US3908257A

US3908257A - Go, No-go rivet gun

Info

Publication number: US3908257A
Application number: US497309A
Authority: US
Inventors: Franklin S Briles
Original assignee: Individual
Current assignee: Individual
Priority date: 1974-08-14
Filing date: 1974-08-14
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30

Abstract

A gun for upsetting the shank terminal of a metallic rivet projecting from work comprises: A. A FORWARDLY EXTENDING TUBULAR BARREL, B. A PLUNGER TUBE DRIVEN FORWARDLY WITHIN THE BARREL FOR TRANSMITTING UPSETTING FORCE, C. AN ANVIL CARRIED BY AND MOVABLE AXIALLY RELATIVE TO THE BARREL BETWEEN THE PLUNGER AND RIVET TERMINAL TO RECEIVE SAID UPSETTING FORCE AND TO DELIVER SAME TO THE RIVET TERMINAL, D. AND MEANS RESPONSIVE TO DISPLACEMENT OF THE ANVIL RELATIVE TO THE BARREL AS THE BARREL IS ADVANCED TOWARD THE WORK WITH THE ANVIL IN ENGAGEMENT WITH THE RIVET TERMINAL FOR ENABLING SAID FORWARD DRIVING OF THE PLUNGER WHEN THE ANVIL IS WITHIN A PREDETERMINED AXIAL RANGE OF POSITIONS RELATIVE TO THE BARREL, AND FOR DISABLING SAID FORWARD DRIVING OF THE PLUNGER WHEN THE ANVIL IS OUTSIDE SAID RANGE OF POSITIONS.

Description

United States Patent [1 1 Briles 1 GO, NO-GO RIVET GUN Franklin S. Briles, 3600 Catamaran, Corona Del Mar, Calif. 92625 [22] Filed: Aug. 14, 1974 [21] Appl. No.: 497,309

[76} Inventor:

[52] US. Cl. Z9/243.54; 29/509; 72/19; 72/39]; 173/2; 173/133; 227/8 [51] Int. Cl. B23? 11/00 [58] Field of Search 72/19, 391; 227/8; 173/2, 173/133; 29/243, 54, 509

[56] References Cited UNITED STATES PATENTS 657,449 9/1900 Prange 29/243,54

1,014,639 l/l9l2 Calwell 173/2 3.088.440 5/1963 Wilmer l 173/2 X 3,253,440 5/1966 Baker 72/19 3.348.571 10/1967 Henning.... 227/8 3,559,449 2/1971 Steinmetz 227/8 X 3,581,373 6/1971 Murdoch ct al. 29/243.54 3,747,194 7/1973 Christensen 29/243.54

Primary Examiner-Charlie T. Moon Attorney, Agent, or FirmWilliam W. Haefliger 5 7 ABSTRACT A gun for upsetting the shank terminal of a metallic rivet projecting from work comprises:

a. a forwardly extending tubular barrel,

b. a plunger tube driven forwardly within the barrel for transmitting upsetting force,

c. an anvil carried by and movable axially relative to the barrel between the plunger and rivet terminal to receive said upsetting force and to deliver same to the rivet terminal,

12 Claims, 10 Drawing Figures U.S. Patent Sept. 30,1975 Sheet 1 of 7 3,908,257

US. Patent Sept. 30,1975 Sheet 2 of7 3,908,257

m m? 09 g @w @m US. Patent US. Patent Sept. 30,1975

Sheet 4 of 7 U.S. Patent Sept. 30,1975 shw 5 of7 3,908,257

U.S. Patent Sept. 30,1975 Sheet60f7 3,908,257

U.S. Patent Sept. 30,1975 Sheet 7 of7 3,908,257

G0, NO-GO RIVET GUN BACKGROUND OF THE INVENTION This invention relates generally to riveting apparatus and systems, and more particularly concerns riveting equipment facilitating more rapid and efficient riveting with associated substantial reduction in noise levels.

