Bore measurement apparatus and method

A bore measurement apparatus and method is provided for measuring with a single apparatus the inner diameter of a bore and the outer diameter of a cutting tool mounted on a boring bar. The apparatus comprises a set of clamping jaws secured to an elongate bar having a magnetic graduated strip positioned thereon, an indicating head slidably mounted on the elongate bar, and a measurement arm having a stylus, the measurement arm slidably mounted on the indicating head for movement between an inner measurement position wherein the stylus contacts the inner surface of a bore and an outer measurement position wherein the stylus contacts the upper surface of a cutting tool.

BACKGROUND OF THE INVENTION 
This invention relates to a bore measurement apparatus and method and, more 
particularly, to a bore measurement apparatus and method for measuring 
with a single measurement apparatus the inner diameter of a bore and the 
height of a cutting tool mounted on a boring bar, without adjusting the 
apparatus. 
The inner diameter of a bore typically is measured with calipers which are 
placed within the bore and then extended outwardly to measure the bore's 
inner diameter. To place the calipers within the bore, a boring bar for 
mounting a cutting tool thereon should be removed from the bore. After 
measuring the inner diameter, the boring bar must be remounted within the 
bore and the cutting tool adjusted thereon prior to beginning the next 
cutting iteration. Removal of the boring bar is also generally required 
for measurement of the inner diameter with a micrometer. Repeated removal 
and remounting of the boring bar in the bore for each iteration of the 
cutting process is time consuming and may lead to mispositioning of the 
apparatus and inaccurate cutting of the bore's inner surface. Moreover, 
the use of calipers or a micrometer to measure the inner diameter of a 
bore may lead to inaccurate measurements because an operator must visually 
read the diameter from the device. 
The height of a cutting tool mounted on a boring bar typically is measured 
with calipers by placing one caliper arm on the upper edge of the cutting 
tool and one arm on the bottom of the boring bar directly opposite from 
the cutting tool. The operator then subtracts the diameter of the boring 
bar from the measurement to determine the cutting tool height. The use of 
calipers to measure the height of a cutting tool, or the diameter of a 
bore that would be cut by the cutting tool, may lead to inaccurate 
measurements because the operator must visually read the measurement from 
the device. This disadvantage is also present when measuring the outer 
diameter of the cutting tool with a micrometer. In addition, the elongate 
caliper arms or the micrometer measurement screw, in certain situations, 
may not fit within the bore to measure the inner diameter or may not fit 
around the boring bar and the cutting tool to measure the outer diameter. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a bore measurement apparatus and method 
is provided for measuring the inner diameter of a bore and the height of a 
cutting tool mounted on a boring bar without calibration of the apparatus 
between the two different types of measurements. The apparatus comprises a 
set of clamping jaws secured to an elongate bar having a magnetic 
graduated strip positioned thereon, an indicating head slidably mounted on 
the elongate bar, and a measurement arm having a stylus, the measurement 
arm being slidably mounted on the indicating head for movement of the 
stylus between inner and outer measurement positions. 
Accordingly, it is an object of the present invention to provide an 
improved bore measurement apparatus and method for measuring the inner 
diameter of a bore and the height of a cutting tool. 
It is a further object of the present invention to provide an improved bore 
measurement apparatus and method which facilitates measurement of the 
inner diameter of a bore without removing a boring bar therefrom. 
It is yet another object of the present invention to provide an improved 
bore measurement apparatus and method which facilitates measurement with a 
single apparatus of the inner diameter of a bore and the height of a 
cutting tool mounted on a boring bar without adjustment of the apparatus. 
It is still another object of the present invention to provide an improved 
bore measurement apparatus and method which facilitates digital display of 
the inner diameter and cutting tool height measurement dimensions. 
The subject matter of the present invention is particularly pointed out and 
distinctly claimed in the concluding portion of this specification. 
However, both the organization and method of operation, together with 
further advantages and objects thereof, may best be understood by 
reference to the following description taken in connection with 
accompanying drawings wherein like reference characters refer to like 
elements.

DETAILED DESCRIPTION 
Referring to FIG. 1, a front elevational view of the bore measurement 
apparatus with the clamping jaws in a closed position, the system 
according to a preferred embodiment of the present invention comprises a 
bore measurement apparatus 10 including a set of clamping jaws 12 secured 
to an elongate bar 14 having a magnetic graduated strip 16 positioned 
thereon, and an indicating head 18 slidably mounted on the elongate bar. 
The indicating head includes an internal magnetic reader for reading 
magnetic graduated strip 16. Indicating head 18 may be purchased as a 
complete unit, i.e., the Digimatic Scale Unit 572, from the Mitutoya 
Company of Japan. Clamping jaws 12 include a stationary upper clamping jaw 
24 having a recessed region 26 for receiving a boring bar therein, and a 
movable lower clamping jaw 28 pivotally secured to upper clamping jaw 24 
by a clamp arm 30. Clamp arm 30 may be purchased as a premanufactured unit 
from the Stenco Company. 
