[mark123]

I know I'm doing something wrong but I can't figure out what. I have a 2" by 4" block and I'm milling an open pocket .500 deep with a .250 radius all around. In the corners I always have a small triangle of material left that I need to remove somehow. What is the "trick" to milling this feature.

[txcncman]

Doh! Draw a picture and upload it here.

[jimhurlburt]

Use a 1/2 ball end mill (for at least the last 1/4 for width.
If the pocket is very big, I'd probaby do it in two stages, take out the middle with a square end mill, leaving just a smidge more than 1/4 on all sides to remove with the 1/2 ball end mill. Only real trick will be to get the finishing pass at exactly the same depth as the floor of the open part.

That'll leave you with a 1/4 radius fillet in all internal edges.

Jim