Conclusion:

It looks nice and feels very sturdy. I might eventually put some cross braces in the u channel just so the legs wont push apart if you really crank down the bolts, but I’m not too worried about it for now. I’m really happy with how nice this turned out.

Next up is the butt. My first challenge was finding the material to make it out of. Pretty much any plastic would work. Even so I called around and had a hard time finding a reasonable price on anything less than a large sheet. I originally though mcmaster was too expensive, at $20, it turned out to be my cheapest option. The piece I got was a 12″x6″x1″ block of HDPE. I would have gone with 1.5″ if I could find it.

First (not shown) I used a table saw to cut the stock to the correct height. After that I milled off the depressed area on the top. I’ve never machined HDPE before, it cuts great! Nice clean shavings and no melting!

I decided to tackle the radius for shoulder surface next. This was going to be the hardest part, so I wanted to get it out of the way early, lest I ruin the part when it’s almost finished. My plan is to attached the work piece to a board and mounted the board such that it can pivot around the center point of the radius. That way I can sweep the part under the endmill in an arc. The radius is 6″.

Here's the whole (rickety) setup. The bottom board is attached to the vice. The top board is pivoted the drill bit you can see on the right.

Hey it worked! The cutting was a bit rough, in retrospect I should have done a rough cut with a bandsaw first so I didn’t have to plow through so much material.

The next step is to make the cutout in the center. The vertical and horizontal slots were easy enough.