puny extruder?

[alaris2 1]

I don't understand this, so someone please explain it to me -

I calibrate steps per E, using the Cura approach. I extrude 100mm of filament with E=821.29. it's a V2 bolt extruder with Bertho's extruder mod applied.

100mm comes out. all is good.

I attach the bowden tube again, and this time extrude through the hotend. procedure now is to run the following to bring me up to working temperature -

M107

M92 E821.29

G21

G90

M109 S230

G92 X0 Y0 Z0 E0

G0 E20

G92 E0

and ensure the nozzle is primed. then I mark the filament as it goes into the extruder and execute

G0 E100

mark again. withdraw the filament and power down.

what I expect to happen is 100mm or thereabouts is extruded. but what actually happens is -

1) when the nozzle was empty (after heating) the act of priming it with 20mm of filament actually only moves 10mm of filament through the system.

2) when the nozzle is primed, pushing 100mm of filament actually moves 25mm of filament through the system!

Daid says my filament is slipping. He's a clever guy so he's probably right, where else could the filament be going? but WHY is it slipping then? is my extruder really so puny?

did I totally misunderstand the g-code?

my observations are that in order to get good quality prints I have to set the material amount to 130% of normal to ensure I don't get under-extrusion.

maybe this is why I've never had a bowden tube pop on me...

[Daid 306]

It could also be missing steps.

And don't assume I am right, I'm also just guessing.

[alaris2 1]

what would make it miss steps? or how could I find out whether it's missed steps or slipping? I've tried observing the movement of the filament, but it looks pretty smooth - wouldn't I expect it to be jerky if it were slipping?

[Daid 306]

If it's missing steps then you usually can see that it doesn't turn smooth, you can also check by simply trying to turn the extruder gear by hand while the motor is powered, this should be quite hard (but not impossible)