pF: hub motor epoxying magnets, machining can

To machine the parts of the motor can I first made a lathe jig. This will help fixture individual parts and eventually help  with the machining of the assembled can.

I started with a round plate and a 1″ DIA boss to grip in a lathe collet. I machined a square pattern into both to help ensure torque transfer. This was easy to do on an Eztrak mill.

The two parts are first press fit together.

press fit together

some screws, since the press fit length was so short. This will help keep the parts together.

First thing I did was use it to turn the outside face plate which will have a bearing in it. Waterjet does not leave a finish that is good enough for a bearing seat, so it is nice to be able to use a boring bar to make a clean hole.

bearing seat is bored out, also never hurts to do some polishing

Now for actually putting the magnets in: The steel plates used the hold the magnets were just barely under 1/4″ inch, I measured 0.245″. However, the magnets were right on for 0.500″ wide. So I had to cut some clearance for this extra width in the two rings sandwiched next to the steel rings. Again, having the lathe fixture was awesome.

cutting a clearance step for the magnets

completed rings with 0.010" depth steps

Before gluing in the magnets, I assembled these two newly machined rings with the steel ones. The steel I used was cold-rolled so after I waterjet the rings, they warped slightly. So it was important to clamp everything together to flatten things out, before the magnets were glued in. I also tried to align the warped rings so that there would be even spring tension around the whole thing. I didn’t want to steel pieces to warp the aluminum ones, too. Seems to be okay.

magnets epoxied in. I mixed way too much epoxy...

I used an epoxy with a slow hardener. I put in way too much slow hardener, so its going to take like 20 hrs to cure, but be sure to give yourself some work time. I also added some phenolic micro balloons to the epoxy mix, which is an epoxy filler. I don’t really think this step was necessary. Apparently phenolic micro balloons are used mainly for better sanding characteristics, and aesthetics (cite). But I do think it can help make the epoxy more viscous without shortening your work time. This is definitely helpful.

I spread epoxy into each of the indentations for magnets, and then just let the magnet snap itself into its proper spot. BEWARE OF POLARITY. Lots of epoxy squeezes out, and you can just wipe it off with a paper towel. The magnets are really smooth, so if you accidentally get a thin layer on them, you can still wipe it off even after the epoxy is pretty well set.

close up of epoxied magnets


One thought on “pF: hub motor epoxying magnets, machining can

  1. Pingback: pF: cleaning up the motor can « Amy Qian

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