High precision gaging block

A device and a system for ascertaining dimensions includes at least one gaging block held by negative pressure to a workpiece. The gaging block has a body with a first face and a second face. The first face includes a recess portion therein and the second face defines a measurement reference surface. The body includes a port in communication with the recess portion and adapted for communication with a negative pressure generating device such as a vacuum pump. The gaging block is held by negative pressure in intimate and highly accurate contact with a workpiece in order to provide a reference point for measurements that might for a variety of reasons be most difficult to obtain.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The invention relates to a technique for ascertaining measurements, more 
particularly, the invention provides an apparatus whereby a high precision 
gaging block is held by the application of negative pressure to a 
workpiece surface in order to provide a reference point or a reference 
plane for a measurement. 
Quite often, a product or workpiece is of such a configuration as to render 
itself virtually impervious to conventional measurement techniques and 
devices. The precise measurements of such configurations can be quite 
difficult for any of a number of reasons including, for example, 
inaccessible surface area, sloped or curved surfaces, the lack of 
sufficient area for the application of a gaging apparatus or the fact that 
the act of measuring requires the proverbial "four hands". 
It is therefore an object of this invention to provide a technique whereby 
a gaging block can be held firmly in place, against the element to be 
measured and regardless of the material from which the workpiece is 
constructed. 
SUMMARY OF THE INVENTION 
The invention is a system for providing a reference point and/or a set of 
reference planes for use in ascertaining dimensions. The system includes a 
negative pressure generating device and one or more gaging blocks held in 
intimate and accurate contact with the workpiece surface by negative 
pressure. The gaging block comprises a body with a first face adapted to 
conform to a workpiece surface. The first face also includes a recess 
portion therein. A second face of the body defines a measurement reference 
surface. The body includes a port in communication with the recess portion 
of the first face and adapted to be in communication with the negative 
pressure generating device. The gaging block is removably secured to the 
workpiece surface by the generation of a negative pressure in the recess 
portion as the first face rests against the workpiece surface. Alternative 
embodiments of the present invention include the features of a gasket or 
seal-like member disposed about the recess portion, multiple recess 
portions and a depth micrometer to provide gaging precision regardless of 
seal deflection. The distance or relationship between the first and the 
second face of the body has been generated to a high degree of accuracy in 
the manufacture of the block and is a known measurement, thereby 
preventing the introduction of errors into the dimension to be measured.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention provides a technique for ascertaining measurements. 
The invention provides an apparatus whereby a high precision gaging block 
is held by vacuum to a workpiece surface in order to provide a reference 
point and/or a set of reference planes or surfaces for measurements. 
Turning now to FIG. 1, a large generally cylindrical-shaped member 
indicated by the reference character 11 represents an object to be 
measured using the apparatus of this invention. The cylindrical object 11 
has an outer surface 13, an inner surface 15, and a conical surface 17 
which could typically not be measured accurately with conventional 
instruments. A gaging block according to this invention and indicated by 
the reference character 19 is disposed at the uppermost portion of the 
conical surface 17 and at the lowermost portion of the conical surface 17. 
Each gaging block 19 is firmly and intimately attachable to the surface to 
be inspected by means of a negative pressure generating device such as a 
vacuum generator 21. Turning now to FIG. 2, the vacuum-held gaging blocks 
19 according to this invention are illustrated as being removed from the 
large cylindrical device to be measured so that the manner by which these 
gaging blocks are removably secured can be appreciated. The gaging block 
19 comprises a body 23 having a first face 25 adapted to conform to the 
workpiece surface as at 17 of the object 13. The first face 25 includes a 
recess portion 27. Thus, the portion of the first face which surrounds the 
recessed portion as at 25, represents a seat by which the gaging block 
intimately rests against the surface to be measured. At least one 
additional face of the gaging block 19 defines a measurement reference 
surface 29. As will be described in detail below, a gaging block can 
include two or more reference faces. The body portion 23 of the gaging 
block 19 also includes port means 31 in communication with the recess 
portion 27. The port means 31 is adapted to be in communication with the 
negative pressure generating means 21. The aforementioned communication 
can be established by means of vacuum hoses 33 extending between the 
vacuum generator 21 and the gaging block vacuum port 31. Valve means 35 
can be provided in the line 33 as can a vacuum gage 37 in order to monitor 
a level of vacuum being provided to the gaging block, thereby ascertaining 
the accurate location of the blocks. A low vacuum reading, caused by 
excessive leakage between the gaging block and the workpiece indicates a 
misplaced or misaligned gaging block. 
The vacuum feature of the gaging block permits the gaging block to be 
firmly attached to an element or surface of a workpiece to be inspected, 
regardless of whether the workpiece is made of a magnetic or nonmagnetic 
material. Once firmly in place, the gaging block provides either a 
reference surface, an attachment fixture, or if two blocks are being used 
as is the case illustrated in FIG. 1, a set distance which can now be 
measured with conventional devices is presented. The vacuum to hold the 
gaging block to the work surface can be provided by any number of means. A 
small vacuum pump as illustrated in FIG. 1, an air ejector, a water 
aspirator or the intake manifold of the engine of a forklift, a truck or a 
car can be used to provide the vacuum. 
