"PrecisionmachinisT" wrote in message
news:Eu6dnbtA66U_z7zOnZ2dnUVZ_rCdnZ2d@scnresearch. com...

"Bob La Londe" wrote in message
...
"PrecisionmachinisT" wrote in message
news:IN2dnVBu1YhZYoLOnZ2dnUVZ_qidnZ2d@scnresearch. com...

"Bob La Londe" wrote in message
...
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

Actually it's extruded and then stretched.

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.

blink blink

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?



http://www.speedymetals.com/information/Material74.html

Flatness= .004 per inch of width.


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

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

aluminum. However, if .004 per inch is normal I've been incredibly lucky

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.

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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