After I decided on a cylinder with a removable end, my first thought was the radial slots you see here. It's pretty, but my printer made a hash of the variable-width spaces between the slots. Transparent PETG made even the internal mis-extrusions visible. Wider spaces between the slots helped, but not enough.

🧵 2/N

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I started with standard screw threads. I've used those successfully in other projects. But I had three problems.
- couldn't get a consistent fit. They were either too loose or too tight.
- printer couldn't deal with the overhangs on inside curves.
- took too long to unscrew.

🧵 3/N

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So I learned how to make custom threads. It's actually kind of fun. All of these use a trapezoidal cross section.

The custom threads solved two of the problems above, but they made getting a consistent fit much harder -- less thread surface and shallow engagement angle mean less friction, right up until it's way too much friction.

(I started making minis because the full size cylinders were wasting a lot of plastic and time. (Those vertical slats take forever.)

🧵 4/N

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So I started over with a bayonet style latch. It took three tries to get the clearances right -- the first two were ridiculously loose and very loose, respectively. The third one is in the center.

So I thought I had a good latch (foreshadowing), and moved on to the slots.

🧵 5/N

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Here are some sketches of slot patterns. There were others that I didn't even save.

🧵 6/N

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So I modeled all the slots (crashed Fusion 360 a few times along the way -- I set up the sketch constraints badly and sent it into never-never land) and printed a full size version. It was way too loose. What worked at 40mm diameter didn't hold at 70mm.

So I reshaped the can's neck to allow thicker engagement tabs without making the lid huge.

And it worked. Wasn't that easy?

🧵 7/N

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I decided to use opaque PLA for the lid because the knurling didn't show up in transparent PETG. I like the knurling.
🧵 8/N

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(What, is he still talking about this?) When I browse Printables or other 3D model sites, I'm disappointed at how most of the stuff people throw up there hasn't gotten this kind of polish. And then I get a vivid reminder of how hard this kind of polish is.

Anyway, I'm done grousing, for now. Thank you for your indulgence.

🧵 9/N

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I decided to make a funnel that screws right onto the desiccant canisters. Then I decided to try some stuff I'd seen about making G3-continuous surfaces in Fusion 360. This isn't perfectly G3, but it's close.

I made it ten times harder to model by flaring the funnel's outer surface out 45º to match the chamfer on the bottom ring, but keeping the inner surface G3 with the canister's inner surface. But I got it to work.

🧵 10/N

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The basic shape is a difference of two lofts. These images show the profiles and guide rails of both lofts. The curvature combs are for the inner loft.

The curves are 5th degree splines (and two circles). The top profile is not a closed curve, but it overlaps through enough control points to have G3 continuity.

Note that the inner loft extends further down than the outer -- I continued the curve to the lid's bottom surface.

🧵 11/N

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Uh... I continued the curve to the lid's inner top surface. That's what I meant. Words are hard; look at the pretty picture.

It seems like a trivial detail, but it stood out like a barking hyena in the zebra analysis.

🧵 12/N

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It's on Printables now (finally).

Tagging @matt because he asked for it.

https://www.printables.com/model/1610013-desiccant-canister-and-funnel

🧵 13/N

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