Latching mechanism for reciprocating impact tools

An improved latching mechanism for retaining bits, such as chisels, chippers or scalers in reciprocating impact tools. The improved latching mechanism includes a latch member that is located in the hollow nose of the tool and is rotatable between latched and unlatched positions. A split spring encircles the nose and engages the latch member to prevent inadvertent rotation of the latch member and to retain the latch member in the nose. The latch member extends into the hollow nose and, when in the latched position, engages the bit to retain the bit in the tool while permitting limited reciprocating movement of the bit. When in the unlatched position, the latch member frictionally engages the bit to inhibit inadvertent discharge of the bit, while permitting intentional insertion and removal of the bit.

BACKGROUND OF THE INVENTION 
This invention relates generally to improved latching mechanisms for 
retaining bits in impact type tools. More particularly, this invention 
relates to an improved latch for an impact tool that inhibits the 
inadvertent discharge of a bit therefrom when in the unlatched position. 
One example of a similar latch is described in U.S. Pat. No. 2,716,393, 
issued Aug. 30, 1955 to H. R. Fischer. While the latch shown therein is 
very effective to retain the bit in the tool when in the latched position, 
the latch is arranged to move to a position where it cannot engage the bit 
when rotated to the unlatched position. Movement of the latch in this 
manner facilitates removal and insertion of bits, but the lack of 
engagement with the bit in the unlatched position can result in the 
inadvertent, and possibly dangerous, discharge of the bit if the operator 
fails to rotate the latch to the latched position prior to operating the 
tool. 
An object of this invention is to provide an improved latch for retaining 
bits in impact type tools. Another object of this invention is to provide 
an improved latch that positively retains a bit in an impact type tool 
when in the latched position and that inhibits the discharge of the bit in 
the event the tool is operated with the latch in the unlatched position. 
This invention provides an improved latching mechanism for retaining a bit 
in an impact-type tool that includes a nose portion having a 
longitudinally extending opening for receiving the bit and a radially 
disposed port intersecting the opening, the improvement comprising a latch 
member extending through the radial port for engaging the bit, the latch 
member being rotatable therein between latched and unlatched positions; 
and, resilient means located on the nose portion in engagement with the 
latch member for preventing inadvertent movement of the latch member from 
one position to the other and for urging the latch member into frictional 
engagement with the bit when the latch member is in the unlatched position 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing and to FIG. 1 in particular, shown therein and 
generally designated by the reference character 10 is a pneumatically 
powered impact tool. The tool 10 includes a nose 12 for receiving a bit 14 
(illustrated as being a chisel), a latching mechanism 16 for retaining the 
bit 14 in the nose 12, a power cylinder 18 having a reciprocating hammer 
20 (see FIG. 2) located therein, and a handle assembly 22. 
The handle assembly 22 includes a gripping portion 24, a trigger 26 and, at 
the extreme end thereof, a fitting 28 for connecting the air supply to the 
tool 10. 
As can be seen in FIG. 2, the nose 12 has an opening 30 extending 
longitudinally of the tool 10 for slidingly receiving a shank 32 of the 
bit 14. As illustrated, the shank 32 is octagonal in cross-section (see 
FIG. 3) and the opening 30 is formed accordingly. The shank 32 may also be 
of the standard square cross-section if desired. In either case, a latch 
recess 34 having rather abrupt ends is formed along a portion of the 
exterior of the shank 32. 
The nose 12 also has a radially oriented port 36 that extends therethrough 
intersecting the opening 30. The port 36 is sized to receive a generally 
cylindrical portion 37 of a latch member 38 that is rotatable in the port 
36 between latched and unlatched positions as will be explained. 
The end of the latch member 38 outside the nose 12 is formed into a 
rectangular gripping portion 40 and between the portion 40 and cylindrical 
portion 37 is a rectangular portion providing short surfaces 42 and long 
surfaces 44. The surfaces 42 and 44 in the unlatched and latched positions 
respectively, are in engagement with the flat ends 45 of a split spring 46 
that is disposed in a recess 48 formed in the exterior of the nose 12. The 
split spring 46 overlies part of the cylindrical portion of the latch 
member 38 thus retaining the latch member 38 in the port 36. Also, the 
flat ends 45 of the spring 46 engage the short surfaces 42 as shown in 
FIG. 5 to retain the latch member 38 in the unlatched position. The flat 
ends 45 engage the long surfaces 44 as shown in FIGS. 2 and 3 to retain 
the latch member 38 in the latched position. 
Referring again to the construction of the latch member 38, it can be seen 
that the end thereof that is disposed in the opening 30 is provided with 
angularly disposed latch surfaces 50 that are on sides corresponding to 
the short surfaces 42. The latch surfaces 50 are disposed at a large angle 
(about 60 to 70 degrees) relative to the axis of the tool 10 so that, upon 
engagement with the ends of the latch recess 34, the latch member will not 
be forced upwardly and the longitudinal or reciprocating movement of the 
bit will be limited thereby. It should also be pointed out that the length 
of the latch member 38 is selected so that any downward force exerted by 
the spring 46 on the latch member 38 is not imposed on the shank 32 
leaving the bit 14 free to reciprocate within limits. 
