So here goes nothing… I’ve used a lathe, but never to make something that needed to be this precise. I’m going to make the back of the cannon first.
There will radial screw holes around the circumference eventually, but I’m putting that off for now.
I ran into a problem right off the bat. I only have access to a small lathe, and the 3 jaw chuck (which is self centering) won’t fit this disk. There’s a 4-jaw chuck that would fit it, but that one’s not self centering.
To find a rough center I used a caliper to scratch some half-diameter arcs on the disk. Where they converge is a pretty good center point. I punched the spot and then used a drill press to make a hole there.
I centered the piece by putting the live center in the hole and pining the piece to the chuck. I then very gently tightened each of the jaws. After that I incrementally tightened them down, slightly tightening one apposing pair, then the other until they were all tight. (The pic’s from the second time I did this, after I finished the first side).
Here’s the finished part after I turned and faced the other side, and cut the o-ring groove. To cut the groove, I took the advice of some people on the practical-machinist forum and ground an old broken tool down to so it had the same profile as the groove. The tool was wide with a flat nose, so I didn’t think it would cut well, but I used a lot of cutting fluid and it actually cut a perfect groove without too much trouble.
It came out really nice. No alignment issues at all. I kissed the edges with a file to take the sharpness away.
It fits perfectly too. I’m so happy.
I decided to try to make the piston back next.
The centering and facing went well. (Look at that awesome surface!)
…Unfortunately, while I was turning the diameter I accidentally made too many passes without measuring. (It’s supposed to be 3.74″)
I’ll have to start over. ..And that’s when I decided to call it a night.