Re: Measuring concentricity and flatness on diy CNC machine
You don't need a fancy tool, sometimes simple is better. I use a welding rod on my router.
The welding rod is brazed into a 1/2 inch slug that fits in the router spindle. In this case I was using a piece of paper as a feeler gauge. Paper works better because you can feel the drag, a feeler gauge is too slick to properly feel it in this case. First get the tram as close as you can, then take a light skin cut on the table. That's just to get the table level relative to the rest of the machine. Then tram again to get final tram. Mine is < 0.002 in 36 inches, that's close enough for any work.
On my milling machine, I just swing an indicator in the spindle. That's the old school way of doing it, but I'm old.
Jim Dawson
Sandy, Oregon, USA