I decided that it was time to upgrade to SketchUp. I used my Heavy Duty Bar Clamps as a learning exercise. I made a few modifications on the original plan regarding the front jaw. The plans can be downloaded here.
Another mod that I would suggest is to use steel or aluminium for the draw bar on the back jaw as the wooden dowels don’t fare so well when pressure is applied.
-- There are some things that money can't buy - Manners, morals and integrity