Re:I forget, but radiused end mills

Sorry I can't recall the thread title, but the one that diverted to the radiused corner end mills? Those little devils are sometimes called "Bull Nosed", as opposed to the full radius which is known as "Ball Nosed". They have a few different names for the woodworking ones too. One of the nice things about this tool geometry is that you can sculpt 3D surfaces with an end mill that has a very large diameter, relative to the size of the radius. A major problem with Ball end mills is that at the center of the mill the effective SFM is nearly Zero and the cutter tends to tear or rub, rather than cut. With a Bull end mill, all the cutting at the bottom of the radius is at a distance away from the evil slow center and so the surface finish is much better, the feedrates are faster, and the required RPM may easily fall into the 3000 or less range, to get as good or better of a finish as that with a Ball nose. Less chatter too!

The only problem is concavities and ridges. You cannot sculpt the bottom of the inside of a hemisphere, oriented like a bowl. There will always be a flat left behind ( or gouges, depending on your Cad-Cam software, not to name any names here).

Summary if given the choice, use Bull nose cutters to both rough and finish. Use ball nose only if you have to to match the geometry. Even with geometry filled with canyons and craters, a Bull nose with small radiused corners will usually produce better surface finishes and cut faster than a Ball nose.

Oh yes in parting, they ARE available from industrial suppliers. MSC for example stocks 2 & 4 flute, 1/8-1" dia, with corner radius of .015-.125. They get quite expensive over about 1/2 inch. Just think how much more stronger a 1/4 endmill with a .015 radius, is than a 1/32 ball end mill. Here is a reference part number & price from last year's MSC catalog 1/8 dia, .015 corner radius, 3/8 loc, $10.92/ea. Tolerance on the corner radii is +.003/-.000. Check out mscdirect.com to find the page from the part number 00427260.(not an endorsement, J&L has them too)


Best Regards, Fred Smith- IMService
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