6061 Aluminum Flat Bar - WARPED

I've been using a lot of 1/2 thick aluminum bar stock for making parts the last few years. Most of it I buy online from one of a half dozen sources because I can buy it cut to length (+/-) for less than I can buy 20' bar uncut locally. Anyway, in the last month or so I have been buying more from a vendor that is nearer my side of the continent. The last couple orders of 1/2 x 6 have been warped across the grain (not lengthwise) by as much as .02 inches. Most of it is bowed in the middle by atleast as much as .01. Now I know this is mill rolled aluminum stock and its not going to be perfect, but I've been buying this sort of bar stock for almost 5 years. I've been buying more in the last 2-3 years. In the past I've found .003 to .005 facing pass was enough to get a clean straight surface to work from. I just plan on skimming .005 off every piece and I don't worry about it.
Imagine my surprise when I had to take four passes to get a clean face on a piece of this stuff. I mentioned it to the vendor and he told me he was a retired machinist before he started selling metal online and its all like that, and if I got any that was finishing with only .003 to .005 skim pass it must have been plate because all bar stock is off by more than that.
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Well, that might be true, but I have to say I've never gotten and 6061 bar stock that was warped that much before... and if the stuff I was getting from other vendors was plate it did a good job of mimicking bar stock with roll marks, and rounded corners like bar stock.
So, is it really all that bad and I've just been lucky or what?

Bob La Londe wrote:
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Sounds to me like your supplier found a cheaper source . With lower standards . I'd change suppliers .

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Actually it's extruded and then stretched.
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http://www.speedymetals.com/information/Material74.html
Flatness= .004 per inch of width.

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Speedy metals is NOT one of my primary sources. They are only a secondary source for stuff if I just can't find it anywhere else, and almost never for aluminum. However, if .004 per inch is normal I've been incredibly lucky over the last few years. .003-.004 out of flat in a ripple or wave is pretty normal, but linear compound error has not been. Heck. At that rate you don't need to order large pipe. Just order really large bar stock. LOL.

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I only linked you to them because they have the ansi tolerances listed on their website...
--if you'd rather to have an actual copy it will cost you $48.00
http://www.astm.org/Standards/B221.htm
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I buy 6061 aluminum bar from Copper and Brass Sales, ordering a little over a ton every 3 weeks or so which gets me a fairly substantial price break.
Lately the Kaiser material in 1/4 x2 (from one particular die) has been coming in at about 1.978 which causes problems since the product finishes at 1.975 wide and the first milling operation is done in multiples using high density vises for fixturing.
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Ouch. Can you setup a QC standard with the vendor. Basically pull a Ford on them and make them take it all back or would they just cut you off if you did that?

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Oh, I have (do!), pretty much consistently across five or six vendors. If I need flat stuff, I buy cast stock.
Even then, the mook clerks at the various suppliers beat up the edges or ping the middles, right through the protective peel-off.
I have to put a comment in EACH order to the effect, "If there are ANY dings in this piece... it's coming BACK at your expense."
LLoyd