I just received my M4-2000 1/2-28 TPI brake, nice piece, I can't wait to shoot it.
I was reading the instructions, yeah I actually read them, and the excerpt below made me curious.
AAC Instructions wrote:... the ports of the muzzle brake must be oriented at 9 and 3 o-clock. The ideal method of achieving this orientation is to have a depot level armorer machine a stainless steel washer of the proper length that allows the muzzle brake to thread on so that the ports align at 9 and 3 o-clock. ..."
I have a lathe and some machining experience, but how in the hell do you machine a stainless washer that is say 0.035"?
It took 28 lb-ft of torque to perfectly align my brake with a 0.010in shim. Clearly I don't need to turn a custom shim, but I'm curious how it would be done.
The way we do it is to simply drill a hole in a piece of barstock and part it off.
It generally takes a pretty ridgid machine to part off and leave a smooth surface finish.
If it needs to be trimmed to size we use whats call emergency collets. This picture pretty well says it all.
The collets locks into a collet chuck which squeezes it, so you'd need to have a 5C collet chuck on your machine. The collets are soft material and can easily be machined for another job. %c Emergency collets are a easy to acquire at auction used.
As far as how small a piece of material, dunno, the smallest I've personally ever held is probably only 0.020 or so. I'm sure you could go smaller than that, but you'd eventually reach a point where the collet would crush the material, that's where you have to switch to a surface or Blanchard grinder.
FYI I didn't do the illustration, it's just off the web.
Last edited by AAA on Sat Apr 11, 2009 7:53 pm, edited 1 time in total.
I would say a grinder is the best method for this, we have ground some shims on our surface grinder that were .0004", it was a obscure shape and needed ports through the shim so we made the part at .100" thick on a 5 axis and then put it on the grinder and took it down the the .0004" I personally didn't work on it but I know that guy who did it only felt comfortable drilling the ports with a piece of material that was at least a .100". So what I would do would be make over size washer with the correct OD and ID then grind it down to fit.
