US2257267A - Percussive tool - Google Patents

Description

Sept. 30, 1941` A. T. LUNDGREN TAL 2,257,267

PERCUS S IVE TOOL Filed May 6, 1938 '3 Sheets-Sheet l Sept. 30, 1941. A. T. LUND'GREN ET AL PERCUSSIVE TOOL Filed May 6, 1938 V u v3 Sheets-Sheet f5 Fg. 7

,4a/vf TLU/VDGQEN, Auf/v 5 @oms-Q5 and Patented Sept. 30, 1941 PERCUSSIVE TOOL Agne T. Lundgren,

Trollhattan. Alvsborgs Lan. Sweden, and Allan B. Rogers and Vladimir lavlecka. Santa Monica, Douglas Aircraft Company, Inc., Calif., a corporation of Delaware B. Calif., assigner: to Santa'Monica,

Application May 6, 1938, SerialNo. 206,364 y (CLglZl-ZD 11 claims.

This invention relates in general to fluid pressure actuated percussive tools and in particular to single impact riveting hammers particularly adapted to iiush riveting.

In certain industries, such, for example, as the airplane industry, metal sheets are secured tgether by iiuSh-riveted joints. It is found that for many purposes the most suitable hush-riveted joint is that wherein rivets having heads of the counter-sink type have lsuch heads seated in recesses, herein referred to as dimples, formed by bending inward the annular metal portions of the overlying sheets surrounding the openings through which the shank ol the rivet passes. as

distinguished from the ordinary type of countersink which .is formed by cutting away sufficient of the metal of one or more of the sheets to form a recess which will receive part or all of the rivet head.

It is an object of the present invention to provide` simple and eilective means for forming a flush-riveted joint wherein the rivet head is received in a dimple formed by impacting the head of the rivet while the assembly of overlying sheets are buck'ed from 'the back in such a manner and with such cooperative buckingv means that the head of the rivet thus impacted will deilect the edge portions of the sheets surrounding the rivet holes inwardly and thereby form a dimple in cooperative relation to the rivet head. i

It is a further object of the invention to provide means of simple and effective character for forming a flush-riveted joint of the type set forth in the preceding paragraphs, which will consistently position the heads of the rivets in co-planar alignment with the-surface of the front sheet of the assembly of over-lying sheets included in the hush-riveted joint.

An important object of this invention is to provide a single-acting riveting hammer which produces an impact greater than heretofore attain- 'fluid pressure is surrounding metal, as well as in securing relation with the dimpled portions of the sheets.

Another object of the invention is to provide a riveting. forward-movement of the hammer piston until a built up behind the piston approximately equal to the pressure in the fluid supply line with which the device is connected.

Another object is to provide the riveting hammer with a differentially operable pressure transier valve together with means operable bythe valve for restraining and releasing the piston.

Another obiect is to provide the riveting hammer with a manually operable main valve, a Dressure transfer valve that is differentially responsive to operation of the main valve, and means releasably restraining the piston at the breech of the cylinder, this releasing means operating in Va. timed relationto the transfer valve.

Another object is to provide means for maintaining a pressure in back o f the hammer piston A of a riveting hammer at approximately the presmer from the front to preparatory to the work 4o pacting the rivet head together with a able with a riveting hammer having a piston of the same weight and diameter,a stroke of the same length, and an air supply at the same pressure.

Another object is to provide a riveting hammer for use in flush riveting which produces a single impact of sufficient force to impact-dimple a plur'ality of metal sheets into nested relation with the head of a rivet.

Another object is to provide a riveting hammer for use in ush riveting which produces a single impact of suiiicient force 'to upset the shank of a rivet into concentrically sealing relation with the sure in the air supply line during the work stroke of the piston and to provide means for reducing to a minimum the back pressure in iront of the piston of a riveting hammer during the work stroke of the piston.

Another object is matically returning the to provide means for autopiston of a riveting hamthe rear of the cylinder stroke of the piston. Another object is to provide a riveting hammer which operates with maximum economy for the reason that the loss of air therefrom is minimized.

