Sometimes a part can be held solidly, and part of the rough machining done leaving a skim needed to finish, the solid holdings moved, and the other portion rough machined. The with a lighter holding the part skimmed to finish.
Much like using a big grit wheel to rough in a grinding part to +.005 (or what) and then finish with perhaps an 80 grit.
Grinding the whole operation with the 80 would take a coon's age.
OK, got it. I would go into my stock bin and grab a 4" square piece of stock, 0.500" thick. That gives 0.150" for a carrier and facing which is more than enough.
I keep a lot of plate/rectangular bar and not a lot of round bar, so I would grab square stock. If I only had round stock, I would use V-blocks in a vise, or use soft jaws*, or use those funny round rotating Talon grips.
Talon grip jaws are very low profile and have a sharp edge that bites into the stock to hold it. You do not need to tighten it up with bear strength, just snug is plenty. They work great on softer metals and IMO not so great on plastics. I grabbed a photo for you; the thing on the left is a work stop.
* One of the best things I ever did was mill a set of soft jaws with a square pattern rotated 90 degrees, for holding round parts in a vise.
QT Op: [The part is 3.75 od, .35 thick. I do not know what talon jaws are, can you explain.]
Having a 3jaw lathe chuck mounted to a plate that can be set on a mill table flat, or stood up clamped to an angle plate can become a good part holding fixture. holding a part close to the cutting tool action can be very good to keep vibration down.
Thanks to everyone. I have learned more from this thread than all the reading I have done up til now. My Sprutcam has the adaptive toolpath and can set feed in chip load, I just had not used those features before.
Still waiting on my Helicals, but I got the equivalent Melin rougher, 6 mm diameter, and using the info for O-1, which is approx the same for Melin and Helical, 200 SFM and .0013 chip load, and using 0.020 step over on the adaptive toolpath, the results are superb. My feed and speed from before for the 3/8 Onsrud were about right as it turned out, I was just taking way too big a stepover, and I was slotting. The info here and extra reading has convinced me to never slot again. I also need to put Y fittings in my coolant locline to get multiple streams for better chip clearing to avoid the recutting. I used handheld coolant on this part along with the single locline. The 0.020 stepover was probably smaller than needed, I will have to experiment as suggested as I make more parts
Moving on to the next part of the project, I have a post in grinding, looking for advice on that.