At the present time there are many problems involved in the riveting of panels, as for example in aircraft fabrication. Among these are the requirements for selection and use of rivets of desired length; removal from the work of upset rivets which are too long or too short, which substantially slows down productivity; and the delivery by a rivet gun of a large number of blows or impacts to the rivet head, in order to gradually upset the rivet shank terminal, a so-called heavy mass or bucking bar being held against that terminal to form the upset. Not only is this latter procedure extremely noisy, but it also produces rapid oscillation of the rivet back and forth in the panel bore during the riveting process, which tends to gall the bore and remove anodizing on the rivet shank due to back and forth frictional contact of the shank with the bore. Further, the impact shock loading or hammering is repeatedly delivered via the rivet head to the work panels, tending to separate them slightly at their interface, and resulting in an undesirably loose riveted connection and/or buckling of one or both panels, in many instances. Additional problems include unwanted flattening and cracking of rivet heads, marring of the panels, so-called clinching of the upset and tipping or cutting of the driven head.

SUMMARY OF THE INVENTION It is a major object of the invention to provide solutions to the above problems, through method and apparatus to be described.

Basically, the method of riveting contemplated by the invention concerns operating a rivet gun to discriminate between rivets which are of acceptable length or lengths, and rivets which are not of acceptable length, the steps of the method including:

a. applying a rivet to a work piece so that one end portion of the rivet protrudes from the work piece,

bv applying a rivet gun to said end portion of the rivet, and advancing the gun toward the work, and

c. operating the gun to impact the rivet only if the protruding end portion of the rivet is of acceptable length as determined by the extent of said advancement of the gun toward the work relative to the rivet end portion.

Accordingly, rivets which are of unacceptable length, and as determined by the gun, can therefore be quickly removed from the work to facilitate replacement by rivets of acceptable lengths. This eliminates the problem of removing unacceptable rivets from the work after deformation, as when an inspector might discern that a rivet upset is too large or too small. Further, the method contemplates adjustment of the gun to adjust the acceptable length range of the rivets to be length gauged" by the gun, prior to the riveting operation.

The apparatus contemplated by the invention includes a gun for upsetting a rivet shank terminal, and comprises:

a. a forwardly extending tubular barrel,

b. a plunger to be driven forwardly within the barrel for transmitting upsetting force,

d. and means responsive to displacement of the anvil relative to the barrel as the barrel is advanced toward the work with theanvil in engagement with the rivet terminal for enabling said forward driving of the plunger when the anvil is within a predetermined axial range of positions relative to the barrel, and for disabling said forward driving of the plunger when the anvil is outside said range of positions.

As will be seen, the means for disabling the forward driving of the plunger may include a safety valve openable to pass fluid pressure when the anvil is within the predetermined range of positions, and a cam member movable to operate the safety valve in response to axial movement of the anvil relative to the barrel as the barrel is advanced toward (and preferably engages) the work, with anvil in engagement with the rivet terminal. A sleeve typically couples movement of the anvil to the cam member, with lost motion coupling so as to displace the cam member only after predetermined axial rivet length gauging movement of the anvil rearwardly relative to the barrel; further, the cam member has first and second risers spaced so as to determine the acceptable length range of the rivets to be upset, as will be seen. In addition, the barrel length is adjustable so as to adjust said acceptable length range.

These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following description and drawings, in which:

DRAWING DESCRIPTION FIG. 1 is a side elevation showing a riveting system incorporating the invention;

FIG. 2 is an enlarged fragmentary elevation, taken in section of the forward portion of the riveting gun shown in FIG. 1, and prior to deformation of a fastener inserted into a work bore;

FIG. 3 is a section taken on lines 33 of FIG. 2, and partially broken away to show interior details;

FIG. 4 is an enlarged vertical section showing application of the FIG. 1 system components to a rivet inserted into a work bore;

FIG. 5 is an enlarged elevation like that of FIG. 2, showing the gun components during force application to the rivet;

FIG. 6 is an enlarged fragmentary elevation showing system components in relation to a rivet which is too short, prior to riveting;

FIG. 7 is a view like FIG. 6 showing system components in relation to a rivet which is too long, and prior to riveting;

FIG. 8 is a view like FIG. 4 showing system components applied to an acceptable rivet, and after upset formation,

FIG. 9 is an enlarged section showing upset formation, as in FIG. 8, and

FIG. 10 is a view like FIG. 2 showing another form of the invention.

DETAILED DESCRIPTION In FIGS. 1 4, 5 and 8 of the drawings, the work is shown in the form of two panels or skins l0 and 11 to be interconnected as by a rivet or rivets 12; however,

the work may take other forms. The rivet is shown as inserted into a bore 13 that extends through both panels, with the rivet head 14 at one side of the work. The shank 15 includes a portion 15a within the bore, a terminal portion 15b protruding from the bore at the opposite side of the work, and a tip at 150. The rivet may have loose fit, push fit or other fit in the bore as desired.