Considering both FIGS. 1 and 2, it can now be appreciated how the inside 
diameter of the outer edge of a conical surface can be accurately 
measured. With the vacuum held gaging blocks 19 in place directly opposite 
one another on the conical surface 17, two perfectly flat reference 
surfaces are provided for measurement purposes. An abutment 39 disposed 
adjacent the first face of the gaging block provides a reference point to 
ensure that the gaging block is properly referenced on the conical surface 
17. Such an abutment or similar surface-like device ensures accurate and 
consistent location of the gaging block. Thus, the reference surface 29 of 
the diametrically located gaging blocks 19 provide the points between 
which a measurement is taken. This resulting measurement is the base 
figure to which is added a second measurement representing each gaging 
block. Each gaging block will have a high precision known dimension which 
must be added to the previously ascertained dimension in order to account 
for the offset created by the gaging block. 
The first surface 25 of the gaging block can be custom made in order to 
conform exactly to a certain configuration, or curved to fit cylindrical 
or other curve surfaces. In the case in which a gaging block is made for 
use with one particular surface configuration, the known dimension each 
gaging block provides that must be added to the otherwise ascertained 
dimension represents a fixed value. Additionally, in a custom fit gaging 
block where metal-to-metal contact between the gaging block and the work 
surface is desirable, the proper placement of the gaging block can be 
determined by detecting any vacuum leakage between the workpiece surface 
and the gaging block. A vacuum gage in the system or directly associated 
with each of the gaging blocks can provide this information. 
Turning now to FIGS. 3 and 4, an alternative embodiment of the vacuum gage 
block of this invention is generally indicated by the reference character 
51. This embodiment of the gaging block 51 is useful for straight inside 
diameter measurements. The gaging block includes a body portion 53 having 
a first face 55 which defines, in this case, two recessed portions 57. It 
is to be appreciated that while at least one recessed portion must be 
provided in the first face of a gaging block, it is, of course, possible 
to provide two or more such recessed portions for use in securing the 
gaging block to a given surface. A port means 59 is provided in the body 
portion and is in communication with the recessed portions 57 thereof. A 
second face 61 of the gaging block 51 provides the reference measurement 
surface. In order to provide a single gaging block which can accommodate a 
variety of radii, the gaging block 51 includes seal-like members 63 
disposed about each of the recessed portions 57 in order to provide a good 
seat between the gaging block and the workpiece surface 67. Because this 
particular embodiment of the gaging block 51 is designed to accommodate a 
variety of workpiece surfaces, it is equipped with the additional feature 
of a depth micrometer 69. Mounted in the body 53 so that the ball tip 71 
of the depth micrometer 69 extends from the first face 55 of the gage 
block, the micrometer can be adjusted in order to determine the exact 
additional dimension which must be added to account for the use of the 
gaging block in ascertaining dimensions. 
FIG. 5 illustrates an alternative embodiment for use with tapered surfaces. 
The gaging block 81 has a first body portion 83 and a second body portion 
85 pivotably connected thereto by hinge means 87. The first body portion 
83 has a first face 89 which defines the recessed portion 91. A vacuum 
port 93 is provided to establish communication between a vacuum pump and a 
recessed portion 91. The second body portion 85 includes thereon the 
second face or reference surface 95. Means such as the magnet 97 are 
included to maintain the second body portion in a fixed relation with the 
first body portion. In all other respects, the embodiment of the gaging 
block 81 functions identically to those previously-described embodiments. 
It is to be appreciated that the exact configuration of the gaging blocks 
illustrated herein, are provided as exemplars only and that the actual 
relationship of the reference surface of each gaging block relative to the 
face having the recessed portions therein can be modified to provide a 
virtually endless variety of gaging block configurations. FIGS. 6A, B and 
C are provided to show but three examples of gaging block configurations 
all according to the teachings of this invention. FIG. 6A shows a gaging 
block 101 which is useful in the measurement of a device 103 having an 
inside projection 105. The gaging block 101 is generally triangular in 
shape with one point of the triangle resting against the inside abutment 
to ensure proper gaging block location. The reference surface of the 
gaging block is defined by the second face 107. Vacuum port means 109 can 
be provided at any convenient location. The gaging block 121 of FIG. 6B 
illustrates that it is possible to provide multiple reference surfaces on 
a single gaging block. A first face 123 includes the recessed portion 125 
and also illustrates the vacuum port means at 129. The remaining nine 
surfaces of the gaging block 121 can provide either singly or in 
combination, a reference surface for use in making measurements. FIG. 6C 
represents a gaging block 131 which includes a first face 133 having dual 
recessed portions 135 therein. The gaging block 131 provides a trough-like 
mounting portion as at 137 for contact with a workpiece requiring 
"V-block" fixturing. Any of the remaining surfaces of this gaging block 
can then function as a reference surface as necessary. 
What has been described is a high precision gage block held by vacuum. 
Because the dimensions of the gage blocks are made to the highest 
precision and are known, the necessary additions or deductions for block 
elements or components are easy to calculate or adjust for when making 
final measurements. While the gage blocks can be made flat, they can also 
be made to conform exactly to a certain configuration or curved to fit 
cylindrical or other curved surfaces. Also, in order to provide a 
universal gage block to fit a certain range of radii, the gage block can 
be provided with an elastomeric seal or O-ring. This type of gage block 
with the sealing media can also be equipped with a depth micrometer of the 
type with a spindle to offset any inconsistency in a deflection of the 
seal. The outboard end of the spindle would be the reference surface and 
the ball-shaped inboard end of the micrometer would be in contact with the 
work surface.