X-axis slippage

Hi there,

I’ve been having some slippage on my x-axis intermittently over the last month. It’s only happened a couple of times and each time I caught it before any damage was done, but it finally destroyed a part today so I took the entire x/z axis carriage apart and went through it piece by piece. I changed the aluminum piece that the belt went on for the x axis thinking it might be that because I’ve had to do that before on the z axis, but when I went to change it I noticed the stepper motor (while plugged in) was able to be turned by putting a good amount of force on it with my hand. My question is, is that normal? Or do I have a bad stepper? I don’t think it’s the belt tension as I went and tightened it last time I had this issue, my thought is that I could have a bad motor, but don’t know what should be normal. Any help would be greatly appreciated!


Not normal. How to tell if the stepper is damaged, or it’s a wiring issue:

  1. Disconnect the stepper from the harness.
  2. Connect TWO of the pins, a paperclip works well.
  3. Hard to turn? No->connect the other two pins (keep trying pairs of pins, there are only 3 possibilities here) until you find a pair that makes it hard to turn.
  4. Connect the OTHER two pins together, and see if it’s hard to turn. It should be. If it’s not, the stepper is damaged. If it is hard to turn, the wiring has a fault somewhere, or it’s a driver on the controller.

hey mike, thanks for the quick reply. Do you mean stick a paper clip into a couple of the holes on the connector and touch them to two of the prongs on the motor? Also, I just tried to turn my z axis by hand, it was harder, but I could still turn it by hand as well. Does that point to something going on with the controller?

Disconnect the stepper connector from the harness, and the stepper side will have a white connector with 4 holes in it. Stick the paper clip into two of the holes (should be the two at one end of the connector) and it should be hard to turn. Then do it with the two at the other end. It should be really easy to turn with nothing connected, and harder to turn with a coil shorted together.

Slippage OR are you pushing it too hard? The motor only has (about) 18 pounds of force…

I assume you have checked so see that the motor pulley set screw is ON THE MOTOR FLAT?



Have you upgraded grbl?
Can you post your settings?
$1 should be 255

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18 - 22 lbf is apparently where the motors slip (when they are properly connected). Get a scale and measure it?

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I did…I measured the motors (XY & Z)…the belt stretch…and mapped every square inch for accuracy…its what retired JPL/NASA guys do…or as my daughter calls it…overkill.


I actually just replaced the entire component (don’t know the name) so new set screws, etc. I’ll let you know how it fares. I also opened my controller unit and it does look like my x axis might not have been fully seated so I’m hoping that is what solves it.

Sorry - I suspected that you had! My suggestion was actually intended for kyle to help him determine if he really had a problem. IMO, 18 lbf should be more than enough in any axis with the S3’s. What I don’t understand is why everyone seems to think it’s limited by belt rather than stepper motor slippage.

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IMO Because they are carpenters and not mechanical engineers… Belt slippage on a timing belt…hahahaha.


I would think that the thought is belts are a limit as compared to a drive system that provides mechanical advantage, like a ballscrew. I see a lot of discussion around skipped steps, not slipping belts.

Care to share what you learned from those measurements? How do they compare to Stepcraft’s D Series Specs.?

I have posted the mapping data (search under my name and (belt) calibration ), and learned that unless you have overstretched the belts (which is nearly impossible due to their construction) adjusting the steps per inch is not necessary; meaning the machine is just about as accurate as it can get. Making sure the machine is square and parallel is probably more important.

The belt research was to measure the difference in stretch and strength between the old 6mm vs the now standard 9mm (width).

Lastly, I have not looked into the Stepcraft data, so no comment.


OOPs - I forgot to insert this link to the Stepcraft data - sorry! Did you measure torsional stiffness?

Of the machine?

No, but I have set up a few models and clearly the 16" model with an aluminum bed is much stiffer (less twist, and deflection), and is the only model I recommend for metal cutting.


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