Another object is to provide a riveting harnmer with a drivinghead which is adapted to the seating of the rivet-and shank where the sheets being joined together are suillciently resilient to permit upsetting. by imy portion of that is also adapted to bucking the rivet and to holding the rivet headflush with the surface of the outer sheet in the operation wherein upsetting is accomplished by impacting the shank.

Another object is to provide a riveting ham mer with a driving head having means for auto# matic parallel alignment' of the work with the surface of the outer sheet.

Another object is to provide a riveting hammer with a driving head having means for preventing slippage while being held against the work.v

Another object is to provide a riveting hammer with a bucking head which is adapted to bucking the outer sheet,and

'55, the sheets while the rivet is being seated and hammer having means for restraining t to the upsetting of the surface which is adapted to the upsetting operation where upsetting is accomplishedby impacting the shank.

Another object is to provide a riveting hammer with a bucking head having means for automatically co-planarly aligning the surface of the rivet head with the surface of the outer sheet while the hammer is being used as a bucking tool f during therivet seating operation.

A further object of the invention is to provide a method of flush-riveting of the general character discussed in the foregoing, wherein the head of a rivet is impacted so as to seat the same in nested relation to dimpled sheets, and pressure against the rivet head is sustained after the impacting theeof and during the upsetting of the rivet shank so as to expand the same into circumferential sealing engagement with the edges o'f the sheets forming this perforation and so as to form a head on the rear end of the shank. Some further objects and advantages will appear in the following part of the specification.

Referring to the drawings which are for illustrative purposes only,

Fig. 1 is a fragmentary sectional view showing how two riveting hammers, embodying a part of our present invention, may be cooperatively employed in the practice of our method of ush-riveting, one being in position for seating the rivet and the other in position for aligning the rivet and bucking the sheets.

Fig. 2 is a fragmentary view showing the driving head, of th'e riveting hammer used to seat the rivet, fully extended by an impact blow of the hammer piston, and the rivet seated in a dimpled recess in the sheets'as the result thereof.

Fig. 3 is a fragmentary sectional view illustrating the further steps of upsetting the rivet strain a piston hammer from forward movement and build up a fluid pressure behind the same.

Fig. 8 -is a fragmentary partly sectioned view pressure may be built up prior to the forward movement of the piston hammer I8.

As shown in Figs. 1 and 9, the hammer I5 is provided with a piston grip 33 forming part of a metal body 32 which extends downwardly'from the cylinder I6 and has therein an air passage 34 into which air is admitted through a spring seated main valve for a suitable air connection 36, the spring 31 of the main valve 35 operating to continuously exert a force to close the valve. A pivoted trigger 38 is mounted on the handle 33 in such position that when it is depressed, or, in other words, moved from its position of Fig. 1 towards its position in Fig. 9, it will engage,9 the stem 39 of the' main valve and open the same. The upper end of the trigger 38 has forks 4I adapted to engage a pin 42 which projects laterally from an air distributor or transfer valve mechanism 43 disposed below and substantially in alignment with the barrel I6.

The transfer valve 43 comprises two cooperating valve members, namely, shuttle valve 45 disposed within the sleeve 44, the pin 42 being secured in the shuttle valve 45 and projecting through longitudinal slots 46 in the sleeve valve 44. The two valve members 44 and 45 are slidably fitted into a bore 41 in the metal body 32 of the hammer device I5. Two recesses 48 and 49 are cut away from the bottom of the shuttle valve 45, and two recesses 50 and 5I are cut away from the top thereof. In addition, the shuttle valve 45 is provided with twb annular recesses,'or passages, 52 and 53. The forward portion of the shuttle valve 45 is smaller in diameter than the rear portion, forming a shoulder 54.

'I'he sleeve valve 44 ts over the forward portion 69, and an opening vthe sleeve valve 44 showing the cooperating parts of thevhammer in position to release the hammer piston and apply the Whole force of the impelling fluid to the same during its impacting stroke.

