Minimum recommended steps per mm for extruder
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Hello!
Can somebody with direct (I mean without bowden tube) extruder tell me is print quality of surfaces decreases with lower microstepping?
What is minimum recommended steps per mm for extruder to get decent print quality with 1.75mm filament?
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The issue with less micro-stepping and ungeared direct extruders is pulsing with low flow rates which can cause artefacts. I was using 93 steps/mm at 1/16th microstepping with a mk8 extruder and pulsing was evident. You need to be at 200+ steps as a ball park estimate to avoid it most of the time, if printing very slowly you'll get some pulsing at this step/mm also. Something like a 3:1 gearing helps like the E3d titan which at 1/16 needs between 300-400 steps/mm. I've a small direct extruder based on a nema 14 with 5:1 gearbox. Why do you want to use less than 1/16th microstepping? Consider making some gears.
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@DjDemonD thank you for your answer!
I'm thinking about something like this solution: http://forums.reprap.org/read.php?1,661444,page=1
For example, Pololu's geared micromotor with carbon brushes: https://www.pololu.com/product/3054 and magnetic encoder (12 counts per rev): https://www.pololu.com/product/3081 will provide 12*210 = 2520 steps per revolution.
My current setup is 200 steps/rev stepper with 5.18:1 planetary gearbox with 1/16 microstepping and about 450 steps/mm setting. I'm using long bowden tube. So it's about 16582 steps per revolution.
So with DC motor I will get about 450 / (16582 / 2520) = 68.39 steps per mm with the same hardware. Seems like quite low for me, that's why I'm asking about this.
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I am not sure whether the pulsing will occur with a DC motor, if anything I'd say since the drive for it is either on or off, it should provide much smoother extrusion. Whether its as precise is another matter altogether.
I like the DC motor idea for an extruder its certainly light. The question is whether it will compete with something like flex3drive or (if they can get it to us) Zesty where the extruder is 30-50g and the flexdrive and worm gear is around 35:1 so steps/mm are in the 1800 range at 1/8th or 3600 for 1/16th - no issue for duet. The issue with these is fast retractions are difficult to achieve because of the gearing. I still use a flex3drive and am very happy with it, although I sheared the flexdrive after around a year of printing with it, easily replaced..
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Yes, I know both about flex3drive and Zesty's extruder. But I thought to do everything myself. This is just small experiments with my delta printer in spare time.
About gearing - seems like highly geared dc motors from Pololu will be very slow with 12 CPR magnetic encoders. For example, 1:1000 geared dc motor will have only 32 RPM speed with no load.
I have also various high density (150-180 lines per inch) circular optical discs (encoders) from inkjet printers, but they are quite large (relative to motor itself).