In this environment, a system for securing the rivet to the work includes first means at one (right) side of the work applying back-up force to the rivet head tending to urge the head toward the work. Such first means may for example include a so called bucking bar 16, having heavy metallic mass or body portions 16a and a terminal 16b that may be concavely recessed at 16c to fit the domed curvature of the rivet head. Force exerted via the bucking bar, as indicated by arrow 17, is transmitted to the head 14, and then to the work panel 11 tending to keep the inner face 14a of the head engaged with side 11a of that panel. Such steady force may, for example, be less than 50 pounds.

The system also includes second means at the opposite (left) side of the work for delivering an impact to the rivet shank terminal 15b in a longitudinal axial direction (indicated by arrow 18) tending to urge that terminal toward bore 13, and with sufficient impact velocity as to radially expand and axially shorten the bulk of the terminal, thereby to form an upset (asat 15b in FIG. 8) engaging the opposite side of the work (as at 19 in FIG. 8) while the head 14 extends or remains closely adjacent the one side of the work, as at surface 11a. The upset is preferably formed in response primarily to only a single impact, as described, so that the rivet does not oscillate in bore 13, and the time required to form the upset is minimized. Also, impact force is utilized to form the upset rather than being substantially dissipated by transmission via the rivet head to the work, as in the past. Note that the head surface 14a remains engaged against the work surface 11a during completion of upset formation, whereby a tight rivet connection to the work is always assured. These conditions may be met when the velocity of impact exceeds about 800 to 1,000 feet per second. Merely as illustrative, the materials of the rivet and panels may be selected from the group consisting of aluminum, aluminum alloys, titanium and titanium alloys, and other ferrous and non-ferrous metals and alloys.

The referenced second means may, with unusual advantage, include a gun 22 having structure such as anvil 20 for engaging the tip 15c of the rivet shank terminal and a plunger 21 to deliver the high velocity impact to the anvil at inner surface 20a thereof for impact transfer to the rivet head. The illustrated gun 22 also includes a body 23 and a pair of

handles

24 and 25 enabling it to be held by a worker, using both hands. Pneumatic means including a piston is provided to drive the plunger or striker forwardly, such means including for example a compressed air source 27 seen in FIG. 1 as supplying air via line 28, air pressure regulator, cleaner and lubricator 29, and line 30 to the gun 22 via handle 24. Within the latter, air flows via duct 31 to air reservoir 34. From that reservoir, air passes via duct 35 to a poppet type safety valve generally indicated at 36, in FIG. 2, and which, when opened, passes air pressure to a trapped air chamber 38 via duct 37. A trigger controlled valve, indicated at 39 in FIG. 1, controls sudden release of pressurized air from chamber 38 to the main cylinder or bore 40 to drive piston 41 therein forwardly. The elongated striker or plunger 21 has an enlarged section 21a connected via screw 42 to the center of the piston as seen in FIG. 8.

The gun also includes an outer barrel 43 carried by nose section 46 of the body 23. Section 46 may be connected to body 23 via adapter block 50, as shown, a fastener 50a retaining the nose section to the block. The barrel may advantageously include

sections

43a and 43b which have axially threaded interconnection at 44. Relative axial adjustment of the barrel length is achieved by rotating section 43a relative to section 43b, followed by tightening of set screw 200 (carried by section 43a) against a cylindrical shoulder or land 201 on section 43b. This operation adjusts the range of acceptable rivet lengths, as will be seen. Note that section 4312 has fixed position relative to body 23 and nose section 46, as facilitated by retention of a flange 430 on section 43b between shoulder 202 and washer 203. The latter is retained by shoulder 204 on block 50.

In accordance with an important aspect of the invention, means is provided to be responsive to displacement of the anvil relative to the barrel as the barrel is advanced toward the work, with the anvil in engagement with the rivet terminal, for enabling forward driving of the plunger 21 when the anvil is within a predetermined axial range of positions relative to the barrel, and for disabling such forward driving of the plunger when the anvil is outside said range of positions. Such means may typically include a cam member movable in the body (for example in block 50) to effect operation of the safety valve in response to axial movement of the anvil 20 relative to the barrel 43 as the barrel is advanced toward the work with the anvil in engagement with the rivet terminal.

