I am a hobbyist and use this mill for hobby uses so it seldom gets ran for long periods of time - I made 9 parts Sunday that take about 30 minutes each to run. At the end, I noticed that the last part i ran was about .020" thinner than the first - I face off the back so I can make these work, but after checking each part, it looks like the Z axis is dropping a few thousandths of an inch with each part. I rechecked the Z axis part 0 and it confirmed that it had dropped by about .020" according to my reference tool (an electronic edge finder). Belt is tight, no pulleys slipping. It seems pretty consistent to be encoder counts being dropped - any other ideas? Could this be a bad encoder? Any thoughts on this? The machine was ran from start to finish on the same session - now new homing or new part zero setup during the several hours I ran it - just making the same part over and over.