Extruder cable shielding improved surface finish (slightly).
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Long story short, all three axis stepper motor cables are shielded (EMI mesh sleeve) on my delta printer (although this could apply to any style) so I skipped doing it on the extruder. Half-assing it bit me again and it may be what got rid of the irregular surface ripple that kind of looked like a salmon skin/moire pattern that you only really see when the surface is glossy. Yeah, that really fine one that drives some of us crazier than massive ghosting does. Until this point I had no indication my electronics had any glaring issues and wrote it off thinking I had that well in hand. I just glared at the delta my mechanics blaming them as the source leaving me completely stumped for what the real cause was though. Anything that seemed a plausible mechanical source I reached out to fix hoping it would be the thing to remove those tiny artifacts even though it didn't match up with anything obvious math wise.*
I discovered this while I was playing with the new input shaping plug-in. My hotend fans are normally always on and I unplugged them while using the accelerometer to decrease the noise level on it. Then while toying with the plug-in I heard extruder noise that was almost a whine that I couldn't hear over the hotend fans. I noticed it while homing and then dead quite after homing was done made it stand out though. So I homed again and reached over to feel the motor, and it's vibrating with some oscillation when the axis motors are going. I just sat for a minute with my face in my hand and wishing I could give past-me a slap to the back of the head for stopping 3/4 of the way through on shielding the motor cables. I wanted to share my success on this in case it can help anyone else frustrated with calming the waves in the specular reflections even if it is also a facepalm moment of shame.
*- That isn't to say there aren't other things causing it in another build. I just have happened to already done my best to mitigate them in previous rabbit holes on belts, pulleys, eccentricities on anything round and rotating, arm lengths, arm joints, arm spacing, then arm rigidity, all the extruder bits, fan vibration, frame vibration, bearings (both the linear slides and stepper motor bearings), chasing this stupid pattern.
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@lord-binky I'd love to see some photos to compare with/without shielded wiring (-;
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Do you shield them singly, in pairs, or shield all four wires with a single shield? Are the wire pairs twisted before shielding? How long is the cable? Are there other wires running alongside the motor wires?
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@oliof I plan to do this, i had fixed it right before i got started doing a bunch of gardening prints for my wife and i wasn't delaying justification for my hobby. I'll get before and after prints comparison probably saturday unless my son does the impossible and goes to bed on time tonight.
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@mrehorstdmd Link below to the sleeve i used, I've used grounding strap before as well but that was much larger than necessary although cheaper. The extruder motor cable crossed a few other cables perpendicular to them so i thought interference would be low and ran up a couple feet parallel to other cables about 8 inches away from hotend wiring (fans, probe, thermistor, heater). I have twisted the stepper wire pairs before but haven't this time, i needed the length.
Still, none of the power hungry hotend components were active when I identified the issue, so i suspect the extruder wires running across the duet near the motor drivers is where it picked up noise. Ideally making a new duet enclosure and shielding that in a safe manner would reduce noise on anything else unshielded too. I don't see any indication of EMI issues elsewhere though...well besides the occasional heatbed mosfet singing. That'll have to wait till i finish with replacing the hotend fans with a cpap blower though.
If you have concerns about bare metal sleeving floating about, gutting paracord is an inexpensive way to get some nonconductive (nylon) sleeve to run the shielding. As to the specifics, i just popped out the pins of the connector on one end and ran all 4 wires in the sleeve (taped them together while sleeveing). Grounded it initially with an alligator clip between the sheath and input ground.
Electriduct 1/8" Tinned Copper Metal Braid Sleeving Flexible EMI RFI Shielding Wire Mesh (0.08" Diameter) - 25 Feet https://www.amazon.com/dp/B01BIBQBCK/ref=cm_sw_r_awdo_7CQKEEDRMG84QEZYV47S?psc=1
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So i couldn't recreate the issue with another cable..Frustrating when trying to show shielding fixed the issue, but I'm still confident that was what helped...mostly. Still, I had another test print showing what i have moved away from when EMF was an issue regardless of the solution ( cable pathing or shielding). I adjusted contrast so the visibility was clear even if the colors are looking a little artificial. The surface issue was apparent in any print with the outer layer lower than 60mm/s.
