Hi all. Again a quick question regarding extrusion.

Hi all. Again a quick question regarding extrusion. When I extract 100mm if actually extracts 100mm. Every time. When then retracting 100mm it retracts 101-102mm. Every time… Any hint on where to look for this issue? I already decreased the microstepping, checked the hobbed bolt and the bowden. Using an Infill 3D Geared extruder.

Any hints welcome. Thanks.

When you talk of extraction and retraction, I assume you mean forward and reverse feeding of filament through an extruder body?

Is this an unconstrained length of filament i.e. not feeding from a spool?

I can imagine you would only get the same feed amount in both directions if the loading is the same in both. A significant load in one direction might lead to some slippage which is not evident in the other direction.

In practice this should not matter because you calibrate E_STEPS_PER_MM for forward feed and adjust retraction independently for best results.

@Neil_Darlow yes, exactly. No Hotend connected. Just the extruder and the bowden. Is without a spool.

I can not see any difference in loading. Even when holding the filament, to provde some counter force, it still behaves the same way …

Are retraction speeds different? - did you tried to use same g-code for one and other directions.
If you use pronterface or other tool to retract and extrude - take a look at commands you send to printer - are they similar in values?

@Mateusz_Perlak I actually sent it manually, “G1 E100 F300”, trying feedrates up to 600, consistent result…

weird, maybe measurement process is not correct… nothing else comes to my mind

When extruding it may compress the filament slightly, perhaps the compression translates to an elongation of the filament?

I think you’re trying to fix something that seems well within tolerance.
You have a 1-2% difference, only on retraction. For a long retraction on a Bowden system, you might order 5mm and get 5.05mm. Even if you don’t have a purge after extract, you only end up 0.05mm short when you go to push filament again, which is insignificant. This is a high example. For direct-drive, the retraction is even less.
Am I missing something?

Is it multiplicative or additive error? Does retracting 10mm typically do 11-12mm, or 10.1-10.2mm?

Øystein Krog, If correct shouldn’t it extrude more, instead of retract more? If the Filament get compressed and longer when extruding?

@Carlton_Dodd May be yes, I am just trying to fix my print quality, and I assume it has something to do with exstusion. Going to post a some new pictures soon. Maybe I am on the complete wrong track here.

@Jim_Peterson When goind 10mm it does around 10.1. Hard to meassure, but when repeting it it slowing retracts more then extrudes.

Hmm, do you have any backlash in the extruder?
Double check that grub screws are tight and that gears/belts are tight when moving back and forth.

Interesting. I’m surprised that is causing any printing issue. If you were to extrude and retract 100mm ten times each, alternating, would it end up 10-20mm behind where you started, or only 1-2mm? (In other words, is it cumulative, or just some form of initial settling?)

@Oystein_Krog Can’t see any. Everything thight and filament is reacting instantly when turning the gears.

@Jim_Peterson Made some test gcode now where it extracts and retracts 100mm of filament 20 times. And, surprisingly, after 20 times it is still only 1 mm short. So seems to be initial. Thanks for the tip!