PETG Retraction tests etc

[curious aardvark]

have you actually measured the actual width of the extruded petg ?

Seems to me you're pretty much just changing things at random without any actual logic.

The extrusion width setting should be set to the actual extrusion width. So when you load filament and it extrudes. That's what you need to measure and that's the number you put for the extrusion width. Otherwise the slicer is just working off incorrect settings.

[curious aardvark]

okay just started using the esun petg I bought a week or two back.

And what makes the difference as far as stringing goes isn't how far you retract it - but how FAST you retract it.

I'm currently using 40mm/s - but basically keep increase that till the printer cries uncle !
(never did understand that phrase)

Currently printing at 235 and 40mm/s print speed.
Getting nice prints.

[dunginhawk]

Thanks aardvark. I too get great quality prints, but if I had 10 things on the huge platform, it may not look great due to movement between parts, although it got MUCh better with m y testing. I built the EZBOT arm w/ 4 servos etc and 15 parts on the platform and it worked pretty well.
Ill run a test with a huge retraction speed.

[dunginhawk]

strangely enough that had an adverse effect... I ran at 40mm/s print speed, 40mm/s travel speed, and 50mm/s retraction speed and it was one of the worst tests I had run... lots of stringing and globs at the top of each spire. going to run another control test at 25mm/s with the same settings/

[curious aardvark]

weird - perhaps it's down to different brands of petg.

Tried colorfab and esun so far - esun definitely less stringy.
It also sticks better to the printbite and didn't show any sign of warp (shrinkage) whichthe coorfabb does a wee bit.

Got some real cheap stuff coming today or tomorrow: technologyoutlet petg.
£20 a kg !
See how that compares.

[Alibert]

My two cents worth:

While printing, there is a temperature differential between the heating element and the nozzle as energy must be transported to the nozzle to melt the plastic. This is analogous to electricity, a current can only flow if there is a voltage differential (the driving force). Heat energy can only flow if there is a temperature differential (the driving force). The faster you print, the larger the temperature differential will be.

When you retract, you relieve most of the pressure from the nozzle. However, when extrusion stops there is no more loss of energy through the extruded plastic. Thus the temperature differential will resolve itself and the temperature in the nozzle will rise a bit. Because the plastic also rises in temperature, it will expand. As the nozzle opening is the only place it can go, it will continue to ooze until the temperature in the nozzle is constant.

There will always be a little bit of ooze (unless you can actually retract the plastic and create an air bubble in the tip of the nozzle, but with viscous PETG it is very difficult to do this), so some stringing will remain.

From this point of view, you want to travel as fast as possible from one point to another, not slowly. When going slow, you allow more time to generate this temperature-induced final oozing, thus more whiskers/strings.

In the end a good profile is a balancing act of multiple variables, there is no clear cut solution to one problem, without creating a new one somewhere else.

[curious aardvark]

worth a try.
I just find that with any plastic, going from a slow print to a fast travel, tends to pull the plastic up into little spikes that can catch on the printhead.