machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment. I read every comment and respond to most. n.b. There is a list of my first 800 posts in my post of 17 June 2021, titled "800 Posts"
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.
Hi John
The correct terminology for the thread is, the point at the top of a thread is the crest and the bottom of the thread is the root. Also realigning the tool after regrind can be very tricky especially internal threads when I had to do this on my old lathe I would use the compound slide to align the tool to the thread groove after first backing off on the diameter and visually and slowly coming back to start recutting the thread, this is not a great explanation but is all I can do will have to give you a demonstration next time I come to Geelong.
Cheers
John Emery
johnsmachines 
Hi John
The correct terminology for the thread is, the point at the top of a thread is the crest and the bottom of the thread is the root. Also realigning the tool after regrind can be very tricky especially internal threads when I had to do this on my old lathe I would use the compound slide to align the tool to the thread groove after first backing off on the diameter and visually and slowly coming back to start recutting the thread, this is not a great explanation but is all I can do will have to give you a demonstration next time I come to Geelong.
Cheers
John Emery
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Makes sense John, thanks.
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