The thread form comes from the insert and the pitch from the machine, with no dies or chasers made for one thread. So the same set-up covers large diameters, non-standard pitches, and forms such as Acme (ASME B1.5) and buttress (ASME B1.9).
The last passes are very light, so the thread can be taken into a tight class, such as 3A with no allowance (ASME B1.1), and gauged to it. What it leaves is a cut thread: the grain is cut across and the root is not cold-worked, so under repeated loading a rolled thread lasts longer.
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model dataFeed per revolution equal to the pitch (8 threads per inch = 0.125 in. per turn), every pass synchronised to the same spindle position, the insert pulled out at the end of the thread and returned to the start: thread-turning practice. Modified flank infeed as the first choice, each pass shallower than the one before and the last about 0.003 in. (0.07 mm): a thread-turning tool maker's guidance. Thread 2-1/4-8 UN Class 2A (ASME B1.1; 8UN over 1 in. and Class 2A unless otherwise specified, ASTM A962), drawn with a rounded root and a 45° chamfer; Acme 29° (ASME B1.5) and buttress 7°/45° (ASME B1.9) drawn as basic profiles at the same pitch for comparison. The lathe, turret, insert, nozzle and gauges are generic; the cut is slowed down and the later passes sped up; the number of passes and their depths are illustrative, and the section is enlarged.
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