I will be making some form tools for my new (to me) turret lathe in 3/8 inch thick O1 steel.

I'm planning to use a 3 flute HSS 10 degree tapered mill which is 3/32 on the thin end (and will be about .225 at the top of the material). What are appropriate speeds and feeds? The simplest way to cut this would be to just plow into the material cutting a slot outside the desired outline.

If necessary, I could take multiple passes gradually increasing in depth.

Does this make sense? My trusty calculator (ME Consultant) tells me that even with a constant diameter of .225 I would need to take multiple passes. (I'm assuming that O1 steel is a high carbon steel for the purposes of ME Consultant). ME Consultant wants to limit me to a depth of 1.5 times the tool diameter.

My guess is that I should pick an RPM that works for the large diameter. About 45 SFM for that material would give an RPM of about 750. Then set 750 RPM as the speed and use a tooth loading that is suitable for the .093 diameter (ME pro suggests .00006 per tooth) to calculate the feed rate of .140 IPM.

I suspect that I could go back to my High School calculus and consider the taper to be a stack of gradually increasing steps in diameter. Then for each step, I could do a depth of 1.5 times the diameter of the step. The limit of the sum as the step height goes to zero should give the depth that I could use per pass.

But I can't be the first one to want to do this. Can someone tell me the answer? Or is there a different way to approach the problem that I should be looking at?

Thanks,

Ken