I've discovered that I'm outputting way too much plastic.

3D Printing
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1

I’ve discovered that I’m outputting way too much plastic. I don’t recall the plastic diameter changing drastically between the old stuff I have and the new black plastic, which leaves a question:

I just tried printing with my newer plastic, and it came out at the right fill (relatively even and flat) 100% fill at 75% flow.

So - do I leave the profile at 75% flow, or do I adjust the extruder steps?

2

I had similar experience more like 80%. I ran a couple more tests at that lower flow percent and then changed the E steps permanently. Just seemed logical to let the printer have the right setting instead of messing with sliders every time I started repetier.

3

I’ve noticed different colors and brand have different e step settings by 10-20%. I’m attributing it to different plastic hardness leading to different extruder gear bite. I change it in the slicer just because it’s easier to keep track of for different filaments as I can save different profiles

4

See http://reprap.org/wiki/Filament on die swell and stretching - different plastics will have different swell rates, and different formulations for each type can lead to needing additional tweaking. This, on top of the extruder gear bite issue that @Eric_Moy already pointed out.

5

Die swell makes no difference to plastic volume. If it comes out wider it will be shorter and volume out equals volume in. It is the hardness versus spring tension that makes all the difference as it affects the effective pinch wheel radius.

6

Thanks, @nop_head — I realize that if you extrude a certain volume of plastic, that plastic should by definition fill that volume. But, wouldn’t the swell affect the “bead” of the extrudate as it’s being laid down, and that (based on the understanding I have to date) if that is poorly matched, it will not fill the intended volume neatly?

7

The size of the bead is purely defined by the volume extruded per unit length. I.e. if the plastic wants to come out wider it simply gets stretched to the size the slicer intends. If it has more die swell it get stretched tighter so it does have an effect of bridging, etc, but not on fill density as the volume never changes. The extruded plastic in the object has the same density as the plastic on the spool once it has cooled, so volume in equals volume out.

See http://hydraraptor.blogspot.co.uk/2011/03/spot-on-flow-rate.html

8

Thanks. I get it intellectually. It still doesn’t feel intuitively right (but that’s how one gets led astray!). I have read your page before, but had forgotten about it – it’s a great write up (as always).

You mentioned a really simple and effective way to measure what’s going on – measure the input length of filament to determine the volume. With many extruders, you could drive filament without feeding through the nozzle - perhaps that could be used to quickly determine relative tweak factors between two different samples of filament. Run the drive for so many E-steps, then measure the length (and multiply by circular area).

9

@Joseph_Chiu I never change the E setting. Usually the filament is larger than normal in case like yours. I had some PLA that was 1.8.

10

@Alan_McNeil , no, I wasn’t suggesting changing the E value - but instead the flow tweaking/packing density compensation between filament in the various slicers.