Delta printer twisting beginning of print

kjiwa

Thanks for the tips @giostark. But as discussed earlier, I'm fairly certain the rod length is accurate, and as I had mentioned, I was able to make good quality prints before when I was using the RAMPS board.

We're at a point where the twist is gone from my prints. It is a small print, but this indicates that my towers are likely straight, and not bowed or highly angled.

The issue I am seeing now is with layer shifting in the calibration cube where the letters begin and end. What could be causing that? There are entire sections of the print that are straight. It's only when there is a change in the object that the layers shift a little bit.

Calibration cube side profile

bot

The angle that the firmware was adjusting for was the tower's placement around the circle. IE the Y tower was not evenly spaced compared to the other two.

giostark

What happen if you try to print this object on one side of the bed? Maybe close the border?
The shift is there but the right side is more bended of the left one. The center is more narrow of few mm (from the picture).
Please try also to give the full power at the motors.

giostark

OT/
Bot , so this is you !!! (just kidding )
https://www.reddit.com/r/3Dprinting/comments/fohhwo/muahahaha/?utm_source=share&utm_medium=web2x
/OT

kjiwa

I put some more work into my build and managed to get rid of the twist. My prints are coming out very nicely now. Thank you everyone for the help.

I believe my issues came from two major areas:

I mentioned earlier that my bed had some tilt to it. I was aware of the tilt, but I was under the impression that the Duet controller could compensate for it. The documentation states that a level bed "isn't essential, because RepRapFirmware can compensate for [it]." Anyway, I redesigned my bed mounting parts and gave the bed a lot more support.
I am using FSRs, but I had not done a great job of calibrating them. This meant that in some cases the nozzle had to depress the bed a lot to generate a reading. When I redesigned the bed mounts, I also used the opportunity to calibrate the FSRs and to make sure that their ambient resistance was in a range where they would be sensitive enough to detect approximately 500g of mass.

I still have some other settings to dial in now, but at least I can move on from worrying about the straightness of my prints. Thanks again!

kjiwa

I was a bit premature in declaring victory. I continue to have issues with layer shifting and autocalibration. At this point I've tried almost everything except replacing the steppers. I've taken everything apart, measured parts to ensure they are sized accurately, and replaced the timing belts, pulleys, and idlers. Still, no improvement to the layer shifting.

What's really confusing me is why the autocalibration gives me such wild results between runs. Here is the output from the last few invocations of G32:

Diagonals 215.000:215.000:215.000, delta radius 105.620, homed height 236.757, bed radius 70.0, X 1.482°, Y 0.880°, Z 0.000°
Diagonals 215.000:215.000:215.000, delta radius 110.722, homed height 237.256, bed radius 70.0, X -14.987°, Y -7.550°, Z 0.000°
Diagonals 215.000:215.000:215.000, delta radius 106.415, homed height 236.746, bed radius 70.0, X 1.289°, Y 0.492°, Z 0.000°
Diagonals 215.000:215.000:215.000, delta radius 105.221, homed height 236.595, bed radius 70.0, X -1.524°, Y -0.171°, Z 0.000°
Diagonals 215.000:215.000:215.000, delta radius 106.281, homed height 236.804, bed radius 70.0, X 1.278°, Y 0.430°, Z 0.000°
Diagonals 215.000:215.000:215.000, delta radius 106.814, homed height 236.817, bed radius 70.0, X 0.138°, Y 1.348°, Z 0.000°
Diagonals 215.000:215.000:215.000, delta radius 106.660, homed height 236.546, bed radius 70.0, X 0.512°, Y -0.868°, Z 0.000°

This is just a sample from today. There are times when the control board detects nearly 0 degree offsets, but most of the time it's something like 0.5 degrees. The second one you see is a bit crazy though -- it thinks my build has a nearly -15 degree angle! This is my first ever build, so I may not have done a great job, but I can assure you that nothing about my build is this inaccurate. I have also watched every moving part very closely, but my eye is unable to detect any sort of wobbling or movement.

@dc42 You mentioned two things that I thought might be the culprit: my belts and the diagonal arms. I tested the arms and they are all the same size (measured as best as I could with my tools). I also wondered if I had abused my belts, so I replaced them in case there was any stretch or wear.

Any other suggestions? Could it be my linear rails? Or might the motors have some issues?

kjiwa

Just to close out this thread... since this is not a Duet-related issue I've moved the thread to the deltabot forums on Google Groups: https://groups.google.com/forum/#!msg/deltabot/MKpY_hvHnLE/vij7Q4LOAwAJ.

Thanks again for all of the suggestions here.

dc42

@kjiwa said in Delta printer twisting beginning of print:

Any other suggestions? Could it be my linear rails? Or might the motors have some issues?

Loose pulley grub screw?

kjiwa

@dc42 Thank you. I also replaced and tightened down the pulleys. They seem firm and in the right positions.

kjiwa

I think the next thing I'm going to try is a new set of arms. It seems like the preassembled rods on AliExpress are about the same as the cost of materials, so I'm going to give them a shot as well as making some new ones of my own. I'll update the thread once they arrive (which will not likely be any time soon given lead times from China these days).

giostark

Can you do something like this?
https://forum.duet3d.com/topic/6951/not-yet-solved-tevo-little-monster-duetwifi-errors/137
In my experience, unlucky (but I have to admit that the adversity helped me to understand the things) the cheap china product are similar to the roulette.
In my specific case, and I hope truly is not your too:

holes of the towers not aligned with the holes of the top and base.(so basically everything was a little twisted)
rods of different length (supersonic mess)
bltouch not accurate as stated.
the bed glass is glued not parallel to the aluminium frame , so it look like always bend. (I had to use spring under the bed and with the digital caliper pinch the glass and the frame and measure the right height between the towers)
I had to dismount everything 4 time before to understand all the tolerances.
I'm still working on it.
The Haydn rods are really sturdy and accurate but not cheap. And...not suited for hight temp working (hot chamber with 50/60+ degree)

kjiwa

Thanks @giostark.

Frame alignment: When I disassembled the printer and began reassembling it, I checked for alignment on the top and bottom frames. I also tightened them down with belt clamps. I think they are in good shape.

Rod length: I'm beginning to suspect my rods more and more. Currently the measuring tools I have can only give me accuracy to within +/- 0.2 mm, so I don't think I can detect errors to the degree stated in the post you linked.

I did not get them from China, but when I inspected them more closely I found one that had a loose ball joint and another one that had the ball joint glued in at a slight angle. When I repaired them, I measured them all to be the same to within that 0.2 mm margin, but I'm guessing that perhaps that is too wide of a margin for accuracy.

BLTouch: I'm not using a BLTouch.

Bed: This was previously an issue, but I've since fixed the bed mounting and the glass is very secure and level on the frame now.

giostark

Ok,
Also I suggest you to verify those alignments.
Those must be at the same equal distance.
Doing this I reached that the X and Y of M665 are gone from several decimal to some cents.
In those trap we must gain as much precision everywhere
In my case for obtain the more possible equal distance , I was not able to keep the tower aligned with the top frame.