After getting the stator out of its housing, the next step is to do the post-machining on the rotor. Here, I didn’t want any of the original bearing housing, and just needed to drill out a hole in the middle big enough to put my sun gear holder through. I figured I would experiment with some custom fixturing, so broke out Fusion 360 and drew up a set of “soft jaws”… i.e. *really* soft jaws, since they would be 3D printed.
I printed these on my Prusa MK3s, at 60% infill in PETG, then mounted it up on a vise in the drill press.
I ended up needing to get an even bigger drill bit than the biggest I had, and took a few passes with progressively larger bits, and it was still slow going.
Despite that, I managed to mess up my English / Metric conversions and the hole still wasn’t big enough, so I had to go at it with a dremel to finish it off. However, now the sun gear holder does fit in nicely!
A Modicum of Fun 
I like the idea of the 3d printed fixture; might have to try that in the future. What did the inside/shaft part of the rotor look like prior to machining? Hard to tell from dys.hk’s images/drawings on their site
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The inner part of the rotor had a cylindrical bore on which the primary bearings rested.
https://photos.app.goo.gl/abW8pvAcJP361mAU6 has a decent picture of it from my initial disassembly of that rotor.
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Cheers! Makes it a lot easier to model, considering mine are still being shipped 🙂
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You are of course welcome to use my models if you like. They’re all Apache 2.0 licensed and most of the newer things are in Fusion 360 (which is free for hobbyist / low-revenue company use).
The rotor and stator are in:
https://github.com/mjbots/moteus/blob/master/hw/be8108_gearbox/BE8108_Gearbox.f3d
Although, there I didn’t bother to model the original rotor internal geometry, I just modeled it in the post-machined state.
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