US2923940A

US2923940A - Certificate of correction

Info

Publication number: US2923940A
Authority: US
Publication date: 1960-02-09
Anticipated expiration: 1977-02-09

Description

Feb. 9, 1960 R. c. KVAVLE SAFETY MECHANISM Filed Oct. 28, 1957 INVENTOR. ROBERT C. KVAV L E BY BUCKHORN CHEATHAM 8 BLORE ATTORNEYS work surface.

United States Patent SAFETY MECHANISM Robert C. Kvavle, Newberg, 0reg., assignor to Omark Industries, Inc., Portland, 0reg., a corporation of Oregon Application October 28, 1957, Serial No. 692,711

7 Claims. (Cl. 1106) This invention relates to a safety mechanism for power actuated tools and more particularly to a mechanism which will prevent a sear from being moved from a firing pin holding position to a firing pin releasing position by inertia forces on the sear when the tool is dropped or otherwise subjected to an impact.

Powder actuated tools, particularly those of the type employed for driving studs into work surfaces, are frequently employed at considerable heights and it is not uncommon for a loaded tool to he accidentally dropped by a workman. Such tools have their firing pin springs energized to condition the tool for firing either by a movable member which is moved directly by the hand of the operator or by pressing the muzzle of the tool against a The firing pin is held against the force of such spring by a sear. When a dropped tool strikes the ground or other solid object, the sear may be moved to firing pin releasing position by inertia forces due to the resulting impact. Such inertia forces can also cause the movable member, referred to above, to be given in a direction which energizes the firing pin spring and can thereafter cause the sear to release the firing pin. It is not practical to attempt to employ perfectly balanced scars in production tools so that such sears have no resultant inertia forces acting thereon. A considerable number of accidents have been caused by tools being fired when inadvertently dropped.

In accordance with the present invention, a sear is mounted in the tool so that it has a definite unbalance and is therefore subject to the type of inertia forces above referred to. The inertia forces which are in a direction to release the sear can, however, be restricted to a definite range of directions such that they must have a component in one given direction in order to tend to move the sear to firing pin releasing position. Also in accordance with the present invention, an inertia member is mounted adjacent the scar and the mounting of such inertia member is such that any impact tending to move the sear to firing pin releasing position will simultaneously tend to move the inertia member in an opposing direction. The inertia member has a portion in contact with the sear to apply a force thereto opposing and greater than the inertia forces acting on the sear itself and the result is that there is no possible direction of an impact force which will cause the sear to be moved to firing pin releasing position by inertia or impact forces.

It is therefore an object of the present invention to provide an improved powder actuated tool which has incorporated therein a safety mechanism which prevents release of a firing pin sear due to inertia forces acting on the sear.

Another object of the invention is to provide a safety mechanism for a powder actuated tool in which a firing pin resiliently urged toward firing position is restrained by a scar and an inertia member is employed to prevent release of the sear due to inertia forces acting on the sear when the tool is subject to an impact.

"ice A A further object of the invention is to provide a powder actuated tool having a drop safety mechanism by which a pivotally mounted sear is prevented from releasing a firing pin by a pivotally mounted inertia member applying a force to such sear which is opposite in direction to any inertia force acting directly on the scar and tending to release the sear.

Other objects and advantages of the invention will appear in the following description of a preferred embodiment shown in the attached drawing of which:

Fig. 1 is a plan view of a powder actuated tool in accordance with the present invention with the tool shown in partially open position and with a portion broken away to show the pivot between the barrel and handle portions of the tool;

Fig. 2 is a longitudinal vertical section through the tool of Fig. 1 with the tool shown in closed position;

Fig. 3 is a vertical section taken on the line 33 of Fig. 2 and showing the sear and inertia member of the present invention;

Fig. 4 is a fragmentary horizontal section taken on the line 4-4 of Fig. 3 showing the scar and inertia member in plan; and

Fig. 5 is a diagrammatic view of the scar and the inertia member providing the safety mechanism of the present invention indicating the direction of the inertia forces acting on such members.

Referring more particularly to the drawings, the tool shown includes a front or barrel portion 10 and a rear or handle portion 12 pivotally connected to each other to provide for opening of the tool as illustrated in Fig. 1.