Fig. 9 is a fragmentary partly sectioned view showing the'lcooperating valvef-parts inl the respective positions assumed thereby as they return to initial position, such as illustrated in Fig. 6.

As shown in Fig. 1, ,the embodiment of the in-` vention chosen for the purpose of illustration comprises a riveting hammer I5 having a cylinder I6 in which a conventionally packed hammer piston I8 is adapted to bereciprocated so as to strike the shank I9 of a selected die or head, held in the socket opening 28 at cylinder I6. The cylinder I6 is closed at its breech by ahead 2| having a stop 22, and the muzzle end of the cylinder is provided with threads 25 to receive a spring 26 adapted to hold theshank I9 in the operative position shown. The fimction of the stop 22 is to provide, as

shown in Figs. 6 and 7, a chamber 28 in which air the front end of the of the shuttle valve 45 and two notches 68 and 18 in the exposed portion of exposes the shuttle. Diametrally aligned ports 1I are formed in the sleeve valve 44.

A Avalve spring latch 18 is sleeve valve 44 from moving with the shuttle valve 45 during part of the trigger movement. 'I'he free end of the valve spring latch 18 bears against the shuttle valve 45 either through notch 68 or notch 69 in the bottom of the sleeve valve 44.A A friction device of some kind could be lused to retard the movement of the sleeve valve 44, in but the latch is preferred provided to keep the by. the inventors.

The cylinder I6 is provided with front and rear air ports- 55 and 56, connecting the respective ends thereof with the bore 41 in which the distributar valve 43 is slidable. Ahead of the inlet port 56 there is an opening 51 extending from the cylinder space to the bore 41, in which opening a pawl 54 is mounted on a transverse pivot 58 so that it:may bev-rotated vertically-to such position that its rear end will engage an annular recess38 in the piston hammer I8, when the same is at the rear end of the cylinder. A spring 59 is provided to rotate the pawl 54 into the recess and to there hold it until it is disengaged-by the action of the shuttle valve 45,`to be hereinafter explained.

'I'he complete cycle of operation of our riveting hammer I5 will now be described. Figs. 1, 6, 7, 8, and 9 show the positions of the piston I8, the pawl 54, the sleeve valve 44, and the shuttle valve 45 at ilve stages during the complete cycle. In Fig. 1 all of the ports are in effect closed, and the main valve is likewise closed.' When operating pressure is applied to the trigger 3l it will be iirst moved into the position in which it is shown a sleeve 44 and a'- position wherein I forward end of the cylinder in Fig. 6. This moves the pin 42 back in the slots 46, thereby moving the shuttle valve 45 independently of the sleeve valve 44 into the ilrst the annular passage 52 will connect the ports 1|, the lower of which ports 1I is in communication through a port 80 with the air passage 34. The stem 39 of the valve 35 will be now depressed and air will enter the passage 34 and will travel through port 80, passage 52` and port 1I to an opening 8| which connects with the far end of an air passage 82 leading to the exhaust port 55. 'This air will enter the I6 and will move the piston I8 rearwardly from the position in which it is shown in Fig. y1 to its position of Fig. 6. The piston I8 will now be engaged and latched in such rearward position by the pawl 54. Air contained in the cylinder I6, behind the piston I8, may pass out through the inlet port 56 and through an opening 64 Vin a plug 85- which is threaded into the rear end of the bore 41.

Movement of the trigger 38 fromits position of Fig. 6 to its position of Fig. '1 moves both the sleeve valve 44 and the shuttle valve 45 simultaneously into a new position wherein' the ports 1| and the passage 52, respectively, of the sleeve valve 44 and the shuttle valve 45 will be offset rearwardly from the ports oropenings 80 and 8|, and the passage 53 in the shuttle valve 45 and a port 86 which connects the rightward end of the bore 41 with the rightward end of the air passage 34, so that air will pass under pressure from the passage 34 through the annular passage 53 and the inlet port 56 into the space 23, thereby permitting an air pressure to be space and against the rear face of the piston I8. It will be noted that at this time the piston I8 is restrained from forward movement by the pawl 54.

