Is there a canonical definition for a unit measure of E steps?  That is,

3D Printing
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1

Is there a canonical definition for a unit measure of E steps? That is, is it based on extruded cubic-mm of ABS? Or input cubic-in of PLA? or ???

2

Back in the day, it was supposed to be millimeters of extruded plastic (into open air, which was a terrible thing to try to measure, as the filament would contract and/or curl as it left the extruder, and these effects were even harder to calculate than they are now because none of the components were precision-machined.

Now, everyone has switched to “volumetric 5d”, which measures the movement of the plastic going into the extruder. This, combined with the (much easier to measure) filament diameter (to calculate cross-sectional area) gives you the volume of plastic going into the extruder. Assuming the melting and cooling process does not cause a change in density, the volume in will always equal the volume out. The length of input filament is what the extruder steps/mm refers to.

Some of us are now pushing for another move, from specifying the length of (input) filament to extrude specified in gcode to specifying a unit of volume, and providing the cross-sectional area (or filament diameter to calculate it) so that the firmware can do the volumetric calculation itself. This filament diameter data could come either from the slicer in the form of an M code, from an eeprom chip attached to the filament (more info here: https://plus.google.com/communities/107859862288161234107) or from the filament measuring device attached to the printer.

3

What about the packing density differences between PLA and ABS? I certainly have observed differences in the fill when directly switching from 1.75mm ABS to 1.75mm PLA, for example. In theory, the extruder drive gear (Mk7 and Mk8’s in my case) are turning, and hence pushing similar amounts of plastic.

I suppose the softer ABS could end up riding a little further into the gear teeth and turning on a smaller diameter, resulting in less extruded material.

4

We currently use fudge factors (“packing density”, “extrusion multiplier”, etc.) to account for this. In my setups, it usually doesn’t seem to be necessary, but it’s possible that more marginal extruder mechanisms allow some materials to ride higher/lower on the gear teeth than others