More specifically, the cam member may comprise an annulus 205 received about the plunger 21 and movable axially within a bore 206 in block 50. Member 205 has axially spaced cam risers, the first 207 of which is frusto-conical and angled forwardly and radially outwardly to transmit opening movement to the safety valve in response to first predetermined rearward movement of the cam member relative to the barrel. The second riser 208 is also frusto-conical and angled rearwardly and radially outwardly to transmit closing movement to the safety valve in response to second predetermined rearward movement of the cam member relative to the barrel. The cam member also has a plateau 209 located to maintain the safety valve open when the cam member is within the predetermined axial range of positions, i.e., between the positions seen in FIGS. 2 and 7, with the plateau 209 urging the safety valve ball 53 upwardly as seen in FIG. 4. In this regard, ball 53 couples between plunger 52 and the plateau 209. The poppet valve plunger 52 (downwardly pressure urged) works within a cylinder 55 to open and close communication between

ducts

35 and 37, as via a side duct 56 in valve cylinder 55, and auxiliary duct 57 in block 50, as seen in FIG. 3. Cylinder 55 is resiliently urged at 58 against stop 59, and air pressure exerted on the poppet head 158 normally urges the plunger 52 against ball 53. When the forward end 60 of barrel section 43a is urged against the work surface 10a, and the anvil 20 has been sufficiently displaced rearwardly relative to the barrel, cam member 205 displaces ball 53 radially outwardly to also move plunger 52 outwardly, opening the safety valve by unseating the poppet head 158. Accordingly, working air pressure cam flow to chamber 38 only after the gun has been applied to the work, and cam member 205 has been sufficiently rearwardly displaced by the anvil 20.

Coupling between anvil 20 and cam member 205 is provided by a sleeve 210 axially movable within the barrel. The sleeve typically and advantageously has lost motion coupling with the cam member so that the latter will only be displaced relatively rearwardly after predetermined axial movement of the anvil rearwardly relative to the barrel. Further, yieldable means is provided to urge the sleeve, anvil and cam member axially forwardly relative to the barrel, such yieldable means for example including a first coil spring 211 at the rearward side of the cam member urging the latter forwardly, and a second coil spring 212 at the forward side of the cam member and urging the sleeve and anvil relatively forwardly. Note the confinement of spring 21 1 between block shoulder 213 and inwardly recessed shoulder 214 in the cam member, and the confinement of spring 212 between right face 215 of the cam member and the sleeve internal shoulder 216. The latter is provided on a flange 217 which seats against recessed shoulder 218 on the anvil. Sleeve 210 slides within barrel bore 219, and spring 212 is received lengthwise within the sleeve, providing a very compact and unusually efficient assembly. Barrel shoulder 230 limits spring urged rightward travel of anvil shoulder 231.

A typical lost-motion coupling between the sleeve and cam member is provided by operative engagement of the left end 210a of the sleeve with the cam member surface 215 only after predetermined leftward displacement of the sleeve by the anvil through a distanst d. Further, the anvil, sleeve and cam member must then be displaced leftwardly by the additional distance d corresponding to the axial length of the cam riser 207, in order to open the safety valve. Accordingly, the protruding length R of the rivet must be sufficient (i.e., the rivet must be of sufficient length) that anvil 20 is displaced a distance D to the left of at least about d d before the barrel tip 60 engages the work, to enable forward driving of the plunger 21, as in response to opening of the safety valve and trigger released pressure application against the main piston. Note the axial distance d equal to the axial distance from near the bottom of riser 207 to near the bottom of riser 208.

If the protruding length R of the rivet (as in FIG. 7) is such that D is greater than about d d then the gun will be disabled, whereby the protruding length R of the rivet, for the gun design shown, must be such that D lies approximately between two limits, identified as follows, for the gun to be operable:

d+d a D a a +d The acceptable length R of the rivet is controlled by adjusting the barrel length, as for example rotating barrel section 43a forward or barckward on section 43b.

Note in FIG. 8 that anvil 20, sleeve 21 and cam member 205 move slightly to the right upon formation of upset b.

In operation, the riveting method is carried out so as to discriminate between rivets which are of acceptable length and rivets which are not of acceptable length, and involves the steps:

b. applying a rivet gun to said end portion of the rivet, and advancing the gun toward the work, and

c. operating the gun to impact the rivet only if the protruding end portion of the rivet is of acceptable length as determined by the extent of said advancement of the gun toward the work relative to the rivet end por- 5 tion.

