Armstrong 110pr RBL -4. Tapping the breech.

by John

This is the breech piece. From a 1.25″ high tensile bolt, with an 18mm hole drilled and reamed. The thread is 8tpi. An unusual pitch for the size. 60º form. Further shaping of the ends to come, but I decided to make the female thread in the breech first.
I cut the thread on the lathe manually, but the HSS cutter tip broke and I had to regrind it after the thread had already started to form. As you can see, the reset cutter position was a bit out. But I corrected the position and pressed on. How do the experts reposition a threading cutter? As per the original threads, I left flats in the female floors, and ground off the peaks of the male thread. (someone can correct my terminology here…)
Anyway, the breech piece threads in snugly and nicely. Quite tight but screws in by hand.
…and an 18mm silver steel rod fits well into the breech piece and into the bore of the barrel, so the threads are well aligned.

Despite the errors, this thread has worked out pretty well. I have learned a lot, and I reckon that the next one will be better.

The breech piece will next act as a tailstock centre for turning the exterior of the barrel between centres, after removal of the fixed steady.