Is this normal? I was lightly leaning on the rail while the machine was idle and I assumed it was locked but it broke free and started moving with maybe 10lbs of force.
Recreated the issue in video:
As long as the machine is On, the stepper motors are trying to hold position. You created enough force to make the stepper motor slip past its holding point.
Keep this in mind. Taking a bite that is too much for the machine can do the same thing causing lost steps and one upset operator. People blame the program or the machine when, in reality, it is doing just what we told it to do.
Good luck
I have an SO3 XXL. If your gantry moves with the power on check your v-wheels for adjustment. To check them power off your SO3. The lower v-wheels on each end of the gantry and the bottom ones on your Z are adjustable. With the power off use your finger to push on the lower v-wheels and see if you can get the gantry to move. If it does not move then the v-wheels likely need adjustment.
Power off your Shapeoko and using a stiff nylon brush move the gantry slowly and clean all of your v-wheels so they are clean and free of contaminants like dust or any stuck on chips. Then clean your alum extensions. I use a white 3M finishing pad. It is abrasive enough to clean the extrusion but not abrasive enough to scar the extrusions. Clean both top and bottom.
To adjust use your allen wrench to loosen the bolt slightly. Use the correct size wrench on the eccentric and rotate it until the v-wheel feels snug. Hold the wrench in position on the eccentric and tighten the bolt. If you fail to hold the eccentric in place tightening will change the adjustment due to the torque of tightening the bolt. You want the v-wheel to be firm against the extrusion but not so tight it deforms the v-wheel.
After getting your v-wheels tight and/or checking them check your belt tensions. With the gantry all the back front or back put your finger under the Y belts and your finger should feel tight under the belt. There are a bunch of ways to more scientifically check belt tension but that is a good test.
Also check your stepper motor set screws. There should be one set screw on the flat of the stepper motors. If the set screws or loose or one is not on the flat then loosen both and move the pulley until one set screw is over the flat. Tighten up your set screws. Those set screws are 3MM allen set screws and you can strip them easily. They have to be tight but not over tightened. Some people take the set screws out and get an allen headed bolt that is about 10MM long and replace the little set screws. When all your allen head set screws are in place and tightened put a magic marker across the center of the pulley so that the mark goes over the center of the stepper motor shaft. That will give you a quick visual reference that the pulley and stepper motor are lined up and not slipping. If in the future you see the mark is misaligned stop and fix that.
So your problem could be a loose belt, loose v-wheels or a loose stepper motor pulley. Check them all.
When you get everything checked and/or adjusted with the power off move the gantry front to back and back to front slowly. It should be relatively easy to move. If you move it too fast it will sound like the belt slipping because the powered off stepper motors will generate their own field called EMF. Just move slowly and steadily. If you find any rough spots find out why and fix that. Also move the router back and forth right to left and left to right and fix any tight spots.
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Amazing thanks! I’ll look into this now. I did adjust the vwheels not too long ago but maybe they came loose or its one of the other issues you mentioned.
The machine still cuts well and works. One thing I noticed is the machine seems a bit stiff and jerky to roll front to back while it’s off / unlocked. Almost like the vwheels and rails are dirty but the issue persists even after a good cleaning. I’ll put some time into that now.
It looks like to me that you created enough force to move the belt around the toothed pulley. I’d check the belt and pulley teeth, especially if you see little black specks laying on the Y rails near the belt.
That is normal. It’s the stepper motors energizing when you manually push the gantry when powered off. If you move it really slowwwww you won’t feel the jerking.