looking at a pic of a long lead like this makes me think creating an internal thread with 2" lead is as much a broaching op as turning. given that the feed rate is going influence the cutting speed as much as the rpm's, I'd guess this is a slow sfm job, else how could the carriage keep up? if that's the case, grind up a hss tool for the job so you know you have clearance. In other words, if you are busting inserts likely because its such odd shape tool you require to give adequate clearance, and if i'm right and you can't get the sfm to benefit from carbide, grind up a hss tool and see if it solves your problem. |