Re: Threading a barrel
I pretty much agree with all the replies. I'm not a skilled machinist, and internal threads are a little more tricky for me, but I have made several muzzle brakes and flash suppressors and I like 24 tpi for muzzle tenon threads over 5/8", and 28 tpi for all smaller diameters. My lathe won't cut a 32 tpi, but if it would, I'd use that pitch on 1/2" tenons and smaller. It's easier for me to thread the brake first and then cut the barrel tenon thread to fit it. Also, if the brake has to be timed on the barrel, the tenon shoulder and tenon length are easier to adjust, and you're already set up to crown the muzzle when you finish the brake installation. I only do single-point crowns with no chamfers.
1/2" 28 tpi is the standard pitch for AR-15 brakes, flash suppressors, etc.
On the setup, I usually set up (if the barrel is long enough) with a spider on the back of the spindle, and brass shimstock around the barrel to prevent the jaw faces from marking the barrel (tapered or straight). Doesn't take a whole lot to hold the barrel for me. I stick just enough of the barrel out of the jaws to clear the tools and tool holders, and I take very shallow cuts while turning and threading, and keep track of where my compound is on the feed dial. I always start at zero on the compound and zero on the crossfeed, stop a lot to try the thread fit, and then record where the compound feed dial is when the thread fit is made. I really like the feel of a well-fitted fine thread.
It's good to use a range rod to perfectly center the bore in the chuck, and it's good to use a tiny boring bar to finish the baffle and exit holes. I use a minimum of .020" and am comfortable with .030" over bullet diameter. Some recommend only .010 over bullet diameter, but I believe it adversely affects accuracy, and doesn't improve brake performance.
If you have a "Super Spacer" for your mill, it is great for making your own brakes.
Since Im not a skilled machinist, I can only relate the things I've learned that work for me. Just my opinion, based on some experience. Gun work is not rocket science, just sound planning, meticulous workmanship, precision fits, and no "close enoughs".
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