In the closed position, as shown in FIG. 1, lower clamping jaw 28 is 
positioned directly below and spaced apart from a recessed surface 32, 
also called a V-base, of upper jaw 24 by a distance 34 of approximately 
4.0 in (10.2 cm). In the preferred embodiment distance 34 is approximately 
the same as a diameter 36 of a boring bar 38 (FIG. 4) such that the 
clamping jaws may be releasably secured to the boring bar. Lower clamping 
jaw 28 can be adjusted with respect to upper clamping jaw 24 by adjusting 
the securing machine bolt 29 on clamp arm 30 which secures jaw 28 thereto. 
Clamping jaws of different dimensions may also be used such that apparatus 
10 may be secured to boring bars having differing dimensions. 
To secure the clamping jaws to the boring bar, clamp arm 30 is moved 
outwardly along arc 40 from upper clamping jaw 24 such that lower clamping 
jaw 28 pivots away from the upper clamping jaw along arc 42, as shown in 
FIG. 2. Recessed region 26 of upper clamping jaw 24 is then positioned 
over the boring bar. Clamp arm 30 is moved inwardly along arc 44 toward 
the upper clamping jaw to move the lower clamping jaw upwardly along arc 
46 toward the boring bar. In this manner, the clamping jaws securely 
fasten bore measurement apparatus 10 to a boring bar. Lower jaw 28 
typically has a flat bar-contacting surface 48 so that the lower jaw will 
contact the boring bar at only a point thereby ensuring that the clamping 
jaws are secured to the boring bar across the full diameter of the boring 
bar. The operator must be careful, however, that the clamping jaws are not 
positioned over a keyway 49 (FIG. 4) of the boring bar when the jaws are 
fastened thereto in order to avoid inaccurate measurements. Accordingly, 
clamping jaws 12 ensure quick and accurate mounting of apparatus 10 on the 
boring bar for measurement of the inner diameter of a bore or the height 
of a cutting tool mounted on the boring bar. Other means for securing the 
apparatus to a boring bar, as known by those skilled in the art, may also 
be utilized. 
Referring to FIG. 2, a rear elevational view of the bore measurement 
apparatus with the clamping jaws in an open position, lower clamping jaw 
28 is shown moved away from stationary upper clamping jaw 24 to facilitate 
placement of the apparatus on a boring bar. Elongate bar 14 is secured to 
a backside 50 of the upper clamping jaw by four fasteners 52. The 
fasteners preferably are tightened so that the elongate bar is immobile 
with respect to the upper stationary clamping jaw and so that the elongate 
bar does not extend downwardly into recessed region 26, which would hinder 
placement of the boring bar within the clamping arms. 
Indicating head 18 is slidably mounted on elongate bar 14 such that the 
indicating head surrounds the elongate bar and moves along the elongate 
bar with respect to boring bar 38. Elongate bar 14 includes a stop 54 such 
that the indicating head cannot inadvertently be removed from the elongate 
bar. As shown in FIG. 1, indicating head 18 includes a read out window 56, 
an ON/ZERO switch 58, an OFF/DATA switch 60, and a HOLD switch 62. The 
indicating head further includes a unit conversion switch 64 for switching 
the display units from inches to millimeters and vice verse, a battery 
compartment 66, and internal circuitry (not shown) having a memory, as 
known by those skilled in the art. A lock screw 67 (FIG. 2) may be 
tightened to secure the indicating head against movement with respect to 
the elongate bar. The lock screw does not hinder movement, however, of a 
measurement bar 70 (FIG. 2) secured to the indicating head. 
The internal circuitry and magnetic reader of the indicating head 
facilitates magnetic measuring of the position of the indicating head 
along magnetic graduated strip 16 as the indicating head is moved along 
the elongate bar from an operator preset zero position. Accordingly, as 
the indicating head is moved along the magnetic strip, the distance of the 
indicating head from the preset zero position is displayed in the read out 
window. 
In another embodiment, the indicating head may include a preset button to 
input the known diameter of the boring bar into the internal memory. A 
mathematical formula to determine a diameter position of the indicating 
head may be input into the memory of the internal circuitry prior to 
delivery to a customer. Based on the input of the known diameter of the 
boring bar, as the indicating head is moved along the magnetic strip, the 
read out window digitally displays the diameter position of the 
measurement bar mounted on the indicating head with respect to the center 
of the boring bar. In another embodiment, the indicating head may further 
comprise a reverse mode button to change the direction of the counting 
direction along the magnetic graduated strip. 
Referring again to FIG. 2, indicating head 18 includes a back surface 68 
having measurement bar 70 slidably mounted thereon by use of fasteners 72. 