Further movement of the trigger 38 simultaneously moves the sleeve valve 44 and the shuttle valve 45 from their position of Fig. 1 to their position of Fig-8, to bring the annular valve passage 53 of the shuttle valve 45 into fully open communication with the inlet port 56 and the air port 86, and at the same time bringing a shoulder 90, formed at the front end of the depression 50, into engagement with the lower end of the pawl 54, to rotate such pawl into retracted position thereof, as shown in Fig. 8, and against the yieldable force of the spring 59, thereby releasing the piston I8 so that the air pressure in the rear end of the cylinder I6 may drive the same forwardly at high velocity into engagement with the inner end of the shank I9.

Upon release, the trigger 38 is moved toward its initial positin by a spring 60. The first return movement of the trigger 38 will be transmitted through the pin 42 to the shuttle valve 45, to move the same forward in the sleeve valve 44, thereby disaligning the annular passages 52 from the ports 1|, as shown in Fig. 9, so that as further forward movement of the trigger toward its initial position in Fig. 1, will simultaneously move the-sleeve valve 44 and the shuttle valve 45 past the ports 80 and 8| in disaligned position whereby no air will ybe permitted at this time to pass from the passage 34 into the passage 82. Thereafter the parts of the device will remain substantially in the position in which they are shown in Fig. 1. the piston I8 will requiremerely a single rearward movement of the trigger 38 through the positions described relative to Figs. l, 6, '1, 8, and 9.

built up in this A further single actuation of From the above description of the riveting hammer and its operation, it is apparent that the piston I8 will travel to the front of the cylinder and strike the pin I9 at comparatively high velocity, for three reasons. First, the pistonis held atth'e rear of the cylinder I6 long enough to permit the pressure in that portion of the'v cylinder behind the piston to build up to substantially the pressure in the air supply line, so that the pressure against the piston tending to impel the same forwardly will be at a maximum value at the beginning of the stroke. Second, the piston is not released until the pressure `in the air passage 34 has been built up to substantially the pressure in the supply line 36 and until the inlet valve and the inlet port 56 have been opened to full. extent so that when the piston I8 is finally released a large volume of air at high pressure is provided against the back of the piston throughout its entire, forward stroke. And third, since the piston I8 is not released until the exhaust port 55 has been fully opened, as shown in Fig. 8, it is also apparent from the foregoing description of our riveting hammer and its operation, that the loss of air through leakage is reduced to a minimum. Although it is possible to arrange the cooperative transfer valve element so that the piston I8 will be returned to the rear end of the cylinder I6 immediately upon release of the trigger 38, we prefer the arrangement shown whereby the piston is returned on the first rearward movement of the trigger .36, for the reason that when the operator hears the piston strike the stop 22 he knows that the tool is ready for operation before the trigger is pulled all of thevway back to released position.

The `driving heads and the bucking head 9| are basically the same. Each has a swivelable contacting member resiliently Aheld against a spherical end portion of a member fastened to the muzzle of the hammer by means of a spring 26. In the practice of our new riveting method" two of the riveting hammers I5 are employed in opposed relation, as shown in Figs. 1, 2, and 3, one being for the purpose of driving or impacting the driving head 90 against the head of a rivet while the sheets being riveted are bucked by the bucking head 9| carried by the other of the harnmers, the drive head 90 being then employed to buck the head of the rivet during the upsetting of the rivet shank.

The driving head 90 comprises an anvil 92 which is mcunted'on the semi-spherical forward end 93 of the shank I9 which has a collar 94 to serve both as a stop to keep the stem from being inserted too far into the muzzle opening 20 and has a shoulder to be engaged by the coil spring 26 which resiliently holds the stem I9 in operative position. 'The anvil 92 has a recess 95 which receives the head 93 of the shank I9 anda rubber bushing 96 is placed in the recess 95 adjacent the rear face of the head 93 to hold the parts in engagement and permit a swivel movement of the head 90 on the shank I9.

