Impact tool assembly with bit isolating means

A foot assembly for an impact tool reduces tool bit rebound shock to the operator and minimizes tool bit bouncing on the work surface by isolating and attenuating energy reflected from the work surface through the tool bit. The unique system comprises a collar support fabricated from a tough elastomeric material, which engages the inserted inner end of the tool bit and is maintained firmly against the collar thereof by a coil spring. Mounted inwardly within the longitudinal passageway of the foot assembly housing is a bushing, which has an outer contact surface against which the collar support will be thrust by the inwardly moving bit, the elastomeric material thereby serving to attentuate the rebound energy.

BACKGROUND OF THE INVENTION 
It is common practice to provide cushioning members in percussion or impact 
tools, such as power hammers, concrete breakers, and the like. Tools 
having such members are described, for example, in the following U.S. Pat. 
Nos. 1,470,622 and 1,481,641 to Jimerson; 1,774,905 to Smrdel; 2,185,471 
to Mall; 3,179,185 to O'Farrell; 3,244,241 to Ferwerda; 3,266,581 to 
Cooley et al; 4,133,394 to Wohlwend; and 4,168,751 to Deike. Despite the 
level of developmental activity evidenced by these patents, a need remains 
for a system for effectively absorbing and attentuating shock and 
vibration in impact tools, to reduce bouncing and thereby make them easier 
to control. The high levels of sound produced during use are also, of 
course, a most undesirable characteristic of such power driven tools. 
Accordingly, it is a primary object of the present invention to provide a 
novel foot assembly for an impact tool, and a tool incorporating the same, 
having means therein for absorbing the kinetic energy that is reflected 
from the work surface through the tool bit, and for reducing the noise 
produced during use thereof. 
It is a more specific object of the invention to provide such an assembly 
and tool wherein an elastomeric damping member serves to reduce shock, 
recoil, and vibration. 
Additional objects of the invention are to provide a foot assembly and tool 
of relatively simple and yet highly effective construction, affording the 
foregoing features and advantages. 
SUMMARY OF THE DISCLOSURE 
It has now been found that certain of the foregoing and related objects of 
the invention are readily attained in a foot assembly for an impact tool, 
comprising an elongated housing having a passageway extending 
longitudinally therethrough, from a tool bit end to a drive end, and means 
within the passageway providing an abutment surface facing the tool bit 
end of the housing. A tough, elastomeric damping member, having a contact 
surface on its outer end, is slidably mounted within the passageway of the 
housing between the abutment surface and the tool bit end, and has a bore 
which is axially aligned with at least a section of the passageway lying 
adjacent the abutment surface. The bore of the damping member and the 
passageway section are dimensioned and configured to receive the inner end 
portion of a tool bit inserted axially from the tool bit end of the 
housing, with the passageway section being dimensioned and configured to 
permit sliding of the associated tool bit end portion therein. Within the 
housing is also included limiting means spaced from the abutment surface 
toward the tool bit end a distance sufficient to permit limited travel of 
the damping member therebetween, and biasing means acting upon the inner 
end portion of the damping member to urge it away from the abutment 
surface. Thus, kinetic energy reflected back from the work surface through 
an associated tool bit operatively mounted in the housing will be 
transmitted to, and attenuated by, the damping member through contact with 
a stop element on the bit, with the biasing means serving to maintain the 
damping member in position thereagainst. 
In the preferred embodiments, the means providing the abutment surface will 
comprise a generally cylindrical bushing mounted within the passageway of 
the housing inwardly of the damping member, with the bore through the 
bushing providing the passageway section. The outer end portion of the 
bushing may be spaced radially from the corresponding wall portion of the 
housing to define an inwardly-extending circumferential recess 
therebetween, within which may be mounted the inner end portion of a 
compression coil spring, to provide the biasing means of the assembly. The 
damping member will advantageously also be of generally cylindrical 
configuration to provide a substantially annular contact surface for 
cooperating with a circumferential collar portion of the tool bit, and 
most desirably the damping member will have at least one ring of 
wear-resistant material extending circumferentially thereabout and exposed 
on its outside surface, to maximize the useful life of the member. 
Other objects of the invention are attained by the provision of an impact 
tool comprising a drive mechanism operatively engaged with the drive end 
of the foot assembly housing, including a hammer and means for 
reciprocating it substantially along the axis of alignment of the 
passageway section and damping member bore. The hammer will be so 
positioned as to enable repetitive direct impact upon the inner end of a 
tool bit, inserted as hereinabove described.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
Turning initially to FIGS. 1 and 2 of the drawings, therein illustrated are 
an impact tool and a foot assembly, respectively, embodying the present 
invention. The foot assembly, generally designated by the numeral 10, is 
affixed by nuts 12 upon the lower end of the tool body portion 14. The 
latter contains a hammer 16 (seen in FIGS. 4 and 5), with means (not 
shown) for operating it by the force of hydraulic fluid introduced and 
discharged through the inlet and outlet hoses 20, 18 connected to the back 
head portion 22 of the tool. The latter is configured to provide a 
tansverse handle portion 24, and an actuating lever 26 serves to control 
the flow of fluid for powering the hammer, in a conventional manner. A 
concrete breaker tool bit, generally designated by the numeral 28, has an 
inner end portion 30 inserted axially into the foot assembly 10 and 
separated from the outer, spike portion 34 by the circumferential collar 
portion 32. 
The assembly 10 includes an elongated housing 36 with a passageway of 
compound circular cross-sectional configuration extending longitudinally 
through it. The passageway consists of a throat section 38, a somewhat 
larger intermediate section 40, and a further enlarged outer end section 
42; a compound counterbore section 44 is formed at the inner end of the 
passageway adjacent to the throat section 38. 
