So I have a shaft with several different diameters that is always bent between .010 and .020 off the CNC machine. Our internal print calls out for a bunch of true positions. I told engineering to change it to straightness because that seemed more intuitive (since the part is always bent so much). Now I am writing the CMM program for it. I probe each diameter, create a 3D line between them, and dimension straightness of that 3D line. I'm only getting a result of .001, but when spin the part on the optical comparator it is for sure .010 bent...Any ideas what's going on here?
I just need a consistent way to measure the average straightness of the part that can be validated with a dial indicator or optical comparator.
Hmmm...so, measure the different diameters as circles, construct a line between the circles, level to that line, re-measure the different diameters, and then what do I do for dimensioning?
Well I had an interesting idea this morning. I could just take one cylinder with a gigantic prehit retract (or run in manual mode) and get all of the different size diameters. And then simply dimension straightness of the cylinder.
Make sure you are measuring an adequate number of circles to create the 3D line. Make sure it is the centerline that is toleranced so it isn't the generatrix (surface) of the shaft.
Also note the difference
JEFMAN mentioned in his post (runout/straightness).