Oops, that one got away from me befor I finished typing.
Making your own glue-lams allows you to cut out the defects
so that all the lamiantions are all perfect wood. If you buy a
commercial laminated product it is likely (all but certain) that
the internal layers will contain defects and voids. That is
allowed by the standards orgs for most grades of plywood.
Even then marine grade or aircraft birch plywood, which are
supposed be free of internal voids, are cross laminated and
for most beams or columns that is weaker than wood with
a uniform grain direction. The advantages to cross-lamination
are dimensional stablity and resistance to splitting, not
You can get a better strength to weight ratio by using composite
beams, built-up sections like I-beams or box beams. Probably
that was the source of your confusion. Those aren't stronger than
solid wood of the same overall dimensions, they're lighter.
I'm not clear on the geometry of how you are using this particular
member but you would almost certainly get a stonger piece by
gluing 1x or 2x lumber instead of plywood. Three 2x4s glued
together in the shape of an I-beam would be much stronger than
the same three glued side by side. Unlike the example above,
that would keep the wieght the same but increase the strength
by changing the overall dimensions.
Like Joat, I don't see any reason to use any treated lumber
anywhere in the press.