I did a little experiment hobbing the shaft of a stepper motor for driving filament.
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The stepper is the not so great NEMA17 motor that Sparkfun sells and the shaft is hobbed with a M4 tap from its 5m size down to 2.75mm. The basic idea is to give the filament the least amount of lever arm as possible against the shaft. It seems to work at least in concept. I will stick it in my cupcake and see how it holds up.
The filament tensioner is a Wade's style 4 bolt + springs pushing a bearing against the hobbed shaft. Instead of mounting the other side statically to the motor I clamped it with bearings to the shaft itself. The tensioner is prevented from rotating by the filament and the top of the hotend.
The hotend is a nophead style resistor heater block with brass block and a brass nozzle made from rod. The filament tube is 1/8 galvanized pipe nipple with 5/16 PTFE rod inserted into it. The PTFE rod is tapered in two steps. At the nozzle down to 1/4" and again at the tip so a piece of tiny (1/8" long) copper tubing can be placed over the tip. The idea is to reduce the insulating value of the PTFE right at the tip. This could be done with drilling the nozzle, but was easier for me to get the effect this way.
btw. What exactly is the point of the common use of brass instead of aluminum for heater blocks and nozzle? Brass really is not that great a heat conductor.
Any comments are much appreciated.
