Calculating the force of applied by a vise jaw

[garythetiler]

Its been many years since i studied mechanics at school and I need to know how to calculate the force applied to a vice jaw by turning the vice handle .i am guessing that it could be worked out by measuring the length oF the threaded bar and also the length from the pivot on the handle but haven't got much of a clue after that any help would be appreciated

 

[klawlor419]

Can you explain more, where you are trying to measure the force? Do you have schematics of the vice jaw? More details are needed if you want to get a theoretical estimation of this.

Your best bet is to probably using something like this http://www.phidgets.com/products.php?product_id=1131 and determine how turning the vice handle affects the amount of force the vice is exerting experimentally.

 

[Studiot]

Hello gary.

The force exerted by the vise is not determined by the vise it is determined by the 'resistance to squashing' of the object between the jaws.

If you place a brick between the jaws you will have to crank the handle very hard to obtain even a small squashing.

On the other hand, if you replace the brick with a sponge car cleaner you can squash the sponge easily.

Objects placed between the jaws push back with a a resistance force that depends upon a property called stiffness and also the amount of squash you give them.

If we consider a fixed amount of squash, say 1mm, then to squash a brick 1mm requires considerably more force than for a sponge. The force equals the stiffness times the squash. Or the stiffness can be called the amount of force needed to squash the object 1mm and is measured in force units (Newtons) per mm.

Now 1mm closure of the vise jaws is determined by the pitch of the leadscrew. This determines how many turns (or part turns) you need to make to close the jaws 1mm.
In turn the length of the handle determines how hard you have to pull on the handle to close the jaws 1mm.

Either way the number of turns to squash a brick is the same as the number of turns to squash a sponge 1mm. The difference is the force you have pull on the handle.
The difference at the other end is the force applied to the object, which depends upon the stiffness of the object as already discussed.

Does this help?

 

[HallsofIvy]

Again, "conservation of energy". The total energy applied in turning the handle is the force times the distance the handle has moved through ("work= force times distance"). That same amount of work (energy) is applied to the object and the force applied is that work divided by the distance the jaws have moved.

 

[Kiapina]

Can't you use an http://www.qualityforcegauges.com/models/ for it? It would make calculations so much easier! I am not really sure though if it's good for this application

 

[Nugatory]

Its been many years since i studied mechanics at school and I need to know how to calculate the force applied to a vice jaw by turning the vice handle .i am guessing that it could be worked out by measuring the length oF the threaded bar and also the length from the pivot on the handle but haven't got much of a clue after that any help would be appreciated

A vise is really nothing more than a complicated lever and wedge system for multiplying forces.

With the vise unloaded, turn the handle one full turn, see how far the vise jaws move.
Calculate how far your hand moved (pretty close to $2\pi$ times r, how far out on the handle the force is applied). The ratio between them is the force multiplier for the vise.

You can also calculate the distance the vise jaws move from the thread pitch - if the thread has five turns per centimeter then one turn will move the jaws one-fifth of a centimeter.