Before I put stock in the chuck, I install the live center into the spindle to make sure that my cutting tool that I ground lines up with the live center so that when I am cutting threads on the stock, it is cutting on center. Afterwords, I remove the live center and install the four jaw chuck, fallowed by the stock.
Next, I get the stock (in this case, a barrel) as close to center by eying it, the fine adjustments will be made by using a dial indicator and a soft aluminum piece that I turned previously, to match the size of the bore with no play. Through indicating the bore of the barrel and not the outside dimension of the barrel, it allows the threads to be cut concentric with the bore. If you do this right, you should be able to get within .001 (one thousandths) of an inch.
The next step is to decide how much material you want to remove and leave enough for thread relief.
Time to start turning the diameter down to the correct diameter before thread cutting. In this case, I turned it down to .505 for roughing so that there is enough stock left for finishing.
After a few passes, this what it looks like. Still have .141" to go. Take measurements often to keep track where you are at and take your time. Often times than not, you only get one chance at this.
The barrel has been turned down to the proper diameter, now it is time to setup the lathe for cutting threads. This includes changing the gears, changing to the threading tool, squaring the thread tool with the stock with the 60 degree gauge, and turning the compound by .5 degrees into the stock. By doing this, it will cut on one side of the thread and not both sides. If we were to cut on both sides, it would rip the thread roots out, with ugly results. We are cutting 1/2-28 threads.
When you are cutting threads, it is important to take light passes (.005-.010) and every third pass, take a spring pass (meaning do not increase the cutting depth every third pass) so that you can clear out the chips in between the threads.
Timing is everything: watch the tread dial. To simplify things, I always cut my threads on 1 as any thread can be cut this way, even or odd threads. Before you can reengage the threads, you must watch the thread dial each time and reengage it on the correct number for the threads you are cutting.
Cutting all done.
Test fit. Off camera, I measured the threads with thread wires and a micrometer that measures the pitch of the thread. Plugging that measured number into the formula with tell you how much more you have to go. (The fit was perfect, no slop but still easy to thread on and off with the flash hider.)
After I was satisfied with the fit, it was time to finish the raw surface with cold bluing.
The last thing I will do to complete this project is to make a thread protector that matches the diameter of the barrel if I decide I don't want to us the A2 flash hider. However, a compensator would look better.
