…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.

I made the back of the piston tonight. It took about 5 hours. Turned out perfectly though.

The o-ring guide I’ve been looking at recommends about 20% compression of the o-ring (.110 for my 1/8″ o-rings). That fit was a bit tight on my last part, so I decreased the compression to 10% (.124). My pipe is 3.745 ID, so I turned the bottom of the o-ring groove to a diameter of 3.497. It still felt too tight, but I applied some oil and now it slides pretty easily.

I had to take off a lot of material…

Alright, I got another part done yesterday. Nothing too tricky, but I left to go make this one at 10pm and didn’t get home until 5am. Towards the end I was terrified that I would make a mistake and ruin it. Didn’t though :)

I did hit one snag. I didn’t have the right fixture to hold a boring bar. Luckily I was able to reach in just far enough with a regular tool.

Pre-post today. I’m going to try to drill the radial screw holes.

I don’t have the proper tools to do this (a large indexing head). On top of that, if I mess up, I’ll ruin my back plate. I’ve got an idea for how to do it though, and I’m going to go for it today.

I can’t fit this pipe on the lathe at all, so even scribing an accurate circumference line will be difficult.

My plan is to polish the OD, and carefully measure the circumference. I’ll then print out a template to wrap around it. If I pull the paper flat and line up the ends, it should sit fairly square on the pipe. I’ll punch through it to mark the holes.

I’ll also use the edge of the paper to mark a circumference line on the back edge of the pipe. That way I can square it up with a file.

I’ll fix the back plate on somehow and drill it at the same time. That way even if the holes aren’t perfect they’ll still line up. If I really nail it, the end cap might even fit in any orientation. ..We’ll see how that goes. Wish me luck.

Here's the template I made. For some reason, it came out about 1/16th too short when wrapped around the pipe. Maybe the paper thickness? Anyway, I just adjusted the grid size and reprinted it. After Getting it all lined up and square, I punched through paper at the crosshairs. I also slid the paper cylinder back just a hair and marked with a sharpie the bit that protruded. I filed the marked area off with a hand file the get the end perfectly square to the holes. ..well that’s the theory. All I know is that it’s square now as far as I can tell.