Triple corner boring bar

A boring bar having a body with standard shank portion at one end and a fluted, adjustable portion at the other end thereof which rigidly supports two standard triangular carbide tips. The tips are adjustable simultaneously to the desired size by means of an accurately shaped and angled adjusting plug together with accurate angles formed in the fluted end of the bar itself.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to devices for boring accurate holes in 
metal and utilizes a fluted boring bar having two standard triangular 
carbide tips with a unique adjustment structure for changing the position 
of the tips in order to change the size of the hole to be bored. 
2. Description of the Prior Art 
Known prior milling and cutting devices use specially shaped and formed 
cutting tips and edges which must be provided especially for the 
particular device. This limits to some extent the use of the device and 
certainly increases the cost thereof. Also in many areas of the country a 
supply of replacement cutters and tips is not always readily available. 
Another problem with known boring and cutting tools of the rotary type is 
that their adjustments are rather rough, and subject to variation under 
the stress and strain of the cutting and boring operation. Also in many of 
these devices the adjustments tend to change much more than desired during 
use. 
Another common problem with known devices is that their cutting tips are 
not fixed against both radial and axial movements in a positive, secure 
manner. This causes a change in size of the hole being bored due to the 
variation in adjustment rather than through normal wear and tear of said 
tips. 
Another problem with known tools is that since the cutting tips are 
specially sized and fitted for the specific tool, the tips are relatively 
expensive and not readily available which necessitates the re-working of 
the tips after they become worn rather than simply throwing them away. 
Tips which are inexpensive and of the throw-away type are much to be 
preferred. 
Known prior art patents which may be pertinent to this invention are as 
follows: 
J.t. bennett; 3,125,799, Mar. 24, 1964. 
W.j. greenleaf; 3,205,559, Sept. 14, 1965. 
C.e. grueninger; 3,217,385, Nov. 16, 1965. 
None of these known prior art devices offer the new and unique features of 
the invention disclosed herein. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a boring bar which may be 
made available in a range of sizes and with each bar being capable of a 
limited range of adjustment within its particular size. 
Another object of this invention is to provide a boring bar having a 
standard shank and a fluted end provided with two standard triangular 
carbide tips which are adjustable and replaceable. 
A further object of this invention is to provide a boring bar utilizing 
readily obtainable triangular carbide tips which are adjustable and which 
after becoming worn can be discarded and replaced with new tips. The cost 
of the standard tips is so low that it is better to throw them away and 
replace them with new ones than to re-work them. 
A still further object of this invention is to provide an adjustable boring 
bar which has an accurately formed angle in each of the fluted ends of the 
bar and an accurately angles adjustment plug for providing an accurately 
sized triangular area for supporting and receiving triangular shaped 
carbide tips. 
An important feature of the boring bar of this invention is in the fact 
that the cutting edges are provided by two triangular shaped carbide tips 
of standard construction. These tips are readily available as a standard 
item from many manufacturers of carbide cutting devices. 
Another important feature of this invention is that the two fluted sections 
at one end of the boring bar have accurately angled recesses therein for 
receiving the carbide tips and positively holding same at a desired 
cutting angle. Another important component of this device is the tapered 
adjusting plug used therewith which also has an accurately formed 
triangular tip engaging surface for complementing the angled surface of 
the fluted ends to securely and positively maintain the carbide tips at 
the proper cutting angle. 
These together with other objects and advantages which will become 
subsequently apparent reside in the details of construction and operation 
as more fully hereinafter described and claimed, reference being had to 
the accompanying drawings forming a part thereof, wherein like numerals 
refer to like parts throughout.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 of the drawings, reference numeral 10 indicates the 
boring bar of this invention. The boring bar has a standard shank portion 
12 which is conventional and well known in the field. The reduced end 14 
of the bar has fluted ends 16 and 18 provided thereon. 
The component parts of the boring bar are best seen in the exploded view of 
FIG. 4. The end segments 16 and 18 have conical recesses 15 appropriately 
formed therein. The member 16 has additional recesses 17 provided near the 
end thereof with an aperture 19 extending from said recesses through the 
member to the slot 13. The member 18 is provided with holes directly 
aligned with the holes 19 in member 16 with said holes being tapped with 
screw threads for receiving the locking screws 20. The locking screws 20 
have threaded portions 22 and knurled heads 24 with said heads each being 
provided with an Allen wrench receiving socket 26. These enlarged head 
type screws 20 freely pass through the apertures 19 of the member 16 and 
are then screwed into the threaded apertures 28 in the member 18. By 
tightening the screws 20 until the head portions 24 engage the bottom 
portion of the recesses 17 the two fluted members 16 and 18 may be drawn 
together by said screws since the slot 13 allows a slight amount of 
bending and flexing of the steel members 16 and 18. 