A bushing 46, having a bore 48 of hexagonal cross-section, is affixed 
within the intermediate section 40 of the housing passageway to slidably 
receive the correspondingly configured inner portion 30 of the tool bit 
28. As can be seen, the lower portion of the bushing 46 protrudes into the 
enlarged section 42 of the passageway, and provides a generally annular 
abutment surface 49 facing the tool bit end of the housing; it also 
defines therewith an inwardly extending circumferential recess 50. A 
compression coil spring 52 is mounted upon the protruding end of the 
bushing 46 with its inner end portion disposed within the recess 50, and 
is thereby securely seated within the enlarged passageway section 42. 
The opposite end portion of the spring 52 bears upon a collar support or 
damping member, which is generally designated by the numeral 54 and is 
shown in full view in FIG. 6. The collar support 54 is fabricated from a 
tough, elastomeric material, and has a pair of integral, wear-resistant 
annular strip bearing 58 exposed on its outer surface. A bore 56 is formed 
through the member 54 in alignment with the bore 48 of the bushing 46; it 
is of hexagonal cross-sectional configuration, and is dimensioned to 
frictionally engage the inserted portion 30 of the tool bit, for movement 
therewith (in the drawing, the size of the bore 56 is exaggerated, for 
clarity of illustration). A circumferential shoulder portion 60 is 
provided on the inner end of the damping member for seating the coil 
spring 52, and a generally annular contact surface 76 is provided by the 
opposite end. Spring 52 biases the collar support 54 in the direction of 
the tool bit end of the housing to the limit of travel, which is defined 
by the retaining ring 62; the ring is snap fit into a small 
circumferential groove 64, machined into the inner surface of the housing 
36 within the passageway section 42. 
A latch is pivotably mounted by a bolt 68 upon the outer end of the housing 
36. Detent 70 is urged against the latch 66 by the coil spring 72, both of 
which are mounted within a small bore 74 formed longitudinally into the 
housing 36. The detent biases the latch toward its closed position, as 
shown, and the latch 66 functions in a conventional manner to permit 
insertion, retention, and release of the tool bit 28. 
FIGS. 1 and 3 depict the impact tool in its unloaded condition; i.e., they 
show the positions assumed by the components in the absence of any load 
due to the mass of the tool itself, the weight of the operator, or under 
the force of an external device. The damping member 54 is urged by the 
spring 52 away from the abutment surface 49, so that its contact surface 
76 bears upon the internal retaining ring 62. 
The normal operating position of the impact tool is illustrated in FIG. 4, 
with the tool bit 28 held against the work surface 78 by the spring 52, 
acting upon the collar support 54. In operation, the hammer 16 strikes the 
top of the inner end portion 32 of the tool bit to transfer the impact 
energy to the work surface; energy reflected back therefrom is 
substantially absorbed by the elastomeric material of the collar support 
54. The spring 52 serves to help maintain the collar support 54 in 
position firmly against the stop element 32, as well as to resist inward 
tool bit movement and store or absorb energy reflected by the tool bit. 
The effect of the damping system is to isolate the tool bit, to thereby 
reduce the shock and vibration transmitted to the operator, and in turn 
increase control by maintaining the bit in a practically stationary 
condition on the work surface during initiation of an operating cycle. As 
will be appreciated, after the cycle has continued and a substantial 
cavity has been formed into the surface, control of the bit becomes 
significantly less difficult. The system also reduces the tendency for the 
bit to become lodged when driven into the work surface, and the sound 
level is substantially reduced because the tool bit is restrained from 
vibrating or "ringing" when impacted by the hammer 16. 
Finally, FIG. 5 shows the fully compressed positions of the spring 52 and 
the collar support 54, with the latter bearing upon the abutment surface 
49 of the bushing 46. The elastomer of the collar support most effectively 
attentuates reflected rebound energy and vibration in this condition. 
Although a hydraulic impact tool has been illustrated, it will be 
appreciated that the hammer may be driven by electric or pneumatic means, 
if so desired. Moreover, the coil spring used to bias the collar support 
could be replaced by equivalent pneumatic or hydraulic means, in 
appropriate circumstances. The materials of construction for the various 
components of the foot assembly of the invention will be evident to those 
skilled in the art, particularly in view of the foregoing description. 
Obviously, the assembly will be made primarily of steel, parts of which 
(e.g., the bushing) may be hardened or otherwise treated as appropriate to 
provide necessary properties. The collar support member may be fabricated 
from any suitable tough elastomeric material, synthetic resinous materials 
such as polyurethane being particularly suitable; for example, a 
thermosetting elastomeric polyurethane of 85-100 Shore A hardness, 2800 
psi minimum tensile strength, 580 percent elongation, and minimum Bayshore 
resilience of 38 percent, has been found to be especially effective. The 
wear rings formed on the collar support member may also be made of any 
appropriate low friction material, exemplary materials being glass 
reinforced nylon containing polytetrafluoroethylene resin (Teflon), bronze 
or glass filled Teflon, and the like. 
Thus, it can be seen that the present invention provides a novel foot 
assembly for an impact tool, and a tool incorporating the same, having 
means therein for absorbing the kinetic energy that is reflected from a 
work surface, and for reducing the noise produced during use thereof. The 
foot assembly and impact tool of the invention are of relatively simple 
and yet highly effective construction, and incorporate an elastomeric 
damping member which serves to reduce shock, recoil, and vibration.