We just could not bear to scrap the laser-cut MK4 extruder entirely for a printed Wade extruder so we decided to first modify the makerbot extruder that we had. One of the issues with the MK4, which the MK5 addresses, is the filament idler wheel. It is hard to adjust and even harder to adjust consistently. The MK5 replaced the wheel completely with a Durin plunger, but we wanted something less drastic. Taking advantage of the multi-layer construction of the extruder, we switched the motor mount plate (1) with the spacer plate (2). The thicker motor mount plate allowed us to cut a channel in the plate wide enough for a M4 sized bolt. Another cut perpendicular to the channel was made to fit a nut in the motor mount plate (wedged between the filament guide bottom plate (3) and the spacer plate (2)). Although the cut was made slightly larger than the nut, the friction between the plates seem to hold the nut in place fine. This new configuration allows for fast thumb adjustments and also for tensioning of the idle wheel to be in controlled increments (per degrees of rotation of the tension bolt). Now we need to come up with a way to use a stepper motor with the MK4; it is possible, we just have not solidify a method yet. Build process was not fully documented but you should be about to duplicate the process with ease.
First the extruder was disassembled to parts:
Here is the channel for the M4 bolt in the Motor mount plate, click here for a larger image. Cuts were made using a jigsaw and file (band saw at the shop broke), the slot for the nut is slightly too large:
A small slot was drilled then filed on the spacer plate to hold the nut:
Putting the plates together:
Make sure the bolt is on top of the washer (easier if the washer was placed with the beveled surface away from the bearing). Also note the nut slot holding the nut in place between the plates:
All done, now you can adjust with a twist of the thumb!