On Wed, 19 Sep 2007 06:16:56 -0700, jkn wrote:

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! ;-)

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The rigidity is usually achieved by a 'web' of stiffeners (much like a
spider's web or wheel spokes)to reduce the weight of the platen and to
ensure that the edges are under the same pressure as the centre. You can
see that the example you cited uses an extra thickness of timber to
achieve this.

That extra thick vice screw you found *might* be the answer but of course
the pressure generated actually depends on your personal strength and how
well you can anchor the whole press whilst you're twisting the screw. I
think you would create a better working tool by following your original
idea of an hydraulic jack especially if you can work out a satisfactory
lever system for releasing the pressure. Personally I would not feel safe
using the bungee cords as they would sooner or later break down in use.

Cic.

--
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Using Ubuntu Linux
Windows shown the door
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