Fasteners 72 are received within elongate slots 74 of the measurement bar 
such that the extent of movement of the measurement bar with respect to 
the indicating head is determined by a length 73 of slots 74. In the 
preferred embodiment, length 73 of slots 74 is approximately 0.4 in (1.0 
cm). 
Referring to FIG. 3, a side elevational view of the bore measurement 
apparatus shown in FIG. 1, measurement bar 70 further includes a stylus 76 
extending outwardly and away from back surface 68 of the indicating head, 
the stylus including a top surface 78 and a bottom surface 80 separated by 
a stylus thickness 82 of approximately 0.2 in (0.5 cm). The thickness of 
the stylus may be varied but should be less than the length of elongate 
slots 74, as will be described below. 
Measurement bar 70 also includes an arm 84 extending inwardly and toward 
elongate bar 14, the arm including therein a set screw 86 and a locking 
screw 88. Set screw 86 may be tightened in a downward direction 90 such 
that the set screw contacts a top surface 92 of indicating head 18 as 
measurement bar 70 is moved in the downward direction with respect to the 
indicating head. As set screw 86 is further tightened, the extent of 
movement of the measurement bar with respect to the indicating head is 
lessened. In other words, tightening of set screw 86 a predetermined 
extent restricts the movement of measurement bar 70 with respect to 
indicating head 18 to a distance that is less than length 73 of elongate 
slots 74. Set screw 86 may be secured in place by tightening of locking 
screw 88. 
Referring to FIG. 4, a rear isometric view of the bore measurement 
apparatus mounted on a boring bar with the stylus tied to the boring bar 
for calibration of the apparatus, calibration of the apparatus will be 
described. To calibrate apparatus 10 for measurement of the inner diameter 
of a bore and the height of a cutting tool mounted on a boring bar without 
calibration of apparatus 10, thickness 82 of stylus 76 is first measured 
by use of calipers or a micrometer, as known in the art. Apparatus 10 is 
secured to boring bar 38 by clamping jaws 12 and stylus 76 is secured to 
the boring bar by use of a clamping wire 94. The indicating head is moved 
downwardly in a direction 90 until fasteners 72 are positioned within the 
lowermost portion of elongate slots 74. The operator sets the ON/ZERO 
switch 58 to zero. Indicating head 18 is then moved in an upward direction 
98 until read out window 56 shows a number which is the same as the 
previously measured thickness of the stylus, as measured with the calipers 
or micrometer. The measurement bar is secured in this desired position by 
tightening lock screw 67. Set screw 86 in arm 84 is tightened until it 
contacts top surface 92 of the indicating head. Locking screw 88 is 
tightened to retain the set screw in place. Lock screw 67 is then loosened 
to allow movement of the measurement bar. In this calibrated 
configuration, the length of movement of measurement bar 70 with respect 
to fasteners 72 of the indicating head has the same dimension as the 
thickness of the stylus, which is less than the full extent of movement of 
the measurement bar as defined by the full length of elongate slots 74 
when such movement is not hindered by set screw 86. This calibration 
process typically is carried out at the end of the manufacturing process 
and before shipping of the apparatus to a customer. 
Upon receipt of the apparatus, a customer may wish to check the 
calibration. To check the calibration, the customer secures the apparatus 
to a boring bar with the clamping jaws and secures the stylus to the 
boring bar with a clamping wire or like device. The customer moves the 
indicating head downwardly until fasteners 72 are positioned within the 
lowermost portion of elongate slots 74. The read out window should display 
"0.0". The customer then moves the indicating head upwardly to its fullest 
extent. The read out window should display 0.2 in (0.5 cm), the nominal 
thickness of the stylus. If the read out display is not accurate, or if 
the customer determines that the stylus has a thickness other than 0.2 in 
(0.5 cm), the customer may perform the above described calibration 
process. 
Referring to FIG. 5, a rear isometric view of the bore measurement 
apparatus mounted on a boring bar with the bottom surface of the stylus 
positioned on the upper edge of a cutting tool for measuring the height of 
the cutting tool, the process of measuring the height of a cutting tool by 
use of apparatus 10 will be described. Indicating head 18 is first turned 
on. Clamping jaws 12 are then moved to the open position and are placed 
around boring bar 38. The clamping jaws are secured around the boring bar 
such that the jaws do not contact keyway 49 of the boring bar. The stylus 
should be positioned over the boring bar in a position where a cutting 
tool 104 will be secured to the boring bar. Indicating head 18 is then 
moved downwardly on elongate bar 14 in direction 90 until bottom surface 
80 of the stylus contacts the boring bar and fasteners 72 are in the 
lowermost portion of slots 74. The operator then pushes the ZERO switch. 
The internal circuitry of the indicating head will set this position as 
the zero position and the read out window will display a reading of "0.0". 
