Belt or Pulley Slippage on XCP, You Can Know

Learned something I should have figured out. Mark your belt pulleys to know if you are experiencing Belt OR Pulley slippage. I’ve marked all my pulleys and shafts.

Left pulley might be a little light in the pic, but there is a pencil mark like the right pulley. Mark your shaft and pulley. Run a know project file that slips. Then check the pencil line.

From my test of Pinewood at 160 ipm, 48 ipm plunge with a 1/4" end mill. The X-axis slipped ~1/8". When the project was over the bit was clearly 1/8" off home. Neither of the X-axis pulley lines were misaligned, so I have belt slippage. Time to try 130 ipm. I should note, I use the Triquetra to home my bits with the material.

NOTE: For the belt tighteners on XCP, note you can over tighten and break the X-Axis spindle shaft. Translation, be careful tightening your belts on the XCP.

This information was per Inventables Customer Support.

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yeah, it’s a real bitch they couldn’t design it better.


With chains?

Chains ???
To much slop.
Woodruff keys on the shafts and pullies, Yes.

you guys make it sound like snow chains on tires in the mountains.
it’s just a timing chain instead of an unstable rubber belt like stretch arm strong

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Right, but for this application belts are appropriate. Good belts will have minimal stretch and tend to “settle in”. The issue brought up in this thread is that of the pulley slipping on the shaft.
Timing chains have there own downsides too. They’re harder to tension and the sprockets wear causing similar issues to belt stretch.

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I agree 100 percent, most of the problem comes from abuse and not use (pushing the unit harder than it was intended for).

That’s what machines are for!


Some seem to think so,

Neal what are your thoughts on this product?

GT2 9mm Width Open Belt Polyurethane Steel Core

not sold in a closed loop design needed for the XCP… but are good for the standard XC… but where did you find 9mm though? I’ve only found the steel core in 6mm width and 2mm pitch. . . . good for the orginal XC design with 6mm 2mm pitch…

not the 3mm pitch the XC with 9mm upgrade calls for

Also technically it’s not a GT2 because as Gates defined the GT2 to include a fiberglass core, not a steel one. It is a “2GT-9 (with steel core)”

And even better solution to the XCP would be a coupler and directly mount the stepper to the shaft… no silly belts, or chains at all.

close loop is available special order ( i put in a request), open loop is available 6,8,9, and 10 widths

I wouldn’t recommend steel core belts for these machines. The tight radius on the pulleys can cause premature wear on the stiffer steel.
Carbide 3D moved to steel reinforced belts and fairly quickly went back to kevlar. Once one of those thin steel stands breaks, you’ll get a pretty significant failure.
Increasing belt width, where possible, would be your best bet.

didn’t think about the other wear and tear.

I am having a similar issue with my Y-axis.

I double checked the Y-Axis belt tension both from the perspective of the eccentric pulley and the motor mount. I even went so far to got through entire CNC squaring procedure from the assembly guide and run the 11" Y2 tightening process.

For contour cutting this has not been an issue, but for the V-carving it is going out of square almost all the time. I

I am at lose of what I can do now. I put a message into Inventables, hopefulley they can help.

@AlexanderElkins There are two stepper motors controlling the Y-Axis. From what I saw in the video, it appears one of the Y stepper motors is chattering. Hence making you out of square.

Let me (us) know anything you learn from Inventables. I’m also having the conversation.

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Wondering out loud: If one marked the X-axis belt and pulley at a spot, say one-side of XCP. Can you expect the belt to return to the same spot on the pulley when you return the X-axis to the same side?

If so, that would be one way to actually determine if the x belt slipped or something else happen. And tell how much the belt slipped.

Well, lost steps wirhin the stepper would cause the same result. :man_shrugging:

…as well as the pulley slipping on the shaft (but this is easier to rule out by also marking the shaft/pulley clocking)

An overheating stepper driver can also cause the stepper to operate abnotmally when it goes into overheat protection and that presents just like lost steps as well…

But it would indicate that one of those items is at fault… I guess so although it doesn’t pin point a specific root cause, it might be worth a test

@SethCNC That’s what I’m thinking.
Mark the Pulley and Shaft to determine if shaft is slipping
Mark the Belt and Pulley to determine is the Belt is slipping
Lost position with no Shaft or Belt Slipping would mean Stepper losing steps


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Belts don’t slip unless they’re extremely loose.

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