I realized the dimensions on a part was out of spec and checked the responsible finish end mill. Sure enough the 1/4" EM diameter was actually .247". Using a caliper and carefully measuring across the cutters on a 2-flt cutter and realized it was somewhat subjective with a +/- .001, depending exactly where I called it. I took a scrap piece of delrin and ran a shallow slot in it and then measured the slot gap to achieve the .247" on the 1/4 EM. This seemed like a more accurate method and the recently cut part error matched the difference. I recall a earlier post about measuring a 3-flt EM but was unable to locate it.
How do you guys measure up?
-uman