Geometrical instruments – Gauge – Surface plate or gauge block
Patent
1994-04-27
1995-07-11
Will, Thomas B.
Geometrical instruments
Gauge
Surface plate or gauge block
G01B 330
Patent
active
054309506
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention pertains generally to step gages for calibrating measuring instruments. More particularly, the invention pertains to stacked block step gages having measuring surfaces on the neutral axis and high compressive forces between the blocks.
BACKGROUND OF THE INVENTION
Step gages are used for calibrating extremely accurate measuring instruments. A step gage typically comprises a metal block (or blocks) of a known height with opposing, parallel surfaces which are precision lapped to extremely tight tolerances. Since the height of the step gage is known to an extremely high accuracy, a measuring instrument can be calibrated based on the value measured for the height of the step gage.
Known prior art gages comprise a single block of a specified height. The opposing faces of the block are precision lapped to the desired height. In single block gages, the measuring probe can contact opposing faces of the block on the neutral axis of the gage, i.e., the axis parallel to the dimension that is being measured on which the center of gravity of the gage lies. Gages which allow measuring on the neutral axis are advantageous since any bending of the gage assembly due to gravitational forces or other factors has a minimal effect on the height of the gage at its neutral axis. Single block type gages tend to be extremely precise. However, such gages are useful for measuring only a single height, whereas it is commonly desirable to test a measuring instrument at several different heights.
Step gages are known in which a series of blocks are held in non-contacting relation by a gage assembly. The precision lapped surfaces of the blocks comprise the measuring surfaces which the probe contacts. Non-contacting block probes, such as disclosed in U.S. Pat. No. 4,445,276 issued to Voneky et al., not only provide multiple measuring surfaces at several heights along the gage, but also allow the measuring surface to be located on the neutral axis. Such gages, however, are not particularly popular because of the complexity and expense of their design and because they tend to be less accurate than other types of block gages.
Probably the most popular type of step gage is the contacting block or stacked block step gage in which a series of precision lapped blocks are stacked in contacting relationship and held together by either a through-bolt extending through mating holes in the blocks or individual screws which couple each block to a preceding block via mating holes.
U.S. Pat. Nos. 3,162,955 and 3,276,312, both issued to Egli, disclose particular stacked block step gages. U.S. Pat. No. 3,162,955 (hereinafter Egli '955) discloses a block gage assembly comprising multiple blocks, each block being coupled to a preceding block by a "hermaphrodite" bolt. Each block includes a hole which is drilled through the center of the block and countersunk. A bolt slightly longer than the height of the particular block is inserted in the hole so that the threaded distal end of the bolt extends below the bottom surface of the particular block and, when the gage is assembled, extends into the block immediately below it. The holes are countersunk to a depth that will cause the head of the bolt inserted therein to be approximately flush with the top surface of the associated block. The head of each hermaphrodite bolt includes a threaded cylindrical cavity that accepts the distal end of a bolt inserted in the hole in the block placed above it. Each block is assembled to the block below it by screwing the distal end of the hermaphrodite bolt into the cavity in the head of the hermaphrodite bolt which has been inserted in the preceding block.
U.S. Pat. No. 3,276,132 (hereinafter Egli '132) discloses a step gage assembly similar to the one disclosed in Egli '995 except that the bolts inserted into the holes in the blocks do not engage the cavity in the head of the preceding bolt (i.e., they are not hermaphrodite bolts). Instead, the uppermost portion of the hole in each block is internally threaded to engagedly receive an
REFERENCES:
patent: 3162955 (1964-12-01), Egli
patent: 3276132 (1966-10-01), Egli
patent: 5231768 (1993-08-01), Beckwith Jr.
Brown & Sharpe Mfg. Co.
Will Thomas B.
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