Hammer drive tool

A hammer drive, powder actuated tool having a main barrel housing, fastener drive and guide means telescopically slidable in one end of the housing and having a muzzle end for orienting a fastener and a breech end for orienting a fastener-driving powder charge, the other end of said main housing having first anvil means thereon, second anvil means including firing pin means, spring means of substantial force biasing said first and second anvil means apart, and movable safety means disposed between the breech end of said fastener drive and guide means and said firing pin means preventing unrestricted axial movement therebetween and contact between said firing pin and powder charge.

BACKGROUND OF THE INVENTION 
The invention relates generally to fastener drive tools, and more 
particularly to anvil-type or hammer drive, powder actuated tools. 
Many types of fastener drive tools and like explosively actuated equipment 
have been developed over the years, and such tools have generally had 
complex mechanisms for firing pin operation, for ejecting or extracting 
spent cartridge shells and for meeting safety standards. Recent 
developmental trends are toward improved low velocity tools of the type in 
which a piston ram member is explosively driven to actuate a nail or like 
fastener into a workpiece such as concrete or wood. One type of low 
velocity tool is described in U.S. Pat. No. 3,066,302, which tool uses a 
pistol-type firing pin mechanism having a trigger and sear to trip a 
spring-loaded firing pin that is cocked by compressing the muzzle end of 
the tool telescopically rearwardly within the tool housing. Many such 
pistol-type low velocity tools are disclosed in the prior art. 
Another type of low velocity tool is described in U.S. Pat. No. 4,025,029, 
which tool, like the present invention, is a hammer-activated, powder 
actuated stud driver. Such hammer drive tools are conventionally operated 
by placing the muzzle end of the tool against the workpiece and striking 
the rear end of the tool with a hammer to fire the cartridge or like 
powder charge. Hammer drive tools heretofore, while simple in construction 
and operation, have been inherently dangerous due to the fact that a 
loaded tool could be fired if accidentally dropped. U.S. Pat. No. 
3,688,964 discloses another low velocity hammer drive tool designed for 
caseless powder loads and having some safety features. 
SUMMARY OF THE INVENTION 
The present invention comprises a low velocity, powder actuated tool of the 
type utilized in construction and other trades, and particularly adapted 
for use in the home, shop or the like by semi-skilled persons. 
The principal object of the present invention is to provide a novel 
fastener drive tool of the hammer drive or impact type; one that is of 
simple, rugged construction and eliminates the complex and expensive forms 
of closure, trigger, sear, firing pin, cartridge holding and ejection and 
like mechanisms of prevalent tool design. 
Another object is to provide a powder actuated tool that is highly 
efficient in operation and provides exceptional safety standards against 
drop-fire and other accidental tool discharge incidents. A more specific 
objective is to provide triple safety means requiring positive manual 
operation as well as substantial striking force to accomplish firing 
actuation of the tool. 
Still another object is to provide a hammer drive tool that meets the three 
safety requirements of the American National Safety Code. 
These and still other objects and advantages will become more apparent 
hereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings wherein the hammer drive, powder actuated tool 10 
is illustrated as a presently preferred embodiment of the present 
invention, the tool 10 comprises a main cylindrical housing member 11 
having a rear firing pin bore section 12 and a front barrel bore section 
13 with an intermediate breech or loading area 14. A primary solid anvil 
member 17 is rigidly secured in the firing pin bore 12 of the main housing 
11 by a cross pin 18, and a "floating" firing pin assembly 19 is housed in 
the firing pin section 12 between the primary anvil mass 17 and the breech 
or loading area 14, as will be defined more fully hereinafter. A safety 
lever assembly 20 is pivotally mounted on the main housing 11 intermediate 
to the firing pin section 12 and breech area 14, and one of its purposes 
is to limit or restrict free floating forward movement of the firing pin 
assembly 19 toward the breech section 13. The main housing 11 has a 
lateral breech opening 21 for access to the inner breech or loading area 
14 for purposes of cartridge ejection and reloading of the tool 10. The 
main housing 11 is provided with a two-piece outer resilient hand grip or 
housing covering 22 which circumscribes the rear firing pin section 12 and 
is associated with the safety lever assembly 20, as will be described. 
