I've got quite a bit of 4140HT left over from a customer project making some press dies a few years ago. I've been using it periodically for various projects. Its decent, strong, modestly hard steel for hand tools. Some of you may have seen the ER collet wrenches I made for my TTS tool holders. Well, I've got another project I'd like to do with some of it, and I need to remove quite a bit of material. A lot more than any previous project using this material. Even the press dies.

My Hurco currently has a major issue with one of the axis. It suddenly in the middle of a job went from about 0.001" backlash in one axis to 0.037". Something in the screw failed catastrophically. Of course its the hardest screw to get to. I'll fix it eventually, but in the mean time I want to get this job done.

With the PCNC1100 a 1/4 4 flute endmill taking a modestly deep cut and relatively small width of cut I can get theoretically around 0.99 CI^3. I don't know that I have run it that hard, but that 1/4 mill sounds really good in the 4140HT. When I plug numbers (with generic mills) into HSM advisor with 5/16, 3/8, and 1/2 I still only get about 1.07 CI^3. I've never really gotten good sounding cuts with the larger mills in the 4140HT although they rip through other steels like it isn't even there. The 1/4 inch Altin coated 4 flute seems to be the magic mill. Even on the larger more powerful Hurco mill.

I'm looking at 20-24 CI material to remove per part, and I want to make 9 of them. I also need to cut a precise undercut with a T-slot cutter of some kind, but that's a secondary problem. Right now I am looking to see if I can get any better MRR for the bulk stock removal without killing my machine.