Boring
Welcome | What’s New?
Site Map | Usage Note

Become a Contributor
Really Boring
What is a Leadholder?
Leadholder History
Leadholder Mechanics
Leadholder Database
Yawn
References
Contributors
Leadholder Links
Contact D. B. Smith

United States Patent 3,627,434 “Mechanical Pencil for Fine Leads” 1971

date of application
date granted
inventor
assignee
patent holder country
primary examiner
attorney
1969 October 10, No. 04/865,254 (1969 May 14 in Japan)
1971 December 14
Yukio Horie, Japan
Bainihon Bungu, Kabushiki Kaisha, Tokyo
Japan
Lawrence Charles
Otto John Munz
patent employed on Pentel Graph Pencil
Pentel Graph Pencil
references United States Patents
2,222,295 Kanner; 1940 November
2,473,149 Juelss; 1949 June
2,627,842 Russell; 1953 February

Abstract

A mechanical pencil for fine leads with a pushbutton-type lead advancing mechanism, a conical ferrule at the writing end of the barrel and a plug connecting the ferrule to the barrel. The plug is so arranged that it reaches deep into the ferrule, thereby rendering the writing end of the barrel more rigid and shortening the distance between the pencil tip and the clutch head which advances the lead.

US 3,627,434


Background of the Invention


1. Field of the Invention

The present invention relates to mechanical pencils, and more particularly to mechanical pencils having a pushbutton-type lead advancing mechanism using a clutch to advance the lead by a predetermined increment, when a plunger button projecting from the rear of the pencil is depressed.

2. Description of the Prior Art

A known mechanical pencil of the type mentioned above uses a hollow cylindrical plug with a single thread on its outer surface to connect the ferrule to the pencil barrel. The plug is screwed into the front end of the pencil barrel by approximately one-half of its length, and with its other half it is screwed into the rear end of the ferrule. The plug has an enlarged bore at the ferrule side and a smaller bore at the barrel side, with a shoulder between them. Within the larger bore is arranged a clutch ring which is slidably movable between the plug shoulder and an abutment shoulder in the ferrule. Arranged inside this clutch ring is a clutch head which holds the lead in place. The ferrule includes in its center bore, near the writing tip, a resilient gasket to frictionally hold the lead, thereby preventing the latter from falling out of the pencil when the clutch head is opened. It serves the additional purpose of preventing the lead, once advanced, from moving back into the barrel with the returning clutch head.

The above design, where the clutch head is located in the region of the rear end of the ferrule, has the shortcoming that a considerable length of lead remains unusable because of the great distance between the ferrule tip and the clutch head. Furthermore, there exists the possibility of the lead breaking, when a lateral force or shock is applied to the tip of the ferrule thereby moving the axis of the ferrule tip and guide sleeve out of alignment with the axis of the clutch head. This disadvantage becomes more important when very fine leads are used. For certain drafting applications, leads as thin as 0.012 inch (0.3 millimeters) are being used nowadays. The addition of a lead guide tube in the tip of the ferrule for the protection of such fine leads further increases the unusable length of lead.


Summary of the Invention

It is an object of the present invention to provide a mechanical pencil with a pushbutton-type lead advancing mechanism, where the possible misalignment between the ferrule tip and the clutch head under a lateral force to the ferrule tip is kept to a minimum, to prevent accidental breaking of the lead.

Another object of the invention is to provide a mechanical pencil of the type mentioned, where the clutch head is located deep inside the tapered ferrule and at a close distance from the writing tip, so as to minimize the unusable length of lead, as determined by this distance.

Other objectives and advantages of the invention will become apparent from the detailed description of the invention, taken in conjunction with the accompanying drawings.


Drawings


US 3,627,434 figure 1
US 3,627,434 figure 1

Fig. 1 illustrates, at an enlarged scale, an embodiment of the invention with portions thereof shown in a center cross section, and with the center portion broken away;

US 3,627,434 figure 2
Fig. 2 shows, at a further enlarged scale, the front portion of the embodiment of fig. 1 in a center cross section:

US 3,627,434 figure 3
Fig. 3 (Prior Art) shows, at a scale comparable to that of fig. 2, the front portion of a known mechanical pencil.



Detailed Description and Operation

The mechanical pencil of figs. 1 and 2 has a slender barrel 2 preferably molded of synthetic resin, a tapered ferrule 3 in the front of the barrel, and an end cap 16 screwed to the rear end thereof. To the barrel is fixedly attached a clip 11.

