Long, small diameter part help

I am running a 2015 Haas TL 2, and was brought a prototype print for a firing pin that needs to be made. It's being made out of 17-4
The part length is 6.360 long, with a major O.D. of .280, a .075 step x. 470 from the face and a groove dia. of .156, .420 wide located 2.112 off the face.
I'm having problems with turning these small diameters.
I'm setting up a piece .375 between centers, and adjusting the protrusion from the chuck as I go to get as much stability as possible. I'm also grooving out .250 behind my countersink so I dont interfere with my live center and tailstock, and picking up z zero from there.
When I try to turn down the .075 diameter, and when I cut the groove, the .075 diameter keeps snapping off.
Does anyone possibly have a suggestion ? Maybe interpolation of that small diameter on the mill, vertically ?

That dia is tough.
Super sharp tooling and for the groove go thin as possible then make in multiple plunge cuts.

Another way is to machine in sections from the end of part completing groove feature then move closer to chuck for next feature etc etc. Kind of like a swiss machine...you keep your ridgy with heavy size stock supporting. Down side is it takes longer and sometimes you have to play with how much you can take off without relieving stress creating a pretzel and how much material you need to support.

Good luck

Use a Roller box turning tool, turn the diameter in one pass.

SIM said:

That dia is tough.
Super sharp tooling and for the groove go thin as possible then make in multiple plunge cuts.

Another way is to machine in sections from the end of part completing groove feature then move closer to chuck for next feature etc etc. Kind of like a swiss machine...you keep your ridgy with heavy size stock supporting. Down side is it takes longer and sometimes you have to play with how much you can take off without relieving stress creating a pretzel and how much material you need to support.

Good luck

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Yes. To add on, go with a small nose radius. We usually rough with as large a nose radius insert but when doing thin parts sticking out we'll go with .0156 for the roughing with the DOC smaller as well probably around .03. Then finish with a .009 nose radius. Positive inserts only. As SIM said, all sharp.

You don't mention the condition of the 17-4. It will cut better in the hard.