Opening of the tool is for the purpose of enabling a blank cartridge 14, shown in Fig. 2, to be inserted into a breech plug 16 positioned in the rear end of a barrel 18 to load the gun and also to provide for the insertion of a stud 20 into the bore of the barrel in advance of the cartridge 14. It will thus be apparent that the gun may be loaded when the tool is in the open position. The pivoting of the two portions of the tool relative to each other is accomplished by mounting the rear portion of the barrel 18 in a barrel block 22 and pivoting such barrel block to a breech block 24 in the form of a yoke by a pivot pin 26, which is not shown in Fig. 2 but the end of which is shown in Fig. 1.

As shown in Fig. 2, the breech block 24 is positioned within the forward end of a rear or action housing 28 while the muzzle end of the barrel 18 extends forwardly through a front or barrel housing 30. The barrel housing includes a front or barrel housing sleeve 32 having a rubber cover 34 on portions thereof and a rear or barrel block sleeve 36 secured to the barrel housing sleeve 32 in any suitable manner, such as by brazing. The barrel block sleeve 36 includes a ring portion 38 surrounding the rear portion of the barrel housing sleeve 32 and side portions 39 and 40 (Fig. 1) of different length extending rearwardly along each side of the barrel block 22.

The rear housing 28 includes a front or action housing sleeve 43 surrounding and conforming to the breech block 24 and extending rearwardly therefrom. Such sleeve has its rear end partially closed by an inner ring member 42 suitably secured in the action housing sleeve in any suitable manner, for example, by brazing. A handle member 44 having a rubber cover 46 is secured to the ring member 42 by means of a screw 48 and forms a rear closure for the action housing. The entire action housing is held in position on the breech block 24 by means of a plunger 50 positioned in a vertically extending bore in the breech block 24 and urged downwardly into a slot 52 in the lower portion of the action housing sleeve 43. The slot 52 is covered by a small cover plate 54 having an aperture 56 therein which in the position of the parts shown in Fig. 2 is aligned with the plunger 50. By pressing the plunger upwardly in Fig. 2 by a suitable punch or other instrument inserted through the aperture 56, the entire action housing 28 including the handle member 44 can be slid rearwardly off the breech block 24 to provide access to the interior of the rear portion of the tool.

The forward end of the barrel 18 has a safety shield 58 mounted thereon, such shield being secured to a safety shield sleeve 60 extending rearwardly around the barrel 18 inside of the barrel housing sleeve 32. The safety shield sleeve 60 is spaced radially outwardly from the barrel 18 to provide room for a safety shield spring 62 which urges the safety shield 58 toward the muzzle end of the barrel. The shield 58 is held on the muzzle end of the barrel by a nut 64 screw-threaded on the end of the barrel. The rear end of the spring 62 abuts against a shoulder on a barrel sleeve 66 extending rearwardly from the muzzle end of the barrel and having its front or muzzle end also screw-threaded on the muzzle end of the barrel 18.

The barrel sleeve 66 also has its rear end engaged by the forward end of another compression spring 68 which has its rear end engaging an inwardly directed flange 70 on the barrel housing sleeve 32. The barrel 18 has a sliding fit in the barrel block 22 and as shown in Fig. 2, has an enlarged portion 71 at its breech end fitting in a socket in the breech end of the barrel block. It will be apparent that the barrel 18 and also the barrel housing 30 including the barrel housing sleeve 32 and barrel block sleeve 36 are held in position with respect to the barrel block 22 by the spring 68. It will be further apparent that the barrel housing 30 and action housing 28 can slide forwardly on the assembly of the safety shield 58, the safety shield sleeve 60, the barrel 18, the barrel sleeve 66, the barrel block 22 and breech block 24 against the action of the spring 68 when the gun is in closed position. and the muzzle end of the gun including the safety shield 58 is pressed against a work piece. The barrel 18 and barrel sleeve 66 can also move forwardly with respect to the safety shield 58 and its sleeve 60 to compress the spring 62 so that the muzzle edge of the safety shield 58 aligns with the muzzle end of the nut 64 on the barrel 18. Such forward movement of the action housing with respect to the breech block 24 conditions the action of the tool for firing.