The operator may move the indicating head away from the boring bar and 
then back to the zero position wherein bottom surface 80 of the stylus 
again touches the boring bar to recheck that the read out window displays 
"0.0". 
Indicating head 18 is then moved upwardly on elongate bar 14 until the 
desired reading is displayed in the read out window for placement of the 
cutting tool on the boring bar. The desired reading is determined by the 
formula: desired indicator reading to set the cutting tool is equal to 
(B-D)/2; wherein B is the desired outer diameter of the cutting tool (also 
known as the desired inner diameter of a bore to be cut by the cutting 
tool) and D is the known diameter 36 of the boring bar. Once the desired 
reading is displayed in the read out window, lock screw 67 is tightened to 
secure the indicating head in place on elongate bar 14. The operator then 
secures cutting tool 104 on the boring bar such that bottom surface 80 of 
stylus 76 contacts upper edge 106 of the cutting tool when the measurement 
bar is moved completely upwardly in direction 98 with respect to the 
indicating head, i.e., fasteners 72 are positioned in the lowermost 
portion of elongate slots 74. The cutting tool is then secured at the 
desired height. During this set up process the operator should experiment 
with and adjust for deflection of the boring bar so as to cut a precision 
diameter bore. 
If the operator desires to know the height of a cutting tool that is 
already secured to the boring bar, the operator moves indicating head 18 
upwardly and away from the stationary upper clamping jaw and secures the 
clamping jaws to the boring bar such that the stylus is positioned above 
the cutting tool. The operator then lowers indicating head 18 on elongate 
bar 14 such that fasteners 72 are positioned within the lowermost portion 
of elongate slots 74 and such that bottom surface 80 of the stylus 
contacts upper edge 106 of cutting tool 104. The height of the cutting 
tool above the boring bar is displayed on the indicating head. The 
diameter of a bore that would be cut by the cutting tool is determined by 
the following formula: bore diameter of the cutting tool=(2.times.R)+D; 
wherein R is the reading displayed in the read out window and D is the 
known boring bar diameter. In another embodiment, this formula and the 
known boring bar diameter may be input into the indicating head memory so 
that the indicating head directly displays the bore diameter of the 
cutting tool. 
Referring to FIG. 6, a rear isometric view of the bore measurement 
apparatus mounted on a boring bar with the top surface of the stylus 
positioned on the inner surface of a bore for measuring the inner diameter 
thereof, the process of measuring the inner diameter of a bore 110 will be 
described. Indicating head 18 is first turned on. Clamping jaws 12 are 
then moved to the open position and the jaws are placed around boring bar 
38. The clamping jaws are secured around the boring bar such that the jaws 
do not contact keyway 49 of the boring bar. The stylus should be 
positioned over the boring bar in a position adjacent to and slightly 
within an opening 112 of bore 110. Indicating head 18 is then moved 
downwardly in direction 90 until bottom surface 80 of the stylus contacts 
the boring bar and fasteners 72 are in the lowermost portion of slots 74. 
The operator then pushes the ZERO switch. The internal circuitry will set 
this position as the zero position and read out window 56 will display a 
reading of "10.0". The operator may move the indicating head away from the 
boring bar and then back to the zero position wherein bottom surface 80 of 
the stylus again touches the boring bar to recheck that the read out 
window displays "0.0". 
The operator then moves the indicating head upwardly and away from the 
boring bar such that top surface 78 of the stylus contacts an inner 
surface 114 of opening 112 of the bore. Indicating head 18 is further 
moved upwardly in direction 98 such that measurement bar 70 is moved 
downwardly with respect to the indicating head and so that fasteners 72 
are positioned in the upwardmost portion of elongate slots 74. The inner 
diameter of the bore is then determined by the following formula: inner 
diameter of the bore=(2.times.R)+D; wherein R is the reading displayed in 
the read out window and D is the known boring bar diameter. In another 
embodiment, this formula and the known bore diameter may be input into the 
indicating head memory so that the indicating head directly displays the 
inner diameter of the bore. Accordingly, there is described an apparatus 
that facilitates measurement of both the height of a cutting tool and the 
inner diameter of a bore without adjustment the apparatus. 
In the preferred embodiment, the components of apparatus 10 are 
manufactured of steel for purposes of durability. Other materials, such as 
aluminum or engineered plastics, may also be used as known in the art. 
Apparatus 10 preferably has a length 116 (FIG. 3) of approximately 15 
inches (38 cm), thereby providing an easily portable device. Any length 
may be utilized, however, as required for a particular application. 
While a preferred embodiment of the present invention has been shown and 
described, it will be apparent to those skilled in the art that many 
changes and modifications may be made without departing from the invention 
in its broader aspects. The appended claims are therefore intended to 
cover all such changes and modifications as fall within the true spirit 
and scope of the invention.