My second attempt at building a gear system.
Individual gears are 1mm pitch, 4mm thick gears, and the whole mechanism steps down from 6 rpm down to 1 revolution per day (with the 80-tooth gear I purchased off of SparkFun). (Without that gear, the last gear in the chain revolves 4 times per day.) This means the last gear in the chain actually is a pinion with a 1mm pitch gear connected to a 32p (32 teeth/diametrical inch pitch) tooth gear.
Things I learned:
I think 3mm is probably the thinnest practical gear I can print. (I’m sure I can print smaller.) Also, my height calculations are not dead on correct; I need to sort out why I have what appears to be about a 1 mm gap. (Though I suspect it’s the washers I’m using between layers; the washers measure only 0.5mm thick, and were advertised as 0.7mm. Five of those puppies with a 0.2mm error gives 1mm.
Meaning “depthing” is something I’m just going to have to do, no matter how well I think everything is measured.
I also need to sort out how I’m going to disengage the gear train for adjusting the time. (Small battery-powered clocks seem to do the trick by overpowering the motor. OTOH, watches appear to use a mechanism which engages or disengages a clutch which then allows the time to be set by rotating the watch stem.) I’m inclined to use something simple, such as a pin which pulls up a set of gears and allows them to rotate freely. (I did a prototype of this here, though it’s poorly executed.)