Hi folks,

I want to build an extra-wide vice (excuse the British spelling - for the American guys, I mean a "vise"). Something with roughly the dimensions of a Black & Decker "Workmate" (http://www.blackanddecker.com/en-us/...nd-vise/wm225), but mounted on a sturdy workbench.

Basically, I want to build a better version of the "Workmate" vice. This means a vice with jaws around 24 inches wide. The vice needs to be able to hold longer objects without additional support (e.g., wooden planks for planing). It will be used for both woodworking and metalworking tasks, but not for welding.

My priorities a

- The jaws should stay parallel
- It should be operable using a single handle
- It should be tough and exert a good clamping force
- It should move smoothly and not jam

I've already built a workbench frame. It's made to the same pattern as the bench I built a year ago, but I haven't fitted a wooden top yet. Here are pictures of the finished bench and unfinished steel frame:
https://www.dropbox.com/s/ycbufnrkf5...bench.JPG?dl=0
https://www.dropbox.com/s/cpw9tw82kf...frame.JPG?dl=0

I've thought hard about how to build the vice, and I've considered a bunch of ideas. Scissor mechanisms, linked screws, bell cranks, etc. I've only come up with one concept which I consider good. I'd like to use a pair of ball bearing slides under the bench frame to keep the vice moving parallel. Thing is, I'm not sure what the right kind of slides would be, or if I could afford them. Are there any guys with experience in linear motion who could help me?

Here are a couple of rough sketches of my concept:
https://www.dropbox.com/s/ci3a3aebm1..._vice.pdf?dl=0

Two slide rails would be bolted to the underside of the bench frame (front to back). The bench frame is built from 100 x 50 mm steel channel section, so it's strong. Four ball bearing carriages (two for each rail) would be bolted to a thick steel plate, which would form the moving part of the vice. A very heavy length of angle (from a transmission tower or similar) would form the moving vice jaw, and the jaws would be lined with hardwood. I would buy a ready-made threaded spindle. As everything would be bolted together, it would allow all the components to be adjusted to ensure parallelism.

So I have a few questions:

- If I want a decent clamping force (say 1000 kgf), this will place a large moment on the ball bearing slides if an object is gripped off centre. If the object is right at the end of the jaws, this would create a moment of something like 3000 Nm on the base plate of the vice. That would create, at a guess, something like a 300 kgf sideways force on each of the ball bearing carriages. This is more or less an abuse situation, I know, but I want a strong vice. Are there any affordable slides which could carry this load, or a reasonable fraction of it? What would you recommend?

- The simplest construction would require a 50 cm unsupported rail length. Is this easy to achieve, or do the rails need closely spaced attachment points?

- Are there any simple alternatives I'm overlooking? Tracks for large up-and-over doors might work, but I'm not sure. Small iron wheels and rails?

- Are there any likely problems? Is this going to work?

I'd be pleased to hear from anyone with experience of linear motion components. If I can get the right components, I'm willing to spend a fair sum on them. I just want to build the ultimate extra-wide vice.

Best wishes,

Chris