true flat bottom end mills

If I understand correctly the premise is as follows:

1. With the cutter on axis above the work a convex profile is produced, as illustrated by the OP

2. With the cutter off axis by more than its diameter (and presumably offset in Z too) then a concave profile is produced

3. Between the convex profile (1) and the concave profile (2) there is a point where the cutter produces a profile that is neither convex nor concave, ie, it produces a cylinder

I agree with 1 and 2, but I do not see how 3 follows as a consequence. I do not think that 3 follows from 1 and 2 because the effects in 1 and 2 are produced in different ways. The convex profile in 1 is produced as a result of the clearance angle on the bottom of the cutter. If the cutter was flat across the bottom, as requested by the OP, then it would not produce a convex profile. The concave profile in 2 is produced by the intersection of the circular cutter and the rotating work. It makes no difference if the bottom of the cutter is flat or concave.

There is a point at which the cutter will produce a profile that is neither convex nor concave, but it is when the cutter is offset such that it touches the work at a single point, and therefore isn't really cutting.

Regards,

Andrew

The only problem with all this off setting is that you also start to alter the overall width of the cut and also loose the straight sides. So to avoid this happening you would need to take take additional cuts to square up the sides to the required width in which case you may as well take several passes with a smaller dia cutter.

The other option is to just take a file to the convex bottob that the OP has now and file it flat

J

Thats definitely the expedient solution for a one-off, Jason.

MichaelG.

Just to do it to death how about :-

Mill slot using standard end mill thus leaving a convex surface

Set up in the lathe and then rotate the work back and forth by hand through part of a revolution to trim off the excess using lathe tool, cross slide, etc. as in normal work. As we are talking small nimbers of thous. this should not take long.