My machine sat for at least a year. Ran some parts this week and noticed some slight stair stepping on one side of the parts but they were not too bad. Now it’s completely unusable. The first depth pass looks fine, but as it goes deeper it moves -X and +Y. Here’s what is supposed to be a 5/16" hole 0.27" deep and a test 1.5" square with a tab on each side, all with a 1/8" bit.
I can jog the Z up and down all day long against a square in any direction and it’s perfectly square. Certainly it isn’t out by .08" over .25". I have checked all the pulley set screws and they are tight. With the machine powered up the x/z carriage doesn’t move around if I push on it. I retensioned the x and y belts with no change. The z belt is definitely a bit loose but I don’t see how that could cause this. I checked the g code with camotics and there’s nothing wrong with the code.