Corner rounding end mills. Help!

Highpower

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A question for the group:

How do you go about setting the Y and the Z when it comes to using a corner rounding end mill to create a radius?

As an example, say you have a piece of rectangular bar stock that you want to put a 1/8" radius on one of the corners, the length of the part.
How do you determine the height and depth of the cutter in order to have the radius properly centered on the edge and not cut into the sides, or end up with a shallow cut? (Not too high, not too low.)

There has got to be a better way than just "eyeballing" it like I have been doing. :-[
 
It depends on the cutter most of the time, but I measure the diameter of the body to confirm what it is, and use that to calculate the X-Y position. The body diameter minus twice the cut radius will yield the minor diameter of the cutter that will be in contact with the side of the work. Using your edge finder, you should be able to locate the work edge accurately. The Z is a little trickier, but from memory, the radius breaks out right on the end(face), so a touch off on the work in the area that will be cut away usually works.

Of course, like I said, it depends on the cutter, so you may need to experiment a little to see what you cutter is like.
 
Tony Wells link=topic=2833.msg19569#msg19569 date=1311464362 said:
It depends on the cutter most of the time, but I measure the diameter of the body to confirm what it is, and use that to calculate the X-Y position. The body diameter minus twice the cut radius will yield the minor diameter of the cutter that will be in contact with the side of the work. Using your edge finder, you should be able to locate the work edge accurately.
OK, that makes sense to me now. Thank you Tony. I'll give that a try tomorrow and see how it works out with my cutters.
I've tried touching off the top surface of the work before - trying to catch the upper portion of the radius, but usually end up undercutting the top by a couple thou.

Today I made a part that needed a 1/16" radius on one corner, and wound up undercutting the side this time (minor dia.) :(
It won't affect the function of the part, but it still bugs me that is doesn't look like a clean radius and has that fine "step" below it.
 
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By eye, I have taken a test cut known to be light, and used radius gages held to the work and gage pins to roll under the radius gage to get a feel for where I was. This works to get pretty close if you have a hand ground cutter, or one that defies the above method. Mostly rounded edges are cosmetic in nature anyway, but some are quite functional, such as molds and dies. Got to be right on sometimes.
 
Yeah. I'm making a couple of drill guides that need clearance going into a corner with a similar radius. Any misalignment in drilling the holes would prove to be very costly, so I want this thing sitting square, solid and accurately aligned.
 
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