The next print failed.
I started this up before I went to bed, and in the morning I found the head merrily moving around a few inches above the prints. What probably happened is what Raise3D suggested previously when I said that the purge cycle didn't purge anything: the "third-party" filament clearly was not being fed.
I looked closer at the feed point.
Now, this image was from after I unloaded the filament, cut off the faulty bit, and was about to load it back in. Here's the faulty bit:
There are a few features to note here. First, on the right, we have the toothmarks from the feeder gear. This is normal. Then, we have a circular depression where the feeder gear ground into the filament. This is not normal, and is what happens when the filament gets stuck. Finally, on the left side you can see a bend in the filament. Also, the filament has changed from semitransparent white to opaque white. This is the result of the filament being bent.
Bending the filament like this produced the exact same result. Now, here's a look at the whole feed path.
Note that there is nothing preventing the filament from being bent around that sharp radius. The printer is relying on the roll of filament being easy to move as the head moves around, and I am not convinced that is true for a 1kg roll of 1.75mm ABS. I used LD Product's brand of natural ABS.
My Ultimaker2 has a tube that runs all the way from the feeder gear in the back up to the extruder. No sharp radius possible. I don't know if the method Raise3D is using is new or not, but I'm a little suspicious.
At this point I am not ready to blame the printer. It could be the filament. I have some Toy Builder Labs 1.75mm ABS filament coming. Raise3D only sells PLA filament, not ABS. So can the printer handle ABS? It's supposed to. Raise3D has also acquired Toy Builder Labs, so I can only hope that the filament Toybuilder sells will (eventually) be compatible with the printer.
While I'm waiting for the Toy Builder Labs filament to come in, I'm going to redo the print using the PLA filament that came with the printer.
Now, when I removed the ABS roll, I found that the filament had come off the roll and was wound around the filament holder. That would absolutely cause an increase in drag.
This is fairly typical. Sometimes filament comes off the roll, and then you're in trouble. The solution is to add a plate which holds the filament on the roll.
I'm going to see if the same problem happens with the PLA. It might not because PLA is not as stiff as ABS and may not come off the roll. After that print, I'm going to print up a plate out of PLA which will fit behind the roll and hopefully help this situation.
I haven't lost hope!