I was cutting some circles that are supposed to be 11.5" but they are 11.75". I measured the 1/4" bit and it's diameter is about 0.23" instead of 0.25". I edited the tool parameters in VCrave and cut the circles again. They are about 11.5". I cut more circles that are 9", 12", and 15". They are just over 9", over 12", and over 15". How do I measure the bits correctly?
with a micrometer you hold the tool between the faces and gently rotate it as you widen the jaws slowly, when it just slips free, that is the diameter. you put that into your CAM as the tool diameter. fact is, tool are pretty much always undersized, tha tis just the way grinding works. there are other ways tool sensors, both physical and laser (requires controller support) optical comparitors
0.25" difference 0.02" difference So, no, not (only) the endmill diameter causing your difference - check mechanicals, then check calibration