' To resist yslippage when in use, the-head 904 is provided with a rubber collar If no opposite longitudinal forces are being applied to move the anvil 92 forward with reference to the collar, ange 99 of the collar engages the shoulder |00` of the anvil, which shoulder |00 defines the forward end of an annular recess |0I in the anvil 92. Therear portion of the collar 91 comprises a rubber spring |02 which fits into the annular recess I0 I. When the front edge of the rubber collar 91 is brought into 91 having a shroud' vto ` pendicular to the sheets |30 and |3I.

' parallel to the outer face of the engagement with the work, as in Fig. 1, and the anvil 92 is then moved forwardly, the rubber collar 91 will, in eilect, move rearward on the anvil 92 in the mannei` .indicated in Fig. 2. At this time there will be an expansion of the rearward portion |02 of the rubber collar 91 owing to the fact that the rear edge |03 thereof is restrained from rearward movement by the shoulder |04 at the rear end of the annular channel IOI. The friction of rubber on the metal prevents slippage of the head from position. There are a number of grooves |05 in the front end of the collar 9'! for passage of air from the space between the front face of the anvil 92 and the Work to which the device is applied.

The bucking head 9| `includes a bucking anvil IIO having an axial opening III, van annular front face I|2 perpendicular'to the axis of the opening III, and a conical recess I|3 the angle of which corresponds to the angle of the head I |14 of a ush rivet |I5 with which the bucking head 9| is to be used. The bucking anvil |I0 has a rearwardly faced substantially semi-spherical socket |I6 and a radial iiange IIT. 'Ihe socket I I6 receives the rounded nose ||0 of a tubular tting II9 having an annular ange |20 disposed adjacent to the iiange |I1. A rubber collar I2I having an internal groove |22 is placed over the adjacent anges and |20, to hold the parts III) and |I9 together, but to permit a limited swivelling movement of the part |I0 relative to the part II 9. I

The fitting II9 is held against the muzzle of a riveting hammer |5 of the same type as the hammer I5, previously described, by means of a spring 26'. The opening |23 of the fitting i||9 has therein an axially slidable stem |24, the rear end |25 of which projects throughthe muzzle opening 20 into the front end of the barrel of the riveting hammer I5' so as to be in a position to be Aengaged by the piston I8 of such hammer I5. I'he front end of the stem |24 is provided with a lcylindrical nose |26 adapted to enter the opening of the bucking anvil I|0ivvhen the stem I 24 is driven forwardly by the piston I8 of the riveting hammer I5', as shownin Fig. 3. If the stem is moved forward when the bore I of the bucking anvil I0 is not in axial alignment therewith, the nose I 26, upon entering the bore or opening III, will rotate the anvil IIO into alignment with the stem |24, owing to the fact that the inner end of the bore I I I is flared so as to direct the nose |26 into the bore I|| without damaging the stem |24 or the bucking anvil I0.

In Figs. 1, 2, and 3 sheets |30 shown, such sheets having aligned and I3I are openings |32 receive the shank |33 of the rivet |I5. This rivet II5 is nrst placed, as shown in Fig.- 1, and the driving head 92 is placed thereagainst, preferably in centralized relation. The |I0 is then placed so that its bore III will receive the rear end of the rivet shank |33, the rivbucking head eting hammer I5 being held substantially perthere be some disalignment ci the riveting hammer I5' from true perpendicular position, the bucking head ||0 will swivel onV the nose 8 of the iitting I|9 so that the annular face ||2 of the bucking head I I0 will rest tightly against the face of the sheet |30, and the axis of the bore III will then be perpendicular to the sheets |30 and I3 I, and such -bore I|| will hold the shank of the rivet |I5 in this perpendicular relation, so that the outer face of the rivet head 4 will be sheet |3I. The

