angled striations on faces from extruder

Hi folks,
just about got my head around using Kisslicer, must say I like it a lot.
I've been working through calibrating the extruder by adjusting the flow tweak.

I've noticed an interesting problem with the printed surfaces. They have angled
striations that change depending on settings. Now I know this is caused by
the extruder because as I adjust the flow tweak the angle and density of these
lines change. All the idlers now have sprockets with bearings.

I'm just curious as to what is happening in the extruder that is causing these
striations? Can someone explain?


Many thanks,
Andrew

In my case that effect was caused by the stepper driver. I use drv8825 drivers which can't accurately operating in the bottom 12% of the supplied voltage range, as described here: [cabristor.blogspot.ca]

With some stepper motors that means that instead of a steady rotation it pauses for a few micro-steps, then jerks to the next position. If this happens with the extruder you get an uneven rate of filament extrusion that causes visible banding in the print. The problem is easily solved using back to back diodes in the connections to the motor, as described in the link above.

For sure it's not the only possible cause of extrusion artefacts, but if you are using drv8825 drivers it's probably the first thing to check.

Okay,
just read the article, most of it went over my head at 30000ft in a 747. I was left
with the impression that diodes are good and 12% bad.
The circuit, almost too simple to call it that, is a walk in the park to install. I give
it a go in the next couple of days.

Obvious question, I can assume the people have played with changing microstepping
and had no effect?

Thanks JamesK,
Andrew

Quote

Obvious question, I can assume the people have played with changing microstepping and had no effect?

I didn't, but I would assume it reduces the problem. I like the benefits of micro-stepping and wasn't keen to back off the micro-steps if there was an easy alternative. The trade off with the diodes is you are reducing the voltage headroom that the stepper driver works with, so there might be a reduction of torque at high rpm. I have noticed any loss of performance in practice though, running with 12V supply.

Hi JamesK,

Tried the diode array but ended with a stepper making a nasty thunking noise
which only partially worked in one direction.

Ripped out the DRV8825 and put a A4988(?) in and the ripples seem to have
vanished. Never thought downgrading was the solution.

Thanks folks

Glad you solved it. I had the same thing with the diodes when I accidentally put in a pair facing the same way instead of back to back. Since the A4988 solved the problem you can be pretty sure that you're on the right track with the diodes, so you might want to try it again if you want the higher current capability and 1:32 microstepping of the DRVs back I'm using diode pairs on all of my steppers now, so I know it works.

Thanks folks