Help me with face milling?

Thanks for reading.

I have a 2010 Mag-Fadal 4020 CNC Mill. We are trying to face a 4" x 4" piece of 3/8" thick 304 stainless plate flat on both sides with the minimum amount of material removal possible. I am using a basically brand new Shars (I know, I know) 3" APKT style face mill with brand new inserts. No matter what direction I run the cutter, no matter what speeds and feeds, I ALWAYS get a ~.001" step where the toolpaths cross. I have run the cutter in the X direction, climb and conventional, in the Y direction climb and conventional, I have used zig-zag patterns, circular/spiral patterns and nothing will get rid of it. I went so far as to completely re-tram the mill to within .0006" over 18". I have double checked and changed the inserts for edge quality and checked the torque on the body holding screw. Everything is tight. The only thing I can think of that could allow that much flex is the drawbar, but that was rebuilt no more than 4 months ago and had ~1400# holding pressure. Am I missing something obvious that is preventing me from running what seems like a very simple operation? I'll try anything at this point...

Hi, you could be getting some deflection with the pressure of a face mill as it does take quite a bit of HP to drive it and that means pressure down on the job.......it should be clean if you've checked all your axis for squareness especially the head tilt from side to side and for and aft etc.

If the spindle bearings are loose or worn, they will allow the spindle to lift with the pressure of the cut and drop when the pressure is off at the end of the cut.

Sometimes a plain old fly cutter works well for large flat faces....using small DOC and not too coarse a feed.
Ian.

Fly cutter or face mill.

FWIW, played a bit with some cheaper indexables. Go brand name, more sticker shock, but saves money as inserts last longer, more accurate, better finish, lower spindle load, higher feed.