Problem printing circles

Phaedrux · 17 Jul 2018, 21:50

@obeliks I'm not so sure about that. I've seen detect thin walls do some crazy things.

I think the reason that reducing the resolution makes things a bit better is that detect thin walls is basically pulsing the extruder at the start of a segment and then dragging the blob of plastic out to try and get a thinner extrusion width than you've actually specified. By reducing the resolution you now have fewer and longer segments so it has to pulse less.

On a slightly related note, just the other day I noticed that someone has a pull request outstanding for Prusa Slic3r to completely redo how thin walls are handled. It looks promising.

OBELIKS · 17 Jul 2018, 21:53

Can you check both gcode files, and see how many lines you get for the second ;BEFORE LAYER CHANGE
Because for me it doubled with thin walls disabled.

Phaedrux · 17 Jul 2018, 22:02

@phaedrux said in Problem printing circles:

full gcode

https://www.dropbox.com/s/ormosogim0yaeq2/sliced gcode.7z?dl=1

They can be found here.

OBELIKS · 17 Jul 2018, 22:09

Thanks. I'll check tomorrow.

OBELIKS · 18 Jul 2018, 05:31

I will also try the solution from this thread: https://forum.duet3d.com/topic/6078/core-xy-movement-issues/57

OBELIKS · 18 Jul 2018, 16:12

So in additon to the fix above I also erased firmware and uploaded 1.21 Nothing changed.
Turning off thin wall detection in Slic3r did help with the juddering, but not completely.
Cricles still have flatspots on top and bottom, and printer still sounds rough.

So I need to find some time to wire the old board back in and test the steppers.

Phaedrux · 18 Jul 2018, 16:14

@obeliks In addition to turning off thin wall detection did you also change your extrusion width to 0.4?

OBELIKS · 18 Jul 2018, 17:09

Yes, and it is a different model anyway. So that is not really needed.

OBELIKS · 18 Jul 2018, 18:47

OK, we can stop blaming DuetWifi. I took the time (and anger at some relatives) and I switched to the old board. The uneven circles are almost the same.
Left is DuetWifi and right is Anet board, same gcode

Now that I have the old board on, I will do another test with Cura and S3D. But that will wait for tomorrow.

sigxcpu · 19 Jul 2018, 10:32

That is backlash in Y axis (if this is the printing position). There is also a smaller backlash in X axis, too.

OBELIKS · 19 Jul 2018, 10:36

I hope this is true.
I really need to reduce weight of the bed assembly. I ordered PCB bed without ALU and thinner glass. That should save me around 500g, and if this goes well I will replace the bed frame for ALU also, at the moment I have inox. That would mean at least 200g.

sigxcpu · 19 Jul 2018, 11:24

Unless you have very shitty belts that strech like crazy, there is no reason for the weight of the moving things to generate backlash. I have it too in Y on my CoreXY, but I am sure it is not the axis weight which is pretty thin.
If you suspect the weight is an issue then you can play with motors currents and/or acceleration and see if there are any changes.

timcurtis67 · 19 Jul 2018, 11:43

@sigxcpu said in Problem printing circles:

Unless you have very shitty belts that strech like crazy, there is no reason for the weight of the moving things to generate backlash. I have it too in Y on my CoreXY, but I am sure it is not the axis weight which is pretty thin.
If you suspect the weight is an issue then you can play with motors currents and/or acceleration and see if there are any changes.

I agree with this. @deckingman probably has the heaviest print head axis combo of everyone on this forum and he doesn't complain about backlash.

Ian, do you want to comment about this?

OBELIKS · 19 Jul 2018, 11:57

My bed assembly is in the region of 1,5kg

deckingman · 19 Jul 2018, 11:58

@timcurtis67 said in Problem printing circles:

Ian, do you want to comment about this?

Not really ............................

But since you asked...... I have 4kg split between two gantries so roughly 2 kg per XY mechanism. "No name" 6mm GT2 belts. Max X axis speed 50,000, max Y axis speed 35,000, accel 1,000 for both, jerk 600 for both. I have experimented with high print speeds up to 300mm/sec and my default non-print move speed is 350mm/sec. No sign of backlash but everything is pretty rigid. It'll print OK at higher accelerations but with the mass being over a metre above the floor, the printer tends to start to rock about a bit at high speeds.

As an aside, I don't get ringing either - one advantage of high mass

OBELIKS · 19 Jul 2018, 12:06

Hah, I have a i3 style printer. So it is moving a lot.
I will investigate the whole mechanics of X and Y, something is wrong there, that I am certain.

Aaaand, he deleted the post

deckingman · 19 Jul 2018, 12:08

@obeliks said in Problem printing circles:

Hah, I have a i3 style printer. So it is moving a lot.
I will investigate the whole mechanics of X and Y, something is wrong there, that I am certain.

Aaaand, he deleted the post

Yes, I realised my mistake - hence I deleted the post. For some reason I thought yours was a CoreXY the same as mine.

Edit. So in which case, you could well have backlash or movement issues in Y

Phaedrux · 19 Jul 2018, 19:48

You could try reducing the accel and jerk for your Y axis. I think in your config you have X and Y the same. It's not uncommon to use different values for i3 style printers because of the bed weight.

OBELIKS · 20 Jul 2018, 07:22

I was thinking, and in the end it is probably a problem with the sintered bushes that I use instead of bearings.
Image by Toolson

I made a stupid decision and lubricated them, and they still move, but the moves are "sticky". I will try to clean them, and maybe switch back to linear bearings. I just need to find good ones.

Is this still the right category for this thread?

OBELIKS · 22 Jul 2018, 07:46

I took X and Y axes apart, cleaned all the components, so now it is gliding as good as it can. Positive is that printer got quieter, negative is that the circles are still flat on top and bottom.
I am slowly running out of ideas.
The only part that I still need to investigate is the print head. But it is rigid as it ever was.