US 3042004 A
Description (OCR text may contain errors)
July 3, 1962 H. R. FISCHER ETAL 3,042,004
NAIL DRIVING ATTACHMENT FOR PNEUMATIC Toor.
Filed Ju1y 8, 1960 United States Patent O spaanse Nair parvint; arracrnvrnrsr non rNnUMArrc rootJ 'i Filed uly 8, 1969, Ser. No. 41,519 4 @taime (Cl. 121-32) This invention relates to a nail driving machine and more particularly to a nail driver attachment for the front end of the cylinder of a conventional pneumatic hammer.
An object of the invention is to convert a standard riveting hammer into a nail driver with a minimum substitution of parts and in a minimum time.
Another object is to support and guide the nail driving tool centrally with respect to the driven nail and thereby prevent the tool from accidentally slipping oif the head of the nail under the vibration incident to the hammering action.
A further object is to enable the operator to determine, by the sound and feel of the tool, as well as by visual observation, that the nail has been driven to its desired iinal position.
Still another object is to control the force of the hammer blow against the nail by automatically lengthening the stroke of the piston and thereby increasing the force of impact as the nail penetrates further into the wood and meets with increasing resistance.
Another object is to automatically limit the penetration of the nail into the wood by a predetermined distance, and thereby facilitate driving of a series of nails uniformly to the proper depth without requiring any great skill on the part of the operator.
A feature of this invention is a centralizer sleeve which is arranged in surrounding relation to the anvil which engages the nail, the front end of the sleeve normally encircling the nail head to retain the tool in axial alinement therewith, but being adapted, near the final step of the driving operation, to permit the anvil to drive the nail head a predetermined distance beyond the end of the sleeve and into countersunk relation with the wood.
In accordance with this invention the anvil is formed with `a relatively long shank adapted to extend into the cylinder beyond the normal striking position as compared with the usual riveting tool. The piston reciprocates at first with relatively short strokes to deliver relatively light blows through the anvil to the head of the nail. The operator usually presses forward on the cylinder to restore the relative position of the anvil in the cylinder in time for the succeeding impact. The centralizer sleeve is arranged in such relation to the other parts of the tool that the sleeve and cylinder follow the progress of the nail and anvil until the forward motion of the cylinder is positively arrested by contact between the front end of the sleeve and the surface of the wood. Thereafter continued application of hammer blows causes the anvil to follow the nail independently of the sleeve and therefore independently of the cylinder which is attached to the sleeve.
The result of the progressive ,advance of the anvil in the cylinder is to progressively lengthen the stroke of the piston and the force of the blow. The hammer blows continue until forward motion of the anvil is arrested by engagement with an internal shoulder v in the sleeve. Thereafter the force of blow is taken by the sleeve and not the nail and the penetration of the latter into the wood is automatically limited.
Other objects ,and features of this invention will appear more clearly from the following description, taken in connection with the accompanying drawings and appended claims. In said drawings:
Bhd-2,094 Patented July 3, 1962 FIG. l is a longitudinal section of the front end of a nailing tool provided with an attachment embodying this invention, showing the position of the parts of the tool and the driven nail just prior to the delivery of the first impact;
FIG. 2 is a view similar to FIG. 1 but with the parts of the tool and the nail shown at the completion of an impact and just before the operator pushes the cylinder forward to follow the progress of the nail;
FIG. 3 is a similar view showing the parts of the tool and the nail `at the completion of the final impact of a series; and
FIG. 4 is a cross-section of the tool on the line 4-4 of FIG. l.
In the illustrative embodiment of the invention, the nailing tool is pneumatically powered and comprises a cylinder 1@ arranged to be supported manually by a suitable handle (not shown), the cylinder being bored to provide a piston chamber 11 in which a hammer piston 12 reciprocates. The piston may be reciprocated by means of a distributing valve (not shown) cooperating with air passages 13 and 14 extending between the piston chamber and the valve. The valve and the associated means for supplying live air alternately to the ends of the piston chamber to reciprocate the piston may be of any type welt-known in the art, as shown, for example, in Stevens Patent 1,928,707, October 3, 1933.
The front end of the cylinder is lprovided witha counterbore 15 in which is atiixed a bushing 16. Slidably mounted in the bushing in air-tight manner is the shank of an anvil 17 which is arranged to receive hammer blows in automatic succession from the piston 12. The anvil has an integral collar 18 normally seated against the front end of the bushing 16 to limit rearward movement of the anvil into the cylinder. In front of the collar the anvil has an extension 19 arranged to transmit the impacts to the nail 21 which is driven by the tool.
