I've wrapped up work on the 3D printed Antikythera Mechanism for now. There are a few parts that are incomplete, and I would like to come back to it in future and redesign it. For now, I am out of patience and energy. So let's take a look at what worked and what didn't.
Some things which worked
Overall: the mechanism runs fairly smoothly and without excessive friction. Win!
Frame design: the skeletonized and split frame works well. It is rigid enough and has the right geometry, but without taking an excessive time to print, and it can easily be split into pieces which fit on the print bed.
The splits for the frame and the large gears are also good. Using M3 screws to hold the parts together makes them rigid enough, and adding 2mm dowels as alignment pins also helps. Some of the fixings are a little ugly, especially the brackets to hold the halves of b1 together.
Thin supports for the larger gears where they wobbled on their axes: this eliminated most cases where the mechanism was seizing. I also tried supports for b3/b4, but later found I didn't need them.
Press fit hex fixings for joining gears on the same axis.
Push-on shaft collars for gears where the axle was held only at one end. These worked quite well, I saw them slip off occasionally, and for long term use they should be glued in place. The shaft collars worked particularly well in the cases where I could bury them within the hub of a gear, saving vertical space. Similarly the fixing holes consisting of a hole and a slot worked well. It is possible to get pins into them without excessive force, while having a firm fit which won't work loose.
Most of the axles and pins are standard lengths. In past projects, I've often cut them to length. It's easy with brass and a harder with steel. Standard lengths, by which I mean ones I can easily buy, are better.
The gear sizes are mostly right. I discussed the choice of modules and the exact separation in an earlier post, especially as they deviate from the ones in the HAM.
Some things which didn't
Gear sizes for output: the modules I chose for the output gears meant that they had to sit quite far from the center. It pushed the spirals out while still not leaving much space for the Games, Callippic and Exeligmos dials. With a smaller module they could be moved further in, freeing up space. This is not hard to do but requires reworking the backplate geometry, and I ran out of enthusiasm to do it. Similarly, I never completed the output spirals and a change to the geometry to allow more space for them would make them easier to design.
Some of the shaft collars are not tight enough and slip off. It might work to make them longer where there is enough space. Otherwise, the only solution is to glue them onto the pins.
The planets stages use more vertical space than I would like. I tried thinner gears (doesn't save much, makes the mechanism more unstable), and I looked to see if I could interleave the gears in some way, but didn't find any arrangement that worked.
Finally, as I previous described, the a1 support isn't very stable and could do with a redesign, as part of generally redesigning the mid and back frames.
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