Adjustable boring bar

An adjustable head arrangement for the shank of a boring bar is disclosed having an easily replaceable tool unit and also having an axially adjustable abutment means on the tool unit so that the cutting point of the tool unit is firmly supported and held during cutting operations but is adjustable with respect to the shank of the boring bar in between different cutting operations.

BACKGROUND OF THE INVENTION 
In numerically controlled cutting machines used today, machines are usually 
programmed by tape to perform certain specified operations upon a 
workpiece in a certain preprogrammed sequence. Due to the repetitive 
nature of the work, a reference dimension is programmed into the machine 
on the tape and this reference dimension is usually a certain given 
distance from a datum point on the machine to the actual cutting point of 
a machine tool. 
This cutting point may rest on any one of several differently configured 
cutting inserts depending upon the cutting operation to be performed. 
However, it is the case that the dimension of the cutting point from the 
datum plane of the cutting machine must always be maintained to a very 
precise degree in order to hold the workpiece within the required 
tolerances of manufacture. 
Since most numerically controlled cutting machines use the replaceable type 
cutting inserts of varying configurations, there is a difficulty in 
maintaining the precise dimension mentioned above when interchanging 
cutting insert configurations or replacing cutting inserts when they have 
become worn. 
One of the ways in which this difference in dimensions may be corrected is 
to reprogram the tape in the numerical controlled machine when the 
reference dimension to the cutting point changes due to a change of the 
actual cutting tool itself. 
A preferable way to compensate for the change that may be introduced with a 
new cutting tool is to have a structure that allows adjustment of the 
reference cutting point with respect to the shank of the cutting tool that 
is supported by the numerical controlled type machine. 
It is an object of the present invention to provide an adjustable tool unit 
in a boring bar head so that, as tool units are interchanged in the head, 
the cutting point may be readjusted to agree with the dimension programmed 
on the tape of the numerical controlled machine. 
It is a further object of the present invention to provide a tool unit 
that, while being adjustable, is also firmly supported and held during the 
actual cutting operations. 
It is still a further object of the present invention to provide a 
structure that will accomplish the above objects and yet may be provided 
in some of the smaller boring bar shanks that are required to do machining 
in a very small bore of a workpiece. 
BRIEF SUMMARY OF THE INVENTION 
According to the present invention, a perforation is formed in the face of 
a boring bar shank in a tool unit which is telescopically and slidingly 
engaged in the perforation. The tool unit has one end forming a cutting 
tool and an opposing end which forms a close fit with the perforation in 
the shank. 
Threads are formed on the tool unit between the cutting tool end and the 
opposing end and a threaded ring-like member is mounted on the threaded 
portion of the tool unit and abuts the face portion of the boring bar 
shank. The tool unit is positioned such that the cutting tool end 
overhangs and protrudes from the face of the shank so as to present a 
cutting point for machining operations. 
The threaded ring-like member which abuts the face portion of the shank 
when rotated in one direction or the other will advance the tool unit 
outwardly on the boring bar shank or allow the tool unit to be advanced 
inwardly of the boring bar shank. A recess is formed in the opposing end 
of the tool unit and a clamp means, preferably in the form of a dog-point 
set screw, is located in the body of the boring bar shank in a region 
which is associated with the recess of the opposing end of the cutting 
tool unit. 
The clamp means is operable so as to advance downwardly into the groove of 
the tool unit and engage the groove such that, first of all, the tool unit 
is held in nonrotative relationship with the perforation of the boring bar 
shank and, further, the opposing end is forced into abutment with a 
portion of the walls of the perforation. 
The threaded ring-like member on an oppositely facing surface from its 
abutment surface with the shank has equally spaced machine markings 
thereon which are calibrated in coordination with the type of threads 
between the ring member and the tool unit such that, when the machine 
markings are rotated past a given fixed machine marking, each marking will 
represent an axial advance of the cutting point on the tool unit or will 
represent an axial recession into the boring bar of the cutting point on 
the tool unit.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings somewhat more in detail, shown in FIG. 1 is an 
outer end of a boring bar shank 10 which, on its inner end, is connected 
and supported to a cutting machine, not shown. A perforation 12 is formed 
in the outer end transverse to the axial direction of the boring shank 10. 
This perforation 12 is formed through a face portion 14 which has been 
formed also in the outer end of the boring shank 10 and tool unit 16 is 
inserted in the perforation 12. 
