Cutting Large Radius with Endmill Tilted

[MotoDan]

Hello all,

I'm trying to remember how to calculate cutting a shallow, but relatively large radius on the end of a round rod on a knee mill. The procedure is to tilt the head to some angle and make a pass across the end of the rod for the desired depth. The resulting cut has a much larger radius than the endmill. In my case, the rod is 1" dia and the desired radius is 1.5". Seems like I used a 3/4" endmill the last time I did this many moons ago.

I realize I could make several test cuts until I get the right radius, but I was hoping someone has done this before and has an idea how to figure the head angle.

Thanks in advance
Dan

[RICHARD ZASTROW]

Dan, I don't know if this is applicable to your project, but here's one from "A TREATISE ON MILLING AND MILLING MACHINES" (1951 THIRD EDITION).

C=angle of cutter with axis of work surface, degrees
D=cutter diameter, inches
Rc=desired radius of surface, inches

sin C = D / 2 * Rc

Dick Z

[Kiwi]

I don't know the formula but 12deg looks close on CAD.

[Dr Pete]

Sin angle= d/ 2XR
Where d= diameter of cutter
R= radius to be cut
So for cutter .75" / 2X1.5"
=.25"
Inverse sin of .25" = 14.47 degrees

[MotoDan]

Thanks guys. Dick & Dr Pete have the same answer, so it must be right! Dick, where in the Cincinnati text did you find the reference? I found an older PDF of the same book, but haven't found the discussion on angled cutters yet.

Kiwi - thanks for the empirical estimate - very close to the calculated value.

You guys are terrific! Thanks again.
Dan

[Kiwi]

When drawn with CAD the 14.47deg gives a more correct curve over a narrow arc whereas the 12deg gives a much wider arc with a variation of about .002"

BTW. I read 0.75/2*1.5 = ASIN(0.5625) = 34.23deg.

[RICHARD ZASTROW]

Dan, Section on "Dies, Molds and Cylindrical or Irregular Parts" page#583 of 910.

This old book has a lot of good stuff in it. Was mandatory when I started out *** years ago. LOL

Dick Z