Thursday, February 1, 2018

3D printing mounting components

I built up a 3D printer a couple of weeks ago. I've been using it quite a bit....

The printer is a Prusa i3 MK2S kit that I bought unopened from a friend. I built it up over the course of a couple days (including a lot of hanging out with family etc.) -- it was pretty easy to put together. I hope to get a MK3 kit when they are more available (they are currently brand new and hard to get), as this has Y-axis extrusions that are far easier to assemble accurately, and a couple other neat features like the ability to resume a print after a power loss. Here are some pictures of the build, in an album, from unboxing all the way up to my first prints:

I'm really pleased so far with the ability to make things easily right in my garage!

My first job for the printer is to create some parts for a Citabria strut mount. Here are a few animations of the basic mount geometry. You can see how it's intended to rest on the front and rear mounts, with three vee blocks and a "T-square" shape. The vee blocks are to be bungee'd onto the struts, with the bungees going around the curved parts of the blocks.

The first iteration of this crafty plan involved 3/4" by 1/16" wall thickness aluminum tubes. After some iteration on how to make the parts ("design for 3D printing" is not something I was familiar with, but I'm learning...), I ended up with this behemoth:

That thing was as big and heavy as the proverbial donkey's hind leg. That's no go: We're not going to strap that thing onto the strut of anything and go flying.

I then took some inspiration from my friend Andrew Angelotti of and designed a new mount that involved 1/2" diameter lightweight fiberglass tubing (I could have used carbon fiber but that's more expensive and the fiberglass is available easily at TAP Plastics). I also did more thinking about design for 3D printing and ended up with more parts, bolted and bonded together.

For bonding the parts (PLA to PLA, and PLA to roughened fiberglass tubing), I used Devcon Plastic Welder. That stuff has the most evil smell I have ever had the misfortune to encounter, and I'm sure it's not good for me. I kept my garage as wide open as possible while using it. The result is this little device, which seemed satisfactory in terms of weight, strength and size:

The pivot to which the probe is attached is supposed to be locked in position by tightening the bolt, after adjusting it to be vertical when on the plane. However, I goofed up the design and it turns out the part that is tightened was cracking. In the picture below, the screwdriver points to the developing crack:

Clearly that will not do. :) Now since everything was glued together, I needed to make the whole thing over again. Which is not really a problem since I've now got a reel of Hatchbox blue PLA 
and so my new parts will come out in Official Airball Blue™. (In case you were wondering, Official Airball Blue™ is whatever blue the cheapest available PLA filament happens to come in.)

So here's a pile of reject mount parts:

and here's new parts being made:

This has been an exciting and informative couple of weeks, and I'm looking forward to faster development cycles!

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