Y axis inconsistency - last hurdle

Y-axis shifting, and that’s my last issue!

So, finally got my new X-Carve up and running. So exciting. Assembly went smoothly, did the x-axis stiffening with bolts, and the y-axis stiffening by attaching to the waste board.

Had a few minor tweaks that needed to be made along the way. had to sand off the back edge of the Dewalt 611 router so it wouldn’t hit the top of the Z assembly. The Derlin nut on the Acme threaded bolt on the Z assembly was binding or sticking a bit in 2 spots, but a little dry graphite, running it along the length several times, and upping the z pot seemed to take care of that. Runs great now.

X axis runs absolutely smoothly.

The only thing keeping me from getting a great carve is the Y axis inconsistency. The entire X rail assembly shifts inconsistently when moving either forward or backward along the Y axis. It appears that the left side moves more aggressively than the right side. When the assembly moves, the left side moves smoothly, but slightly ahead of the right side. Then the right side is out of whack. Jogging the Y axis in small increments can get the two sides more closely aligned, but anything more than about 0.1 inches in either directions causes the side rails to be out of whack again. I can move the Y sides almost independently, by pushing or pulling the X bar. I would guess more than .25 inches if I try. I can also get the sides out of whack by physically turning the motor/belt on one side. The other side does not keep up.

From a visual standpoint, it looks like the left Y motor gets more power, or power before, the right Y motor, but that’s just what it looks like.

Here’s what I have tried so far (not in any particular order):
Loosened belt tension on Y rails. This made it worse.

Tightened belts. Back to where I was.

Checked all V wheels, and tightened the eccentric nuts just past where the wheels move freely.

Cleaned all wheels to make sure no loose material stuck on any of them.

Triple checked all wiring to make sure I didn’t miss something. All seems fine.

Upped the power on the Z pot over several tests. This did not seem to fix anything.

Checked squareness of entire assembly, as well as straightness of the Y rails. All good and solid.

Any suggestions?

Disconnect your belts and loop them out of the way so that you can move the gantry forwards and backwards by hand. Does it move freely and easily? If not, readjust your v wheels until it does.

I had issues with overly tight wheels that caused too much drag to allow the motor to easily move the gantry. Once everything moves nicely without belts, then you can look at belt tension as a factor. They should be tight, but not so tight they impede movement.

Thanks, Rodger

I did try as you suggested, but I am still getting slop or twist when the left side Y plate moves first, and the right side needs to “catch up”. I adjusted all v wheels with the belts off, made sure the toothed spindle nuts were firmly in place, and repositioned and tensioned the belts. Now I am getting a bit of chatter along the Y axis as well, almost 100% on the right side. I did some air cuts, and noticed that the right motor spindle seems to have a “lag” and back and forth jog for a 1/4 of a second before engaging to catch up with the left side.

So now I am stumped.

Hmm, the lag sounds like maybe a loose pulley. Are you sure that the pulley set-screws are positioned on a flat of the motor shaft? I had them offset initially and there was enough torque for the motorshaft to rotate within the pulley for a few degrees before the set screw caught it.

Also, when you notice the lag, is the lag in the motor moving, or the pulley moving? You can tell if you put your finger on the motor case and feel for it to turn. If the pulley doesn’t move at the exact time you feel the motor turn, it’s slipping.

I checked the grub screws on both sides. Made sure that both pulleys are set against a flat side of the shaft, so that’s secure. Moving the assembly and making the spindle turn shows no lag.

At this point it is starting to feel like it may be an electrical issue, but I am at a loss as to what that may be. I have adjusted, loosened, tightened, and everything physical I can think of, and I feel like I am starting to make the situation worse. Getting into the weeds, as it were.

One thing I did try this morning was to replace the 4 button M5x10mm screws in each gantry that attach the the X axis with hex head M5x14mm bolts with a lock ring washer on each. Both sides. That seemed to decrease the “flex” of the X axis vs the Y rails about 50%, surprisingly. I also took off the Y axis stiffening L brackets that attached to the waste board, just to make sure they weren’t pulling the Y rails and creating some binding along the length. Can’t say it really changed anything, but it somehow feels smoother along the length. I did check the distance between the Y rails agina after that just to double check, at multiple points, and it is dead on, like within 0.5mm at any point. Not sure I could get closer than that.

