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.
Ok, when I make a 3D line between cylinders instead of circles I get .0032. That's a little bit higher but I am still confused. It must have something to do with the fact that circles are 2D features?
If I was checking straightness on a shaft. I would put it on 2 "V" blocks. Run a single line from one end of the shaft to the other, report it, Rotate 90 degrees, single line, rotate ...etc. Do this 4 times. Take the worst reading. Problem with reporting this as a whole, The Demon is creating an averaged line and straightness is to itself.
Yeah I figured it was taking an average of some sort :/
i think runout might be what you're looking for
Runout seems like what I want. But I want runout of several different diameter sizes in one total dimension. I deleted all my circles and made them cylinders. Open to any ideas!
KIRBSTER269, well they were true positioned to each other. I just think with a shaft so bent, straightness of the axis just seems like the right call out.
Look how it Functions, Are the Diameters rotating together? Then Yes Runout, Position would technically be Concentricity, This tends to wear the diameters in their weakest spots. That's why ASME Y14 is eliminating this callout along with symmetry. When Diameters run together, they need to Runout together, but if your just checking to see if its bent. Do what I told you above. In fact if it were me, I would do both.
Yes, I think you're trying to compare runout with a comparator to straighness of an axis.
I would measure the axis with some circles on different diameters, then level on it and remeasure it. It would give the right straihness of the shaft axis, and it would also give a value different than the comparator one !