As shown in Fig. 2, the rear or handle end of the breech block 24 terminates in a rearwardly extending tubular member 72 which receives and guides the forward end of a reciprocable firing pin 74 extending longitudinally of the tool. The firing pin has a shoulder 76 near its forward end which engages a notch 78 (Fig. in a sear 80 (Figs. 2, 3 and 5). The sear 80 is pivotally secured to the rear end of the breech block 24 by a screw 82 (Fig. 3) for pivotal movement about an axis parallel to and laterally spaced from the axis of the firing pin 74. The end of the sear 80 engaging the firing pin is urged toward the firing pin 74 by a helical spring 84 4 surrounding the screw 82 and having one end engaged in a small aperture (not shown) in the breech block 24 and the other end engaging a rearwardly extending trigger engaging portion 86 of the sear. When the action housing 28 is moved forwardly with respect to the breech block 24, the rearwardly extending trigger engaging portion 86 of the sear is positioned below a sear engaging portion 88 on the upper portion of a trigger 90 positioned in a slot in the handle member 44 and pivoted on a pivot pin 91. The trigger is spring urged toward the non actuated position shown in Fig. 2 by a U-shaped spring 92 also positioned in the slot in the handle member 44. Upon manual actuation of the trigger, the sear engaging portion 88 thereof moves downwardly and engages the trigger engaging portion 86 of the sear 80 to pivot the sear about the axis of the screw 82 to thereby release the sear from shoulder 76 on the firing pin 74.

The firing pin has an intermediate shoulder 9 .1

slidable in a bore 96 in the handle member 44 aligned with the tubular member 72 of the breech block. The firing pin is held in position in the bore 96 by the ring member 42 secured in the rear end of the action housing sleeve 43. The firing pin 74 is urged forwardly by a compression spring 100 in the bore 96 between the shoulder portion 94 and the rear end of the bore. Forward motion of the action housing 28 including the handle member 44 does not, however, move the firing pin 74 forwardly with respect to the breech block since the sear engages the shoulder 76 on the firing pin. Such forward movement of the action housing relative to the breech block 24 thus compresses the firing pin spring to load or energize such spring and at the same time positions the trigger engaging portion 86 of the sear 80 for actuation of the sear by the trigger 90. Upon manual actuation of the trigger, the firing pin is released to fire the tool but this can only happen when the action housing 28 has been moved to its forward position relative to the breech block, for example, by reason of the safety shield 58 and barrel 64 being engaged with a work surface and the handle portion 44 being pushed toward such work surface.

The tool has a safety mechanism which prevents forward motion of the action housing 28 to firing position with respect to the breech block 24 when the safety shield 58 has been removed. Such safety shield 58 may be removed by unscrewing the nut 64 from the muzzle end of the barrel 18. This enables the safety shield sleeve 60 and the spring 62 to be withdrawn from the muzzle end of the barrel housing sleeve 32. Withdrawal of the sleeve 60 allows a spring pressed latch 102 carried by the barrel housing 30 to engage a shoulder 104 on the barrel sleeve 66 so that the barrel housing cannot be moved forwardly with respect to the barrel 18. Since the barrel is attached to the breech block 24 through the barrel block 22 and pivot pin 26 and the front end of the action housing 28 engages the rear end of the barrel housing 30, the action housing 28 cannot be moved forwardly to firing position with respect to the breech block when the shield 58 is removed. Reinsertion of the sleeve 60 of the safety shield 58 cams the latch 102 out of contact with the shoulder 104 and this is true even though the rearward end of the shield 60 engages a spring pressed pivoted detent 106 useful for holding the shield 58 in a forward position for use with an extension (not shown) on the barrel 18. The spring pressed detent 106 may be manually moved out of the path of the sleeve 60 by depression of its rear end so that the sleeve 60 can be further inserted into the barrel housing sleeve 32 to the position shown in Fig. 2. The safety mechanism just described is not operative when the sleeve 66 and safety shield 58 are in position on the tool.

