warpage machining 6061

[nightshift]

I had a problem milling a 6"x24x 1/2" plate. nc prog mills .05 off top and periphery, drill and taps a dozen different holes.There are a bunch of M0's to relieve part in vise jaws (3vises). plate starts out at 3/4" thickness and is dusted on both sides initially. After milling ,drill and tap (6-32,8-32,10-32),the part is flipped over and rough milled to thickness leaving .02 for 2nd flip and final thickness.Im using a 3" 4 tooth mill {shear hog ,polished inserts, flood coolant). plate bows about .01 after roughing.I've run these many times in the past without too much trouble.
The stock I got last week warped big time (.03) . The more I mill these things
the worse they get. Would this stock have the wrong temper or be the wrong grade of aluminum ,look the same.

[PBMW]

You're putting stress into the part as you machine it most likely. 6061 is pretty stable. I just did a job that was 22 x 10 x 2.5. Cut lots of pockets and never moved. Pockets both sides. Floors finished at .093. Walls were pretty thin as well. about 80% of the material went in the chip bin. You can control the stress to an extent with speeds and feeds. Use radiused cutters too...

[nightshift]

This part is generally not a problem.raw stock is suspect though