Boring tool having a detachable cutting blade

A boring tool having a detachable cutting blade, and, more particularly a gun drill for boring holes to extremely exacting tolerances.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a boring tool having a detachable cutting 
blade, and, more particularly the present invention relates to a gun drill 
for boring holes to extremely exacting tolerances. 
2. Description of the Prior Art 
A conventional gun drill comprises an elongate shank having a cylindrical 
cutting head on the end thereof. The head has a front end and a 
cylindrically shaped outer surface and includes a V-shaped groove for 
removing chips extending longitudinally rearwardly from the front of the 
head and is open radially to the outer surface thereof. The cutting head 
of the gun drill has a cutting blade brazed into a recess in one of the 
surfaces of the V-shaped groove. The cutting blade is made of carbide or 
some other hard material which is suitable for cutting steel. An example 
of a gun drill having a cutting head of the type described above is 
disclosed in U.S. Pat. No. 3,153,356. 
In the manufacture of a conventional gun drill, the carbide cutting blade 
is brazed into a recess in a surface of the V-shaped chip groove. During 
brazing, the blade is heated to an elevated temperature and then cooled, 
which is believed to result in deterioration of the useful life of the 
blade, that is, the blade material softens and the blade dulls more 
quickly during use. Further, as the drill is used, the cutting blade 
becomes worn and requires resharpening. After the cutting blade is 
sharpened several times, it becomes worn to the point wherein the entire 
gun drill must be discarded or returned to the manufacturer for retipping 
with a new cutting head. Other boring tools having a detachable cutting 
blade or a detachable tip are disclosed in the following patents: 
______________________________________ 
U.S. Pat. No. Inventor 
______________________________________ 
339,544 S. P. Graham 
492,733 H. Meister 
752,863 O. P. Roberge 
923,257 O. Fredrickson 
1,929,801 F. E. Berry 
2,310,992 J. R. Proksa 
2,451,922 A. J. Cox 
3,135,522 W. Bellz 
3,289,273 G. P. Artaud 
3,304,816 L. C. Galorneau 
3,618,962 J. R. Cox et al 
3,859,700 Richard R. Jilbert 
4,060,335 Holloway et al 
4,146,240 Mogens B. Nielsen 
4,232,985 Mogens B. Nielsen 
French Pat. No. 1,274,017 
M. Kleine 
______________________________________ 
It is an object of the present invention to provide a boring tool, also 
referred to as a gun drill, having a detachable cutting blade. More 
particularly, it is an object of the present invention to provide a 
cutting blade that may be removed from the head of the boring tool, 
sharpened and then replaced, or replaced with another blade. It is a 
further object of the present invention to provide a blade that is capable 
of being moved forwardly so that the blade may be repeatedly sharpened and 
then advanced thereby extending its useful life. 
SUMMARY OF THE INVENTION 
The boring tool in accordance with the present invention includes a 
detachable cutting blade which may be removed, sharpened and then replaced 
or replaced with another blade. The term "boring tool" as used herein 
means a tool capable of forming an elongate cylindrical hole in a solid or 
enlonging, or boring out, an existing hole, and is meant to include all 
gun drills. A boring tool in accordance with the invention includes a 
shank having a cylindrical head. The head includes a front end and a 
cylindrically shaped outer surface. A groove for removing chips extends 
longitudinally rearwardly from the front end and is open radially to the 
outer surface of the head. The groove includes a recess for receiving a 
detachable cutting blade. The recess has a floor extending longitudinally 
rearwardly from the front end to a stop surface at the rear thereof. The 
stop surface prevents rearward movement of the blade when it is positioned 
in the recess. The blade includes an interior surface which seats on the 
recess floor so that the cutting edge of the blade protrudes from the 
front end of the shank to enable the boring tool to cut a hole. 
The interior surface of the blade and the recess floor includes a mechanism 
for retaining a seated blade against radial outward movement. In a 
preferred form of the invention, the mechanism for retaining the blade 
comprises at least one elongate protrusion extending longitudinally along 
at least a portion of the recess floor and the interior surface of the 
blade includes an elongate slot for receiving the protrusion. The 
protrusion is moveable longitudinally in the slot to provide for 
advancement of the cutting blade thereby enabling the blade to be removed 
from the recess, sharpened and then replaced in a position advanced with 
respect to its position prior to sharpening. In order to prevent the blade 
from moving rearwardly after it has been advanced, a shim may be placed in 
the recess adjacent the stop surface to account for the portion of the 
blade worn off during sharpening. 
