Left and Right motors seem to move at different rates

When my machine is homed, the left and right sides sit the same distance from the front. It is square in this position. As the gantry moves along the y-axis, it travels further on the right, than on the left. So, if I tell it to move 24" in the Y direction, then measure both sides, to the front, I get 24" on the left, and 24-1/4" on the right. When I noticed this for the first time a few days ago, I went through the machine and cleaned/squared/tightened everything. Had to replace 1 V-wheel because it was seized up. Also, noticed that the toothed wheel on the right motor had slipped from it’s original position. One of the set screws is missing, and the other was digging into the curved side of the motor shaft, and had obviously been slipping. But, I fixed that, and am still getting the same result. I’m baffled. Could the motor itself need replaced? But why would it travel further than the one on the left? Thoughts?

Equal belt tension on both sides? Both side belts in good condition?

It is a long shot, but broken motor shafts have happened before.

Check the pulley on the left as well?
If the set screw is loose as well, it might move shower because of the XZ assembly being on that side.

This. Unless you have EXACTLY equal belt tension on both sides (as in, the exact same number of belt teeth spanning each Y-rail), you’re always going to have a little bit of skew from side to side on your Y-axis. This is just the nature of how the X-Carve is constructed.

When you tell your machine to return to it’s initial position (i.e. move 24" in the opposite direction), does it “re-square”? If you continually tell it to move 24" back, then 24" forward, then 24" back, then 24" forward, etc…, does the offset from side to side ever get any worse? If it doesn’t, there’s nothing wrong with your machine, but you might want to work on equaling out those belt tensions. If the offset does get worse, then you have another problem - loose pulley, damaged belt, damaged motor, etc.

Thanks. Working on Belt tension now. It does do the same thing every time. Comes back to home perfectly. Am I really supposed to count the number of teeth? Best way I could figure was to use the fish scale I just bought, lift the belt a certain distance, and be sure they both read the same.

But, fine tuning the belt tension will cause only that side to move, throwing it out of square, right?

If you want the machine to remain perfectly square along the entire Y-length, that’s basically the way you’ve got to do it. I personally haven’t gone that far, and I’m not sure of anyone else on the forum that has.

This is the way pretty much everyone does it, and we all just live with the fact that the machine goes slightly further out of square the further away from home it gets.

If you choose to upgrade your machine with beefier belts, they won’t stretch as much, and this becomes slightly less of an issue.

I would not expect the two Y belts to be 1/4" different in a 24" span. Unless one was tight and the other loose.
Are both belts from same source? Acquired at same time?
Could one be older and stretched?

I wouldn’t expect that either, but here we are. After equalizing the belt tensions with the fish scale, I’m still getting that or worse over full travel. I can’t remember when the last time I replaced a belt was, but I only did the one that broke. I always buy them from Inventables. Luckily, I have some more, so I will be replacing both belts right now.


If you swap the two motors around, do that change anything?