If the tool having the safety shield 58 in position thereon is dropped after having been loaded with a cartridge 14, the breech block 24 may be driven rearwardly in the action housing 28 by inertia forces, if the handle portion of the tool strikes the ground or any solid object. On the other hand, if the front end of the tool strikes the ground, the inertia of the handle portion of the tool, including the action housing 28, will carry this portion of the tool forwardly with respect to the breech block 24. In either case, the firing pin spring 100 is compressed, since the firing pin 74 is either carried rearwardly with the breech block 24 relative to the handle portion of the tool or is held stationary and the handle portion of the tool moves forwardly relative to the breech block 24. Rearward motion of the breech block 24 with respect to the handle portion of the tool, or conversely forward motion of the handle portion of the tool with respect to the breech block, is limited by contact between the breech block 24 and the ring 42 secured in the rear end of the action housing sleeve. Upon such contact between the breech block 24 and such ring 4.2, the resulting inertia forces may have a component in a direciton which tends to cause the sear 80 to pivot to release the firing pin 74. If this happens, the tool accidentally fires and may cause injury to property or personnel.

In order to prevent accidental discharge of the tool just referred to, the tool is provided with an inertia member 108 pivotally secured to the rear end of the breech block 24 by a screw 110 (Fig. 3) for pivotal movement about an axis parallel to the pivotal axis of the sear. The upper end of the inertia member 108 is positioned to engage the firing pin engaging portion of the sear and is urged into contact with the sear 80 by means of a helical spring 112 surrounding the screw 110 and having one end engaging a bore (not shown) in the rear end of the breech block 24 and the other end positioned in a slot in the lower end of the inertia member 108.

The action of the inertia member 108 is illustrated diagrammatically in Fig. 5. In such figure, the sear 80 is shown as being mounted for pivotal movement about an axis 82' and in a position engaging the firing pin 74 indicated by a dotted circle 74'. The inertia member 108 is shown as being mounted for pivotal movement about an axis 110' and as having its upper end engaging the upper end of the sear 80. The center of gravity of the sear 80 is located approximately at the point 114 such that the dotted line 116 passes through the pivotal axis 82' of the sear and its center of gravity 114. It will be apparent that any impact producing an inertia force which will cause the sear 80 to tend to pivot in a clockwise direction away from the firing pin 74 must have a direction along a radius of the dotted semi-circle 118. That is to say, it must have a component in the direction of the arrow 120. Any impact in the directions of the opposed dotted arrows 122 will have no component in the direction of the arrow 120 and will have no tendency to cause movement of the sear 80 with respect to the firing pin 74. Any impact having a component opposed to the arrow 120 will actually tend to cause the sear 80 to more closely engage the firing pin 74.

The inertia member 108 has a center of gravity 124 which is ideally located on a line 126 which is parallel to the line 116 and which passes through the pivotal axis 110' of the inertia member. Any impact which has a component in a direction of the arrow 120 will also have the same component in the direction of the arrow 128 and will tend to cause rotation of the inertia member 108 in a counterclockwise direction in Fig. 5, such that the inertia member 108 develops an inertia force and applies such force to the sear 80 in a direction which tends to hold the sear against the firing pin 74. By providing an inertia member 108 of sufficiently greater moment of inertia than the moment of inertia of the sear 80 to overbalance the inertia forces acting directly on the sear, there is no possible component of an impact which can cause resulting inertia forces rotating the sear 80 out of contact with the firing pin 74. Thus, to provide a safety mechanism which will inevitably prevent accidental discharge of the gun due to impacts, it is desirable to provide a sear 80 having a center of gravity displaced in a predetermined direction from its pivotal axis 82 so that the result of an impact can be predetermined and then provide an inertia member also having its center of gravity spaced from its pivotal axis but in an opposite direction from that of the sear and of greater moment of inertia so that the inertia forces acting upon the inertia member provide an opposing force which is greater than the inertia force acting upon the sear. This type of operation is preferable to attempting to balance the sear itself, since errors in machining or faulty testing in production runs can easily result in a sear which is sufficiently unbalanced that an impact can cause it to release the firing pin. By the present construction the inertia member can be of sufiicient moment of inertia that impact release of the firing pin by the sear is completely overbalanced.

