UMMD Gets a New Extruder.... Again

My experiment with the Chinese made aluminum Titan extruder was interesting, but it didn't last.  While it had great potential, it came up short.  Some of the problems I found:

• The gap between the feeder tube and the drive gear made loading filament very fiddly, even with my added aluminum extension tube.  I find a similar problem with the original Titan.
• The pinch roller lever pivoting on the motor shaft wore out quickly, leaving black aluminum dust all over the inside of the extruder.
• The concavity of the drive gear was not centered over the filament feed tube
• The screw that passes through the drive gear and holds the extruder to the motor bends the front cover and puts a lot of pressure on the ball bearing that mounts in the cover.  The original Titan has the same problem.
• The pinch roller spring was much too strong which made printing with flexible filament difficult.

Aluminum Titan clone and XCR3D hot end mounted on UMMD.

After more research I decided to give the Bondtech BMG a try.  I have to say it seems very solidly made and there's no chance that screw pressure will distort the body of the extruder.  Loading filament is super easy- just hold it at the entrance of the extruder and tell the printer to extrude some filament.  The dual drive gears grab the filament and pull it into the extruder without any probing around to find the hole.  The filament path is just big enough for the filament and there is nowhere for the filament to flex out of the path.

The BMG extruder parts.  Very solid construction, and unlike the E3D Titan, tightening the screws doesn't cause any misalignment of bearings.

The filament path has two drive gears.  The pivot arm, on which one of the drive gears mounts, is removed in this photo.

When the Bondtech extruder arrived I discovered that it didn't come with a Bowden adapter, so I printed a fitting that would allow me to mount a hose fitting on the extruder.  Then I discovered that it wouldn't fit on the extruder carriage because the hose fitting interfered with the front of the carriage.  I also discovered that unlike the excellent hose fitting on the input side of the extruder, my hose fitting was junk and didn't grip the teflon tube very well.  I ordered the Bondtech Bowden adapter and it fit perfectly, allowed the extruder to mount on UMMD's carriage, and gripped the teflon tube tightly.

The BondTech BMG extruder mounted on UMMD.

I had one other, minor problem installing the BMG.  Only one set of mounting screws came with it and they were a little too short to go through the 5mm thick mounting plate on UMMD.  Fortunately
I had some longer screws handy and was able to get the extruder mounted.

I set the steps/mm to 415 in the config file and ran some test prints.  I still have more extruder tuning to do in the config file, but it's printing pretty well with the default setting.  I'll report on any problems or failures here.

Note- I'm still using the Chinese made XCR3D hot end.  Other than the crappy fan that I replaced  with a Sunon part that is specc'd to operate up to 70C, it has been performing well.

Update 1/26/19

I had an interesting failure.  Someone at the Makerspace was trying to print with the nozzle smashed against the bed surface (to get better first layer adhesion?! - I'll have to revise my training materials) and the extruder kept pushing filament.  It pushed so hard that it pushed the Teflon tube out of the Bowden adapter at the exit of the extruder.  The BMG extruder can really push, so I reduced the extruder motor current so that when a jam occurs, the extruder motor will skip steps instead of pushing the tubing out of the Bowden adapter.  Reduced current means reduced torque and reduced heat which is good because the chamber goes to 50C when printing ABS.  I guess it also means that if I were so inclined, I could use a smaller, lighter, lower torque motor for the extruder.