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.

2014-03-14 13.50.06

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!

2014-03-14 14.36.46

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.

2014-03-14 15.31.37

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″.

2014-03-14 15.34.11

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

2014-03-14 15.40.26

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.

2014-03-14 16.20.30

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:

2014-03-14 17.43.15

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).

2014-03-14 17.40.36

2014-03-14 17.51.39

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.

2014-03-14 19.43.11

2014-03-15 15.40.38

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.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s