Need Help!- cutting a large thin ring

[mikede]

I am trying to turn a ring made of 1020. The ID is 23, the OD is 25 or 28, thw thickness is 2.5, I don't have the print in front of me so I am having trouble remembering the size. Cut it already and had it rejected. The part keeps warping out of flat a .001" causing the 15 degree angle on the OD to be out of tolerance. The tolerance is .001" below is how I cut it.
1) roughed to within .2. Sent out for stress relief.
2) Tack welded four places on plate. Turned back to within .050
3) Broke tack loose, skinned holding plate flat, bolted part on and turned top to within .050
4) Retack welded and finished bottom.
5) Broke tack loose and skinned holding plate, rebolted and finished top.
6) Check best we could between each step.
7) Customer checked with dial indicator and gage part was out .003
8) Had a supplier with a CMM check for us and determined part was out .003 because bottom wasn't flat. When the CMM took the potato chip warp out of equation part was in tolerance.

Anyone have any ideas how to get rid of the warp?

Thanks
Mike D

[LLSHAWNLL]

On the final passes don't bolt it down. Use hot glue from a hot glue gun from hobby lobby. Clean it with alcohol then glue it down. Not between the fixture and part but around it like a weld. Its unconstrained. Cut it dry with an end mill taking .005 deep passes. I have made 20 X 20 6al4v titanium flat within .0005 this way. Smaller stuff parralel and flat within .0002.

[ad64075]

Carpet tape works very well and does not have the cushion of the hot glue. Carpet tape is available at most hardware stores, very thin, and double-sided. I have used it extensively while grinding non-ferrous materials and planing material flat, similar to your application.

Good Luck!