by tmccafferty » Mon Jun 03, 2013 2:41 pm
OK, spent the weekend fiddling with this thing. I disassembled and cleaned the cool end, disassembled and inspected the j-head, and tried endless combinations of temperature and filament size. No improvement. The interesting thing was the consistency of the bad spots on the prints. I was beginning to wonder if it was actually being directed to back off the extrusion rate by the slicer program. From inspecting the parts, it was clear that the extrusion was definitely slowing way down in a repeating pattern. I thought maybe the stepper driver was getting hot and periodically disabling or had some other problem so I swapped it out... no luck.
Finally, I focused on trying to see if there was any variation in the speed of the gear. It wasn't obvious at first, but if you really focused on the gear and the area printing, there was a correlation of the gear orientation (based on the setscrew) and the bad print area. I removed the gear to inspect it but could not visibly see any issue. I had a spare gear so I put it on. It began to print perfectly. It' printed all night with no issue.
I don't know what is wrong with that gear, but it now lives in the dumpster.