I think you could get over the lifting issue by using a single lever which
could be strong enough to retract the jack column and raise the top platen
in one movement.

True, if it could be made elegant.


I would suggest that you check the capacity of the vice screws from
Axminster before you buy. The screw *thread* is actually 23mm diameter
(not 28mm - just measured one I've had waiting around for some time).

Thanks - that's useful to know. They did seem a little thinner than
advertised from the images I'd seen.
The
28mm referred to in the catalogue is the internal diameter of the handle
part - you're supposed to supply your own 28mm cross handle to go through
that. These vice screws are really not intended for applying serious
pressure (I'm guessing) and would probably be damaged if you tried to
apply pressure over a large area such as you're considering.

This guy does a slightly beefier one for about twice the price

http://www.fine-tools.com/G300659.htm

I'm not sure just how much pressure I'll need, and the other thing to
bear in mind is that this depends not just on the screw; old presses
often have large cast-iron plates on the back of the floating platen,
to spread the load I assume. This implies that both platens should be
pretty damn rigid. I've seen a few images of homemade presses and they
don't seem to take this into account...

J

(using Gentoo Linux, as it happens! ;-)