Im in a heap of trouble. Had a big crash on the xxl broke a bunch of pulleys…snapped a belt…learning curve…rebuild and now z axis is acting strange. Drill in holes in aluminum at random depths, sometimes ignoring the zero’s height I set and hovering above.
After a few trys I will get some holes but two of four will be not all the way through.
Also the z axis pulley will turn after it reacheds limit switch (some times), and finally the axis will tram down right off the rails…
Looks like your Z pulley is slipping. Sometimes the set screws are not tight enough or they are not holding even if tight. That would require drilling the holes of the set screws to install larger ones.
Start with the basics. Check that all pulleys are tight and the set screw is on the flats. Check your belts to see if any have missing teeth or are compacted with dust. Turn you Shapeoko off and move the 3 axis very slowly from end to end. The Shapeoko must move mechanically smooth first before it will work under power. While moving the different axis observe the v wheels to make sure they are consistently contact in the rails and there are no binds or catches in the movement. Move each axis slowly. Remember this is a belt driven machine and it moves slowly because if you move it too fast even a well adjusted machine will skip belt teeth.
Keep it simple stupid (KISS). Meaning keep things simple and make changes one at a time.
After you are sure the mechanics are working smoothly then you can start troubleshooting your movements under power.
Most problems with imprecise movements are usually mechanical faults. If the mechanical part checks then check out your spoil board. If your spoil board is inconsistent in height then the outcome will also be inconsistent. Use a straight edge to see if you have any high spots and/or low spots. Use a long enough straight edge that it will cover at least 75% of your spoil board width and length. Using a 6" straight edge will only tell if 6" are flat not if you have a dip in the middle or a high spot in the corner.
Give a Tram pass on your spoil board and check for imperfections. Put pencil marks all over your spoil board and give your machine a pass of 001". If all the marks are gone then the spoil board should be level to the router. If you have bad ridges then you may need to level your router. There are many procedures on this forum and youtube.com on how to level your router to the spoil board.
When you get the basics covered and working then you can go to more advanced troubleshooting if needed. Skipping the basics will not give you good results if you start troubleshooting without a verified stable base on which to start. Mechanics good, spoil board flat and level to the router.
Do not start with assumptions. Verify each thing above before doing anything drastic.
If you think you have a pulley not holding then put a mark on the pulley and shaft then run a cutting operation and check the witness mark is still where it was originally made. If the marks have separated then the pulley is moving on the shaft.