Currently there are 2 methods used to blunt start a stub acme thread at my workplace. Most of our lathes don’t have live tooling so instead we do 1 of 2 things.
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use a grooving tool programmed as a thread tool and offset the start point for z half the lead with a 60 degree thread chamfer out. Then offset the finish point for z a couple thousandths at a time until it makes a close approximation of a blunt start.
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Program 2-3 more thread cycles using the thread tool, using a 60 degree thread chamfer out and offsetting the first start point for z half the lead and the second and third plus or minus from that depending on what is needed. Then offsetting the finish point for z until it makes a close approximation of a blunt start.
The second method is the most used due to the fact you don’t need to load an extra tool.
I was wondering if there are any better ways to blunt start on a lathe without live tooling or if there’s some way of calculating the finish point for z?