If
Size is Inspected Properly, You Usually Will Not Need:
Last month's
Tip illustrated how to inspect a feature of size in
accordance with Rule #1 of the Y14.5 Standard. If size is
inspected correctly, the geometric form (straightness,
flatness, circularity and cylindricity) of the feature must be
within the total size tolerance. Therefore, form controls
are usually not necessary.
If for example,
two point checks were made of this pin and it measured 2.005
everywhere (which could only be possible in theory) and it
could fit a ring gage of 2.005, this pin would have to be
perfectly straight, circular and cylindrical. If production
produces this pin smaller than 2.005 (MMC) straightness,
circularity and cylindricity are allowed, but may not exceed
the total size tolerance of .010.
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