Over the July 4th weekend in 2022, at the request of my friend Tim, I cast an aluminum disc in green sand and then machined every surface of it on the lathe. It was basically my second casting ever, so the process is recorded here in full, rough edges and all.
Molding (July 2022)
Here I'm placing the sprue in the middle of the 3D printed pattern. I wish I'd remembered to make some marks to help me center it, so that I could use it to grip the casting on the lathe.
With the sand packed, I separated the two halves of the flask so I could remove the pattern. The bottom half still has the pattern half-embedded in it, and the top half has the matching impression, with the hole for the sprue.
Digging it out
After the pour, I dug the casting out of the sand. It was looking good so far: you can see the disc, the pillar, and the spoon-shaped sprue coming out of the sand.
Success! It's super rough, though. I think I should have sieved my sand. But every surface is going to get machined, so it should be fine.
Machining (July 4, 2022)
The next morning I started cleaning it up on the lathe. One face took a cut nicely and came up bright, with the rough sand-cast rim still around it. There were going to be some voids and inclusions in the finished part. Tim said that was fine, as long as it held the thing and conducted heat.
Flipping it around to do the other side meant gripping the faced rim with the chuck's outside jaws, with the sprue stub sticking out toward the tailstock.
It was loads easier to cut most of the sprue off on the bandsaw than to machine it away.
And done. The front face, up top, has a raised center step. This is the back: a shallow recess, with a bit of rough casting skin left on the rim. That's as far as I could take it down without running out of material. I should have allowed more room in the casting, so I'm calling the rough edge artistic. A few of the pits made it through, too.
It shipped off to Tim shortly afterward.