Infill Too Fast? Over Extrusion on Short Vectors

DocTrucker

I'll add some pictures soon.

Mean time I've looked again at disabling retracts that cross perimeters and it seems to have had a positive effect. It seems that the extruder dumps an excess of material on unretract which causes more of a probem on a series of short infill vectors than larger infill or perimeters.

My retract settings:

M207 S4.0 R0.0 F2700 T2700 Z0.1

Slower retract perhaps?

sigxcpu

M207 S4 R0 F3600 T3600

These are my settings with a ~45cm bowden tube. I see some very fine strings with PET-G but I'm ok with that. Nothing that can't be solved by a lighter.
I am pretty sure that the retraction, blobbing, pressure advance and all other stuff that tries to compensate for the springiness of the extrusion is highly filament, temperature and nozzle dependent. Maybe the extruder itself a bit. I've noticed that filament type, vendor, batch, age have a noticeable impact, up to being really bad (some 3 years old DD ABS that was simply cooking, moving from transparent green to white brown and becoming very brittle). Also noticed on old filament that it is bubbling when extruder is idling at temperature or right when putting the layers on the bed. I can only assume it can be water or air. But that means that it can expand a lot in the melt chamber and can affect small segments infill.

That is why anyone else settings do not matter. I have a Titan extruder with 418 steps/mm in config and I slice with 0.9 factor in Slic3r.

I've never bothered to adjust the steps/mm, non-linear extrusion, I don't run pressure advance because I need to choose between slow printing and noisy extruder. Eve the bed is not perfectly parallel with the XY plane.

I just watch the first layer carefully and adjust extrusion factor/baby-stepping on the fly.

I have attached a picture with parts in various tuning stages and filaments. Captured top infills as good as I could. White - PLA, Yellow - ABS, Blue - PET-G. Because of the slight underextrusion you can see the not so perfect infill lines touching circles, just like Slic3r preview shows it.

DocTrucker

Decided to us a negative additional un-retract distance which appears to be best around:

M207 S4.0 R-.80 F2700 T2700 Z0.1

DocTrucker

Still making progress but closest yet to having neat, accurate parts. Really is chicken and egg!

I did solid coupons 20 x 20 x 3mm with 100% infill and wound down the extrusion multiplier until I could see gaps that showed tiny bits of the layer below. This was only really visible with an eye inspection glass. This happened at about 0.80 and so I ran initially with 0.9, but wound it down to 0.85. Small areas still suffered so I investigated pressure advance and the retract settings more. Eventually spotted my bowden clip waving like a mad man. Still had accuracy issues so at this point I printed oversize and revisited my linear/non-linear additional advance settings. These weren't great and so I re calibrated.

With the bowden locked down there is only slight 'hair' on the part with 1.0 retract and 0.4 pressure advance. The seam at extrusion start/stop now looked best with 0 additional advance, rather than the negative used previous. The calibration part did however show the negative effect of too much pressure advance - my corners were excessively rounded. I dropped the pressure advance back to 0.2.

I'm now doing a check with the filament diameter corrected (using volumetric extrusion) and slightly lower still extrusion multiplier.

The thing that really foxes me is it looks like there is no need for the xy compensation even with an extrusion multiplier as low as 0.825?!

deckingman

@doctrucker said in Infill Too Fast? Over Extrusion on Short Vectors:

The thing that really foxes me is it looks like there is no need for the xy compensation even with an extrusion multiplier as low as 0.825?!

Hi Wes,

Yes it's quite remarkable how tolerant printed parts are to under extrusion. Take a look at the work that Michael Hackney has done on this http://www.sublimelayers.com/2017/12/musing-on-under-extrusion-prepare-to.html

DocTrucker

@deckingman Thanks, I'll have a read.

DocTrucker

Here's a picture of a recent test. Much improved. Dropping 0.025 on the extrusion multiplier leaves gaps on the large circular flat (away from the curl) but the flats near the bridges are still over stuffed.

Edit: Part is approximately 40 x 40 x 20mm. Extrusion width is 0.5mm. Layer thickness is 0.3mm. Nozzle is still 0.5mm. Volumetric extrusion rates are currently around 5mm3/sec. Accelerations are 1000 for infill, 800 for perimeter. I've a little ghosting on the perimeter so may drop the perimeter acceleration or jerk a little.

sigxcpu

To me those "gaps" are still overextruded.

DocTrucker

There are no gaps on that one, the clear and complete gaps appear when I drop a further 0.025 on the extrusion multiplier. It's better but there is still clearly a difference in the density of the short vector fills and long.

I understand that air in the part is acceptable but i think the model should still be water tight?

DocTrucker

The vertical walls are all over the place but thats the low angle surfaces of the circular holes curling up and causing issues on those layers. The part fan is much improved over standard, but not perfect. Good enough to make the parts for my second machine which has a V6 Lite, which will in turn rebuild this machine with a V6 lite so not wanting to work on fan for the reprap hot end further!