# Vise pressure

I am trying to determine the reasonable maximum pressure applied by my Record 53 vises. I don't have easy access to a load cell or a bathroom scale, so I will have to resort to rough calculations otherwise.
Has anyone ever measured the pressures on a Record 53 vise?
Heavy, man! Scritch
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On Tue, 10 Mar 2009 20:39:15 +0000, scritch wrote

wire it up backwards, so to speak, and use it to stretch fishing lines of known breaking weight to give clamping force followed by a quick division by the jaw surface area to give pressure ?
Your will to live will probably break before the final poundage is determined...
Why on earth you wanna find a figure for this?
I suspect the "unreasonable" result will be limited by operator strength, NOT the vice mechanics.
Very little pressure is necessary to extract a confession anyway. Usually just the threat is enough.. :-)
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http://www.mcasco.com/qa_stma.html

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Squish something in the vise and measure the face to face distance before and during the squish. Use something that doesn't permanently deform when you squish it. A chunk of aluminum rod with clean, square ends is probably good. Or maybe the tension spring from your bandsaw. A chunk of hardwood of known dimension would also be OK. You can relate the compressive strain to the applied load.
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First, it's not pressure, it's FORCE that the vice applies; the pressure depends on contact area, which makes it different every time, in ways that aren't terribly interesting. If you take care not to use slippery materials for the jaws, the vice can grip adequately at low force, so consider materials of high friction (MDF with a coat of primer, or even of dried white glue) for jaw plates, if the work seems ready to slip.
Second, the torque on the handle determines the force, not any particular property of the vise (unless you are concerned with breaking stresses of the vise parts). The force is determined by an operator pushing that handle, who presumably is feeling the resistance and getting things "tight enough".
If we ignore friction (don't lube the screw, though, or the thing might pop loose when you don't want)
force = Torque * 6.28 * pitch-of-screw
That "6.28" is two times pi, and the pitch of my vise screw is four threads per inch, so a hundred pounds on the six-inch handle gives
force = (100 lbs * 6 inch) * 6.28 * 4 per inch = 15 000 lbs
Spread over circa 20 square inches, that's over 700 psi... but it's still only a third of what softwood should handle without damage.