The operation of the safety mechanism of the tool of the present invention should be apparent from the above discussion. When the tool has been loaded with a blank cartridge 14 and the tool is in closed position shown in Fig. 2, the barrel housing 30 and action housing 28 can move forwardly with respect to the breech block 24, the barrel block 22, the barrel 18, and the barrel sleeve 66 against the force of spring 100 and can move forwardly with respect to safety shield 58 with its sleeve 60 against the force of the spring 68. This forward movement of the action housing 28 compresses the firing pin spring 100 since the sear holds the firing pin 74 stationary with respect to the breech block 24. As a result of such forward motion of the action housing 28, the trigger is in position to be actuated to cause its sear engaging portion 88 to engage the trigger engaging portion 88 of the sear 80. Actuation of the trigger pivots the seat in a clockwise direction in Fig. 3 about its axis to release the firing pin and such pivotal movement of the sear also pivots the inertia member in a clockwise direction about its axis. The springs 84 and 112 urge the sear and inertia member, respectively, toward the positions of Fig. 2.

The present invention is concerned with preventing accidental firing of the tool if the tool is dropped or otherwise subjected to an impact. Such impact may cause the breech block 24 to move rearwardly with respect to the handle portion 44 of the tool or conversely cause the handle portion of the tool to move forwardly relative to the breech block to thus energize the firing pin spring 100. When the relative motion of the breech block 24 and the handle portion 44 of the gun is abruptly stopped by engagement between the ring 42 and the breech block 24, the sear 80 may be subjected to impact forces which tend to cause it to pivot away from the firing pin 74. Any impact forces which tend to cause such pivotal motion of the sear also tend to cause a reverse pivotal motion of the inertia member 108 and the result is that the inertia forces acting upon the inertia member 108 causes such member to apply a force to sear 80 which prevents disengagement of the sear 80 from the firing pin 74. In the particular tool disclosed, inertia forces acting on the trigger tending to move it in a sear releasing direction are not active when the sear is in position to be engaged by the trigger but, in any event, the trigger is sufficiently balanced that the inertia member 108 can also overcome any inertia forces acting on the trigger.

The tool of the present invention may have its handle portion 12 pivoted with respect to the barrel portion 10 about the pivot pin 26 between a tool open and a tool closed condition. The tool is held in closed condition by a latch mechanism not shown or described in the present application but which is preferably of the type disclosed and claimed in the copending-application of Wilber J. Cranston, Serial No. 701,635, filed December 9, 1957. Such latch mechanism is released by pulling the handle portion of the tool rearwardly with respect to the barrel housing 30, such action being resiliently opposed by the spring 68 which urges the barrel 18 and barrel block 22 forwardly with respect to the barrel housing 30 and also urges the breech block 24 forwardly since such breech block is pivotally connected to the barrel block.

While the safety mechanism of the present invention has been disclosed in connection with a tool in which the housing for the tool moves forwardly relative to most of the internal mechanism of the gun including a breech block to energize the firing pin spring, it is appareat that such a safety mechanism including an inertia member will prevent an impact from releasing a scar from a firing pin which has had its spring energized in any other manner. Also, it is apparent that the centers of gravity of a pivoted sear and pivoted inertia member need not be on opposite side of their pivotal axes if proper force transmission between such elements is provided, and also that the sear itself need not be pivoted if its direction of motion is properly restrained. In any case the inertia member should be mounted so that any component of an inertia force which tends to move the sear away from the firing pin also causes the pivoted inertia member to develop and apply an opposing force to the sear.

While I have disclosed the preferred embodiment of my invention, it is understood that the details thereof may be varied and that the scope of the invention is to be determined by the following claims.

I claim:

1. In a powder actuated tool having a firing pin actuated by resilient means and a sear movable between a firing pin holding position and a firing pin releasing position to releasably hold said firing pin against actuation by said resilient means, a safety mechanism for preventing movement of said sear to said released position by inertia forces on said sear when said tool is subjected to an impact, said safety mechanism comprising an inertia member for applying a force to said sear in a direction opposed to said inertia force when said tool is subjected to said impact.

2. In a powder actuated tool having a firing pin actuated by resilient means and a sear movable between a firing pin holding position and a firing pin releasing position to releasably hold said firing pin against actuation by said resilient means, a safety mechanism for preventing movement of said sear to said released position by inertia forces on said sear when said tool is subjected to an impact, said safety mechanism comprising means to pivotally mount said sear in unbalanced condition to restrict said forces acting directly on said sear to those having a component in one direction, and an unbalanced pivotally mounted inertia member positioned to apply a force to said sear in a direction opposed to said inertia forces when said tool is subjected to said impact.

