On 17 Jul 2011 02:00:00 GMT, "DoN. Nichols"
wrote:

[...]

I am interested because I am trying to guess how much force I can
develop in this press:

http://www.flickr.com/photos/2768312...57622484352534

Right now my answer would be "not enough" (see the following photos if
you are interested in the process).

Can anybody suggest how such force could be measured?

The first question is -- what force are you trying to measure?
The easiest to measure is the force applied by the jackscrew to the
middle of the plate. There are load cells which display the force
applied as the frame deflects (and it is measured by a dial indicator).

This would do fine. All I am after is something repeatable. The actual
pressure applied across the workpiece can be calculated from the
surface area.

However -- this is not measuring the force applied to the
transfer labels, which is what I think you want. Just knowing the force
applied by the rod is not enough, because both your backing plate and
your top pressure plate are far from rigid enough.

For the top plate, you need something like forged steel with a
platform in the middle (at a guess say 2-3" high) with ribs going out
from there to the corners, and angling down to the corners. This will
even out the force significantly.

There is one commercially available like that. I nearly bought it but
it was 3x as expensive and quite big (the leg span was 18").

However -- your aluminum plate on the bottom also bows, reducing
the pressure in the middle and concentrating a bit more of it out to the
edges.

That I do not understand. The reason it bows in the middle is because
the pressure is applied *there*.

What I would suggest is:

1) Triple the thickness of the bottom plate, and make it steel,
not aluminum.

Agreed except for the steel heat conductivity.

2) Go up to at least one inch thickness on the wood top plate,
and ideally at least two.

Probably also wise.

3) Get a closed cell foam rubber to go between the wood pressure
plate and your transfers. This will crush, and even out the
force from center to edge significantly. At a guess, I would
suggest perhaps an inch thickness or more for the foam rubber.

That's why I use the silicon pad. I wonder if ordinary rubber would
withstand the temperatures. I know hockey puck does not!

With this, you probably won't need as much force as you were
applying in your tests.

I know I can develop forces well in excess of required for the small
pieces (up to 16 in2). I suspect I shall never need to apply the same
pressure over the whole of 80 in2. Right now I suspect consistency
will be a bigger issue.

Michael Koblic,
Campbell River, BC