Pocket Milling

[David S]

CrossSlide with out knowing the design intention of the pocket. The quickest way to mill a pocket is with the largest diameter ball nose endmill the design will allow. Large diameter shorter end mills have more stiffness and the ball nose endmill doesn't have have those "delicate" sharp edges or corners.
Absolutely suck those chips out while you are going. If the pocket does require a sharp corner at the bottom then follow up with a square end two flute.

David

 

[petertha]

Petertha.."over-bite" can occur in corners because the end mill is cutting two surfaces at once. End mills don't like to do that. They cut fine on the end or the side but not both at once. They also do not like to cut on two sides at once, which is what happens when you hit the corner. When I have corners to finish that have to be clean I plunge the corner to get the corner radius and then use a smaller end mill to feed into the corner from two directions.

Thanks. I did take the roughing down to final depth before the finishing so only the EM side is doing the cutting on finishing pass, maybe only a thou on the bottom. I think what you are saying is when the EM is cutting on its side (red line) it just has that tangent contact area. When it goes into the corner, it sees 1/4 the circumference simultaneously cutting at once (green) & maybe that's aggravating the dig-in point? I thought by locking the table I might mitigate it. Its not a real noticeable line before transitioning into the next 90-deg straight, but its there. What I don't get is, how is much different than regular EM milling if I were removing stock at 1/2 the EM diameter and its ploughing on the leading edge like the green circle? I'd have to go back to my notes but maybe another issue is I was climb milling on the straights seeking better finish, but maybe that's a bad thing from terminating in the fillet perspective? Maybe conventional direction is better?

I thought about plunging the corners first as well, but chickened out, The EM is 8mm (.315") and 0.5" depth and these are kind of thin wall finicky parts. And the corner diameters actually intersect. I've also experienced issues on that front where the 2nd hole milling tends to grab the tooth stock of the first one & chatter etc.

Maybe I should look into those spiral edged EM. I did see some improvement going to a brand new sharp carbide. Sometimes aluminum can be gummy.

 

[mikey]

I think its a matter of deflection. Encountering a second surface deflects the cutter from its original path so that now it is cutting on two fronts. I don't have an article to point to for this but over the years I've seen it so many times that I'm aware of it. It occurs more often with smaller diameter cutters of course. I generally don't climb mill unless I'm taking off only about a thou or so, and this is especially so with small end mills.