In the front portion of the pencil is arranged a plug 1 which is composed of three cylindrical sections: the plug section 1a, extending to the rear of the plug 1, has a comparatively large outer diameter provided with a screw thread thereon; the plug section 1b located forward of the plug section 1a has a comparatively small outer diameter equally provided with a screw thread; and the plug section 1c extending to the front of the plug 1 has a still smaller diameter.

The barrel 2 has in the front portion of its bore an interior thread to receive the plug section 1a. The tapered ferrule has a bore with a threaded rear section to receive the plug section 1b, and forward of this threaded bore section a smaller cylindrical bore section tightly fitting the plug section 1c. When assembled as shown in fig. 2, the plug 1 firmly holds the ferrule 3 to the barrel 2.

The plug 1 has a central bore and, in its front portion, inside plug section 1c, an enlarged bore section with a rearward shoulder. Within this enlarged bore section is slidably arranged a clutch sleeve 4. The front end of the plug section 1c contacts an abutment shoulder in the bore of ferrule 3. This shoulder also limits the forward displacement of the clutch sleeve 4, while the rearward displacement of the latter is limited by the shoulder in the plug bore.

A lead guide 12, preferably of fine stainless steel tubing, is fixedly attached to the front end of the ferrule 3 and accurately aligned with the axis of the ferrule bore. The plug 1, by reaching deep into the ferrule 3 with its plug section 1c, renders the front portion of the pencil more rigid, thereby preventing misalignment between the lead guide 12 and the clutch sleeve 4, when the ferrule is subjected to lateral forces or shock. Behind the lead guide 12 is arranged a resilient gasket 5 whose purpose it is to prevent the lead from sliding freely into or out of the pencil.

Inside the pencil is arranged a longitudinally movable plunger assembly which operates in a known manner to hold and advance a lead through the lead guide 12. The plunger assembly consists of a plunger 7 reaching through the bore of the plug 1, a plunger casing 9 connected thereto by a plunger coupling 8 and extending through the barrel 2 into the end cap 16, and a plunger button 14 detachably connected to the rear end of the plunger casing 9 and extending beyond the hollow end cap 16.

The plunger 7 is slidably guided inside the plug 1 and extends a distance into the barrel 2. The plunger coupling 8 is screwed to the rear end of the plunger 7 and thereby retains a compression spring 10 between it and the rear face of the plug 1. The plunger 7 carries on its forward end a clutch head 6. This clutch head has a long thin neck of a smaller diameter than the head portion itself and, like a conventional collet, is slotted longitudinally to form several jaws, preferably three.

The clutch head 6 is screwed into the plunger 7 by means of a thread provided at its rear end, after the plunger assembly 7-8-9, the spring 10, the plug 1, and the sleeve 4 have been preassembled. The clutch sleeve 4 has a central bore to accommodate the clutch head 6 therein, with a smaller diameter in its rear half, a larger diameter in its front half, and a tapered interior shoulder therebetween. The plunger assembly is pulled to the rear by virtue of the spring 10, causing the clutch head 6 to be pulled into the sleeve 4 and against the tapered interior shoulder, thereby closing the clutch jaws around a lead which reaches through the plunger 7 and the lead guide 12.

The plunger casing 9, preferably of thin metal tubing, is fixedly attached on its front end to the plunger coupling 8. The coupling 8 has a peripheral groove into which a wall portion of the casing 9 is pressed. Inside the plunger casing 9 may be stored a number of spare leads.

The plunger button, preferably molded of synthetic resin, has a neck portion removably insertable into the rear end of the plunger casing 9, a shoulder limiting the depth of insertion, and, radially projecting from this shoulder, a nose 13 fitting into a longitudinal groove 17 of the end cap 16. In the front end of the button 14 is arranged a thin pin 15 of a diameter which is slightly smaller than the bore of the lead guide 12 and which reaches into the plunger casing 9. After removal from the casing, the plunger button can thus be used to clear the ferrule tip of fractured lead sections which may have been retained by the gasket 5. The plunger button can be removed by unscrewing the end cap 16.

In operation, the plunger button is depressed to advance the lead through the clutch head 6 and lead guide 12, by pushing the plunger assembly 7, 8, 9, 14 forward against the spring force of the compression spring 10. This causes the clutch sleeve 4, which is in frictional engagement with the clutch head 6, to be displaced forward until its movement is stopped by the abutment shoulder of the ferrule 3. The plunger 7, and clutch head 6 clamping the lead, advance further through the plug 1 and sleeve 4 until the clutch head leaves the clutch sleeve 4, thereby opening its jaws and releasing the lead. The lead, having been advanced by a set increment, is now only held longitudinally by the gasket 5.

