FIELD OF THE INVENTION
This invention relates generally to improvements in fastener
BACKGROUND OF THE INVENTION
Power framing tools for use in driving fasteners into workpieces
are well known. The framing tools are usually portable and are powered pneumatically
or by combustion. Similar pneumatic tools are described in
U.S. Patent Nos. 4,932,480
. Combustion powered tools are described in
U.S. Patent Nos. Re. 32,452
. Such combustion powered tools particularly designed for trim applications
are disclosed in
U.S. Patent No. 6,016,622
Such tools incorporate a generally pistol-shaped tool housing
enclosing the power source, such as a pneumatic cylinder or a small internal combustion
engine. The engine is powered by a canister of pressurized fuel gas also called
a fuel cell. Power is generated from expansion of compressed gasses, either by burning
of fuel in a combustion chamber or expansion of air in the pneumatic cylinder. The
power source moves a reciprocating piston having an elongate, rigid driver blade
disposed within a piston chamber of a cylinder body. A safety interlock prevents
firing of the tool unless a workpiece contact element at the end of a nosepiece,
or nosepiece assembly, is pressed against a workpiece.
Upon the pulling of a trigger, gas or air expansion causes
the piston and the driver blade to be shot downward to impact a positioned fastener
and drive it into the workpiece. As the piston is driven downward, a displacement
volume enclosed in the piston chamber below the piston is forced to exit through
one or more exit ports provided at a lower end of the cylinder. After impact, the
piston then returns to its original or "ready" position through differential gas
pressures within the cylinder. Fasteners are fed into the nosepiece barrel from
a supply assembly, such as a magazine, where they are held in a properly positioned
orientation for receiving the impact of the driver blade. The fasteners are then
propelled through the length of the barrel by the driver blade, exiting the barrel
at the workpiece surface. Force of the driver blade and the momentum of the fastener
drives the fastener to penetrate the workpiece.
Framing tools are commonly used in residential construction
primarily for driving nails into wood. Metal hardware pieces, such as joist hangers,
connecting plates and seismic strapping are frequently attached to the wood framing
requiring relatively accurate placement of the fastener in openings or slots in
the metal hardware. A POSITIVE PLACEMENT® tool is a specialty framing tool
that is used where accurate placement of the fastener is desirable. This tool has
a probe that aids alignment of the fastener with the hardware openings.
At least two different lengths of nail are typically used
for these applications. Current designs for these tools require the user to change
settings on the tool when changing between different nail lengths. The user must
first pull on a spring-biased plunger to disengage it from a rebound lever. The
rebound lever pivots approximately 60 degrees about a pin. While holding the plunger
in the outward position, the lever must be rotated via the handle to the other position.
When the plunger is released, it again engages with the lever to lock it into the
new position. Such an operation requires two hands, one to hold the tool and the
other pull the plunger, rotate it and allow it to reengage. In construction environments,
the user is often in an inconvenient place, trying to align two or more workpieces
to be fastened together. It is not always practical to free both hands to effect
the setting change.
More specifically, the present invention provides a nosepiece
and shear block assembly for a fastening tool that drives a fastener supplied from
a plurality of fasteners. The assembly includes a nosepiece that is configured for
attachment to the tool and defines a portion of a barrel and a shear block configured
to be secured to the nosepiece to complete the barrel. There is an opening in the
barrel for receiving a fastener.
Some tools of this type have a quick clearing feature whereby
the nosepiece easily separates from the shear block by operation of a latch. Forces
in play during firing tend to push against the barrel walls, trying to push apart
the nosepiece and shear block.
Where the nosepiece and the shear block are separable,
stress is placed on the latch mechanism.
It is an object of the present invention to provide an
improved fastener driving tool with a nosepiece and shear block assembly in which
the possibility of latch failure is minimized.
SUMMARY OF THE INVENTION
This object is met by the nosepiece and shear block assembly
for a fastening tool according to claim 1.
It is also met by the power tool of claim 6.
DETAILED DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE INVENTION
- FIG. 1 is a perspective view of the POSITIVE PLACEMENT® tool of the present
- FIG. 2 is a cross sectional view of the nosepiece and shear block assembly and
the magazine of the tool of FIG. 1 with short nails loaded;
- FIG. 3 is a cross sectional view of the assembly of FIG. 2 with long nails loaded;
- FIG. 4 is a detail of a side elevation of the nosepiece windows with the nail
strip shown in phantom;
- FIG. 5 is a detail side view of the nosepice and shear block assembly having
the workpiece contact element and the cap disengaged from a plurality of bosses;
- FIG. 6 is a side view of the assembly of FIG. 5 having the cap engaged with
a plurality of bosses;
- FIG. 7 is a side view of the assembly of FIG. 5 with the shear block separated
from the nosepiece; and
- FIG. 8 is a bottom view of the assembly of FIG. 5.
Referring to FIGs. 1-3, a power tool, generally designated
10, is shown with a nosepiece and shear block assembly 12 having a driver blade.
