Sphere Measurement Question

Sphere Measurement Question
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Posted by: Hup23Hup ^®

04/19/2007, 13:21:06

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I am checking a sphere on a Mitutoyo CMM using Geopak software.
When I check the sphere around a 40 degree arc on four sides I get a Spherical radius diameter slightly below top tolerance and a sphere form out of spec. (Presumably this is because the sphere form tolerance is the difference between a perfect sphere on bottom tolerance (radius) versus a perfect sphere on top tolerance (radius), minus the actual measured diameter.

I.E ((MMC-LMC)-Actual Diameter)= Sphere form Tolerance or
(Actual Diameter-(MMC-LMC))= Sphere form Tolerance (+ 0r -)

However, when I check the part at 45 Degrees around 4 arcs I get a nearly perfect nominal radius sphere and the form of the sphere comes in .( This is because the sphere form tolerance has opened, not because the form value changed).

Our thoughts were as the sphere diameter got smaller, due to the fact that the diameter got smaller on average from the 40-45 degrees arc, that the sphere form would have been got worse, as these points must have been the lowest taken?

Thanks
Melvin

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