I've been looking at SpeedyMetals.com for finding the price for the aluminum for building my cnc router. I'm going to be using a lot of aluminum and am aiming for a very precise machine with hopefully better than .001" positional accuracy over a 15" span. To do this I need to accurately mount my linear rails meaning I need to mill pockets in the aluminum it is mounted to or machine flat a piece of aluminum and mount the flat end right next to the rails which will straighten the aluminum and the rails(if thick enough). My problem is my last email to this company said I shouldn't do that since it will make the aluminum warp making me lose my straightness tolerances. I've been looking at the 6061-t6511 extruded "flat" aluminum sheets they have since it is economical with wide ranges in sizes. Now my question is would I have a problem with warping if I have to drill and tap holes(could be any of the sides) or if I have to machine off .005-.01" on a .5x3x24" piece of stock on the .5x24" side? looking online i have read that it's not worth worrying unless it's really thin and it may warp in the direction you'd expect to warp(the way a piece of cardboard would bend). I've read about so many problems with warping metal i don't know if this is true. If anyone has experience with extruded aluminum(closer to 6061-t6511 the better) or better yet if you've bought from speedymetals. I have extruded aluminum pieces from home depot and drilling holes and cutting metal off one side doesn't seem to do anything(that's with really thin stuff too).