Day 4: Got My Feet Wet Machining

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.

LBC-Back

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.

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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).

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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.

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It came out really nice. No alignment issues at all. I kissed the edges with a file to take the sharpness away.

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It fits perfectly too. I’m so happy.

I decided to try to make the piston back next.

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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″)

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I’ll have to start over.  ..And that’s when I decided to call it a night.

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