On Tue, 18 Sep 2007 16:03:34 -0700, jkn wrote:

Hi Cic.,

I don't think it's just a case of lifting the jack and platen. The
bungee cords will have to force the jack's column back down into the
housing. This requires considerable effort, which is usually applied by
the weight of a vehicle or other load. I think you would have to
experiment to see if the bungees were strong enough to do this or decide
to do it by hand. That shouldn't be a real problem unless you go in for
mass production with a time and motion programme in force.

All fair points. You could have a separate non-elastic rise mechanism - a
cord on a cam or something - such that you release the bottle jack and
then raise the platen in a separate operation. But this is starting to
get over-complicated IMO.


I don't believe the average jack will work upside down. Whilst making a
small press recently to remove car stub axles I came across the
information that most of the common car type hydraulic jacks will only
work on their side if the handle side of the jack is facing downwards.
This restriction would seem to suggest that they won't work upside down
but it's worth testing individual jacks - under load - to see if they
will do so.

I too strongly suspect they won't work upside down. I'm starting to think
that the original plan of a decent press screw may be the best way to go
...

Jon N

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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.

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). 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.

There are screw jacks and ratchet jacks on the market which you might
consider which are obviously designed for heavy work, unlike the Axminster
range. You might use the original press you found as a prototype and work
out how to replace the bungee cords with a lever as I've suggested.

Cic.
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