On 2011-07-15, wrote:
How much force does a common shop vise develop in its jaws? Google was
pretty unhelpful on this - the only reference I could find suggested
up to 7000 lb. Another paper suggested that a minimum required
clamping force for machining is much less - up to 1000 N.

Well ... just as a point of information, I clamped a short
Enerpac hydraulic cylinder rated for 10 tons at 10,000 PSI in an old
Bridgeport milling vise. (I have Kurt vises which I prefer to use.)

I connected it to an electric hydraulic pump intended for
running large terminal crimpers.

That pump is designed to go up to 8400 PSI, and then release.

When I ran it on the Enerpac cylinder, I could *see* the frame
of the vise bowing -- perhaps the center lifted about 1/8" above the
line between the ends (this is without the vise being clamped to
anything -- just resting on wood). So -- at 8.400 tons (16,800 PSI) it
was bowing well beyond normal operation. so let's assume something much
more reasonable in such a heavy vise -- say about 1 ton or less. (And I
would have had to crank the handle a lot harder than I can physically
manage without a long cheater pipe to get to that, I believe.

As the vise returned to straight, it was within the elastic
range.

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).

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.

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.

What I would suggest is:

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

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

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.

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

Good Luck,
DoN.


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