Getting both stringing and underextrusion

Turbo · 27 Mar 2020, 19:45

I cant seem to figure out what would cause such a thing, as it's generally one or the other. After failing many retraction tests, I figured I'd try a benchy to see if anything had changed. Now not only am I getting underextrusion, but I'm also getting stringing, as if theres not enough retraction. When I increase retraction, the underextrusion gets much worse and the same goes for decreasing retraction and stringing.

About the printer:
D-Bot Corexy Printer with an E3D Chimera hotend. Bowden setup with 600mm Capricorn tubing and titan extruders, all genuine.
this was printed with a .4 nozzle with Esun PLA+ at 210c (not a filament issue, works well on any other printer)

PrusaSlicer Settings

Maxed out cooling
2mm of retraction, although same results down to 1.3mm
40mm/s retraction speed, although increasing the speed hasn't helped.
60mm/s Print speed, pretty reasonable for the printer under normal circumstances
No pressure advance at the moment, as I was tuning extrusion shortly before this benchy.

It seems like its retracting more than its de retracting, but I'm new to bowden so I'm not sure if I'm missing something blatantly obvious.

Any more needed info I can hopefully supply.
Thanks

Ex. Benchy:

Phaedrux · 27 Mar 2020, 21:42

@Turbo said in Getting both stringing and underextrusion:

It seems like its retracting more than its de retracting, but I'm new to bowden so I'm not sure if I'm missing something blatantly obvious.

check for loose couplings

Turbo · 27 Mar 2020, 21:52

@Phaedrux
checked. all tight with the little spacer to keep them in place

Phaedrux · 27 Mar 2020, 21:54

How bout temperatures? Are you using an E3D thermistor? Do you have the correct values for it? Have you PID tuned? Have you done a temp tower? Have you tried a different filament?

Next I'd try doing a rebuilt of the Chimera.

Turbo · 27 Mar 2020, 21:56

210c with a PID tune with a genuine e3d thermistor. never strays more than .1c.
Id do a temp tower but i know this filament is good with my other printer, which uses the same pid tune and thermistor, but is direct drive.
I have rebuilt it 3 times now in search of the problem. nothing painfully obvious

Phaedrux · 27 Mar 2020, 22:03

Pinch roller tension adjustment on the titan?
Extruder motor current at 85% of rated motor max?
Extruder calibrated?
Retraction seems like it's in an ok starting point. so try tuning pressure advance now.

Turbo · 27 Mar 2020, 22:05

Yep yep and yeah. I'll try tuning PA again, but last time it went up to about .7. Is that a familiar value with bowden?

Phaedrux · 27 Mar 2020, 22:29

that's not out of reason for long Bowden's. Definitely re read the pressure advance documentation. It's been updated recently.

Turbo · 28 Mar 2020, 21:15

@Phaedrux Pressure advance was right around .75-.8 for best results. however, this did not fix any stringing/underextrusion
I took off the nozzle to check that it wasnt doing more retraction than extrusion, and its perfect. Im at a loss here

Phaedrux · 28 Mar 2020, 22:13

worn out nozzle?

Turbo · 5 Apr 2020, 04:44

SOLVED

For some reason, a medium retraction distance and slow retraction speed works best.
I found 2.4-2.8mm of retraction at 20-25mm/s retraction speed to work best.
I have no idea why the Chimera hotend is like this, and it pretty much goes against what everything on the internet says, even E3D's recommendations, but it works!

Phaedrux · 5 Apr 2020, 16:30

@Turbo said in Getting both stringing and underextrusion:

it pretty much goes against what everything on the internet says

It's not crazy if it works!