I have a billet of 4140 HR annealed that is 9" in dia and about 10" long. It is being made into a spindle. The flange 9" dia is about a 1.25" thick and the rest of the length gets cut down to 3" to 3.3" in dia. So, there is a lot of material to remove from the round billet.
Does anyone have a recommendation on how to get rid of this material quickly? I was going to process it on a 4 axis mill. I was thinking of using a 2" dia EM with inserts (from Ingersoll or Iscar) vs. using the cobalt 1" dia EMs that I have. I don't think that the cobalt tools would last a part.
4 axis lathe, I'm guessing your going to mill/turn it. If that is how you determined to do it, you can haul ass with the inserted cutters. Your finish is going to suck, even with a tail stock. Your tooling cost is also going to be very high just to buy the cutter body. With that being said, I would send it out to somebody with a lathe that can handle the size, I would almost guarantee that it would cost you less. I would wager a guess that the cutter body, at that diameter and length is going to be in the $600+ dollar range, plus inserts.
Now if your determined to make it yourself, I run the Sandvik R390s at work all the time, amazing things. In 4140 annealed at .300 depth of cut and .003 to .004 per tooth, 650-850 SFM, taking smaller cuts of around .010 to .060 DOC which you will probably have to do on a fourth axis, up to 1300 sfm. Run it dry, coolant will just kill your tool life.
Hope you got plenty of HP. Those big indexables like plenty of horses and lots of torque to run at optimal removal rates. I like the Carboloy turbo mill series. They have a very positive rake and are easy on lighter mills. They come in many sizes and configurations. Cost is minimal for an indexable and many are sold in sets with ten inserts. 4140 HR should cut like butter with any good indexable. I agree with bubba, run it dry for tool life.
Turning is still better for this job if you can find a way.