[TXFred]

I need a little advice here. I'm finishing a pocket with a Melin 1/2" 4 flute HSS end mill. Feedrate is 22.79IPM. Spindle speed is 1203 RPM. The pocket was roughed with a carbide insert mill, and 0.030" was left on the walls and on the floor of the pocket. The metal is A36 steel.

The problem is, I'm getting a nasty pattern of circles on the floor of the pocket. For the right hand pocket, I tried cutting the feedrate in half and upping the coolant flow, but it's still making these marks. I'm not hearing any unusual sounds from the cutter.

What's causing these, and how do I get rid of them?

Frederic

[bostosh]

Lighten the cut depth .005 final cut, up the RPM, use a two flute cutter ground for steel with .010 tip radius.

The cutter is pulling a cut chips back into the cut, or has build-up on cutting tip.

Steel cuts like this, normal, does the part need function or superior finishes?

[TXFred]

Thanks for the info. My workaround is to let the carbide rougher define the floor of the pocket. Since the carbide has rounded edges, it's not having the same problem.

The part is still functional with the ugly surface finish, but the perfectionist in me didn't like it.

And it's good to know why it's happening. Thanks for the explanation.

Frederic

[mrquacker]

One of my tricks for surface finish is to use a small brass wire cup brush placed inside one of the TTS drill chucks. At 3000rpm and 20IPM it cleans everything up nicely and leaves a real nice finish. I have it programmed in as an endmill, and let sprutcam make the toolpath. Saves a lot of effort in polishing by hand afterwards and removes all tool marks.

[beanbag]

I blame it on poor chip clearance. Since it is a pocket, the coolant pools up and the chips stay around anyway. Are you able to do air blast plus a dribble of coolant?

It would also help to put a little corner radius on your end mill, i.e. "break" the edge.

Also, offset the cutter just a tiny bit off the side walls, unless you are finishing them as well.

If I were to do this, I'd use a coated carbide end mill with a little corner radius, air blast, and let er rip.

[mike sr1]

Thanks for the info. My workaround is to let the carbide rougher define the floor of the pocket. Since the carbide has rounded edges, it's not having the same problem.

The part is still functional with the ugly surface finish, but the perfectionist in me didn't like it.

And it's good to know why it's happening. Thanks for the explanation.

Frederic

As said in a previous post, steel cuts that way,

I use a high spindle speed and a carbide bit dry in the lathe to get a smooth finish, at the correct feed, speed, depth of cut, it will turn smooth as glass. It takes a bit of experimentation with the feed and speed but it works.
You can experiment with a 3" piece of round stock in the lathe, take a light cut across the end of the stock using your power feed, part of it will be rough, then when it gets to the correct speed and feed the finish gets smooth as glass.
I use the cheap chinese lathe tools for this, i dont think I would try it on an expensive milling cutter.

[DareBee]

IDK anything about the Tormach spindle, but it could be bearings and/or bearing preload.
When I get circles like that in my Fadal it means it is time for spindle bearings.