Note: Descriptions are shown in the official language in which they were submitted.
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FLEXIBLE SHAFT DRILL BIT WITH REMOVABLE CUTTING HEAD
Field of the Invention:
The present invention relates to wood-drilling bits
and, more particularly, to a flexible shaft drill bit with
removable cutting head.
BACKGROUND OF THE INVENTION
Self-feeding wood bits with relatively heavy cutting
heads are known in the art. Those bits have a pilot point
with threads which pull the bit into the wood. They perform
better than spade bits, because they cut faster and require
little axial force. With a heavier cutting head, it becomes
quite difficult and expensive to form the bit as a single
piece. Therefore, the tendency in the art had been to make
the bit in several pieces and then fasten them together by
various means. Often, the cutting head was welded or
otherwise joined to the shaft, and the piloting point was
inserted into a square or other non-circular hole and held
in place with a set screw.
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As might be expected, the piloting points tended to
work loose from the rest of the bit. Also, the cost of
welding pieces together was a substantial part of the cost
of manufacturing these bits.
A bit which does not require welding is shown in U.S.
Patent No. 2,593,823 issued to Wilson. That bit is intended
for relatively light duty. In the Wilson patent, the
cutting head of the bit is very short, which means that
there is little thread engagement between the shaft and the
cutting head, causing instability of the head relative to
the shaft. In that threaded arrangement, most of the forces
between the cutting head and the shaft are borne in a very
small area near the shoulder, tending to cause failure of
one or both parts at that point. Also, because the cutting
head is so short, there is instability between the cutting
head and the workpiece.
United States Patent No. 5,193,951, issued to Schimke
for WOOD-DRILLING BIT, and hereby incorporated by reference,
discloses a two-piece bit in which a threaded pilot point is
part of the shaft. The cutting head has an axial
through-bore which is threaded to receive the pilot point,
so the two parts are held together in threaded engagement.
The threaded joint between the shaft and cutting head is
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also glued together with a permanent glue to fill the spaces
between threads and reduce the opportunity for misalignment
between the head and shaft. The cutting head is therefore
not removable relative to the short shaft. An extended
bearing surface area or bearing neck is provided between the
cutting head and the shaft, in addition to the threaded
joint area, to improve alignment between the head and the
shaft and to spread the forces over a large bearing surface,
which greatly reduces the opportunity for shaft failure.
Two different materials are used for the head and
shaft, respectively, so that the head has optimum cutting
capabilities and the shaft has optimum strength for
transmitting torque and withstanding bending and shear
stresses. There is no need for welding the head itself,
thus reducing the cost of manufacture. Finally, pilot
points cannot work loose. The Schimke patent also
contemplates a conventionally short shaft (albeit longer
than the Wilson shaft, supra), the driving end of which is
adapted to fit into the chuck of a drill.
It has long been known, however, that workers are often
located at a relatively great distance from the surface to
be drilled. This occurs when obstructions are disposed
between the work surface and the worker, for example. It
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can also occur when drilling inside a hollow wall, the
dimensions of which do not permit a body or even a hand to
enter.
Once the drill bit or cutting head, itself, has been
used extensively or has been used to drill into hard
materials, it is not unusual for the head to be dulled.
Unfortunately, it can be rather expensive to replace the
entire assembly of drill bit and shaft when it is the
cutting head alone that must be replaced.
It would be advantageous, therefore, to provide a drill
bit attached to a long shaft.
It would also be advantageous to provide such a drill
bit and shaft with the capability to remove the worn cutting
head from the shaft.
It would further be advantageous to provide a cutting
head removably attached to a long, flexible shaft, the
composite article forming a drill bit.
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SUMMARY OF THE INVENTION
In accordance with the present invention, there is
provided a self-feeding, wood-boring bit. A two-piece bit
has a threaded pilot point as part of the short shaft. The
cutting head has an axial through-bore which is threaded to
receive the pilot point, so the two parts are held together
in threaded engagement. An extended bearing surface area or
bearing neck is also provided between the cutting head and
the short shaft, in addition to the threaded joint area.
