Custom Fidget Spinner in 7075T6 & CZ121

Back in my day, if you didn't pay attention they'd give you a clout 'round the ear, nowadays, it would seem, they give you a fidget spinner.

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A good friend of mine asked if I'd make her seven year old son a custom fidget spinner - in fairness, he's a top little fella and very bright, so a total pleasure to make him something he's gonna (hopefully) enjoy.

Didn't have the first clue about these things, but after a bit of searching (both the internet and my offcuts bin) I decided on a lightweight 7075 body, CZ121 brass weights and a miniscule R188 stainless/ceramic hybrid bearing. I kept the design deliberately simple, as my main priorities here were about focusing on decent interference fits for the weights and the bearing and having the thing actually function! - I may re-visit this project at a later date and try a more 'interesting' shape, but for now I'm okay with the (elegant?) simplicity.

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Here's a vid of the 7075 body being machined:

https://youtu.be/_N5mPFqto7I

..and a couple of pics of the results:

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Then it was the brass - I used a hole-saw to cut out some blanks from a piece of 1/4" scrap - then machined 'em to size - well, 0.025mm undersize with a couple of spring passes.

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Once that was done, I made a little press out of some oak:

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Here it is in action:

https://youtu.be/B-4Ji41Z6Gg

Then it was a case of jigging that lot up and engraving the lad's initial (G) onto the brass, along with a bit of a ball-nose chamfer. Don't have any video of that, but here are the results, fresh from the kitchen sink:

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The last bit (and probably the trickiest) was to make the caps. Here's a vid of the round-over being machined to give a bit of clearance on the underside followed by a clip of the ball-nose cutting the circular contours.

https://www.youtube.com/watch?v=HkGn-YHA4Fk

The female cap needed tapping which meant grinding a flat nose onto one of my M4 taps to give me the extra 'reach' I needed.

The male cap had an extra layer of complexity insofar as it needed to be thread-milled (I don't have a lathe, but really want to get my hands on something small for jobs like this) - the M4 die barely starts cutting by the time it hits the underside of the cap, so no use in this situation. You can find a reasonably detailed write up on how I went about this over on my blog. Here's a vid of the operation:

https://youtu.be/tV-9vug1Ke8

The design relies on a couple of little 'shelves' that clamp the inner race of the bearing. Then there's a bit of clearance within the interior of the rest of the cap - the inner race is a bit baggy by design, so you don't want the outer race that partially protrudes from the body fouling the caps.

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Once these were polished I pressed in the bearing with no issues - and fitted the caps. The finished article:

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...and with a wooden carry case:

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And who could resist revving it up with the air line..? Not me:

https://youtu.be/ul09CFdpVyk

That's only at 2 Bar... <Opens it to 8, thinks carefully, then closes it again..>

Wal.