X/Y Jitter, Middle Assmbly Problems

I have a 5’x5’ build, 48" x 48" cutting envelope with rail supports. I am using all the updated 525 parts, printed by me. Running with mach3 using breakout board and haoyu tb6600 drivers and 42BYGHW811 steppers 67oz-in.

I have been trying to troubleshoot a Jitter problem I have been having. It is being transferred into the work. Here’s what I have done to to try and resolve the issue.

  1. Reconfirmed the frame is square and parallel. Diagonals and side rails are all within 1-2mm.
  2. Tighten the belts to what I what I figure they should be and have adjusted a little beyond. Too tight?
  3. Sanded all rails with 280 grit.
  4. Square the rollers using a measure tape before tuning on the motors and locking it in square.
  5. Played around with different speeds.
  6. Played around with the stepper current with not significant change.

I have also played around with the middle assembly tension bolts and have noticed that I could not get both tension bolts a and tension bolts b to make full contact. Not sure if that matters and if so how to fix it. The jittering also seems worst when x and y are moving at he same time, like circles, curves and diagnonals. I think I have mentioned everything I can think of at the moment. P.s I do love my mpcnc, great design. Also I have used all the electronics on a different cnc with no trouble in the past.

Thanks, Nathan.

Do you inow what your step rate is? Too low and it is noticeably twitchy. Micro stepping at 1/4 or higher is best as far as I can tell. 1/8th is really smooth.

I have the exact same size machine with exact same problems. Performed all the same trouble shooting steps. My worst jitter happens on the x axis more then the Y.

My microstepping is 1/32 i think, all the jumpers on the ramps installed and DRV8825 drivers. Should we change that to 1/8 (jumpers 1 and 2 only, steps/mm = 50)?

My conclusion up to this point is the rails must be flexing on the tiny pits in the EMT conduit causing it to bounce back as it rolls. My solution very soon will be to reprint the entire thing and upgrade to 1" stainless rails.

I’m running at 100 steps per unit with 16t pulley. Running in 1/16. Should I maybe try 1/8 or half?

No, the higher the step rate the better.

Are you using EMT conduit as well?

I don’t think that is really causing the problem as mine doesn’t happen repeatively in a certain area and to the same degree running the same code in the same location, also is seems like a little to play to be the flex only at certain times. Maybe wrong but I don’t think that really seems like my problem. Thanks.

3/4 EMT 23.5mm

I was think about adding a second set of rollers to shorten the axis’ for jobs that are smaller and require more precision. Basically cut the machine in half which would double the rigidity of the gantry rails

Does yours seem worse the slower it moves?

No I would say that it seems better but it’s also moving slower so I think you just can’t notice the twitch because of the speed. But if I cut a piece of material slower it’s seems to turn out the same or maybe a little better.

Do you think the the middle assembly bearing no making full contact all the time could be playing a part, tension bolts a and b. Also I am using unshielded wiring so could interference be causing missed delayed steps and the two motors on the same axis aren’t moving at the same speed for that moment? Just a thought.

I have tightened all the bolts on mine so all the bearings touch and it made it worse. I ran it real tight for a few hours hoping to wear the zinc coating off the rails. It did wear a bunch off but did not improve smoothness of the movement.

I am almost 100% convinced that it has to do with the texture, length and flex of the emt rails at that length. I discovered yesterday that my local hardware store has 1" x 72 stainless closet rods. I am going to start reprinting the 1" version. Those closet rods and quite noticeable stronger then the emt.

@vicious1 can I leave the 3/4" legs in place? Will the 1" corner pieces sit on top of the lock corner?

Yes the other size legs and locks should fit close enough. I just checked, and they are just a bit smaller so you probably won’t even notice the lock to bottom difference.

So i finely tuned my stepper drivers and metered them out and it did see, to make some improve. But i decided to run a breaking code drawing circles and while examining the machine I noticed that on every rollers there is one or 2 bearing not making contact at all times. Could this be causing the Jitter and how would I fix it?

All roller bearing were making contact at time of install

Take the middle assembly out, by removing the roller motor mounts only, and inspect everything again, something obviously moved or seated in a bit more. while apart Check to make sure the frame is square, all the roller bearings touch again, and the middle assembly is still square with the z axis in place.

Pulled the motor mounts, checked the frame everything in the outer rails are square and parallel.

The rollers have all worked loose, I have attached a video below. At time of install they were all tensioned the same and were snug on the rails. What would be the best way to snug these up again?

Also it do look like the middle is out of square. What would be the best tension bolts to adjust this?

The rollers snug up with the long bolts, and the middle is best to try and just mess with the 6 long bolts but if it doesn’t square up take it apart and re assemble it. It doesn’t seem like a bad thing, your parts just relaxed a little I would guess. I know it’s a bummer to have to redo some of it but it will probably be much more solid this time around.

Could be the plastic, could be the weather who knows.

Ok took the middle assembly apart and redid it and made sure it was square. So cut out some circles and they are from circles. What could cause this. It seems like it’s out mostly in one axis. I checked the belt tension and all seems even as before. Any thoughts?

Also… I done some test squares and they were perfect width and diagonals.

Cut larger circles, much easier to calibrate and diagnose issues. Or if they are large put in a tape measure or something to show scale.

Make sure you are not using arcs. It looks like you have arcs on and they do funny things to small circles. I have not calibrated them in the firmware as I haven’t had time to fully dig into the formulas yet.