This structure improves alignment between the head and the
shaft and spreads the forces over a large bearing surface,
which greatly reduces the opportunity for shaft failure.
Two different materials are used for the head and shaft,
respectively, so that the head has optimum cutting
capabilities and the shaft has optimum strength for
transmitting torque and withstanding bending and shear
stresses. A long, flexible shaft is welded to the driving
end of the drill bit shaft assembly, to provide for drilling
operations at a distance from the worker. The cutting head,
itself, can be unscrewed and detached from the long,
flexible shaft, so that it can be replaced with a new head,
when required.
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BRIEF DESCRIPTION OF THE DRAWINGS
A complete understanding of the present invention may
be obtained by reference to the accompanying drawings, when
considered in conjunction with the subsequent detailed
description, in which:
FIGURE 1 is a front view of the drill bit that forms
part of the present invention;
FIGURE 2 is a front sectional view of the drill bit of
FIGURE 1; and
FIGURE 3 is a side view of the drill bit and
conventional shaft attached to a long, flexible shaft, in
accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Generally speaking, the invention is a self-feeding,
wood-boring bit consisting of a cutting head removably
attached to a long, flexible shaft. The two-piece bit has a
threaded pilot point as part of the shaft. The cutting head
has an axial through-bore which is threaded to receive the
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pilot point, so the two parts are held together in threaded
engagement. An extended bearing surface area or bearing
neck is also provided between the cutting head and the
shaft, in addition to the threaded joint area. This
structure improves alignment between the head and the shaft
and spreads the forces over a large bearing surface, which
greatly reduces the opportunity for shaft failure. A long,
flexible shaft is welded to the driving end of the drill bit
shaft assembly, to provide for drilling operations at a
distance from the worker. The cutting head, itself, can be
unscrewed and detached from the long, flexible shaft, so
that it can be replaced with a new head, when required.
Referring now to FIGURES 1 and 2, the drill bit 10 that
forms a part of the present invention is made up of two
parts: a short, conventional shaft 12 and a cutting head
14. The short shaft 12 has an extended central portion 16
with a circular cross-section. At one end of the central
portion 16 is a driving end 18.
At the other end of the central portion 16 is a pilot
point 20 which is threaded with tapering male threads 22 in
the same way as a standard wood screw is threaded. Pilot
point 20 ends in a sharp pointed tip 42. There is a bearing
portion or bearing neck portion 23 on the shaft 12 between
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the central portion 16 and the threaded point 20. The
bearing portion 23 has a smaller diameter than does the
central portion 16. An upper shoulder portion 24 is
disposed between the central portion 16 and the bearing
portion 23. The upper shoulder portion 24 has a larger
diameter than does the largest diameter of the threaded male
end 20.
There is a slight reduction in diameter from the
bearing portion 23 of the shaft 12 to the threaded end
portion 20 forming a lower shoulder portion 25; and a
corresponding reduction in diameter from the mating bearing
portion 27 in the head 14 to the mating threaded portion 28
of the head 14. This is necessary in order for the threaded
portion 20 of the shaft 12 to readily pass through the
bearing portion 26 of the head 14 during assembly.
The cutting head 14 has an axial through-bore 26 which
has female threads in its lower portion 28 that are adapted
to receive the male threads 22 of the pilot point 20 in
threaded engagement. The upper sleeve portion 27 of the
through-bore is unthreaded and has a larger cross-sectional
diameter than does the lower portion 28, defining a medial
shoulder portion 29. The upper sleeve portion 27 is sized
to receive the unthreaded bearing neck portion 23, while the
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medial shoulder portion 29 is sized to receive the lower
shoulder portion 25 of the shaft 12 with a snug fit. This
sleeve portion 27 is preferably 5/8 inch long, but must be
at least 1/4 inch long. The total length of the threaded
pilot point 20 and the bearing portion 23 is longer than the
length of the cutting head 14 along the central axis so
that, when the cutting head 14 is threaded onto the pilot
point 20, the end of the pilot point 20 projects outwardly
beyond the cutting head 14. The top surface 30 of the
cutting head 14 abuts the upper shoulder portion 24, thereby
preventing the cutting head 14 from moving farther inwardly
on the shaft 12.