should No. 203,946, nied riveting hammer 5 may be then actuated so that the piston I8 thereof will strike the stem I9, as shown in Fig. 2', there y driving the head 30 toward the bucking head 9| so as to impact the head 4 of the rivet |I5 into nested relation to the sheets |30 and |3|,thesheets bending inwardly into lthe depression ||3 of the anvil |I0, the annular portions |35 of the sheets |30 and |3| surrounding the openings |32, thereby forming depressions, or dimples, in centralized relation to the opening, the head I I4 being received in the dimple of the sheet |3I, with the fiat, front face of such head II4 ush with the face of the sheet I3I, The upsetting ofthe rivet shank is accomplished in the following Where the sheets being joined are of a flexible character, the rivet shank may be upset by iirst moving the nose |26 of the stem |24 into a|ivanced position in the bore I, so that such nose April 29, 1938. Although We have shown and described a simpractical embodiment of our invention,

` but should scope of the hereto appended claims.

We claim as our invention:

1. In an air hammer of the character described,

scribed, the combination of: a cylinder; a piston movable in ,said cylinder from the rear to the front end thereof to 'deliver an impact; means for supplying a propulsion fluid to said cylinder to move said piston from a position remote from the front end thereof to the front-end of said cylinden; a latch for holding said piston in a position spaced from-the rear end of said cylinder so that` a pressure accumulation chamber is thereby formed between the rear face of said piston and the rear end of said cylinder and restraining forward movement of said piston so that a fluid pressure. may be built up in said pressure accumulation chamber; and means for releasing sald latch.

3. In an air hammer of the character described, the combination of: a cylinder having a, front port, a rear port, and an air inlet space; a piston in said cylinder; means for connecting said air inlet space to a source of air under pressure: and valve means for controlling the feeding of air from said air inlet space to said ports, said means comprising a valve actuating means and a pair of slldably associated valve 'members movable forward by said valve actuating means through consecutive stages so as to first connect said air inlet space with said front port so as to deliver air through said front port to move said piston rearward in said cylinder, then to disconnect said air inlet space from said front port and connect said air inlet space to said rear port to build up a pressure behind said piston, and then tc fully open'said air inlet space to said rear port so that the full pressure of air from said source of air under pressure may propel said piston forward in said cylinder while said front -port is opened to the exterior, said valve members being then returnable to their initial positionwithout connecting'said front port to said air inlet space and so as to disconnect said rear port from said inlet space.

4. In an air hammer of the character described, the combination of: a cylinder having a front port and a rear port; a hammer piston in said cylinder; means for connecting the air hammer to a source of uid pressure; and means for controlling the entry of. fluid under pressure to said cylinder, said control means having a front valve constructed so as to first admit fluid through said front port so as' to move said piston rearward in said cylinder and to then cut off fluid from said front port restraining means to hold said piston in the rearward portion of said cylinder and a rear valve operatively connected to said front valve to then introduce iluid through said rear port to build up a fluid pressure behind said piston and to supply a large volume of fluid under substantially full pressure of said fluid source through said rear port to said cylinder to impel said piston forcibly to the front end of said cylinder, said control means having a part to release said restraining means after fluid has been introduced through said rear port, and said front valve means having means to open the front end of said cylinder to the exterior after said piston has been moved to the rear end of said cylinder.

5. In an air hammer of the character described, the combination of: a cylinder having a front porch and a rear port; a hammer piston in said cylinder; means for connecting the air hammer to a source of fluid pressure; a member movable from an initial position to a final position; and means movable by said member for controlling the entryof fluidunder pressure to said cylinder,

said control means comprising a valuable member constructed so that upon first movement of said member it will first admit fluid through said front port and at the same time connect said rear port to the exterior so as to move said piston rearward in said cylinder, then upon further movement of said member cut off fluid from said front port and introduce fluid through said rear port to build up a fluid pressure behind said piston and upon still further movement of said member,

4supply a large volume of fluid under substantially full pressure4 of said fluid source through said rear port to said cylinder to impel said piston forcibly to the front end of said cylinder, said valve member being arranged to the front end of said cylinder to the exterior after said piston has been moved to the rear end of said cylinder.