A barrel ram guide member 23 is slidably mounted in the front barrel 
section 13 of the main housing 11, the guide member having a bore 24 in 
which a barrel extension 25 is threadedly engaged at the muzzle end. The 
barrel extension 25 has a bore 26 concentric with the ram guide bore 24 
and an annular shoulder 27 is formed between the bores 24 and 26. The ram 
guide 23 also has a breech plug 28 threadedly engaging the breech end of 
the bore 24, the breech plug 28 having an ignition cavity 29 for receiving 
a powder cartridge C (see FIG. 1) or like powder charge. A ram or piston 
member 30 has an enlarged head 31 with a close tolerance sliding fit in 
the ram guide bore 24, and an axially extending cylindrical ram or piston 
rod 32 is slidably positioned in the barrel extension bore 26 with a free 
or working end therein for engagement with a fastener F. The ram head 
member 31 has an annular steel or like O-ring seal 35, and an annular 
abutment shoulder 36 on the head member 31 defines the end of the recess 
between the piston rod 32 and the ram guide bore 24. The ram and ram guide 
members 30 and 23 comprise fastener drive means for orienting the fastener 
member F in the tool 10 and for driving such fastener F into a workpiece 
(not shown) in a conventional manner readily apparent to those skilled in 
the art. The ram head 31 is also provided with an axially extending 
ejection pin 37 for dislodging spent cartridge shells C from the ignition 
cavity 29. 
An important feature of the tool 10 comprises frictional abutment means 38 
adjacent to the muzzle end of the main barrel housing 11. The ram guide 
member 23 has a longitudinal slot 39 extending a major portion of the 
guide member length, and an arcuate transverse slot 40 is formed in the 
main housing wall 11 to thereby accommodate a spring clip 41 forming part 
of the frictional abutment means 38, see FIGS. 1 and 3. The spring clip 41 
has a U-shaped central body 42 extending radially inwardly through the ram 
guide slot 39 into the recess for abutment by the ram head shoulder 36, 
and arcuate friction wings 43 are formed as outward re-entrant curves from 
the opposed walls of this central body 42, FIG. 3. The frictional abutment 
means 38 also includes a spring steel retainer band 45 having an inner end 
flange 46 received between the spaced walls of the spring clip central 
body 42 to maintain the band 45 in circumscribing relationship around the 
muzzle end of the main housing 11. 
Referring to FIG. 2, the tool 10 is shown in its fully compressed firing 
position with the ram 30 and ram guide 23 being retracted in telescopic 
relation within the main housing 11 and the firing pin assembly being 
compressed in the condition of the tool 10 at the precise instant that a 
hammer driven force is applied to the primary anvil member 17 to detonate 
the powder charge C in the breech plug 29. It will be understood by those 
skilled in the art that the force exerted upon the ram head 31 drives the 
ram 30 axially in the ram guide 23 and barrel extension 25 so that the 
working end 33 drives the fastener F from the muzzle end of the barrel 
extension 25 into the workpiece (not shown). Thus, when the tool has been 
fired, the ram 30 will naturally be positioned in the ram guide 23 
leftwardly of the position shown in FIGS. 1 and 2 until the piston guide 
is also moved leftwardly (as in FIG. 1) to its expanded, re-loading 
position. This action is carried out by snapping the muzzle end of the 
tool outwardly in a swinging movement to throw the ram guide outwardly in 
the main housing bore 13 against the frictional force exerted therebetween 
by the spring clip wings 43 of the spring clip 41. In this movement the 
ram guide 23 moves to its fully extended loading position with the 
frictional abutment means 38 engaging the end of slot 39, and the ram 30 
is also engaged with its abutment shoulder 36 against the U-shaped central 
body 42 of the spring clip. Thus, in the FIG. 1 position of the tool 10, 
the ejection pin 37 projects into the cartridge or ignition cavity 29 of 
the breech plug 28 to eject the spent cartridge shell, which is dropped 
through the breech opening 21 by inverting the tool 10 from its FIG. 1 
position. It will be readily apparent that the frictional abutment means 
38 return the ram and ram guide members 30 and 23 to their loading 
relationship for inserting a new fastener F in the muzzle end of the 
barrel extension 25 and a cartridge C in the ignition cavity 29 of the 
breech plug 28. The frictional abutment means 38 also prevents relative 
rotation of the ram guide member 23 in the main housing 11, and the spring 
clip 41 and retainer band 45 act frictionally between the ram guide member 
23 and main housing 11 to maintain the ram guide frictionally in any 
adjusted axial position. The steel friction spring 35 between the ram head 
31 and ram guide bore 24 maintains the adjusted axial position of the ram 
30 in the ram guide member 23. 
