Cutting by use of rotating axially moving tool – Processes – Bit detachable
Reexamination Certificate
1999-06-18
2001-03-06
Wellington, A. L. (Department: 3722)
Cutting by use of rotating axially moving tool
Processes
Bit detachable
C408S128000, C408S137000, C408S141000
Reexamination Certificate
active
06196772
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to positive feed tools, such as right angle positive feed drills, and more particularly, to a method and apparatus for limiting the transmission of power along a drive train of such tools and for causing the spindle of such tools to automatically retract when torque on the spindle or in the drive train exceeds a predetermined value.
2. Description of the Related Art
Positive feed tools, such as positive feed drills, are conventionally known for drilling holes in workpieces formed of substances, such as steel, aluminum, titanium, and composites. Positive feed drills include a drill feed mechanism that feeds a drill bit into the workpiece.
FIG. 1
illustrates an example of a conventional positive feed drill, specifically a right angle positive feed drill
10
that is coupled to a cutter
12
. The positive feed drill
10
generally includes a spindle
28
that, in addition to rotating, advances a predetermined amount per revolution toward the workpiece to be drilled. Conventional applications for positive feed drills include, among other applications, drilling holes in various parts of aircraft.
The right angle positive feed drill
10
includes an air motor
14
. The air motor
14
is powered by a pressurized air source (not illustrated). As described below, the air motor
14
causes the spindle
28
to rotate. The spindle
28
is caused to rotate and feed by rotating the spindle drive gear
18
and spindle feed gear
20
with a differential feed gear
24
and differential drive gear
26
. The spindle feed gear
20
includes internal threads that are threaded on the external threads
27
extending along the length of the spindle
28
. Hence, when the spindle feed gear is rotated in relation to the spindle
28
, the spindle will feed through the spindle feed gear. External threads
27
of the spindle
28
illustrated in
FIG. 1
are left-handed threads. The spindle
28
also includes drive grooves
30
that extend along the length of the spindle
28
. The spindle drive gear
18
includes internal male splines (not illustrated in
FIG. 1
) that engage with the drive grooves
30
on the spindle
28
. Thus, when the spindle drive gear
18
is rotated, the spindle
28
also rotates.
When the air motor
14
is actuated, spindle drive gear
18
is caused to rotate, which will turn the spindle
28
due to the engagement of the internal male splines with the drive grooves
30
. In forward operation, or the drilling mode, the air motor
14
turns in a clockwise direction (as viewed from the rear of the tool
10
), which turns a motor spindle
16
. The series of gears
32
,
34
,
38
,
40
,
26
connect the motor spindle
16
with the spindle
28
. More specifically, rotation of the motor spindle
16
will rotate the pinion
32
, which in turn drives the gear
34
, which is pinned or keyed to a shaft
36
. The spur pinion
38
drives the idler gear
40
, which drives the differential drive gear
26
. In forward drill mode, the differential drive gear
26
is coupled to the differential feed gear
24
so that they turn in unison. The differential drive gear
26
is also engaged with the spindle drive gear
18
. Because the spindle drive gear
18
is engaged with the spindle
28
via the drive grooves
30
, the rotation of the differential drive gear
26
is transferred to the spindle
28
. However, the spindle
28
is permitted to move longitudinally through the spindle drive gear
18
because of the drive grooves
30
.
The spindle feed gear
20
, which is threaded on the spindle
28
, is driven by the differential feed gear
24
while in the forward position, as shown in FIG.
1
. The spindle feed gear
20
threads the spindle
28
through the spindle drive gear
18
and feeds it toward the workpiece. Because a differential exists between the spindle drive gear
18
and the spindle feed gear
20
, the spindle
28
is rotated and will advance toward the workpiece. The desired feed rate is obtained by the differential gear ratio between the spindle drive gear
18
and the spindle feed gear
20
. In sum, when the air motor
14
is actuated, the spindle drive gear
18
rotates, which turns the spindle
28
. When the spindle feed gear
20
is rotated faster than the spindle
28
, the spindle will feed, causing downward motion of the spindle. Conversely, when the spindle feed gear
20
rotates slower than the spindle
28
, the spindle
28
will retract upward.
The right angle positive feed drill
10
also includes a feed stop collar
42
and a feed engagement lever
44
. At the completion of the advancement of the spindle
28
, or at the completion of the drilling cycle, the feed stop collar
42
contacts the feed engagement lever
44
. This contact lifts the differential feed gear
24
away from the differential drive gear
26
and locks it so that it does not rotate. Because the differential feed gear
24
is locked and is engaged with the spindle feed gear
20
, the spindle feed gear
20
is also locked in a stationary position such that it does not rotate. With the spindle
28
continuing to rotate in a forward direction via rotation of the spindle drive gear
18
, and the spindle feed gear
20
held stationary, the spindle
28
will retract.
As illustrated in
FIG. 1
, the cutter
12
includes a drill bit
45
for penetrating the surface of the workpiece to be drilled. A tool nose
46
surrounds the cutter
12
, which attaches the tool to a drilling fixture offset from the workpiece to be drilled. The drill bit
45
is a tool that bores cylindrical holes.
During operation of the conventional tool illustrated in
FIG. 1
, it is possible that the spindle
28
will seize during operation of the air motor
14
. This could occur for a variety of reasons.
For example, during drilling with the drill bit
45
, the metallic chips created during the cutting operation may stick to the wall of the bored cylindrical hole and gall. This will cause the cutting chips to stick to the cutting edge of the drill bit
45
, as well as the wall of the drilled hole. When this occurs, the drill bit
45
may seize in the drilled hole, which naturally causes the spindle
28
to seize as well. This may occur because the drill bit
45
does not have enough flutes for the release of the cutting chips.
Additionally, when the drill bit
45
breaks through a workpiece, it occasionally grabs an edge of the hole and seizes. Furthermore, because the tool nose
46
surrounds the drill bit
45
, chips from the drilling operation tend to pack in the tool nose
46
to such an extent that the drill bit
45
seizes.
It is particularly problematic when the drill bit
45
or the spindle
28
of the right angle positive feed drill
10
seizes. During operation of the drill
10
, the air motor
14
is supplying power through the gear train to the spindle
28
. When the spindle
28
seizes while the motor
14
is attempting to drive the spindle
28
, a high torque situation inevitably results in the positive feed drill
10
, which will cause the air motor
14
to seize, or damage one or more of the gears, bearings, and shafts in the drill
10
. For example, if the spindle
28
seizes during normal drilling with the drill bit
45
, the spindle
28
and/or any one of the pinions and gears may strip or completely break and damage the tool
10
.
One conventional right angle positive feed drill
10
similar to that illustrated in
FIG. 1
has the ability to rapidly advance the drill bit
45
from a retracted position to a position near the workpiece. This feature is not used to drill holes, but to merely cause the drill bit
45
to advance quickly toward the workpiece. This rapid advance feature is disclosed in both U.S. Pat. No. 4,799,833 and U.S. Pat. No. 4,591,299 and is achieved as follows.
With the spindle
28
retracted upwardly, the air motor
44
is reversed. With the differential feed gear
24
located in the upward position where it is locked so that it does not engage with the differential drive gear
26
, the spindle feed gear
20
is also stoppe
Jensen Sam C.
Thames Bruce A.
Carter Monica S.
Coats & Bennett PLLC
Cooper Technologies Company
Wellington A. L.
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