The tool 10 is commonly used for driving a fastener 14 into a workpiece 16, such
as in a nailing or framing operation. The fastener 14 is generally loaded into a
magazine 18 that is removably attached to the tool 10. The fastener 14 is contemplated
as being any type of fastener that is satisfactorily driven into the workpiece 16,
such as nails, brads, staples, tacks and the like. To hold a plurality of the fasteners
14 in the same orientation and to handle many fasteners at once, the fasteners are
generally attached to a collation tape 20, which is typically made of paper or plastic.
The general appearance and the operational details of such power tools 10 are very
well known in the art. Directional references used herein are to be interpreted
as if the tool 10 were oriented with a nosepiece 22 approximately perpendicular
to and in contact with the workpiece 16, as shown in FIG. 1.
Referring to FIGs. 2 and 3, the assembly 12 includes the
nosepiece 22 that is configured for attachment to the tool 10. A tubular barrel
24 is formed at least partially by the nosepiece 22, and guides the fasteners 14
as they are driven into the workpiece 16 by a driver blade 26. The barrel 24 extends
from the resting position of the driver blade 26 near a body 28 of the tool 10 to
an exit 29 at the surface of the workpiece 16 when the tool 10 is ready to drive
the fastener 14. A rear-facing opening 30 in the barrel 24 receives the fastener
14 from the magazine 18 oriented so that a penetrating portion 32 of the fastener
14 is closest to the workpiece 16 and the length of the fastener is generally parallel
with the barrel. When the tool 10 is in contact with the workpiece 16 and a trigger
34 (FIG. 1) is activated by the user, the driver blade 26 rapidly travels through
the barrel 24. At the opening 30, the driver 26 contacts the fastener 14 and propels
it through the remaining length of the barrel 24 and into the workpiece 16.
Optionally, the nosepiece 22 has one or more windows 36
extending to the barrel 24 seen best in FIG. 4. The windows 36 are constructed and
arranged to align with the path of the collation tape 20. Any shape window 36 is
suitable, although a slot shape is preferred. If the collation tape 20 does not
tear off with the previous fastener 14, it is aligned to protrude through the window
36, allowing the next fastener 14 to completely enter the barrel 24. The collation
tape 20 is likely to be dispelled by subsequent shots of the tool 10. Occasionally,
the collation tape 20 will become folded, bent or otherwise misaligned so that it
fails to align with the windows 36, and begins to build-up in the barrel 24. In
this case, the windows 36 permit the user to observe the paper 20 build-up and remove
the tape 20 before a jam occurs. Access to the barrel 24 is provided to facilitate
the clearance of collation tape 20 to jams. Any configuration known in the art for
providing access to the barrel 24 is useful with this invention. One preferable
assembly 12 has the barrel 24 formed partially by the nosepiece 22 and partially
by an adjoining shear block 40 that is configured to be secured to the nosepiece
to complete the barrel. An advantage of forming the barrel 24 so that the nosepiece
22 and the shear block 40 are adjacent to and separable from each other, as seen
in FIG. 7, is that the assembly 12 is conveniently cleared of jams.
Referring now to FIGs. 2 and 3, the assembly 12 includes
a biased fastener-size adjustment device 42. Preferably, the device 42 is in the
form of a rebound lever that is pivotally attached to the shear block 40 and is
positioned such that the rebound lever pivots in response to the length of the fastener
14. The fasteners 14 move from the magazine 18 into the opening 30 in the barrel
24, oriented approximately vertically. The length of the opening 30 is at least
as long as the longest fastener 14 that is intended to be used in tool 10. As the
long fasteners 14 move down the magazine 18 toward the opening 30, a penetrating
end 32 of the fastener 14 contacts the rebound lever 42. The rebound lever 42 is
biased, as with a spring 45 (shown hidden) urging it upward as shown in FIG. 2,
to press it against the fasteners 14. The fasteners 14 push downwardly against the
rebound lever 42, pushing it out of the path of the fasteners 14.
One surface of the rebound lever 42 is referred to as a
blocking surface 46 since it is to obscure unused portions of the opening 30. The
blocking surface 46 is adjacent to the barrel 24 of the tool 10. As the rebound
lever 42 pivots up and down with respect to the length of the fasteners 14, the
blocking surface 46 changes the effective length of the opening 30 as the rebound
lever 42 pivots. The shape of the blocking surface 46 is not critical, however,
an arc shape is preferred.
Following the driving of a fastener 14, as the driver blade
26 retracts up the length of the barrel 24 and moves upwardly past the opening 30,
the next fastener 14 is pushed into the barrel 24 by the springloaded clip or magazine
18. As the tool 10 is fired, the driver blade 26 contacts the fastener 14 and begins
to push it down the barrel 24, it has a tendency to bounce or rebound off the wall
48 and begins to exit the barrel through the opening 30. When long nails 14 are
loaded, the rebounding nail often hits the next nail in the magazine 18 and is reflected
back into the barrel 24. But when short nails 14 are used, they can rotate through
the opening 30, partially exiting the barrel 24 below the end of the next fastener
14. The blocking of the opening 30 by the blocking surface 46 between the bottom
of the fastener 14 and the bottom of the opening keeps the fastener inside the barrel
24 even if it rebounds.
