The positive rake requires less Hp (FM45) I use a 2.5" in aluminum with no issues and also have a 4" with 7 inserts, I use a 2" for ssteel with an R8 and 3 Hp motor. The calculations or for maximum material removal which is seldom the case as a hobbyist. I would not leave out inserts as it will effect the surface finish. As mentioned I would probably go with a 4" FM45 for softer materials and a a 3 or 4" FM90 for harder materials and shouldering with a heavier mill and 5 Hp. You could get a single arbor. I like the larger head for wider stock, but can also be used on smaller stock. You need accurate head alignment, I get almost mirror surface. I use some air to clear the chips.
Are interupted cuts an issue for insert durability and surface finish?
I didn’t phrase it properly. With a 4” diameter face mill on 2” wide stock, the inserts will engaging the material and then coming off of the part. With a 1.25” indexable end mill on 2” stock, the end mill and inserts would not be coming off the part the same. No?Not at all . It's an insert cutter and always has interrupted cuts ! Not sure how it would have a continuous cut ?
Wouldn't make a difference . An insert on a mill cutter is never fully engaged in a cutting action . It cuts in then 180 degrees it's out . Make sense ? The cutter is still parallel with the bottom cut but not actually cutting .
By the way , I'm an old time Kennemetal and Valenite guy .
I understand what you're saying though ! You're talking about re-entering the workpiece with a larger cutter . With the correct grade carbide this has little to no effect . I believe Valenite V02s were the insert of choice years ago .
I may add , why would anyone use an undersize facemill other lack of HP ? Just adds time to the job !