Further, the gun is operated only if the protruding end portion of the rivet falls within a predetermined length range; and the gun is disabled if the protruding end portion falls outside that range. Also, the barrel length is adjusted to control the rivet acceptable length, as previously stated.

The barrel 43 may be considered as an element of tubular means carried by the body to project forwardly, such tubular means also including the anvil for receiving the plunger or 21 striker. The anvil has slidable reception within the bore 62 of the barrel forward section 43a. Means is also provided to confine the tip 15c of the rivet terminal against radial expansion while the bulk of the terminal 15b undergoes such expansion to form the upset, thereby to form a centering indicator at the tip of the rivet. See in this regard the example of such an indicator in 15c in FIG. 8. An inspector can very quickly ascertain, by viewing such an indicator 15c, whether it is concentric as related to the expanded upset 15b. If the latter is concentric, the upset is correctly formed, whereas if it is not concentric, (as for example oval shaped) the existence of an out-ofround condition of the upset and its azimuthal bulge direction, are immediately evident, in relation to the location of the indicator 15c which always remains centered.

For the above purpose, the anvil end wall 20b typically forms a centered recess 20c shaped to receive and confine the rivet tip 150 during the impact delivery, via that tip, to the rivet terminal portion 15b subjected to radial expansion and axial compression. Annular tapered wall 20d of the recess blocks radial expansion of the tip during the formation of the upset.

Maintenance of the recess 200 in centered and centering engagement with the tip 150 may be achieved, in unusually advantageous and simple manner as described below. Firstly, preliminary interfitting of the anvil and rivet shank tip, as described, as aided by compression spring 212, urges the anvil toward the rivet. Note that the anvil flange 64 is guided by a counterbore wall 66 in tubular part of barrel 43a for axial movement; also, the anvil skirt 67 may have axial guided engagement with bore wall 62 in the part 43a for centering purposes. Initially, therefore, the anvil recess 200 receives the rivet tip 150 and the barrel 43 is thereby centered in relation to the rivet as the barrel terminal 60 is pushed into forcible engagement with the work surface 10a. Such engagement is thereafter forcibly maintained during formation of the upset 15b and the force transmitted between barrel terminal 60 and wall 10a develops frictional force resisting lateral displacement of the barrel, anvil and rivet terminal during upset formation, further facilitating the maintenance of the centered conditions as described. Accordingly, problems of malformation of the upset are eliminated or minimized.

Control means is provided to effect application against the piston 41 of fluid pressure sufficient to drive the plunger 21 forwardly in one stroke to substantially fully upset the rivet shank terminal. Such control means includes a trigger 70 operable to open valve 39 to pass control air pressure from line 71 and duct 72 in body 23 to duct 73 in that body. Such pressure shifts

spool valve elements

74 and 75 to the left, thereby unblocking the passage of pneumatic pressure from chamber 38 to the main cylinder or bore 40 for driving the piston 41 forwardly. Pressure delivery to line 71, as from source 76, may be valve controlled at 77 at the side of the work panels opposite the gun 22 and plunger 21, so that the worker who applies the bucking bar 16 can control application of impact force to the rivet, preventing inadvertent impact delivery to the rivet prior to his application of the bar 16 to the rivet head; otherwise, such impact delivery could shoot the rivet from the work and possibly injure personnel. Valve 77 may be carried in the handle 78 of a bucking tool 79, and to which the bar 66 is attached, as shown. A thumb trigger 80 pivotally attached to the handle 78 at 81, controls the valve 77. Cusion 82 arrests the forwardly moving piston 41.

Typical rivet materials include aluminum, Monel, stainless steel, copper and brass.

In that form of the invention seen in FIG. 10, the outer barrel 343 is adjustably carried by nose section 346 of the body. Section 346 is connected to body via adapter block 350, a fastener 340 retaining the nose section to the block. The barrel includes sections 3430 and 343b, which have axially threaded interconnection at 344. A fastener 337 thread connected to section 343b interfits a notch 338 in section 343a and blocks relative rotation of the sections. Relative axial adjustment of barrel length, so as to adjust the range of acceptable rivet lengths, is achieved by forcible rotation of the barrel section 343b relative to nose section 346. Note that these two have adjustable interconnection, as provided by the helical metallic insert 390 which interfits both external thread 391 on the barrel and the internal thread 392 on the nose section. The insert allows such rotary axial adjustment of the barrel, and also provides frictional resistance to same, so that the barrel will not inadvertently rotate.

