Double gear extruder retrofit

At some point of my 3D-printing path I bought something that once was a Makerbot replicator 2x. The previous owner has inflicted some improvements to the point of total dysfunction to it, but, ok, that was the reason why I’ve got it for cheap. After fixing mechanical issues and tweaking the electronics and firmware I’ve got it (somewhat) doing the job except for one annoying effect. After printing ABS for an hour in the heated environment the extruder’s gear started slipping on the filament, grinding it, clogging with the ground material until finally losing ability to push it forward. The investigation took quite some time and several problems were discovered and dealt with, including problems with heater PID control, loose thermistor connection, and finally insufficient filament-gear engagement. The latter factor was becoming even more prominent after the system’s heat-up, when the extruder’s air-cooling became not sufficient to keep the feed-gear temperature below ABS softening point.

I decided to fix both issues by arranging the extruder’s water cooling and creating a new mechanical assembly that includes double-gear arrangement for better filament grip. The assembly must have been designed specifically to fit into existing printer head geometry and provide means of fine adjustment of inter-gear spacing.

Here what the design looked like:

And here is a cross-section for clarity of what’s going inside:

The filament is pushed by a pair of gears, one of which is installed on the motor’s shaft, while the second one is mounted on a ‘cradle’ — part of the housing that has some freedom to move, functioning as a flexure. Position of this cradle can be adjusted by a pair of screws that are conveniently accessed from the top of the assembly (other sides of the extruder are not as easily accessible on this model of printer). Each screw pushes on one side of the cradle’s lip that acts as a lever and induces minor deformation in the cradle’s neck. By tightening the screw that is closer to the motor, the spacing between gear’s meshing teeth is adjusted, while the other screw sets pressure between gears and the filament.

A unique feature of this design is that the whole housing is printed in one piece:

And here it is installed on the motor:

To address the cooling issue I’ve soldered a heatsink from copper plates and a pipe that is installed around the extruder block (and is also in tight contact with the aluminum cold block). On this picture an original black single-gear extruder housing is still installed:

After connecting the setup with PVC tubes to a pump and a bucket of water, the project was nearly complete.

And finally the new white double-gear housing was installed together with the cooling jacket, but unfortunately didn’t find any pictures of the resulting assembly. I can witness though, that the solution did work and the slipping-filament problem has been resolved.

Here is the Fusion drawing of the extruder housing. And model files on Thingiverse.