Leg Vise Chop - Geometry

[Pat Barry]

The leg vise can generate tremendous force. I measured mine made with a LN screw(no longer available) and 6" above the screw was well over 1000 pounds per square inch. If any one wants I can post the photos. The lower the parallel beam the less force on the beam. It is a class three lever the beam is the fulcrum and the screw is the force. Jim

So, if its a class three lever system, the force on the load is actually lower than the force on the screw. The closer the screw is to the vise jaws the higher the load will be applied. I don't think that the leg vise is an attempt to gain mechanical advantage though, it more to create a convenient and flexible clamping system. Ease of use is of higher importance than leverage.

[Al Launier]

I thought this leg vise video https://www.youtube.com/watch?v=B0rz...%40comcast.net was very interesting. I don't have a leg vise on my bench, but after this thread and watching this video I'm now considering a leg vise as a new project.

PS Instead of using the entire web site address as I just did, how does one create a short link to the web site?

[Jim Ritter]

You have it absolutely right Pat. Do you mind if I quote you on occasion. That is the best explanation if ever heard.
Jim

[Mark Fisher]

I did exactly what you are considering. The closer the vise screw is the clamping area, the higher the force. The trade off is how wide a panel you can clamp. The other thing to consider is that when you clamp smaller pieces the vise load is taken up by the dowels that hold the benchtop to the stretcher. After breaking some wood dowels, I ended up going with a piece of 3/4" dia. steel shaft.

[Andrey Kharitonkin]

For a board to be held securely, parts of that board ought to be on both sides of the line running from the guide through the center of the screw. If you have a board held vertically in a 15 degree slanted vise and a 2 1/4 inch screw, the screw needs to be over 8 inches from the top of the bench for this to occur. Twelve inches is adequate.

This gives me an idea of having support and screw not vertically align on the vertical leg vice. I think I saw something like this on The English Woodworker pages (Richard M.). Perhaps not in vertical leg vice but in horizontal front vice on one of his workbenches.

Mine workbench has a wide leg where leg vice is going to be. It is 10" wide from top to bottom stretcher and 28" long in this area. I plan to use linear bearing which wouldn't mind any side forces. So, it is very practical question indeed.