The structure described up to this point, except for the shape of the anvil, is common to a well-known aircraft riveter in commercial use, as shown in Roberts Patent 2,375,691, May 8, 1945. In such a riveter, the anvil is retained against separation from the cylinder by a helical wire commonly known as a beehive retainer. The present invention enables the riveting tool to be converted into a nailing tool by simply adding one or two parts to a conventional structure. In accordance with this invention, a beehive retainer 22 is attached by a screw threaded connection to the front end of the cylinder as before, but instead of engaging the anvil directly it engages a centralizer sleeve 23, which is of novel construction and arrangement, the sleeve being interposed between the beehive retainer and the anvil. The sleeve is essentially in the shape of a two-diameter hollow cylinder having at its front end a bore 24 slidably fitting over the front extension 19 on the anvil and having at its rear portion a counterbore 25 slidably tting over the anvil collar 18. Preferably, the bore and counterbore have a rather close fit with the anvil in order to hold the centralizer sleeve 23 in axial alignment with the anvil 17, which, in turn, is held in axial alignment with the hammer piston 12 by means of its close fit within the bushing 16.
Between the |bore 24 and counterbore 2S, the sleeve 23 is provided with an internal shoulder 26 `arranged to be engaged by the collar 18 to limit forward movement of the anvil relative to the cylinder `and thereby to prevent accidental `detachment of the anvil 17 from the rest of the tool. The shoulder 26 also serves another purpose which will be described later. Preferably, the shoulder 26 is rounded to tit the rounded surface on the front face of the anvil collar 18, thereby minimizing the danger of 4breakage of the anvil or sleeve upon transmission of yan impact therebetween. Separation of the sleeve 23 from the cylinder is prevented by means of an external shoulder 27 on the sleeve which seats against the front end of the lbeehive retainer 22. Preferably, the enlarged portion of the sleeve has such an axial length in relation to the wire retainer that the latter is under slight tension at all times to hold the rear end of the sleeve in engagement with the front extremity of the cylinder. The beehive retainer 22 is resilient to permit the centralizer sleeve 23 to move yforward momentarily out of contact with the cylinder in the event of accidental delivery of an impact from the anvil collar 18 to the internal shoulder 2o on the sleeve while the latter is out of contact with the work, thereby acting as a further safeguard against the danger of breakage.
The primary function of the centralizer sleeve 23, and particularly the front bore 24 thereof, is to encompass the head of the nail 21 and thereby prevent the nail head from moving laterally out of the path of the anvil 17, or vice versa, at any time during the delivery of a series of hammer blows. In accordance with this invention, the sleeve is designed with a front bore 24 of such axial depth that the nail head is not projected beyond the sleeve during impact and does not become detached even if the operator inadvertently releases his pressure on the tool -against the nail. On the other hand, the centralizer sleeve is so proportioned with relation to the anvil that it permits the nail to be driven to its inal position even when the centralizer is prevented from encompassing the nail head due to interference with the wood or workpiece.
In operation, the nail 21 is held in one hand in the desired position while the nailing tool is held in the other hand and moved into operative relation with the nail head as shown in FIG. l. The operator presses forward on cylinder `causing the nail yto penetrate slightly into the wood 29. The reaction of the pressure against the nail forces the anvil 17 rearward so that it seats firmly against the bushing 16 and the rear end of the anvil penetrates a maximum distance into the piston chamber 11. Under these conditions, the head of the nail extends into the front bore 24 of the centralizer sleeve 23 by the distance A shown in FIG. 1. Preferably, the bore is long enough so that the distance A is equal to or greater th-an the maximum distance of axial advance of the nail on any single blow. The operator then opens the throttle valve to reciprocate the piston in a Well-known manner causing the latter to drive the anvil 17 forward out of seating relation with the 'bushing 16, and the anvil at the same time causes the nail 211 to penetrate into the wood 29 by a like amount. Under some conditions of operation, the nail 21` and the cylinder 10 may be somewhat out of axial alignment as a result either of inarvertent handling or of `close quarters. The misalignment has a tendency either to cause the anvil to slip oli` the nail, or to cause the nail head to move laterally and ily away from the tool in response to a glancing blow. However, this tendency is effectively overcome by the present inven- .tion because the centralizer sleeve 23 guides the movement of the entire tool and locks the nail head against any lateral displacement, thereby enabling the operator to steady the nailing tool against the driven nail even under conditions of vibration.