6. In an air hammer of 4the character described, the combination of: a cylinder; al piston movable in said cylinder from the rear end thereof to the front end thereof to deliver an impact; a latch engaging said piston so as to hold the same in a position retracted from the front end of said cylinder; valve means operable to admit a propulsion fluid into the space in said cylinder behind said piston; and means operating in consequence of the operation of said valve means to release said latch after said propulsion fluid has been admitted to the space behind said piston.

7. In an air hammer of the character described, the combination of: a cylinder; a piston movable in said cylinder from the rear end thereof to the front end thereof to deliver an impact; a latch engaging said piston so as to hold the same in a position retracted from the front end of said cylinder; valve means operable.

to admit a propulsion fluid into the space in said cylinder behind said piston; a manually movable member for operating said valve means; and means arranged to receive movement in consequence of the movement of said member to operate said valve means, for releasing said latch.

8. In an air hammer of the character described, the combination of: a cylinder; a piston movable in said cylinder from the rear end thereof to the front end thereof to deliver an impact; a latch engaging said piston so as to hold the same in a position retracted from the front end of said cylinder; valve means operable to admit a propulsion fluid into the space in said cylinder behind said piston; a movable control member connected so as to operate said valve means during a part of its movement, said control member having a further movement after the operation of said valve means; and means arranged to receive movement in consequence of said further movement of said control member, to release said latch.

9. In an air hammer of the character described, the combination of: a cylinder part; a. piston part movable in said cylinder part from the rear end thereof to the front end thereof to deliver an impact, one of said parts having a shoulder; a releasable latch member extending from the other of said parts into engagement with said shoulder to hold said piston in a position near the rear end of said cylinder; a valve to deliver fluid under pressure to the space between said piston and the rear end of said cylinder; a member operable to open said valve; and means operable by said member to release said latch inember.

10. In an air hammer of the character described, the combination of: a cylinder; a piston movable in said cylinder from the rear end thereof to the front end thereof to deliver an impact; mechanical restraining means engaging said piston and said cylinder so as to hold said piston in a position near the rear end of said cylinder; a valve to deliver uid under pressure to the rear face of said piston: a member operable to open said valve; and means operable by said member to releasesaid restraining means after said valve is initially opened.

l1. In an air hammer of the character described, the combination of a cylinder having front port means and rearport means: a hammer piston movable in said cylinder; a valve operating member movable from a tlrst position through a second position to a third position; a. uid pressure supply; valve means operable by said valve operating member, 4said valve means disconnecting said fluid pressure supply from both of said port means when said operating 20 member is in said rst position, said valve means having front valve parts operable by movement of said operating member from the said iirst position to said second position to connect said iiuid pressure supply to said front port means whereby fluid pressure will be applied to the front face of said piston. and to cut off the supply of fluid from said front port means and open said front port means when said operating member is moved from said second position to said third position, and said valve means having rear valve parts operative to connect said iiuid pressure supply to said rear port means when said operating member is moved from said second position to said third position so that uid pressure will be applied to the rear face of the said piston.

AGNE T. LUNDGREN, .ALLAN B. ROGERS. VLADIMIR H. PAVLECKA.

' CERTIFICATE oF coRRETToN. Patent No. 2,257,267. -september 5o, 19in.

AGNE T. LUNDGREN, ET AL.

It is hereby certified that error appears in the printed specificetion of the above vnumbered patent requiring correction as follows: Page'5, first column; line 70, claim 5,'for the word "porch" read -port; and thatA the said Letters Patent should be read with this correction therein that the same-nay-conform to the record o"the case in the Patent Office.

' Signed and sealed this 11th day of November, A. D. 1914;.

Henry Van Arsdale, (Seal) Acting Corrmiasioner of Patents.

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