Release of the plunger button 14 allows the spring 10 to return the plunger assembly into its rest position while the lead remains in the forward position. The clutch head 6, while reentering the clutch sleeve 4, moves the latter to its rear abutment position and upon contacting the tapered shoulder inside the clutch sleeve 4, closes its jaws around the lead, firmly gripping the latter. The nose 13 of the plunger button 14, guided in the groove 17 of the end cap 16, prevents rotation of the plunger assembly. Such rotation could cause a very fine lead to twist and break.

In fig. 3, is illustrated the front portion of a known mechanical pencil with a pushbutton-type lead advancing mechanism. The reference numerals 1', 2', 3', etc. of this figure refer to parts performing the same or a similar function as the parts, 1, 2, 3, etc. of figs. 1 and 2.

A comparison between fig. 2 and fig. 3 shows that the plug 1 of the invention has three successively smaller sections 1a, 1b and 1c, unlike the plug 1' of the prior art, and that this permits arrangement of the clutch head 6 much closer behind the writing tip of the ferrule 3. Even in the case where it is desirable to have a relatively long-tapered ferrule 3 conforming to a gradually reducing profile of the barrel 2, the plug of the invention permits a rigid connection between it and the ferrule 3. Furthermore, the short-gripping distance between the clutch head 6 and the gasket 5 provides better protection of the lead, should the connection between the plug section 1a and the barrel 2 deform under lateral forces or shock. The remaining unusable length of lead, as determined by the distance between the writing tip of the lead guide 12 and the front end of the clutch head 6 is thereby kept to a minimum.



Claims

I claim:

1. A mechanical pencil for fine lead having a pushbutton-type lead advancing mechanism, comprising in combination

An elongated barrel having a bore, a front end and rear end

said barrel including an interior thread in said front end and an outer external diametrical alignment projection on said front end and an upper internal thread and an internal diametrical alignment portion at said rear end;

a rear end cap 1, mounted on the rear end of said barrel having a bore, a front end with an external thread and an external diametrical alignment portion;

said external thread and said external alignment portion of said bore being in diametrical alignment and fitting engagement with said upper internal thread, and said internal diametrical alignment portion of said rear end of said barrel;

a tubular plunger casing, with an upper end and a lower end, having thin metal walls being a spare pencil lead magazine;

a plunger button of cylindrical shape having a necked portion nonrotatingly, slidably and reciprocatingly mounted in said end cap, the said upper end of the said plunger casing being removably mounted with its inside diameter upon said necked portion of said plunger button;

a sleevelike plunger coupling having an internal thread, an external diameter, an external circular groove and a necked diametrical part, said lower end of said plunger casing being fixedly mounted upon said external diameter of said plunger coupling pressingly engaging said circular groove of said coupling;

a ferrule having an outside cylindrical rear portion and a forward tapered portion, an internal diametrical fitting portion at said rear portion engaging fittingly said external diametrical fitting portion on said front end of said barrel;

said ferrule also having, starting in sequence at its said forward portion, concentric cylindrical bores, comprising:

a first small bore.

a second oval-shaped bore,

a third bore,

a fourth bore,

an abutment between said third and said fourth bore;

a fifth bore, and

a sixth bore being an internal thread;

a plug rigidly connecting said barrel and said ferrule; said plug having rear and front parts integrally arranged from its rear to front, said rear part having:

a necked projection,

a larger external thread in fixed engagement with said interior thread in said front end of said barrel,

a relief diameter,

said front part having:

a smaller external thread in fixed engagement with said sixth bore being an internal thread of said ferrule, and

a smaller outside diameter at said front part of said plug engaged aligningly and fittingly with said fourth bore of said ferrule,

said plug further comprising:

a long smaller bore starting at said rear part of said plug,

a conical bore, and a larger bore at its front part,

a tubelike plunger, having an upper part and a lower part,

said upper part comprising an external thread fixedly engaged with said internal thread of said plunger coupling and

an outside diameter, fittingly and slidingly engaging in said long smaller bore of said plug,

said lower part of said plunger having a small internal thread at said lower part, and comprising

an inner bore of a size permitting passing said pencil lead therethrough;

a clutch head having a front end and rear end being concentric, comprising:

a long thin neck;

an external thread at said rear end fixedly mounted and in engagement with said small internal thread at said lower part of said plunger;

an axial bore for slidingly passing and holding said pencil lead;

