Hi, I am prototyping a clock of my own, and making many (hopefully instructive) mistakes along the way. I wanted to ask about something you mention briefly in the PDF that accompanies SP1. You say that the arbor spacing was increased for the gears to mesh properly (top of page 8). Do you have a rule of thumb for doing this? I am using the standard approach that for two gears with X and Y teeth and module m, they should be (X+Y)m/2 apart, or something similar if you use DP. In some places I can see that this makes the gears too tight, whether due to printer tolerance or because the load on the gears puts a bit of sideways pressure on them. I'm experimenting with this, and if you have any guidance it would help the process along.
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Thanks for the reply! I have been using the gear generator in Fusion 360, which allows you to specify the backlash as a parameter, and based on observation of the fit, I was thinking that adding an extra gullet might be a good idea. Your test jig looks like a good idea.
SP1 was my first clock and the gears needed some adjustment to mesh smoothly. The gear profiles were straight from Gearotic without any backlash. They would probably mesh perfectly if they were cut in brass with tight tolerances. However, printed gears only ran smoothly if the distances were spread apart slightly. This was likely caused by a combination of printer tolerances, lack of backlash, elephant foot, shallow gear tooth gullets, plus maybe a few other things.
I have since changed my methodology so the gears can run using the exact center distance they are designed with. I start with a single tooth profile from Gearotic, using around 45% tooth width so there is some extra backlash. Then I manually increase the depth of the gullets to provide room so the teeth don't bottom out. Array this around the center to create the complete gear profile. Clock gears don't mind the backlash since there is always pressure against one side. 3D printed gears for a clock are still plenty strong even with taller than expected tooth heights, although I make the gears near the weight shell thicker to handle the extra load.
I use a simple home-made depthing jig to test the gear meshing. The threaded rod can be turned to change the spacing from 1" to 8". It is easy to spin the gears to find the minimum to maximum arbor distances allowed. Pick a distance near the center of the range. I measure the distance with calipers. The arbors could also be extended through the back with sharp points to mark drill locations directly.