Need Help!- Face milling for best finish on 4340 steel alloy on spline surface

[Lumenium]

I am machining a vertical surface 2" tall that follows a gradual spline profile using a Haas VF2SS vertical CNC mill and looking for the best possible finish. The material is 4340 annealed. I have tried a high performance 4 flute 20mm coated carbide cutter but I am not satisfied with the finish. I can't surface grind the piece because of the spline profile.

Does anyone have a recommendation for an end mill, an insert cutter or process that can give me a superior surface on 4340 with a finish grade N8 (125 micro-inch) or better that is truly perpendicular (no taper) to the horizontal surface.

Thanks for your ideas!

[Glacern]

What speeds and feeds are you running? Are you getting chatter?

Consider trying a variable flute EM like a Hanita Varimill. A milling chuck may help as well... the more rigid, the better.

[Lumenium]

Glacem,

Many thanks for your ideas. I am going to try the Verimill cutter and an accurate milling chuck.

As for feeds and speeds, I have tried everything but my best results were using a 0.5" end mill 4 flute at 4000 rpm at 7 IPM. Is not the spec for the material but yields the cleanest finish.

I suspect it is chatter issue and I know it's not coming from the work piece so your suggestion on the mill and holder is promising.

I will let you know the outcome. I am also planning to try and electro-polish the piece when it's done to see that can do. Thanks again.