Hello Everyone, I just want to share some of the shenanigans I’ve been up to on the off season.
I got obsessed with making a one piece gearbox housing that could bolt to a section of 2x1 box section. Not because we really really need it but more or less to go through the process:
First I started by figuring out a furnace:
I Did some super crude tests with my students regarding how hard it would be to melt aluminum: Result even with the shadiest furnace ever aluminum melted very easy with propane and way faster than we all expected:
I was pretty grossed out by some of the furnaces on Amazon with Kaowool insulation and wasn’t too interested in having the thin fibers of it going everywhere. I found an old empty R134a tank and some castable refractory from Skyline Components in Tucson, AZ. We cast a small furnace. It was pretty easy to work with and has held up really well to multiple firings, no degredation and minimal cracking:
For my first test I made a really simple bracket with curves and shapes that would even be a pain to make with a CNC mill. I cut parts out of foam on my router in 2 halves. (cutting these parts took the longest out of this whole process:
This first bracket was cast using green sand. It was alright. the weather was pretty dry so i was struggling with the sand drying out and things kind of falling apart. This first test I went pretty fast and didn’t sweat so many details. I totally expected it to be a failure. But to my astonishment it worked… even with such small passages (though barely):
I tried the lost foam method in green sand. It was a lot of work with few good things:
- The foam isn’t exactly my favorite thing to machine as it is very flimsy
- Surface finish is garbage
- Tons of nasty fumes probably took a few years off my life
- The positive is consumed
- The aluminum didn’t penetrate very far
I tried cutting the positive out of a chunk of HDPE. Throughout this whole time i’m constantly tweaking the design here and there trying to make it more reasonable for casting. I initially had an idea of having a center positive then spacers that I could put on either side to make it a right or left gear box. I learned the hard way about ALWAYS having draft on the edges I wasn’t able to get a cast from a positive with straight sides. I thought that it was so thin i could probably get away with it… nope.
At this point ive spent a lot of time routing out positives and way more time than i would like trying to cut out the spacer sections that lock onto the aluminum tube. All i was getting was garbage then something happened…
Let me stop here for a second…
Our team first got a 3D printer in 2015 and for the next 4 years I’d come to loathe 3d printers. I had a really hard time justifying putting so much time into a machine that wasn’t cranking out durable parts and that someone would be kind enough to “re-calibrate” every week or so. I hate them… I mean i still kinda hate them but i’m warming up… to them… maybe with an enclosure i’ll warm up much fa… (stop) 
ok back on track…
One of my students had recently pulled the moth balls out of one of our 3D printers and offered to 3d print the part I was struggling to cut cleanly with a router (Anyone else out there do front side and back side 3d contours in 2 ops on an x-carve? yes it does work you just have to plan steps ahead for your Z0) I was schooled the 3d printed part worked perfectly.
One trick I came up with along the way is to make a thin wall where you want holes. In this first successful casting i made my life a lot easier by not packing Petrobond through the entire frame. the sand just formed a 0.030" void between the parts that the aluminum just didn’t flow into:
Holes were then chased through on a mini mill but you could probably use a drill press. I intentionally gave the task of drilling it out to a super new member just to see if it would still work. Fit was alright. A smidge tight for the lower motor but bringing the bolt holes up from a snug fit to a free fit fixed it:
Yes there are 4 holes that have to be in just the right spot on the box section to make this work. We plan on making a template that we can just clamp to the metal and chase the holes in with. we’ll start with an 1/8" pilot then just chase it with a rotabroach hole saw.
So long story short a 3D printer and casting old aluminum off cuts is pretty promising:
I made these pretty key observations:
- Scale up your model by 1.017 before making the positive
- Stay away from aluminum cans there is a lot of paint and plastic in them
- There is a lot to casting I did not cover in this post intentionally, do you homework and find someone with experience
- Oil sand (petrobod) is great for very dry regions
- Don’t even dream of holes just put in spot to drill through
- If you are planning on drilling it out make sure some feature will fit in a vise.
- It’s actually pretty easy
This post is kind of a mess I hope it’s still okay.
Oh also cad files here:
Next… Soduim Silicate and Generative Design… is anyone else running down this rabbit hole?