The boring tool includes a mechanism for releasably securing the blade 
against transverse movement out of the recess. In accordance with a 
preferred aspect of the invention, the securing mechanism comprises a 
plate positioned adjacent the blade outer surface, the plate being held in 
place by a releasable fastner such as a screw fastner. The plate includes 
an aperture for alignment with an aperture in the blade, which in turn is 
aligned with an aperture located in the floor of the recess. The screw 
fastner holds the plate adjacent to the blade and has its end portion 
threaded to engage threads in the aperture in the recess floor. 
A boring tool in accordance with the present invention is particularly 
advantageous in that the blade is detachable to provide for sharpening and 
then replacement of the sharpened blade or removal of the blade and 
replacement with another blade. The boring tool of the present invention 
avoids the time consuming task of brazing the cutting blade into the 
recess and thereby avoids blade deterioration due to heating and cooling. 
Additional advantages of a boring tool in accordance with the present 
invention will be apparent from the following detailed description of the 
invention with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1 thru 4, a boring tool in accordance with the present 
invention comprises a cylindrical head 10 having a front end 12 and a 
cylindrically shaped outer surface 14. The head has been broken away from 
the remainder of the shank to simplify the drawings. The head includes a 
groove 16 for removing chips that are cut away during the boring 
operation. The groove 16 extends longitudinally rearwardly from the front 
end 12 and is open radially to outer surface 14 of the head 12. The groove 
preferably has a V-shape formed by two surfaces 18 and 20 which intersect 
at the axis 22 of the cylindrical shank. The angle, of intersection 
between surfaces 18 and 20 is approximately 120 degrees (see FIG. 1). 
As the boring tool is turned in a hole, the outer surface 14 may tend to 
wear. In order to prevent or reduce this wear, the head includes at least 
one and preferably two longitudinal slots 24 for receiving abrasion 
resistant pads 26, which are typically made from carbide and are brazed 
into the slots. An oil supply passage 28 extends the length of the shank 
and its head 10 to the front surface 12 and provides for supply of oil 
during a boring or drilling operation. 
Surface 18 of the groove 16 includes a recess 30 for receiving a detachable 
cutting blade 31. The recess 30 has a floor 34 that extends longitudinally 
rearwardly from the front end 12 to a stop surface 36. Stop surface 36 
prevents rearward movement of the blade 31 when it is positioned in the 
recess. The recess 30 also extends from the head axis 22 radially 
outwardly to the outer surface 14 of the head 10. 
Referring in particular to FIGS. 1 and 5, the blade 31, which has a 
generally rectangular cross-sectional shape, includes an interior surface 
38 for seating on the recess floor 34. The blade 31 also includes a 
cutting edge 40 which protrudes from the front end 12 of the head 10 when 
the blade is seated in its recess. The cutting edge 40 preferably has a 
sharpened point 42 that is the forwardmost point of the boring tool. The 
cutting edge 40, as best shown in FIG. 4, extends the complete radial 
distance between the tool axis 22 and the outer surface 14 of the head to 
thereby provide a blade sweep of a circular area as the shank is rotated. 
The interior surface 38 of the blade 31 and the floor 34 of the recess 
include a mechanism for retaining the seated blade against radial outward 
movement when the shank and its head 10 are rotated. In accordance with a 
preferred aspect of the invention, this retaining mechanism comprises at 
least one and preferably two elongate protrusions 44 extending 
longitudinally along at least a portion of the recess floor 34. The 
interior surface 38 of the blade includes at least one and preferably two 
elongate slots 46 for receiving and mating with respect to the protrusions 
44. The elongate protrusions 44 and slots 46 preferably have mating 
V-shapes and extend the entire length of the recess floor 34 and blade 
surface 38. The V-shape of the protrusions 44 and the slots 46 are given 
by way of example only and are preferred because it is a simple machining 
operation to cut one or more V-shaped slots in a hard carbide surface. 
However, it should be understood that the slots and protrusions may have a 
semi-cylindrical, rectangular cross-sectional or other shapes. As will be 
described hereinafter with respect to FIGS. 6 and 7, the slots and the 
protrusions enable the blade 31 to be advanced forwardly after it is 
sharpened. 
