Jay Pique wrote:

I could probably live with a 32nd over 16 feet. If I did get a 3/8 x 6
x 192" piece of aluminum that was staight, or had it milled straight,
would it stay that way?

Oh ... now you want durability too? ;-)

When you carry / store that aluminum, never let the 'straight' edge face
either up or down without support under it. All straightness will be but
a memory the next time you try to use it.

You might consider getting a section of box channel iron and having it
surface ground square in a machine shop with a big surface grinder. But
I wouldn't. How would I get it back home and down into my basement sop
without losing all that expensive straightness?

Me? If I was going this route I'd probably rip a couple widths off some
3/4" plywood and lap joint / dowel them, using a third section to line
up the joint.

But I'm new here so what do I know?

Bill
--
If God didn't exist, there would be no need for atheists.