How does hard cutting on a metal lathe not screw up the bit or metal?

[stephen4785]

Seems like it would screw up both the bit and the material. Can anyone explain please?

[turbostang]

There's a lot of other questions/answers before yours gets answered... Since that's obviously a CNC machine, we'll take for granted that it has proper tooling- so using that approach...

They're (in that video) most likely using a ceramic grade insert - they are VERY hard and will cut anything, but in most cases will NOT take a bump or interupted cut. (like the cutter passing over a bolt hole).

Next, the machining operation is most likely a 2nd operation - as in, the part was premachined to a certain spec, heat treated and now is getting finish-machined. Heat treat can be done at any depth, so for instance, this one is something like .030 deep and the finish cut is only .010 or so - leaving about .020 of the hardened surface behind..

If you used standard grade or normal style inserts, it would cut, but they will NOT last long at all...