectangular formation is given to the head the flat surface 26 thereof may be continuous with one of the flat surfaces of the triangular portion. The head of the plunger may then be formed by bending the upper end to provide a laterally extending member 27 for engaging the slot of the spiral tube I3 and the groove 2| in the pencil body.

It will be noted from Figure 2 that the upper and

lower surfaces

28 and 29, respectively, of the lateral extension which engage with the edges of the open spiral slot are pitched to conform to the pitch of the spiral, or in other words, so as to produce a lateral extension which is rhomboidal in cross section. These pitched surfaces enable the plunger to be freely and smoothly cammed in the slot to advance and retract the plunger in both directions in the tube. The head of the plunger also may be formed with a tail piece 29 provi ing additional bearing surfaces in the groove 2| obviously such tail pieces are not necessary.

Although any order of steps for forming the above described plunger may be employed with good results, it has been found in practice that the plunger may be conveniently made by first swedging on a punch press or other suitable machine, the triangular body portion 24 by successive operations on a continuous rod of stock. After or simultaneously with the formation of the triangular body portion, the rectangular head may be formed by a similar swedging operation. The plungers may next be successively cut from the rod of stock and thereafter the head formed on each by a bending operation which by means of dies also forms the

pitched surfaces

28 and 29.

From the foregoing it will be apparent that this invention provides a plunger which has a free and easy camming action within the open spiral tube for advancing the lead as distinguished from plungers heretofore used which are subject to jamming in the spiral due to the tilting and misalignment of the plunger within the tube or to a binding of the plunger in the spiral slot because of a bulging of the metal at the head forming bend.

I claim:

1. The process of making a plunger which consists in swedging a portion of round wire stock into a non-round cross section to provide bearing edges lying on the circumference of a circle having a diameter greater than the diameter of said round wire stock and swedging a flat side adjacent one end thereof and bending the end of said stock in the direction of said fiat side to form a head on said plunger.

2. The process of making a plunger which consists in swedging a portion of round wir-e stock into a non-round cross section to provide bearing edges lying on the circumference of a circle having a diameter greater than the diameter of said round wire stock and swedging a fiat side adof the body of the pencil but jacent one end thereof and bending the end of said stock in the direction of said flat side to form a head on said plunger, and during said bending operation, forming upper and lower inclined surfaces on said head.

3. The process of making a plunger which consists in swedging a piece of round wire stock so as to form a triangular body portion and a rectangular head portion with one flat side of said rectangular portion formed as a continuation of and of substantially the same width as one of the flat sides of said triangular body portion and thereafter bending said head portion toward said fiat side to form a laterally projecting head, and simultaneously with said bending forming cam surfaces on the upper and lower sides respectively of said head.

l. A plunger of the character described composed of wire stock having a round lead abutting end and a body portion having spaced bearing edges located on the circumference of a circle of diameter greater than the diameter of said round lead abutting end, and a head for said plunger extending later-ally from said body portion and being provided with inclined upper and lower cam surfaces.

5. A plunger of the character described composed of Wire stock having a round lead abutting end and a body portion having spaced bearing edges located on the circumference of a circle of diameter greater than the diameter of said round lead abutting end, and a head extending laterally from said body portion and having substantially a rhombcidal cross section.

6. A plunger of the character described composed of wire stock having a round lead abutting end and a body portion having spaced bearing edges located on the circumference of a circle of diameter greater than the diameter of said round lead abutting end, and a head extending laterally from said body portion and having substantially a rhomboidal cross section, and a tail for said head extending parallel to the axis of said plunger from the end of said laterally extending head.

7. A plunger of the character described composed of wire stock having a round lead abutting end and a body portion having at least one fiatside and further having spaced bearing edges located on the circumference of a circle of diameter greater than the diameter of said round lead abutting end and a laterally extending head projecting in the direction of said flat side of said body portion and having inclined top and bottom cam surfaces.

8. A plunger of the character described composed of wire stock having a round lead abutting end and a body portion of triangular cross section having its edges located on the circumference of a circle of diameter greater than the diameter of said round lead abutting end and a laterally extending head projected in the direction of one of the flat sides of said triangular body portion and having inclined top and bottom cam surfaces.

9. A plunger of the character described composed of wire stock having a round lead abutting end and a body portion of triangular cross section having its edges located on the circumference of a circle of diameter greater than the diameter of said round lead abutting end, and a head having a laterally extending portion, and a longitudinally extending portion, said laterally extending portion having inclined top and bottom bearing surfaces.

10'. A plunger of the character described composed of wire stock having a round lead abutting end and a body portion of triangular cross section having its edges located on the circumference of a circle of diameter greater than the diameter of said round lead abutting end, and a head having a laterally extending portion, and a longitudinally extending portion, said laterally extending portion having substantially a rhomboidal cross section and said longitudinally extending portion having substantially a rectangular cross section.

11. A plunger of the character described composed of wire stock having a round lead abutting end and a body portion of triangular cross section having its edges located on the circumference of a circle of diameter greater thanthe diam-eterof said round lead abutting end, and a head having a laterally extending portion and a longitudinally extending portion, said laterally extending portion having substantially a rhomboidal cross section and said longitudinally extending portion having substantially a rectangular cross section, a flat side of said longitudinally extending portion being disposed in opposed relation to a flat side of said triangular body portion and an inclined surface of said laterally extending portion joining said flat surfaces.

JOHN P. LYNN.