Originally Posted by
bergerud
The mpc looks ok. The machine does not actually touch the dowel to find the surface as it does for boards. The machine knows the touch point is 1.75" above the jig axle. If you were carving a 4.25" dowel, the machine would expect the dowel surface to be 2.125" - 1.75" = 0.375" above the touch spot. Using the 4.5" pipe and raising the touch spot by 1/8" gives the same difference. Maybe you could check that the pipe surface really is 3/8" above the touch point.
Use the z sensor data. Put the bit on the pipe and turn on the machine. Now look at the z sensor data (0 - 7 -down arrow a few). It will read 0.000. Move the truck over and touch on the top of the 1/8" shim. The z sensor should read 0.375. (This assumes, of course, that the pipe is centered and really is 4.5" in diameter.)