The vise for my Hybrid Roubo is a prototype of a prototype. I first mocked up the basics with plywood before committing to maple. It looked promising so I went ahead with building it out of 8/4 maple... still convincing myself if it fails miserably, it was still only a prototype.
Turns out it was a complete success.
I finished all the parts, including the screw & nut (Lake Erie Toolworks), with two coats of Watco oil and a coat of butcher's wax. The nut is attached losely with Spax screws. It just has to be held in place to push the beam out while the vise is being opened and not torque sideways. Its left lose to allow for any wiggles, wobbles or wood movement.
The pics should speak for themselves, but if you have any questions leave a comment.