Referring particularly to FIGS. 1, 4 and 5, the firing pin mechanism of the 
tool 10 includes the primary anvil member 17 having a centrally projecting 
impact or anvil block 49 with striking face 50, and a strong drop-spring 
51 is positioned on the anvil block 49 and extends concentrically 
forwardly in the firing pin bore 12 to oppose movement of the ram guide 23 
and its cartridge carrying breech plug 28 toward firing position. The 
spring 51 has a substantial force of approximately 25 to 30 ft. lbs., 
which is several times the weight of the tool and thereby forms a first 
safety mechanism to substantially obviate drop-fire incidents. The 
"floating" firing pin assembly 19 includes a secondary anvil mass or plug 
52 slidably positioned in the firing pin bore section 12 of the main 
housing 11, and a circular firing pin 53 is integrally formed on its 
forward face in the breech area 14 and is axially aligned with the 
ignition chamber 29 of the ram guide member 23. The secondary anvil and 
firing pin member 52,53 is biased forwardly toward the breech area 14 by 
the strong or "heavy" drop-spring 51, but a stop key or pin 54 projects 
radially from the secondary anvil member 52 and is guided in a 
longitudinal slot 55 in the main housing wall 12 to limit forward movement 
of the firing pin assembly 19 toward the breech area 14. 
The firing pin assembly 19 also includes secondary safety means associated 
with the secondary anvil 52. The anvil 52 is bored through, at 56, on 
opposite sides of the firing pin 53 and is counterbored from the back, at 
57, and receives a pair of diametrally disposed headed studs or safety 
rivets 58. The rivets 58 are biased by firing pin safety springs 61 
positioned in the counterbore 57 and retained therein by a tempered 
closure anvil block or plate 62, which is welded to the back surface of 
the anvil plug 52 and serves to retain the forward end of the drop-spring 
51. The secondary anvil member 52 also has a forwardly projecting annular 
shoulder 63 at its periphery, which is adapted to interfit with an annular 
peripheral recess 64 in the breech plug 28 thereby forming a sealing 
arrangement at the point of firing contact of the firing pin 53 with a 
cartridge C. It may be noted that the firing pin 53 has a complete 
centerfire fit with the percussion flange of the cartridge C, and firing 
indentation of the cartridge C by penetration of the firing pin is 
controlled by the sealing arrangement. The safety stud springs 61 are also 
of substantial force or "heavy," each being about the same magnitude as 
the drop-spring 51 (approximately 28 ft. lbs.) whereby the combined spring 
forces to be overcome to fire the tool 10 substantially eliminate 
accidental firing incidents. 
The safety lever assembly 20 comprises the third safety device of the 
present tool 10, and comprises an elongated lever body 66 longitudinally 
disposed along the firing pin section 12 of the housing 11 and contained 
within the davity section 65 formed in the resilient covering 22 therefor. 