Cam surfaces 52 are provided on the inner end of the latch member 38 also, 
but on sides thereof corresponding to the long surfaces 44. The cam 
surfaces 52 are disposed at a relatively flat angle (about 20 to 30 
degrees) with respect to the axis of the tool 10 so that they cooperate 
with the ends of the latch recess 34 to force the latch member 38 
upwardly. Accordingly the bit 14 can be inserted and removed when desired 
provided that the latch member 38 is in the unlatched position. 
OPERATION OF THE PREFERRED EMBODIMENT 
When it is desired to operate the tool 10, the latch member 38 is rotated 
to the unlatched position. A bit 14, which is selected according to the 
job to be performed, is then positioned with the end of the shank 32 in 
the entrance to the opening 30 in the nose 12. The bit 14 is inserted into 
the opening 30 until the end of the shank 32 engages one of the surfaces 
52 on the latch member 38. Since the split spring 46 is exerting a 
downward force on the latch member 38 sufficient force must be exerted on 
the bit 14 in an axial direction to cam the latch member 38 upwardly and 
move the shank axially in the opening 30 until the latch member 38 drops 
into the latch recess 34 under the influence of the spring 46. It should 
be pointed out that the latch member 38 will remain in the unlatched 
position, freeing the operator's hands to insert the bit 14, because the 
flat ends 45 of the spring 46 are in engagement with the short surfaces 42 
on the latch member 38. 
Should the operator fail to rotate the latch member 38 to the latched 
position before actuating the trigger 26 to place the tool 10 in 
operation, the bit 14 will not be discharged from the tool 10 or, if 
discharged, its velocity will be sufficiently low to prevent damage. With 
the latch member 38 in unlatched position, and the tool 10 started, the 
hammer 20 may strike the end of the shank 32 driving the bit 14 to the 
left as seen in FIG. 4. Inhibiting the discharge of the bit 14, is: the 
frictional engagement of the end surface of the latch member 38 in the 
recess 34 caused by the spring 46; the engagement between one of the 
surfaces 52 with the end of the latch recess 34 and the increased force 
exerted by the spring 46 resisting the upward movement of the latch member 
38; and the continued, increased frictional force between the end of the 
latch member 38 and the outer surface of the shank 32. 
Numerous tests run on the tool 10 with the latch member 38 in the unlatched 
position, failed to discharge the bit 14. However, with all circumstances 
exactly right, it would be theoretically possible to discharge the bit, 
but, as can be appreciated, the frictional forces exerted will absorb 
considerable energy so that the bit 14 cannot be discharged with 
sufficient velocity to be a hazard. 
Normally, the operator, after insertion of the bit 14, will grasp the 
gripping portion 40 of the latch member 38 and rotate the latch member 38 
by overcoming the force of the spring 46 from the unlatched position 
illustrated in FIGS. 4 and 5 to the latched position illustrated in FIGS. 
2 and 3. When rotated approximately 90.degree., the flat ends 45 of the 
spring 46 are in engagement with the long surfaces 44 on the latch member 
38, positively retaining the latch member 38 in the latched position. 
As illustrated, one of the surfaces 50 is positioned to engage the end of 
the recess 34 at such an angular relationship that the outward movement of 
the bit 14 will be stopped. Also, and as previously mentioned, the bit 14 
is free to reciprocate because the latch member 38 is not in engagement 
with the shank 32, except to stop the axial movement. 
With the latch member 38 in the latched position, the operator places the 
cutting end of the bit 14 against the work which presses the bit 14 
inwardly into a position for engagement between the hammer 20 and the end 
of the shank 32. Actuation of the trigger 26 causes, by means old in the 
art, reciprocation of the hammer 20 which strikes the end of the bit 14 
driving the bit 14 toward the work. The bit 14 returns due to rebound off 
the work or due to continual forward pressure exerted by the operator. 
Removal of the bit 14 is accomplished by rotating the latch member 38 to 
the unlatched position and exerting sufficient outward force thereon to 
overcome the frictional forces between the latch member 38 and the bit 
shank 32. 
From the foregoing description, it can be appreciated that an improved 
latching mechanism, constructed in accordance with the invention, provides 
a means of positively retaining a bit in the tool when in the latched 
position. Further, such a latching mechanism inhibits, if not prevents, 
the inadvertent discharge of a bit from the tool when in the unlatched 
position while permitting insertion and removal when desired. 
The detailed description of the preferred embodiment is presented by way of 
example only, and it will be understood that many changes and 
modifications can be made thereto without departing from the spirit of the 
invention.