Structural components corresponding to those previ ously described include anvil 320, sleeve 310, cam member 305, springs 311 and 312, and plunger 321. The cam member plateau 309 is directly engageable with the tip of plunger 352 rather than an intermediate ball, as previously described.

I claim:

1. In a gun for upsetting the shank terminal of a metallic rivet projecting from work, the combination comprising a. a forwardly extending tubular barrel,

0. an anvil carried by and movable axially relative to the barrel between the plunger and rivet terminal to receive said upsetting force and to deliver same to the rivet terminal,

d. and means responsive to displacement of the anvil relative to the barrel as the barrel is advanced toward the work with the anvil in engagement with the rivet terminal for enabling said forward driving of the plunger when the anvil is within a predetermined axial range of positions relative to the barrel,

and for disabling said forward driving of the plunger when the anvil is outside said range of positions. 2. The combination of claim 1 including a body car- 5 rying the barrel, and said means includes a safety valve operable to pass plunger operating pneumatic pressure when the anvil is within said range of positions.

3. The combination of claim 1 wherein the barrel includes sections which are axially adjustably intercon- 10 nected, whereby said range may be adjusted by adjusting the axial interconnection of said sections.

4. The combination of claim 3 including a body carrying one of said sections in fixed position relative to the body, the other of said barrel sections having 15 threaded connection to said one section to provide said axially adjustable interconnection.

5. The combination of claim 2 wherein said means comprises a cam member movable in said body to effect operation of said safety valve in response to axial movement of the anvil relative to the barrel as the barrel is advanced toward the work with the anvil in engagement with the rivet terminal.

6. The combination of claim 5 wherein said means also includes a sleeve axially movable within the barrel to transmit said relative axial movement of the anvil to said cam member.

7. The combination of claim 6 wherein said sleeve has lost motion coupling with the cam member to displace the cam member axially of the barrel only after predetermined axial movement of the anvil rearwardly relative to the barrel.

8. The combination of claim 7 including yieldable means urging the sleeve, anvil and cam member axially forwardly relative to the barrel.

9. The combination of claim 8 wherein said yieldable means includes a first spring at the rearward side of the cam member urging the cam member relatively forwardly, and a second spring at the forward side of the cam member and urging the sleeve and anvil relatively forwardly.

10. The combination of claim 5 wherein the cam member is axially movable in said body and has axially spaced cam risers, the first of which is angled to transmit opening motion to the safety valve in response to first predetermined rearward movement of the cam member relative to the barrel, and the second of which is angled to transmit closing motion to the safety valve in response to second predetermined rearward movement of the cam member relative to the barrel.

11. The combination of claim 10 wherein said cam member also has a plateau located to maintain the safety valve open when the cam member is within said predetermined axial range of positions, said plateau located axially substantially between said risers.

12. The combination of claim 1 wherein the gun includes a body having a nose section, and the barrel has axially adjustable interconnection with said nose section, whereby the said range may be adjusted by adjusting the axial interconnection of the barrel and said nose section.

Claims

1. In a gun for upsetting the shank terminal of a metallic rivet projecting from work, the combination comprising a. a forwardly extending tubular barrel, b. a plunger tube driven forwardly within the barrel for transmitting upsetting force, c. an anvil carried by and movable axially relative to the barrel between the plunger and rivet terminal to receive said upsetting force and to deliver same to the rivet terminal, d. and means responsive to displacement of the anvil relative to the barrel as the barrel is advanced toward the work with the anvil in engagement with the rivet terminal for enabling said forward driving of the plunger when the anvil is within a predetermined axial range of positions relative to the barrel, and for disabling said forward driving of the plunger when the anvil is outside said range of positions.

2. The combination of claim 1 including a body carrying the barrel, and said means includes a safety valve operable to pass plunger operating pneumatic pressure when the anvil is within said range of positions.

3. The combination of claim 1 wherein the barrel includes sections which are axially adjustably interconnected, whereby said range may be adjusted by adjusting the axial interconnection of said sections.

4. The combination of claim 3 including a body carrying one of said sections in fixed position relative to the body, the other of said barrel sections having threaded connection to said one section to provide said axially adjustable interconnection.