Assuming that the axial pressure of the operator against the cylinder is relatively light, so that the cylinder does not have time to move during impact, the position of the parts of the nailing tool `at the termination of an impact will be substantially as shown in FIG. 2, in which position the penetration of the nail head into the centralizer bore 24 is reduced to the axial `distance B. At the same time, the anvil collar 18 is displaced from the bushing 16 by an axial distance equal to (A minus B). The operator then presses the tool forward to reseat the anvil against the bushing and thereby increase the penetration of the nail into the centralizer sleeve 23 to the distance A by the time that the piston returns for the delivery of 4the next hammer blow. Under these conditions, which recur near the beginning of the operation, the rear face L of the anvil lies in the plane 311 at the instant of the start of each impact delivered by the hammer piston 12. In accordance with this invention, the striking plane 35i starts out in a position which is located further rearward in the cylinder 10 than the normal striking plane 31 for the standard pneumatic riveting hammer as it was constructed prior `to conversion to a nail-driver. The abnormal rearward location of the striking plane 30 results from the fact that the shank portion of anvil 17 above the collar 13 is abnormally long in comparison with the standard rivet set or anvil as shown for example in Roberts Patent 2,375,69l. rIhe eifect in the change of dimensions and position of the striking plane is that the stroke of the piston, during the early stage of operation is shortened by the distance C. The piston 12, operating at a shortened stroke, does not have as much time to build up speed and momentum as it normally does with the result that the force of blow is less than normal. The light blows, however, are not disadvantageous because they occur only near the start of the operation when the penetration of the nail 21 into the wood 29, and therefore the frictional resistance of the wood, is so slight that it does not require a heavy blow. On the other hand, a light blow is preferable at the beginning of the driving operation because it lessens the tendency of the pointed end of the nail to bounce olf its `selected spot on the wood.
The cycle of operation is repeated until the nail 21 is driven to about the distance A from its final position. At this stage of the operation the front end of the sleeve 23 abuts against the wood to positively limit forward movement of the cylinder 10 and thereby prevent the bushing 16 from following the anvil shoulder 18 into reseat'ing relation. Continued delivery of impacts by the piston 12 causes the anvil 17 to advance step by step with respect to the cylinder 10, thereby causing the striking plane 30 to advance step Aby step toward the normal striking plane 31, with the result that the piston stroke lengthens in increments `and the force of blow increases correspondingly.
Toward the end of the nail driving operation, the stroke of the piston 12 increases until it becomes abnormally long. The progressive advance of the anvil 17 relative to cylinder 10 continues until the anvil attains its extreme forward position relative to the cylinder as represented by broken lines in FIG. l and solid lines in FIG. 3. In that extreme position, the collar 1S seats against the internal shoulder 26 in the sleeve, the front end of the anvil 17 lies substantially iiush with the front end of the sleeve `23, and the rear end of the anvil lies in the striking plane 32 (FlGS. 1 and 3). Continued delivery of hammer blows after the extreme position is attained does not drive the nail 21 any deeper into the wood 29 for the reason that the full force of the blow is now delivered to the sleeve shoulder 26 instead of to the nail. The shoulder, therefore, acts as a limiting device to prevent the nail from being driven too deeply even though the operator may inadvertently continue the delivery of blows for too long a period.
Ordinarily, however, the operator does not waste time by hammering too long on a nail because he is given a signal that the end of the driving operation is approaching, and a later signal that the driving operation is cornplete. The irst signal occurs when he determines by the feel of the cylinder 10, that the latter cannot be pushed any closer to the wood 29 because of contact of the sleeve 23 with the wood, thus indicating that the nail has approached within the axial distance A of its nal position. Thereafter the operator ascertains that the piston blows are getting longer as manifested by the sound and feel of the vibrations with greater amplitude and less frequency. The second signal occurs when contact is made between the anvil collar 18 and the sleeve shoulder 26 at which time the operator can determine by sound and by the feel of the tool that the blow is being delivered to the sleeve and not the nail.