A very important feature of this invention will now be described. The 
triangular shaped carbide cutting tips used with this invention are of 
standard construction and are readily available from manufacturers of 
carbide cutting elements. They come in various sizes and have varying 
degrees of corner radiuses. They generally are perfectly triangular which 
of course means that each corner angle is of 60.degree. . These tips 30 
also have side edges 32 which make a slight tapering angle relative to the 
flat front and back surfaces of said tips. This angle is approximately 11 
degrees and is standard as supplied by the tip manufacturers. Each of the 
outer ends of members 16 and 18 have provided, opposite to each other, 
recessed portions 33 having an angular adjusting surface 34 at the bottom 
thereof. The angular surfaces 34 are extremely important to this device 
and looking at FIG. 3 can be seen as being of 32.degree. from an axis 
perpendicular to the centerline of the boring bar. In addition to this 
32.degree. angle just described the face of each surface 34 also is 
precision cut to make an angle of approximately 11.degree. from an axis 
passing through the vertical, as viewed in FIG. 3, to correspond with the 
11 degree taper of the side edges 32 of the carbide tips 30. Thus it can 
be seen that the side of the carbide tip which engages the surface 34 of 
each of the fluted members 16 and 18 makes a solid and complete engagement 
along the entire surface thereof. This is very important to the 
maintaining of proper adjustment of said tips while the boring bar is 
being used. 
The other important component of this device is the tapered adjusting plug 
40. This plug has a specially tapered conical surface 42 and a hub portion 
44. The hub portion 44 smoothly fits into a hole 46 drilled at the 
centerline of the boring bar. A suitably tapped hole 48 is provided at the 
bottom of hole 46 and within the portion 14 of the bar, as best seen in 
FIG. 3. An adjusting bolt, much larger, but similar in configuration to 
the adjusting lock head-type screws 20 already described, is provided for 
fastening the adjusting plug 40 to the end of the tool. This adjusting 
bolt is provided with threaded portion 52 for engagement with the threaded 
hole 48 in the body of the tool and has a shank portion supporting an 
enlarged head 54 with an Allen wrench adjusting socket 56 therein. The 
enlarged head 54 will engage with the recessed seat 58 within the 
adjusting plug 40. As seen in FIG. 3, the head 54 will apply force to the 
adjusting plug 40 as the adjusting bolt 50 is screwed into the socket 48. 
The conical surface 42 (FIG. 3) is accurately machined to form an angle of 
28.degree. to a plane perpendicular to the centerline 70 of the boring 
tool. Thus this surface 42 at 28.degree. complements the surfaces 34 on 
the ends of segments 16 and 18 of 32.degree. to form an angle therebetween 
of 60.degree. . This exactly complements the 60.degree. angle of the 
tungsten carbide cutting tips. As can be visualized by looking at FIG. 3, 
if the screw 50 is unscrewed to permit the adjusting plug 40 to move to 
the left, the angle between surface 42 and surfaces 34 will be maintained 
at 60.degree. but the size of the area between said surfaces will be 
increased and will permit the two triangular shaped tungsten carbide tips 
30 to move inwardly toward the centerline of the tool. This will 
effectively reduce the cutting area of the tool. But while the cutting 
area of the tool is decreased none of the strength, rigidity or support 
for the carbide tips is lost. The tips are always maintained at the proper 
cutting angle with only the outer circumference of the tips being changed. 
This is a very, very important feature of this new and unique invention. 
Obviously, once the proper circumferential size is obtained, locking 
screws 20 are tightened to draw the segments 16 and 18 together and to 
firmly lock the tips 30 between same. An aperture 60 appropriately 
provided with screw threads is also provided in the well known manner. 
From the above description it can readily be seen how the boring bar of 
this invention provides a strong, positive supporting structure for the 
easily replaceable triangular shaped tungsten carbide cutting tips. These 
tips may be quickly and easily replaced upon becoming worn at low cost for 
either the tips or for the labor required to replace same. The cutting 
accuracy of the boring bar of this invention is extremely high because of 
the tips once firmly locked into place do not change adjustment through 
ordinary usage thereof. 
The foregoing is considered as illustrative only of the principles of the 
invention. Further, since numerous modifications and changes will readily 
occur to those skilled in the art, it is not desired to limit the 
invention to the exact construction and operation shown and described, and 
accordingly all suitable modifications and equivalents may be resorted to, 
falling within the scope of the invention.