radius change on a conventional mill

That is simple geometry if it is what I think that you are doing is. You're trying to put a concave surface to a piece of metal down the piece. The angle ends up being the perpendicular angle of the two edges of the curved section in one direction. The other angle is the amount of depth that you want the curve

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I came up with 26 degrees 41 minutes and 28 seconds (or 26.691 decimal) from vertical. The radius is not perfect but a bit ellipsical.

Fred

Fred

I am at a loss to figure how you can cut a 6" radius with a 6" diameter tool. If the tool has a 3" radius how can you get much else from it. Leigh@MarMachine

Take a 6" plate out of your cupboard. Hold it front of you level. Now tip it slightly toward you. See the radius that the edge of the plate makes in profile? It's more than 3" isn't it?

Fred