So, I throw down the challenge gauntlet once again. Any further suggestions?

Triple check motor coils, all wiring to the motors, swap motors and see if problem moves, run motors with out belts on bench. You will find something I promise.

I will try that in the morning. I have to ask though, what do you mean by checking the motor coils? That part of the machine is certainly not my area of expertise. :slight_smile:

I did run some air cuts with no belts, and there did not seem to be the lag and jog on the spindle, but the left gantry definitely still moves first, almost jerking forward. I will swap motors around tomorrow and see if the problem persists.

Well, swapping the right motor with the Z motor seemed to help substantially, but it’s still not perfect. The new Z motor (previously right Y) is still smooth, and the jerking of the gantry is less. I lowered the feed rate to 20 for an air carve, and that minimizes the jerking. After a couple of more tests, anything over about 40 seemed to cause jerking and substantial shudder along the Y axis. The jerking of the gantry is worst when the machine goes from home position to the start of the carve. Is there a way to slow down that movement so the harsh jerk in the Y axis is lessened?

I feel like I am 99% there, everything else is working great. But there is noticeable shudder in the Y axis now. Even moving the gantry back and forth slowly by hand, it feels like I can feel the teeth of the pulley and belt, like little bumps along the entire length. The X and Z axes don’t seem to have this feel, they are smooth as silk.

I have tried upping and lowering the belt tension, and it only gets worse either way, so I feel like I am at a sweet spot for that, but maybe not.If I could get the bumpiness out of the Y axis movement, and slow down the machine when jogging distance or starting from a far away home position to start a carve, I would have this thing dialed in.

I appreciate all the help and suggestions so far.

Just loosened the belt tension on the Y belts, and reseated the teeth on the pulleys, and fine tuned the position of the pulleys in and out to get a consistent belt position without it moving in and out. That seemed to help quite a bit, but the shudder is still there when running too fast or slow.

And none of this has done much of anything to eliminate the fact that the left Y side still moves first, more smoothly, and seemingly more powerfully, which causes the entire gantry to get out of perpendicular to the Y rails, every movement either backwards of forwards.

Very frustrating.

Problem solved! Cover the dogs ears, but this thing is now purring like a kitten!

I went to rewire the connections on the right Y plate, the lower ones linking from the opposite side. As soon as I undid the screw for the gray one, the ring connector fell off the wire. Guess I didn’t crimp it down well enough. fixed that, and all problems are totally gone. No flex out of true on the X axis, and both Y assemblies move smoothly and chatter free.

3 days of tracking it down, and it ended up being the simplest thing. Lesson learned.

I truly want to thank Roger and Joshua for being supportive and getting me to this point. Thanks guys. Glad I stuck with it.

And now, on to some carving!


Hooray!!! So happy for you that you found the problem. Now I can’t wait to see what you make with it.

Thank you all for this topic. I had the exact same problem.

Went over the entire machine doing mechanical adjustments.

As it turns out the black right side motor wire was completely disconnected
at the left side terminal block.

Smooth as buttah now. The upside is that it’s all calibrated now.

Thanks again.

Good advice. It was put together some months ago though with no problems - what happened here is that the wire got snagged on something and pulled free. Remarkably the machine still mostly worked, resulting in an agonizing troubleshoot.
The X-Carve does have quite a few exposed, at risk connections - Need to build some wire guardians.

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Hi, I am currently experiencing the exact same problems right now. I triple checked my wires, theyre all nicely connected. Tried adjusting V wheels for both Y1 and Y2 over and over again… Cant find the solution… My belts also are as tight as the X Axis which runs like a charm. I also tried runing with only one motor at a time on the Y axis. When I do so i get a nice consistant pull on the motor that runs but it seems that I have a wobble on the other hand. I just cant get the 2 motors on the Y to run perfectly timed and perpendicular. Need help!!!

If its any help I run the 1000mm X carve with the X controller with 23 NEMA stepper motors.


I may have just realize that the polarity from one motor is inverted. How can I change that on only one side?

Yes I just saw that from other topics. Thanks alot Phil! Your a beast and dont stop your good contribution to this community!!!

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