Machining the Butt

Here’s the goal:

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.

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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!

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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 ccan sweep the part under the endmill in an arc.

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The pictures a bit blurry, but you can sort of see the center point I drilled on the left side of the board. The radius is 6″.

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The drill  bit sticking out of the  board is the pivot point. I locked the end mill 6″ out from that point.

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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.

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The diagonal slot was harder. I can’t make a straight cut diagonally on the mill, so I have to somehow fixture the part at an angle. ..I don’t really want to make a jig for this one cut.

I thought about it for a bit and realized that if I cut the corner off now I can use the scrap piece to hold the part at the right angle like so:

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The diagonal slot and the tapered front are parallel, so it works out.

To keep the pieces from slipping I put a threaded rod through both pieces. (I quickly viced the piece and drilled the bolt holes first).

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And cut. mrrrrrrrrrrrrrr. The quarter inch endmill isn’t long enough to do the whole depth at once so I had to flip the piece after this and make the other half of the cut.

To finish the stock up, I put a 5/8″ endmill on the lathe and used it to counter-bore the bolt holes. Because the centers were already drilled plunge cut went really easy.

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Looks awesome! That’s one part down. The right bolts hadn’t come in yet, but I really wanted to get it mounted so I scavenged some bolts from around the shop.

Next up: mounting the ak47 grip.


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