It does sound like something loosing precision from the spindle down. That is pretty thick to cut in one pass with such a small bit as well. I cut 3/16" lexan in two passes with a 3/16 carbide bit. It will full cut it in one, but the cut is much nicer in two. I am feeding about 150 IPM with a PC router. I really have to slow it down on tight arcs or they don't come out right. I run those at 80 IPM.
If there are any adjustment points in the Z axis, I would look into those.
One way to see any slack or movement is to chuck up a center drill. Slow the jog rate down to about 10% and jog down into some scrap wood a little. You should be able to see any slack in the Z this way. Up and down a few times might help. Not deep, mind you, but just enough to take the spindle weight off.
If you have any movement there, then you have to fix it.
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Lee |