Cura

I've been struggling for a while (besides being out of town) with the open source ReplicatorG software used in conjunction with the Marlin/Sprinter firmware. It seems that there isn't a fork of ReplicatorG being maintained for the Ultimaker community, so if you choose that route (as opposed to buying software like Nettfab) you are pretty much on your own.

Now admittedly, a lot of the time was spent trying to understand the new open source development paradigm around Git and Github, but my progress was almost zero and I was getting pretty down-hearted.

Then I saw Florian's post about Cura and leaped on it. I'm glad to say the results were quite good.

I was a bit put off by a disconnect between the E (extruder axis) scale and the usual Marlin/Sprinter scale.
From what I understand, the E axis had always in the past been the amount of "filament", i.e. 2.9mm diameter input to the extruder. Then somebody in the Marlin/Sprinter group decided that wasn't correct - I don't know who - and started defining the E value as the amount of "extruded" plastic, i.e. 0.4mm diameter hot output from the extruder.

Obviously there's a ratio of 50 between the areas of the filament and the extrusion, so if you aren't careful, your slicer will generate G code that will drive the extruder too hard (and back up plastic into the Bowden tube, see Nozzle cleaning) or have nothing being extruded at all.

To get the firmware and the slicer to agree, Cura makes a custom firmware based on the Marlin/Sprinter source. It's important to use the Cura feature that updates the Ultimaker firmware. And then the generated G code has E extrusion values in the old fractional values and uses a calibrating M92 code to set the steps per unit of E (for me it was calibrated at 848.17073123).

The really annoying thing is these calibrated values are not stored in the profile.ini file for the program, but some secret as-yet-undiscovered location.