Referring in particular to FIGS. 1 and 5 as well as the other figures, a 
mechanism 51 for releasably securing the blade against transverse movement 
out of the recess 30 will now be described in detail. The securing 
mechanism comprises a plate 52 for positioning adjacent to the outer 
surface 50 of the blade 31. The plate 52 is held in place by a releasable 
screw fastner 54 and includes an aperture 56 for receiving the shaft 58 of 
screw fastner 54. The blade 31 includes an aperture 60 sized to receive 
the shaft 58 of screw fastner 54. A threaded aperture 62 in the recess 
floor 34 is provided for receiving the threaded shaft 58 of screw fastner 
54. As shown in FIGS. 1, 2 and 5, the blade 31 is positioned in recess 30 
and the apertures 56, 60 and 62 are aligned to receive screw fastner 54. 
The rear end portion 53 of the plate 52 includes a mechanism for retaining 
the plate 52 against longitudinal and radial movement with respect to the 
groove surface 18 when the fastner 54 is tightened by rotating it. The 
plate retaining means comprises a pin 64 extending from groove surface 18 
for being journaled in a bearing hole 66 in the securement plate 52 (see 
FIG. 1). When the screw fastner 54 is turned in a clockwise direction as 
shown by arrow 68 (FIGS. 1 & 2) the rear end portion 53 of plate 52 would 
normally swing in the direction shown by arrow 70 in FIG. 2. The 
interlocking pin and bearing hole prevent movement of the plate 52 in the 
direction shown by arrow 70. 
The manner by which the blade may be removed, sharpened and then replaced 
will now be described. Referring in particular to FIGS. 1, 6 and 7, when 
the blade 31 becomes dull after a period of use, screw fastner 54 is 
unscrewed and the plate 31 is either lifted upwardly as shown in FIG. 1 
wherein pin 64 disengages from bearing hole 66 or, alternatively, the 
plate 31 can be pivoted about pin 64 to a position so that the blade may 
be removed from the recess 30. When the blade 31 is sharpened, part of the 
front portion of the blade 31 is ground away and the length of the blade 
is shortened. To account for this shortening of the blade during 
sharpening, one or more shims such as that shown in FIG. 6 may be 
provided. Shim 72 as shown in FIG. 6 has a width 74 that accounts for the 
portion of the blade ground away during sharpening. It should be 
understood that the thickness of the shim shown in FIGS. 6 and 7 is 
slightly exaggerated to better illustrate its function. As shown in FIG. 6 
the shim may include a pair of slots 76 which are sized to seat on 
protrusions 44. It should be understood that slots 76 are optional and 
that the shim may simply be a thin sheet of noncompressible material such 
as sheet metal. Referring to FIG. 7, the shim 72 has been positioned in 
the recess adjacent stop surface 76 so that the front surface 80 of the 
shim becomes the new stop surface. As shown in FIGS. 1 and 7 the aperture 
60 of blade 31 is elongated to enable the blade to be advanced but to 
still be secured in the recess by the screw fastener 54. After the blade 
has been positioned in its recess, the securement plate 52 is fastened in 
place and the boring tool is ready once again for use. As shown in FIG. 7, 
the blade 31 has been advanced a distance as shown by reference character 
82. The end portion of the blade shown in phantom has been ground away 
during sharpening so that the ground cutting edge 40 is in the proper 
position with respect to the front surface 12 of the tool. 
As can well be appreciated, the boring tool of the present invention 
enables the cutting blade 31 to be removed and periodically sharpened 
thereby prolonging the useful life of the boring tool. Furthermore, use of 
a detachable blade avoids brazing of the carbide blade which would 
ordinarily degrade its hardness properties thereby decreasing its useful 
life. Furthermore, once the blade has been sharpened several times and is 
no longer useful, the blade may be removed and replaced with a new carbide 
blade thereby minimizing the down time of the tool. Furthermore, the blade 
change may occur while the boring tool is in its turning socket thereby 
minimizing the downtime required when a conventional boring tool becomes 
dull and removal of the entire tool is necessary. 
It should be understood that although specific embodiments of the invention 
have been described herein in detail, such description is for purposes of 
illustration only and modifications may be made thereto by those skilled 
in the art within the scope of the invention.