So today I finished the magnet array.
First task was to complete the inner ring by milling the magnet pockets. I set up the indexer on the mill to be as precise as possible, but I could likely have eyeballed it given that the ring has 24 gear teeth on it. That said, I did it right by using the rotary table to rotate the rings 60 degrees after milling every pocket. I did not have an end mill the same diameter as the magnets so the holes are slightly wider than the magnets. I figured that I'd be epoxying them in anyway so no big deal.
I didn't have enough material on the other gear to easily make the magnet retaining ring due to clamping forces causing a thin ring to potentially deform. So I used a round of UHMW polyethylene that I had on hand to make a plunger for a hydraulic sausage stuffer. I chucked the plastic up on the lathe, turned the exterior to diameter close to what I thought would work. Then I drilled a center hole and then bored it out to the OD of the phenolic ring.
I had to take a little more material off the ID of the retention ring because the OD seemed to shrink a lot when the part cooled.
When I did a test assembly and ran spindle and both tachometers the the end result did not show any negative impact of potentially allowing the magnets to move ever so slightly in the pockets, so I wont be gluing them in place at all. The retention ring slides on with a snug fit, but is difficult to remove. Just what I wanted.
The magnets are very strong, easily read thru the retaining ring and at a distance of another 1/4" or so on both sensors.
Here is how I assembled the rings. I used a magnet inside the ring to hold the magnets in the pockets while I was assembling the rings.
You can see how much extra room there is in the pockets making the magnets on the back handy. Once the ring was in place I used a magnet stack to assure all the magnets were oriented correctly.
Finally on the spindle.
