This in turn meant that I had to cut a new Hobbed groove in the bolt (the extra washer meant that my first groove was now not aligned with the filament feed point) – but I was getting good at “Hobbing” bolts by now, so this was no real problem!
I actually find this quiet extraordinary – that it is possible to design and fabricate a complex high-precision assembly like this, that a complete novice like me can build. Think about this: the extruder motor has 200 steps per revolution, and with 1/16 micro-stepping, this makes 3,200 controllable micro-steps per revolution. The pinion gear has 11 teeth, and the big gear has 39, and is driving an 8 mm diameter pinch shaft. Each revolution of the motor therefore gives 11/39 of a revolution of the pinch shaft, which is equivalent to feeding 11/39 * pi * 8 = 7.1 mm of filament; each 1/16 controllable micro-step feeds the equivalent of about 2.2 microns of filament – just amazing!