Friday, July 28, 2023

Digi-Key fairy, and sealing

The Digi-Key fairy delivered a new bunch of Newhaven 2.4" displays today. In other news, I finally got a relative low-labor stackup of nose parts to seal together without leaks:

The no-leak seal between the manifold parts was created by sanding the faces of the 3D printed parts on a flat surface with 220 grit sandpaper, then assembling using gaskets out of 3M 468MP adhesive film. This product is used to secure 3D printer bed covers to the beds, and should hold up to extended high temperatures and other forms of abuse. At some point I'm going to show a montage of the full process, but for now, this is the setup I use to cut the gaskets. I clamp these templates onto the material, and cut out the holes with a sharpened stainless tube that's held in a pin vise:

This is one of the aspects of the project I've been working on for many weeks, but has been sort of unsung because progress happens in fits and starts. I have tried many, many options....

One thing I wanted to do was to not have to sand down the "grainy" surface of the MJF plastic. It turns out it's impossible to do this and get a decent seal. So maybe I'll have a quicker way to clean up the surface, or maybe I'll find an economical but smoother 3D printing process, but either way. Needs to be smooth.

I tried to use silicone rubber gaskets of various sorts, relying on clamping pressure. This does not work very well -- they all leak.

I tried silicone rubber foam, about 1/32" thick -- and that works fine. However, the foam "squeegees" out of the sides of the seal, and can interfere with the aerodynamic shape. It requires post-trimming, and never looks really "finished".

I tried Jo-Ann Fabrics thermal adhesive, baked in the oven. But some of my "manifold" parts include some electronics pre-assembled, and a heat soak sufficient to melt the adhesive also fried the electronics.

I did not try anything involving grease. Maybe that too would work, but if the 3M adhesive film works, it's likely ideal. It is not messy and seems to "wet" the faying surfaces pretty well.

Another minor hurdle cleared. :)

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