Throughout the nail driving operation, the sleeve 23 acts as a centralizer or guide to prevent the anvil 19 from shifting laterally relative to the head of the nail. During most of the stage of operation, the centralizer acts as a positive means for preventing such lateral displacement because it completely encircles the head of the nail 2l as shown in FIGS. 1 and 2. At the instant when the front end of the centralizer sleeve 23 makes contact with the wood, the centralizer still surrounds the head of the nail for the full axial depth thereof. Thereafter the centralizer surrounds the nail head for only a part of its depth as the latter is being driven into counter sunk relation with the wood. However, by the time that the axial depth of engagement between the sleeve and the nail head is diminished, the sleeve engages the wood surface with such force that the friction therebetween prevents the sleeve from moving laterally relative to the wood and, therefore, relative to the nail.
As shown in FIG. 3, the nail driving operation automatically terminates when the top face of the nail 21 becomes ilush with the surface of the wood 29, for the reason that the front face on the anvil extension 19, in the illustrative embodiment of invention, happens to be tiush with the front end of the sleeve 23 at the instant when the anvil collar 13 engages the sleeve shoulder 26. If desired, the nail could be driven more deeply into countersunk relation with the wood by merely lengthening the extension 19 on the anvil so that the front end is permitted to extend slightly beyond the front end of the sleeve. The increase in the length of extension 19, in the absence of any other change in design, would not aiect the location of the striking planes 3U and 32 or the distance A therebetween, although it would reduce the maximum penetration of the nail head into the sleeve bore Z4, as compared with the distance A shown in FIG. l.
From the foregoing description, it is apparent that the centralizer sleeve Z3 acts as a guide to hold the nailing tool and driven nail in axial alinement with each other throughout the driving operation, and does not interfere with the driving of the nail until the latter reaches its predetermined final position, whereupon the sleeve suddenly acts as a limit stop to prevent delivery of further impacts to the anvil.
If desired, the throttle valve may be of the gradually opening type, which is commonly used in riveting hammers to permit the operator to restrict the supply of air when the valve is first opened so that the rst few blows of a series will be relatively light. The use of such a valve (sometimes referred to as a teasing throttle) in association with the nailing attachment of this invention makes it possible for the operator to vary the force of blow in three stages. In the rst stage, with the tool and nail in the FIG. l position, the tool may deliver light blows with the throttle valve only partly open. After the point of the nail is more securely embedded in the wood 29, the operator opens the throttle valve wide to deliver more powerful blows for the second stage. When the nail approaches its home position as shown in FIG. 3, the blows become even heavier, because the centralizer sleeve 23 holds back the cylinder l0 and piston 12 relative to the anvil 17 and nail 21 in a position where the stroke of the piston is automatically and progressively lengthened as explained previously.
What is claimed is:
l. A tool retainer for a power hammer including a hammer cylinder and a hammer piston reciprocable in the latter, comprising an anvil having a rear portion adapted to project into the front end of the hammer cylinder to receive impacts from the hammer piston, said anvil having a collar adapted to seat against a shoulder at the front end of the cylinder to limit rearward movement of the anvil into the cylinder, a sleeve surrounding the anvil and seated at its rear end against the front end of the cylinder, the sleeve having an internal shoulder adapted to seat against the anvil collar to limit forward movement of the anvil relative to the sleeve, and yieldable means for retaining the sleeve in contact with the cylinder, said yieldable retaining means comp-rising a helical wire surrounding the cylinder and sleeve, the rear portion of the wire having threaded engagement with the front end of the cylinder, the sleeve having a smooth conical external shoulder, the front end of the wire having an inwardly directed ilange providing a seat for the external shoulder on the sleeve, the wire being open at its front end and the sleeve having a reduced extension beyond the said shoulder projecting through said opening.
2. In a pneumatically powered nailing hammer for driving nails having iiat heads, including a cylinder providing a piston chamber, a hammer piston reciprocable in the latter, and including a bushing mounted in a bore at the front end of the cylinder; a sleeve having an enlarged rear portion, a reduced front portion, and a coned external shoulder between the two portions; the sleeve being arranged with its rear portion in end abutment with a front end of the cylinder; a recess in the rear portion of the sleeve having an internal shoulder at 4its forward end and having an open rear end adjacent to the bushing; a beehive spring in part sleeving over the enlarged portion of the sleeve, the spring having an inturned `forward end seated about the external shoulder of the sleeve and having a rear part threadedly retaining the sleeve in such abutting relation to the cylinder; an anvil having a rear extension slidably supported in the bushing for movement through the latter into .the piston chamber to receive impacts from lthe hammer piston, the anvil having a forward extension sleeved over by the reduced portion of the sleeve land having sliding movement in the latter, and 4the anvil having an integral collar between the extensions slidable in the recess to limit against the bushing when the anvil is moved rearwardly, and to limit against the internal shoulder when the anvil is moved forwardly; the rear and front extensions of the anvil being such that when the collar is limited against the bushing the front extension is disposed in the reduced portion of the sleeve at a substantial distance inwardly of the open end of the latter, and the rear extension projects into the piston chamber for a substantial distance whereby the stroke of the hammer piston is correspondingly reduced while the collar is so limited; and that when the collar is limited `against the internal shoulder of the recess, the end of the rear extension of the anvil is positioned at the front end of the piston cylinder and the front extension of the anvil is positioned Hush with the front end of the reduced portion of the sleeve; and the reduced end of the sleeve having an open end and adapted to receive with a slide fit therethrough the at head of a nail for a distance as determined by the rearward disposition of the anvil relative to the sleeve, and the front extension of the anvil having a flat end face adapted to transmit the impacts of the hammer piston to the dat head of a nail so received into the sleeve.