Tool unit 16 is preferably cylindrical in nature and has opposing ends with 
one end 18 forming a cutting tool and the other end 20 forming a close 
sliding fit with the configuration of perforation 12. An axially 
adjustable abutment ring 12 is mounted on the tool unit 16 between 
opposing ends 18 and 20, preferably by interengaging thread means between 
tool unit 16 and the ring 22. 
Ring 22 has a face 24 that abuts against face portion 14 of boring bar 
shank 10. Wrench flats 26 are placed on protruding portion 28 of ring 
member 22 in order that the ring member may be rotated. Machine markings 
30 are shown on ring member 22 and extend completely around the periphery 
of the dial portion 32 of ring member 22. 
Referring now to FIG. 2, what is shown therein is the outer end of the 
boring shank 10 shown with perforation 12 with the cutting point end 18 of 
the tool unit 16 overhanging shank 10. The ring-like member 22 is 
threadedly mounted on the tool unit 16 and the face 24 is in abutment with 
the face portion 14. A clamping means 34, which is preferably a dog-point 
set screw, is located in the body of boring bar shank 10 and extends 
downwardly into slot 36 which is formed in the opposing end 20 of tool 
unit 16. 
The clamping means 34 is operable upon rotation to advance either radially 
inwardly on the boring bar or radially outwardly of the boring bar 10 so 
as to engage and disengage with slot 36. When clamp means 34 is advanced 
radially outwardly, it will be disengaged with slot 36 and tool unit 16 
along with ring member 22 may be completely removed from the outer end of 
the boring bar 10 and replaced with a new and different tool unit 16, 
possibly having a different configuration from what is shown. 
The tool unit 16 is placed in the perforation 12 and abutment is achieved 
between face 24 of ring member 22 and the face portion 14 of boring bar 
10. Rotation of the ring-like member will positively advance cutting tool 
portion 18 from the boring bar 10 or allow the cutting tool 18 to be 
actually advanced inwardly of perforation 12 to a desired reference 
dimension. 
When the desired reference dimension is achieved, clamp member 34 is 
advanced radially inwardly of the boring bar shank 10 such that it engages 
the recess 36 and firmly holds the opposing end 20 of tool unit 16 between 
the clamp member 34 and a wall 38 of perforation 12. The clamp member 34 
also by engaging the recess 36 will hold the tool unit 16 in a 
nonrotatable relationship of the boring bar shank 10. 
Referring now to FIG. 3, what is shown therein is, first of all, the 
cutting point 40 of the cutting tool 18 and the ring member 22 is mounted 
on the tool unit 16 and has machine markings 30 completely around the dial 
portion 32. The machine markings 30 are rotated past a fixed machine 
marking 42 which is permanently marked on a convenient surface of boring 
bar 10. 
The machine markings 30 are calibrated with the specific pitch of the 
threads that interengage ring member 22 with the tool unit 16 so that 
rotation of machine markings past the stationary machine marking 42 will 
provide a known axial movement on cutting point 40 in relation to the 
boring bar shank 10. 
Referring to FIG. 4, what is shown therein is tool unit 16 opposing unit 20 
which has a close sliding fit with the perforation 12 in the boring bar 
10. The clamp member 34 which is again preferably a dog-point set screw is 
shown engaged with the recess 36 formed in opposing end 20 of tool unit 
16. The clamp member is shown operated radially inwardly into a fully 
clamped position such that conical portion 44 of clamp member 34 engages 
sloping walls 46 and 48 of the recess 36. 
The clamping force from clamp member 34 is transmitted to the walls 46 and 
48 of recess 36 so as to firmly hold the opposing end 20 clamped between 
the clamp member 34 and the walls of the perforation 12. 
The lower end portion 50 of clamp member 34 engages parallel walls 52 of 
recess 36 with a very close fit so that the opposing end 20 is held in a 
nonrotatable relationship with the boring bar 10. Preferably, the lower 
end 50 of clamp member 34 is dimensioned so as not to contact the bottom 
walls of recess 36. 
Other advantages of having an adjustable cutting point according to the 
structure herein disclosed are that the adjustable cutting point provides 
a means of adjustment for machining various diameters on a workpiece. By 
simply adjusting the cutting point, the machine operator may change the 
diameter of the bore of a workpiece which is being machined or he may 
increase or decrease the outside diameter of a round bar which is being 
machined. This adjustment, of course, is also available when the tool 
itself is rotating and the workpiece is held stationary. 
Modifications may be made within the scope of the appended claims.