Quote Originally Posted by bob ward View Post
Thanks Ew. When ever I tackle this material I use CNMG 432 inserts and I reckon I have tried just about every combination of speed, DOC and feed the lathe has - Hafpos 2hp 14 x 40 - and always get the nasty blue ribbon, no chips.

But industry turns tons of 4140/4340 so there must be an answer. What would be your starting point for steel 55 dia? Available speeds in high are 2000, 1300, 710, 450.
Hi Bob,
Like Michael i would start at 710, although you may find the slower speed with a higher feed may work better in the end, just to give the motor a bit more leverage. If i was too attack it on the Antrac i would probably run at 1200rpm, feed of .25mm and a DOC of 2mm. But I have 5hp to put to use, not 2.

The other thing to try might be a Cermet insert, there is a guy on ebay with some Kyocera inserts, i have been using the CCMT's to good effect.

The other thing is what sort of chip breaker has the inserts your using have? Is it just a straight one or is it "wavy"? The waves are there to interrupt the chip flow and help break it up.

Ew