3. A nail driver unit adapted to be removably attached to a pressure tool of a type having a housing externally threaded at its lower end, and a hammer piston reciprocable in a piston chamber of Ithe housing which chamber terminates in a reduced passage opening axially through the bottom end of the housing; the nail driver unit comprising a beehive open ended spring reduced in its lower portion `and enlarged in its upper portion, an open ended sleeve slidably entered lin the spring having a reduced lower part extending through the ylower portion of the ispring and an enlarged upper part disposed in the enlarged part yof the spring, the sleeve having its upper end substantially below the top end of the spring, an anvil slidably workable in the sleeve having a lower extension slidably disposed in the reduced part of the sleeve, a shoulder dened in the sleeve above the reduced part thereof, a collar on the anvil movable with the lanvil in the upper part of the sleeve and adapted to seat upon said shoulder, :the extension of the anvil extending at least to the bottom end cf the sleeve when the collar is so seated, the upper part of the spring being adapted to threadedly engage the housing until the up-per end yof the sleeve abuts tightly against the bottom end of the housing of the tool, and the anvil having an upper extension above the collar adapted when the sleeve is in such abutting relation to extend through the reduced passage of the housing to the bottom end of the piston chamber, and the reduced end of the sleeve being adapted to receive a nail therein to cause the upper extension of the `anvil to project into ythe piston `chamber to receive impacts from the reciprocable hammer piston.
4. A nail driving attachment for a reciprocating power hammer including a cylinder, a hammer piston reciprocable in the cylinder, and the cylinder having an end wall defining an annular shoulder at its front end, comprising: an anvil having a cylindrical shank adapted to project into the front end of the cylinder to receive impacts from the hammer piston, and having a collar adapted to seat against the shoulder at the front end of the cylinder to limit rearward movement of the anvil into the cylinder, said anvil having in front of the collar an extension terminating in a front face, a centralizer sleeve surrounding the anvil, said centralizer sleeve having a bore extending from its front end adapted to fit slidably over the anvil extension, said sleeve having a counterbore surrounding the anvil collar, said sleeve having an internal shoulder connecting the bore and counterbore and arranged to seat against the anvil collar to limit forward movement of the anvil relative to the sleeve, the sleeve having a front end wall with which the front face of ythe extension is Hush when the anvil is limited in its forward position, and the said bore being suited when the anvil is moved rearwardly of its forward position to receive with a slide fit the head end of a nail until the head abuts the front face of the extension; in which the rear end of the sleeve abuts against the front end of the cylinder, a retainer is arranged `in surrounding relation -to` the front end of the cylinder and the rear end of the sleeve to hold the sleeve in position on the cylinder; and in which the rear portion of the retainer has threaded engagement with the front end of the cylinder, the sleeve having a smooth conical external shoulder, the front end of the retainer tapering inward to provide a seat for the external shoulder on the sleeve, the retainer having `an open end beyond the seat, and the sleeve having a reduced extension beyond the said shoulder projecting through said opening with a slide fit to thereby inhibit axial movement of the sleeve forwardly of the cylinder.
References Cited in the tile of this patent UNITED STATES PATENTS 1,722,330 Hasty July 30, 1929 2,257,267 Lundgren et al Sept. 30, 1941 2,372,029 Stair Mar. 20, 1945 2,679,044 Bacon et al. May 25, 1954 2,890,455 Etzborn Tune 16, 1959 FOREIGN PATENTS 792,047 Francel Dec. 21, 1935