3. In a powder actuated tool having a firing pin actuated by resilient means and a sear movable between a firing pin holding position and a firing pin releasing position to releasably hold said firing pin against actuation by said resilient means, a safety mechanism for preventing movement of said sear to said released position by an inertia force acting on said sear when said tool is subjected to an impact, said safety mechanism comprising means for pivotally mounting said sear in unbalanced condition to restrict such forces acting directly on said sear to those having a component in one direction, said forces tending to cause pivotal movement of said sear away from said firing pin, and an inertia member pivotally mounted so as to tend to be pivotally moved by inertia forces having said component, said inertia member being mounted to apply a force to said sear in a direction opposed to said inertia force acting directly on said sear when said tool is subjected to said impact.

4. In a powder actuated tool having a firing pin actuated by resilient means and a pivotally mounted sear movable between a firing pin holding position and a firing pin releasing position to releasably hold said firing pin against actuation by said resilient means, said sear being subject to an inertia force tending to move said sear to said releasing position when said tool is subjected to an impact having a component in one direction, a safety mechanism to prevent said movement of said sear to releasing position comprising a pivoted inertia member for applying a force to said sear opposed to said inertia force when said tool is subjected to said impact.

5. In a powder actuated tool having a firing pin ac tuated by resilient means and a sear movable about a pivotal axis between a firing pin holding position and a firing pin releasing position to releasably hold said firing pin against actuation by said resilient means, said sear having its center of gravity spaced from said pivotal axis in one direction so that subjecting said tool to an impact having a component in a second direction at right angles to one direction will tend to produce an inertia force acting directly on said sear to move said sear to said releasing position, a safety mechanism comprising an inertia member movable about a pivotal axis and having its center of gravity spaced from its pivotal axis in a direction parallel to said one direction, said inertia member being positioned to apply a force to said sear opposed to said inertia force when said tool is subjected to said impact.

6. In a powder actuated tool having a firing pin actu ated by resilient means, a casing for said tool, action parts positioned in said casing, said casing being movable forwardly of said action parts when the muzzle of said tool is pressed against a work piece to energize said resilient means, and a scar carried by said action parts for releasably holding said firing pin against actuation by said resilient means, said action parts being capable of being moved rearwardly relative to said casing by inertia forces when said tool is dropped and said sear being subjected to inertia forces tending to move said sear to release position when relative rearward motion of said action parts with respect to said casing is abruptly stopped by reaching the end of said relative motion, a drop safety mechanism for preventing movement of said sear to releasing position including an inertia member carried by said action parts and positioned to apply to said sear a force opposite to said inertia forces when said relative motion is stopped.

7. In a powder actuated tool having a firing pin actuated by resilient means, a casing for said tool, action parts positioned in said casing, said casing being movable forwardly of said action parts when the muzzle of said tool is pressed against a work piece to energize said resilient means, and a scar carried by said action parts for releasably holding said firing pin against actuation by said resilient means, said action parts being capable of being movedrearwardly relative to said casing by inertia forces when said tool is dropped and said sear being pivotally mounted and unbalanced so as to be subjected to inertia forces tending to move said sear to release position when relative rearward motion of said action parts relative to said casing is abruptly stopped by reaching the end of said relative motion, a drop safety mechanism for preventing movement of said sear to releasing position including a pivoted unbalanced inertia member carried by said action parts and positioned to apply to said sear a force opposite to said inertia forces when said relative motion is stopped.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,923,940 February 9, 1960 Robert C. Kvavle It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 34, for "to be given" read to be driven Signed and sealed this 2nd day of August 1960.

(SEAL) Attest:

KARL AXLINE ROBERT C. WATSON Attesting Officer 7 Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,923,940 February 9, 1960 Robert C. Kvavle It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 34, for "to be given" read to be driven Signed and sealed this 2nd day of August 1960.

(SEAL) Attest:

ROBERT c. WATSON Commissioner of Patents KARL H. AXLINE Attesting Officer UNITED STATES PATENT oFFIcE CERTIFICATE OF CORRECTION Patent No. 2,923,940 February 9, 1960 Robert C. Kvavle It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

Column 1,, line 34 for "to be given read to be driven Signed and sealed this 2nd day of August 1960,

(SEAL) Attest:

KARL H6 AXLINE ROBERT C. WATSON Attesting Oflicer Commissioner of Patents