(4) Discard all blocks with pits that could prevent accurate
(5) Clean gage blocks with ethyl alcohol and place them on a
cloth laying in a wooden tray.
(6) Clean the inside of the gage block case.
B.
Demagnetizing
(1) Check for residual magnetism by holding each gage block
near a suspended, very light piece of steel which has low
permeability.
(2) Demagnetize, if residual magnetism is perceptible, using
demagnetizer.
C.
Deburring
(1) Inspect visually each gage block for scratches, burrs,
nicks, or other surface defects.
Replace gage block if
necessary.
(2) If necessary apply light pressure and slide the wringing
surfaces of each gage block across a deburring plate.
(3) If necessary, to shear off any large burrs that may be
present. Repeat step 2 above using a deburring stone.
(4) Clean gage block with ethyl alcohol, or gage block cleaner,
wipe dry, and place on a cloth laying in a wooden tray.
(5) o guarantee good wringing quality and complete removal of
burrs, use an optical flat to check gage block for wringing
quality.
D.
(1) Place monochromatic light (Figure 1) on a bench, preferably
next to an inside wall, away from windows or bright lights. If a
semilighted space is not available, place monochromatic light
within a screen of dark cloth.
(2) Connect monochromatic light to AC source.
E.
Environmental Requirements
Allow gage blocks to normalize at room temperature for at least 8
hours with an additional 1 hour per inch for gage blocks larger
than 1 inch.
3.
CALIBRATION PROCESS
Gage blocks are called test instruments (TI) in this process.
A.
Flatness check
(1) Test the wringing surfaces of TI for flatness, as follows:
(a) Place TI under the monochromatic light and lay the
principal face of optical flat (see Figure 2) on surface to be
tested.
Apply light pressure directly above one of the edges
until the desired fringe pattern appears (Figure 3).
(b) Arrange the fringes to appear first in one direction on the
TI and then the other.
(c) Interpret flatness errors from the fringe patterns (Figures
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