Help - extruded filament has tiny ridges every mm

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Re: Help - extruded filament has tiny ridges every mm

Postby cvoinescu » Thu Feb 26, 2015 1:43 pm

In that case, the 400 step-per-mm motor will help, but there are other things you can try. Try increasing the current: the small stepper drivers control the microstepping much more accurately at currents closer to the maximum rating. Use the finest microstepping available for your driver -- 16x, 32x -- because that reduces quantization artefacts. Supply voltage can also have an effect: 12 V can give smoother movement and more accurate microstepping than 24 V under certain conditions.
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Re: Help - extruded filament has tiny ridges every mm

Postby rocketwiz » Sat Feb 28, 2015 3:04 am

Increasing current doesn't do anything except make the stepper run hotter. Just a 1.8 extra turn resulted in a massive 30deg temp rise in the stepper!
I'm also using 1/32 microstepping on my 4988 clones.
The whole system runs at 12v.

I realise can hear the stepper 'step' during printing and now I wonder if the stepper that QU-BD supplied just hasn't enough torque to smoothly drive the filament against the pressure of the Bart's mode spring lever. In any case I have my new stepper in hand (it's longer than the QU-BD 48mm vs 40mm) and hopefully this improves things when I install it.
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Re: Help - extruded filament has tiny ridges every mm

Postby cvoinescu » Sat Feb 28, 2015 12:09 pm

The A4988 does not support 32x microstepping, so I'm sure you have another chip, perhaps the DRV8825. 32x is overkill anyway. Just out of curiosity, what's the current rating of your 40 mm motor?
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Re: Help - extruded filament has tiny ridges every mm

Postby rocketwiz » Sat Feb 28, 2015 12:54 pm

Sorry - my bad. I meant 1/16 microstepping.

The motor is rated at 1.2A according to the manufacturer spec sheet. The one I'm going to try has a more common rating of 2.4A.
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Re: Help - extruded filament has tiny ridges every mm

Postby cvoinescu » Sat Feb 28, 2015 4:09 pm

The bad news is you won't be able to get anywhere near 2.4 A with the A4988 (its design limit is 2 A, and that's only with excellent power dissipation and the correct choice of external components -- for instance, the original StepStick limits it to 1 A, on purpose). Depending on the actual specs of the motors, you may get more torque out of your old 1.2 A 40 mm long motor than out of your new 2.4 A 48 mm long motor. The good news is you probably don't need all the torque anyway, and the much lower impedance of the new motor will get you smoother microstepping.
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Re: Help - extruded filament has tiny ridges every mm

Postby rocketwiz » Sat Feb 28, 2015 10:24 pm

Hopefully that will be the case. My XYZ motors (full size nema 17s as you know) already run smoothly on these same steppers even at low speed. Although I'd never seen this filament pulsing issue raised with the QU-BD extruders before.
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Re: Help - extruded filament has tiny ridges every mm

Postby rocketwiz » Sat Apr 04, 2015 8:57 am

I think I've worked out the reason for the ridges - wet filament.

The filament I was using is quite old and was 'sealed' in ziplock with a bit of dessicant. I just took out another reel which had its bag torn and was exposed for a LONG time! Plenty of steam and popping on that test. Anyway the wet reel was put in the oven at about 70deg for 5 hrs and just did a quick print and no ridges/moire! It was the extruder gear biting into the filament after all. In fact I noticed that first lot of filament I was using started getting shaved in the extruder with bits of fluff coming out on each print.

Surprisingly though the original filament printed quite well ! The dried batch I think will need a lower temp.

Thanks for the help!
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