When it is desired to change to smaller nails 24, the improved
nosepiece and shear block assembly 12 allows the tool 10 to adjust automatically
to the different length fastener. As short fasteners 14 pass through the magazine
18, they do not cause the rebound lever 42 to rotate as much as the long nails.
Compared to the long nails 14, the biasing force of the spring 45 is not overcome,
and rebound lever 42 is not depressed as far by the short nails, so that more of
the blocking surface 46 adjoining the barrel 24 closes off the unused portion of
the opening 30. When the short nail 14 rebounds off of the wall 48, it encounters
the blocking surface 46 instead of entering the shear block 40, and is deflected
back into the barrel 24. Reducing the effect of rebound is particularly advantageous
on a POSITIVE PLACEMENT® tool 10 as to fastener 14 is urged along a straighter
path through the barrel 24, improving the accuracy of its placement.
When the clip or magazine 18 is changed or refilled with
an additional supply of fasteners 14, the rebound lever 42 automatically adjusts
to the length of the newly loaded fasteners. The fasteners 14 push the rebound lever
42 sufficiently out of the way to allow them to pass by unimpeded, while the biasing
force provided by the spring 45 pushes the rebound lever 42 upward to contact the
penetrating tip 32 of the fastener 14, closing the unused portion of the opening
30. Regardless of the length of the fastener 14, the rebound lever 42 pivots to
contact the penetrating tip 32.
Referring to FIG. 7, some tools 10 of this type have a
quick clearing feature whereby the nosepiece 22 easily separates from the shear
block 40 by operation of a latch (not shown). This feature is used to quickly open
the barrel 24 of the tool 10 to clear a jam and close the barrel again without having
multiple parts to disassemble. Such features are well known in the art. Forces in
play during firing tend to push against the barrel 24 walls, trying to push apart
the nosepiece 22 and shear block 40. Where the nosepiece 22 and the shear block
40 are separable, stress is placed on the latch mechanism or other apparatus normally
holding the nosepiece 22 and shear block 40 together. If the latch is worn after
a great deal of use, it could possibly disengage during firing, allowing the nosepiece
22 and the shear block 40 to fly apart.
The possibility of latch failure is minimized by incorporating
at least one boss 52 on the shear block 40 that matingly engages a raised cap 54
on a movable element 56, such as a workpiece contact element. When in its lower
or resting position, as shown in FIG. 5, the workpiece contact element 56 interlocks
with the firing mechanism (not shown) to assure that the tool 10 does not fire unless
in contact with the workpiece 16. In this position, the nosepiece and shear block
are separable, allowing the user to clear a jam if needed. As the workpiece contact
element 56 is pushed upward, in a motion parallel to the length of the barrel 24
to a firing position shown in FIG. 6, the workpiece contact element 56 engages the
shear block 40 as described in more detail below. This position allows the tool
10 to fire but prohibits separation of the nosepiece 22 and shear block 40. The
workpiece contact element 56 is preferably spring biased to automatically return
to its resting position when the tool 10 is lifted from the surface of the workpiece
16. After firing of the tool 10, the firing mechanism is locked out until activated
again by engagement of the workpiece contact element 56.
The raised cap 54 is designed to easily move over the boss
52 in a direction that is parallel to the barrel 24, but to prevent movement that
would allow separation of the nosepiece 22 from the shear block 40. As shown in
FIG. 8, the boss 52 has a cross section that is generally semi-circular, but other
cross sectional shapes, such as triangles, rectangles and the like are also suitable.
When the workpiece contact element 56 moves upward in response to placement of the
tool 10 on the workpiece 16, the cap 54 slides over the boss 52 as seen in FIG.
6. FIG. 7 shows disengagement of the tool 10 from the workpiece 16 that also disengages
the cap 54 from the boss 52, allowing quick separation of the nosepiece and shear
block assembly 12. Thus, the nosepiece 22 and the shear block 40 cannot accidentally
separate during firing of the tool 10 and a jam can be cleared only when the tool
10 is disabled from firing.
Still referring to FIGs. 5, 6 and 7, the shear block 40
optionally has one or more of the bosses 52 also referred to as first bosses, and
the nosepiece 22 has one or more second bosses 60. Although the use of multiple
caps 54 is contemplated, an economical embodiment uses a single cap to engage multiple
bosses 52, 60 that are arranged linearly and coaxially. The bosses 52, 60 are preferably
arranged so that both of them are covered by, and can engage the cap 54 of the workpiece
contact element 56 when it is engaged with the workpiece 16. The use of additional
devices to further secure the cap 54 and the bosses 52, 60 are contemplated, such
as a flange on the cap engaging a slot on the boss, or a pin inside the cap that
engages a bore through the boss. The most preferred arrangement includes two bosses
60 on the nosepiece 22 and at least one boss 52 on the shear block 40, shown in
FIGs. 1, 5, 7 and 8.