A safety latch or lug 67 is formed substantially at right angles on the 
forward end of the lever body 66 and extends radially inwardly of the 
cylindrical main housing 11 through a transverse slot 68 and defines the 
forwardmost limit of the firing pin assembly 19 as a secondary stop to the 
limit plug 54. More importantly, the latch 67 acts to prevent accidental 
rearward movement of the ram guide member 23 as will be described. The 
other end of the lever body 66 is provided with a handle 70 extending 
outwardly of the resilient covering 22, and the lever body 66 is hinged or 
pivoted on the main housing 11 on a fulcrum mounting lug 69 intermediate 
to the latch 67 and the outwardly extending handle portion 70. A 
wrap-around spring 71 or the like compresses the latch member 67 inwardly 
to form the safety abutment in the main housing bore, and the spring 71 is 
overcome by depressing the handle 70 radially inwardly against the hand 
grip covering 22. It will be apparent that the handle-fulcrum-latch 
relationship can be modified to provide optimum safety lever action. 
In the extended, loading position of the tool 10 as shown in FIG. 1, a new 
cartridge C is inserted into the ignition cavity 29 thereby pressing 
against the ejection plug 37 and axially moving the entire ram 30 slightly 
to the left, where the ram 30 is held in position with the ram guide 23 by 
the friction sealing spring 35. A fastener F is inserted in the muzzle end 
of barrel extension bore 26 against the ram work face 33, and the fastener 
drive and guide means 30,23 is moved rearwardly toward the firing pin 
section 13 to close the breech opening 21 and position the breech plug 28 
of the ram guide 23 against the ends of the safety guide rivets or studs 
58, which project axially beyond the safety lever latch 68, FIG. 1. 
Although the safety lever mechanism 20 forms the only positive 
interference safety device, that prevents unrestricted axial movement of 
the guide means 23 and firing pin assembly 19 into contacting or firing 
abutment, the combined force of the two firing pin safety springs is 
approximately 56 ft. lbs. and effectively prevents compressive firing 
action by the operator or other inadvertent compressive forces of great 
magnitude, such as accidental drop-fire incidents. Therefore, it will be 
seen that in the normal sequence of compression, the drop-spring 51 would 
first become compressed to bring the ram guide 23 into abutment with the 
safety latch 68 before the firing pin safety springs 61 will give way to 
striking engagement between the firing pin 53 and cartridge C in the 
breech plug 28. 
In actual operation, when the tool 10 is positioned against a workpiece 
(not shown) and ready for firing, the ram and ram guide 30,23 will be 
telescoped into the barrel housing with the breech plug 28 abutting the 
ends of the safety rivets 58. The safety lever handle 70 is then depressed 
to pivot the latch 68 out of the barrel bore 14 against the action of 
spring 71, and the primary anvil 17 is struck solidly by a heavy hammer 
(not shown) weighing about one pound or greater. It is again emphasized 
that the hammer force must overcome the 25 to 30 ft. lbs. force of the 
spring 51 to drive the primary and secondary anvil members 17 and 52,62 
together and also overcome the combined forces of firing pin safety 
springs 61 to provide firing contact of the firing pin 53 against the 
cartridge C, as shown in FIG. 2. 
It will thus be readily apparent that the two firing pin safety studs 58 
and springs 61, as positioned immediately adjacent to the firing pin 53 
and acting in opposition to relative firing actuation, assure the 
deliberate and safe operation of the tool 10 and assure against 
substantially all inadvertent tool mishaps. From the foregoing description 
it will be readily apparent that the present fastener drive tool 10 meets 
the various objectives of simplicity, safety and efficiency in 
construction, handling and operation. The essential simplification of the 
invention pertains to the "floating" secondary anvil 52 that is spring 
loaded by a "heavy" spring 51 away from the primary anvil mass 17, and in 
the provision of a positive safety latch 20 that is manually retractable 
to condition the tool for firing. It may be noted that the handle 70 of 
the safety lever 20 is positioned radially inwardly of the large end 
flange of the resilient hand grip 22 so that it is also protected against 
release do to accidental dropping incidents. Various changes and 
modifications of the tool 10 will be apparent to those skilled in the art 
without departing from the inventive concept. Accordingly, the invention 
is limited only by the scope of the claims which follow.