Z Axis jumping only while cutting

Had my SO3 xxl for a while now. Haven’t really had any issues until recently. Randomly the z axis appears to be slipping. When I see the motion, it appears that the motor is jerking. The belt is fine, the belt is tight, the pulley is locked in the correct orientation. Has anyone had an issue other than the belt or pulley? The CNC has worked fine for about 30 projects. This is very frustrating! It doesn’t do it if I run the program without a cutter. I can’t complete a project, HELP!!! P.S. my feeds and speeds on the MDF are 75 feed by 12 plunge with the router at around 2.75 on the carbide router.

If the Z-axis has such problems it’s either electro-mechanical (check the connections/wiring, and the pulley set screws, eccentric V wheels, belt tension, try removing a spring temporarily), or a feed and speed issue.

Belts are good, feed and speeds are recommended on the wiki, if it was a switch wouldn’t it be less intermittent?

If the plunge is too slow that shouldn’t cause such an issue should it?

I’ve come across this before, it’s usually one of 2 things

your z belt is loose or damaged
the set screws in your z stepper motor have come loose or fallen out

if you don’t think it’s the belt, try marking where your pulley is sitting on the shaft of the motor with sharpie and push down on the spindle until it slips, you should be able to see if it’s the belt or the set screws


I will try that. Thank you

Update, was able to get a mark on the motor shaft that correlates with the pulley. With very little force the motor “slips” but the marks stay lined up when the SO3 is turned on and playing the motion back on my phone in slow motion the belt is moving with it. It is clearly the motor slipping. This amount of force I use is just my thumbs on the router mount and 2 fingers each side on the bottom of the Z cartridge rails like a large pinching motion. There is surprisingly little force used to cause it to slip (though I don’t know how strong this motor should lock). It appears though that this would have issues plunging into all but the softest materials such as HDPE.

Check the wiring. If that’s okay, see if both motors require the same effort to skip a step. If not, power down and swap the X-axis and Z-axis connectors and see if the problem swaps motors.

Contact us at support@carbide3d.com and let us know what you’ve tested/investigated and we’ll do our best to work through this with you.

We’ve replaced a couple motors over the years with this issue, both on the z axis and after a year of full time projects. I think the z get the most wear since end mills will always dull on the very tip first, and to be fair I’m not easy on them… if you plunge too quickly enough times with a dull bit it can wear out and break the z belt.

Installed my first HDZ last night, super impressed with the upgrade. Carbide 3d support has been awesome with us every time, answering emails same day and shipping parts next day at very reasonable cost / free.

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I did contact you. Only got one reply saying you needed more info (which I provided) and I haven’t heard back.

After switching the wires it appears that the same amount of force is needed to cause the same result. Feels like a little more force is needed to replicate it on the X axis (could be less leverage too).

Apparently not a motor or stepper driver issue — I suspect belt tension, but we have your ticket open and will do our best to work out a solution with you as quickly as we can.

I ordered new belts arriving today. I have a video of the problem.

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