Found a chunk of aluminum in my scrap bin. Dusted the edges on the mill to make them somewhat parallel and easier to clamp. If I ever make another, I'd seriously consider using black colored acetal. Strong enough, even easier to work and permanently colored. Anyway, aluminum it is for now. Marked the center line.
Centered up on the milling machine. Need two holes. The gas tube is 0.875" in diameter and my barrel measures 0.555"--just over the 14mm nominal size.
Spotted then just through drilled the 0.875" hole (7/8"). No drill chuck. Clamped the shank in a collet.
I didn't have a custom sized 0.555" drill bit, so after spotting the hole it was first drilled with a 0.500".
Thought about taking it to the lathe and boring the hole to size, but then I remembered I had this small boring head. Pump and Products Co. Tool Division, Cleveland, Ohio. Patent probably still pending. Got it from a co-worker a year ago. Guess it's at least 30--OK, probably at least 50 years old. Anybody know anything about the company? The setscrew clamps a 0.375" boring bar.
The two screws on the back allow you to change the angle of the boring bar relative to centerline.
Well, I've never used this tool before, but after looking at it for a minute, I realized that this is probably wrong. The cutting edge of the boring bar likely needs to be in the same plane as the adjustment angle. Here, it's at approx 90 degrees.
Lined up. Adjusting the two upper screws makes the cutting edge move in or out. Set it just slightly larger than the hole diameter and plunge. Downside? There's no micrometer reference on the tool like there is on a modern boring head. It's bore, measure, adjust, bore, measure, adjust... After a couple adjustments, the hole was done.
So now, I've got this incredibly cool block with two holes in it.
With the front sight, and the gas tube cap removed, it was a successful test fit.
Back to the mill to clean up the faces. Gotta get them now while it's still rectangular and easy to clamp.
After it was faced, I penciled in some lines and started milling edges. Eyeballed all the set ups--just made the line look parallel to the top of the vise jaws, then milled to the line. It's not like this is a precision part.
Starting to look like something. Eventually, I did nine edges.
Did some more magic marker layout and drilled for a setscrew to clamp to the gas tube.
Tapped M4 x 0.7mm.
It's done for now. May need some additional shaping/fitting in the near future. No set screw for the barrel as yet. Not sure if it'll need one.
Hope to start the stock next.