Insane chatter / jumping when jogging x and y

No idea why this is happening. I’ve tried my best to adjust the bearing bolts so nothing is too tight or too loose but cannot figure out why its so jumpy. Below is a video link where I put a cut of water in to visualize vibrations.

Any suggestions?

@moderators any ideas?

What’s your build size? Larger MPCNCs start to swing, mine was 75x55cm and had the problem, being worse in the middle.

Mostly didn’t affect the cuts though, but was definitely noticeable and made a noise while cutting.

There may be only one person to fix that…

Yes, I passed on the Jurassic Park reference. That was too easy. :clown_face:

build size is 30x30 inches. And it doesn’t seem to get worse in the middle. It seems to be jumpy just all the time. even towards the corners of the machine.

I’m starting to thing it has something to do with the belt tension? I quite literally have no idea how to set the belt tension. Everything i’ve found basic just says “tighten it until it feels right…” wtf does that mean lol

I also have some gouges in the conduit rails from where the bearings are starting to dig in. Is that normal?

Overall, The machine just really seems to be struggling to move the gantry (hence the vibrations/ shakiness/ chatter). I am thinking something with the belt tension. But hey, I could be wrong and am totally open to suggestions.

My issue seems to be similar to this guy’s issue

The bearings should be touching the rails, but that’s about it. They shouldn’t be “grabbing” the rails. The belts should just be at the point where they start to thrum rather than flop when you pluck them. Not an actual note, but just enough to generate a vibration rather than overdone fettucine.

If you turn off the machine (and unplug the steppers for good measure, so the back EMF doesn’t wreak havoc on your controller), how easy is it to move the gantry by hand? You should be able to move it with very little effort.

Everything is basically just constraining everything else. There’s surprisingly little clamping action going on in the design. Really the only places that clamp are the feet and other fixed-locations on rails. I think Ryan (or someone) has mentioned running a rig without nuts on the bolts holding some of the bearings. If you have those cranked down too tightly, you could be braking the bearings… Although I think there are “bushings” designed in to the parts to prevent or minimize that.

I am not seeing or hearing anything unusual. Maybe I’m just not getting it.

What does it look like when you draw a crown?

@kvcummins Thanks for your reply. When I remove the belts altogether and remove the stepper motor, the trucks slide like butter. So i don’t think the clamping force is an issue. As soon as I attach the belt, I cannot move the gantry by hand without pulling the entire machine around. Gantry is basically locked in place.

I just adjusted the belt tension just past fettuccini (so it makes a low thud when i pluck it), and it now takes like 10ish pounds of force to move the gantry. (that is without the z-axis mounted. literally just the gantry sliding on the rails). So i think im making some good progress! Thanks! I also think my z-axis may not be perpendicular so I am currently printing a perpendicularity tester.

Also, is the gouging on the conduit normal? The bearings seem to be digging in a bit.

Gonna throw everything back together and run a test to see what’s up. If yall have any more suggestions please let me know! Thanks!!

Landon

That is quite large and explains the chatter you are seeing. You can measure the tension of the belts with an app called “Carbon Drive”. It is meant for bikes with belt drives, but works for an MPCNC as well. There are two topics buried in this forum that give you a few ideas about which range you are gunning for. :smiley:

I don’t see how this is even possible unless steppers were engaged? With steppers not engaged, it should be very easy to push around with less than 1lb force. If something around the steppers is binding, that’s going to be really bad.

Can you show a picture of how the belts are wrapping around the stepper pulley? Can you find where the resistance is coming from?

Really??? No link??? I thought you were better than that!!! LOL

F… off… Here you go: Belt tension test rig
Mind you, this is for 6mm belts. The 10mm belts are different, but also calculatable.

/edit: This is also interesting: Measuring belt tension, squaring and calibration - Shapeoko - Carbide 3D Community Site but!!! way too tight for the LR or Primo. But it gives you some good ideas.

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Perhaps try unplug the steppers and see if it still moves freely? You could have a dead driver or shorted coil in one of the stepper motors.

Maybe you have one of the 4 wires on steppers not making contact. Do a continuity check and make sure you didn’t crimp wire sheath and not the wire conductor.