The large bearing surface area between the unthreaded
upper sleeve portion 27 of the cutting head 14 and the
unthreaded bearing portion 23 of the shaft 12 provides for
proper alignment of the head 14 with the shaft 12. This
large bearing surface area also causes bending and shear
forces on the shaft 12 to be greatly reduced, thereby
reducing the opportunity for failure of the shaft 12.
When the bit 10 is driven by a drill (not shown), the
force of the wood or other substrate (not shown) on the
cutting head 14 is in a direction which would further
tighten the cutting head 14 onto the shaft 12. Thus, there
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is no tendency for the cutting head 14 to work loose from
the shaft 12 during use.
The cutting head 14 has front and back surfaces 32, 33,
respectively, which terminate at the sides in edges 34. The
forwardmost portions of the edges 34 are the cutting points
40. Cutting edges 41 extend from the cutting points 40
radially inward to the bore 28.
The cutting head 14 has a rounded outer surface,
including trailing wings 36. The trailing wings 36 are
recessed radially inward from the cutting points 40 and
provide stability to the drill bit.
When drilling begins, the pointed tip 42 of the pilot
point 20 enters the wood or other substrate to keep the bit
10 centered on the substrate. The threads 22 on the pilot
point 20 begin to pull the bit 10 into the substrate. When
the cutting points 40 reach the substrate, they begin to cut
into the substrate. Then, the cutting edges 41 begin
cutting forward into the substrate, shaving the substrate
into small pieces which pass upwardly in front of the
respective face 32 or 33 and out the top of the hole. As
the bit rotates in a clockwise direction, the cutting force
of the bit on the substrate is exerted in a clockwise
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direction, and the opposing force from the substrate is
exerted in the opposite (counterclockwise) direction,
thereby causing the cutting head 14 to be tightened further
inward onto the pilot point 20 to tightly abut the shoulder
24.
In the preferred method of manufacture of the bit 10
(best seen in FIGURE 2), the shaft 12 is formed as one
piece, and the cutting head 14 is cast as one piece. Then
the faces 32, 33 are ground to sharpen the cutting edges 41.
In order to make the axial through-bore 26 in the cutting
head 14, first a hole is drilled through the cutting head 14
with the diameter the same as the minor diameter of the
threads 28. Then, the upper sleeve portion 27 is drilled to
a diameter larger than the major diameter of the threads 27.
The threads 27 are then tapped in the lower portion of the
cutting head 14. Threads 22 are also cut into the tapered
pilot point 20. The bit is then assembled simply by
threading the cutting head 14 onto the shaft 12 until it
abuts the shoulder 24.
Referring now also to FIGURE 3, connected to the
driving end 18 of the short, conventional shaft 12 is a
long, flexible shaft 44, on the order of four to six feet
long. Both the driving end 18 of shaft 12 and the proximal
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end of flexible shaft 44 are tapered. They abut at their
respective points, shown generally at reference numeral 45.
A welding process, such as metal inert gas (MIG) welding in
the preferred embodiment, is used to permanently connect
both of the shafts 12 and 44 together. Once the weld is
accomplished, the outer surface of the composite unit is
ground by a process well known to those skilled in the art,
in order to reduce the cross section at the weld itself, and
to provide a unitary, flexible shaft 12, 44 that is
connected to the removable cutting head 14. The distal end
of the long, flexible shaft 44 can also be configured with a
hexagonal cross-section, as shown, to facilitate its
insertion into and use with the chuck of a drill, not shown.
Since other modifications and changes varied to fit
particular operating requirements and environments will be
apparent to those skilled in the art, the invention is not
considered limited to the example chosen for purposes of
disclosure, and covers all changes and modifications which
do not constitute departures from the true spirit and scope
of this invention.
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