Stock Aluminum Tolerance 2

[ARamsay]

Can anyone tell me what the tolerancing of stock aluminum bars is in 6061 T6.
For example if I were to use an aluminum 6061 T6 bar 1/2" thick what would be the variation of the dimension, plus or minus how many thousands of an inch.

 

[nate2003]

EMJ (Earle Jorgensen) has the following published tolerances.

For Al extruded squares and rectangles, .250-.500 cross section area is ±.008". From .500 to .750 cross section area the tol. is ±.009". For Al sheet 18" wide or less, the thickness tol. is ±.025" for thicknesses of .439-.625"

I don't know if these are standard tolerances or if they vary by supplier. I know that you can order ground stock that is precision thickness from some suppliers.



"I have had my results for a long time, but I do not yet know how I am to arrive at them." Karl Friedrich Gauss

 

[swall]

Those tolerances for bar agree with those in the Aluminum Association handbook, so those are industry tolerances (extruded bar).

 

[MikeHalloran]

Because the stock that you buy is sold by nominal weight, but the raw materials are purchased by actual weight, you will very, very rarely see a bar on the plus side of the tolerance zone.

It's like selling air for the price of an equivalent volume of metal. The volume, and the savings, become significant in mill order quantities.

Extending the same logic, selling you a fatter than nominal bar at the nominal weight price amounts to giving away metal, and no sane mill manager is going to do that.

I get the impression that all metal mills aim their processes at a point below the midpoint of the lower half of the commercial tolerance zone for each dimension.

If you're going to use the as- delivered stock in a stackup where the dimension is important, and I suggest that you don't, don't assume that the mean of the delivered distribution will come in anywhere near the center of the standard tolerance zone. Also be aware that 'normal handling' will produce burrs and scars that may affect your stackup, unless you pay extra for individual wrapping on each bar, and there goes your savings.



Mike Halloran
Pembroke Pines, FL, USA