a colletlike clutch portion at said front end of said clutch head for alternately holding, feeding and clamping said pencil lead, said clutch head having at least two longitudinal slots in said front end portion and being located in said forward portion of said ferrule,

whereby a larger portion of said pencil lead can be used up;

a clutch sleeve slidably mounted in said larger bore in said front part of said plug, said clutch sleeve having an upper smaller bore and a lower larger bore and a conical clutch-affecting middle portion;

a compression spring axially mounted between said plunger coupling and said plug being held concentric by said necked diametrical part of said coupling and said necked projection of said plug;

a pencil lead-supporting gasket fixedly located in said second oval bore of said ferrule;

a pencil lead guide being of tubelike shape fixedly located in said first small bore of said ferrule,

all above parts in concentric alignment.

2. A mechanical pencil for fine lead having a pushbutton-type lead advancing mechanism, comprising in combination,

a barrel forming the main portion of said pencil, said barrel including an interior thread in the front end portion of its bore;

a tapered ferrule adjoining the front end of said barrel and including an interior thread in its rear portion and a writing tip at its front end;

a plug for connecting said ferrule to said barrel, said plug comprising a threaded rear section screwable into the front end of said barrel, a threaded middle section adjacent thereto and screwable into the rear end of said ferrule, and a front section of a diameter smaller than said middle section and extending forwardly therefrom, said plug being hollow and having in its front portion a bore section of enlarged diameter adjoined by an interior abutment shoulder;

a hollow plunger means arranged inside said barrel, reaching through said plug and being longitudinally movable from a rearward rest position into a forward position and back, said plunger means including clutch means in its front portion, said clutch means being guided inside said enlarged diameter bore section of said plug and capable, by this movement, of gripping a lead placed inside said clutch means when said plunger means returns to its rest position, and of releasing said lead when said plunger means moves to its forward position;

said tapered ferrule further having in its middle portion a central positioning bore, the wall of said bore closely fitting over said front section of said plug, so that axial alignment between said clutch means and said writing tip is maintained regardless of any misalignment between said ferrule and said barrel;

said plunger means further including spring means to urge said plunger means into its rest position, a plunger casing attached to and extending rearwardly from said clutch means and through a major part of said barrel, and a plunger button removably inserted into the rear end of said plunger casing and projecting therefrom and beyond the rear end of said barrel; said plunger casing being arranged to hold a supply of leads for successive insertion into said clutch means;

said barrel further including an interior thread in the rear end portion of its bore, a hollow end cap having a threaded forward portion screwable into the rear end of said barrel, said end cap including a longitudinal interior groove, and said plunger button including a matching radial nose slidably retained by said groove, to prevent said plunger means from rotating.

3. A mechanical pencil for fine lead having a pushbutton-type lead advancing mechanism, comprising in combination,

a barrel forming the main portion of said pencil, said barrel including an interior thread in the front end portion of its bore;

a tapered ferrule adjoining the front end of said barrel and including an interior thread in its rear portion and a writing tip at its front end;

a plug for connecting said ferrule to said barrel, said plug comprising a threaded rear section screwable into the front end of said barrel, a threaded middle section adjacent thereto and screwable into the rear end of said ferrule, and a front section of a diameter smaller than said middle section and extending forwardly therefrom, said plug being hollow and having in its front portion a bore section of enlarged diameter adjoined by an interior abutment shoulder;

a hollow plunger means arranged inside said barrel, reaching through said plug and being longitudinally movable from a rearward rest position into a forward position and back, said plunger means including clutch means in its front portion, said clutch means being guided inside said enlarged diameter bore section of said plug and capable, by this movement, of gripping a lead placed inside said clutch means when said plunger means returns to its rest position, and of releasing said lead when said plunger means moves to its forward position;

said tapered ferrule further having in its middle portion a central positioning bore, the wall of said bore closely fitting over said front section of said plug, so that axial alignment between said clutch means and said writing tip is maintained regardless of any misalignment between said ferrule and said barrel;

said plunger means further including spring means to urge said plunger means into its rest position, a plunger casing attached to and extending rearwardly from said clutch means and through a major part of said barrel, and a plunger button removably inserted into the rear end of said plunger casing and projecting therefrom and beyond the rear end of said barrel; said plunger casing being arranged to hold a supply of leads for successive insertion into said clutch means;

said plunger button including a forward-projecting pin, said pin having a diameter not larger than that of a lead, said plunger button and pin, when removed from said plunger casing, being adapted to remove fractured lead sections from the writing tip of said ferrule.