Correct tolerance call out for extruded Aluminum bar

[CanosSon]

Hello all,

I have an extruded bar of Aluminum 6061, with a small inner design but mostly solid. The profile is 0.90" x 6" and it is 60" long, lets call this piece the stock. I need to machine the stock down to 0.875" +/- .01, by removing material evenly both top and bottom. However, the twist on the stock is significant to the point I have to machine down pass the target, 0.875", just to get the two faces parallel. I would like to avoid this issue in the feature by setting tolerances for flatness, straightness, and twist. Any advice on how to go about generating these tolerance values? and get a more rectangular stock.

thanks

 

[3DDave]

See the Aluminum Association document on specifying an extrusion. It is a collective of aluminum suppliers, including extruders, and forms a basis to discuss expected variations. See

https://www.aluminum.org/aluminum-standards-and-data