Very slight systematic waves every about 2mm on the prints

luc

Hi all,
I am trying to eliminate what you see in the photo against the light.. I have done several trials but can't find the cause. The curious thing is that it would appear to have the 2mm pitch of the belt but actually the pitch of the artifact is about 1.7mm. It is an XY core and the movement without the belt is very smooth, the pulleys run smooth and have no play. I had the X linear guide with some play but I changed it.
I print tests at 60mm/sec the outer perimeters.
M566 X900.00 Y900.00 Z60.00 E3000.00
M203 X15000.00 Y15000.00 Z600.00 E6000.00
M201 X1000.00 Y1000.00 Z100.00 E6000.00

I would like to hear your opinion?
Don't look at the angles in the picture it was a PA test.
Thank you

o_lampe

@luc It could be the infamous dual drive extruder pattern. Do you have a dual drive extruder?
Maybe the filament tensioner is too tight then?

Does the same pattern appear on all sides? If it's only on the opposite side, you might have a mechanical issue with this axis. ( damaged idler bearing or wobbling idler?)

luc

@o_lampe
Yes, on all sides it is the same.

Yes, it is a dual drive extruder. What can I try in this case? Change it? Change it to which one? (I will have to redesign the whole stand).

I don't see that the spring load tension of the dual drive makes any difference. I tried varying it during printing.

luc

Tried loosening the whole spring of the dual drive extruder without getting any change.

Checked all rollers and pulleys and.....incredible!!!
I have never seen such a thing!!! Belt rubber or maybe dust stuck in the tooth recesses!!!
I can clean it but with the occasion I put two new pulleys.

Notepad

@luc This could be many things, and is generally referred to as VFAs (Vertical Fine Artifacts)
Whilst there is not much you can do about it as it could be a variety of issues, I have a few tips that might be able to help find out where the problem lies.

Belt tension, If the belts are too tight the tooth patten may show up in the printed surface
Motor accuracy. Motors have predefined "steps" which the microcontroller smoothes out. Try printing the part faster or slower, and see if that changes the surface regularity. If it does, then it means you might have a printing speed close to the motors resonant frequency
If speed doesn't fix it, then it might be a bearing, either the motion system or the extruder.

In general on a 20T belt pulley, I find printers have 2 resonant speed frequencies, 60-80mm/s or 100-130mm/s. Try to find out which one your motor doesn't like, and avoid those speeds.
You also want to loosen your belts as much as possible without compromising your accuracy or risk belt slippage. its VERY easy to overtighten your belts if you don't have measurement equipment.

o_lampe

@Notepad said in Very slight systematic waves every about 2mm on the prints:

you might have a printing speed close to the motors resonant frequency

Interesting stuff! In car gearboxes they often use gears with a prime number toothcount to avoid such stuff. There it's torque-curve related, which is similar to the stepper motor.

I wonder if the resonance frequencies would be an issue with 17 or 19 tooth pulleys?
I may resin-print some pulleys to test this theory.

luc

Cleaning the pulleys slightly improved that effect but did not solve it.
I am waiting for new pulleys that I will install along with a new belt but I don't think I am getting any improvement.

I tried printing with a higher speed without getting any change.

I have tried printing at 45° with no change.

I tried printing with a 0.3 layer instead of 0.2 and got no change.

I tried redoing the PID of the bed and found no change.

By now it has become a war....me against her!

Translated with DeepL.com (free version)

luc

@o_lampe
The engines I use on X and Y are these:
https://www.omc-stepperonline.com/it/nema-17-bipolare-0-9deg-46ncm-65-1oz-in-2a-2-8v-42x42x48mm-4-fili-lunghezza-d-cut-completa-17hm19-2004s1

o_lampe

@luc said in Very slight systematic waves every about 2mm on the prints:

I tried printing with a 0.3 layer instead of 0.2 and got no change.

This should at least change the distance between the lines?

Your motors are perfectly fine. What we discussed about resonance is a common thing among steppers.

luc

@o_lampe said in Very slight systematic waves every about 2mm on the prints:

@luc said in Very slight systematic waves every about 2mm on the prints:

I tried printing with a 0.3 layer instead of 0.2 and got no change.

This should at least change the distance between the lines?

Your motors are perfectly fine. What we discussed about resonance is a common thing among steppers.

No, almost nothing changes. Maybe very little for the better but the imprint of those vertical waves remains.

luc

@luc
To assess whether the motors are the cause, I might try setting a different current.
They are currently set at M906 1700.

Are you thinking of trying a print at 1800 or 1600 or less?

Notepad

@o_lampe OO very interesting, I never considered the difference between 19 20 and 21 tooth. Id say start with 21 tooth as bigger pulley = more grip

Notepad

@luc Less current normally means less vibration force. If it works, Try 1200 or 1400