need stiff wood

You can buy the cast iron clamp jaws. Any time I've seen these used, they've just been fitted up with good old 2x1 pine.

Suck it and see - it won't cost the earth and I expect it will do you fine.

Cheers

Frank

"John Keeney" wrote in news:3fcef648 snipped-for-privacy@news.iglou.com:

I imagine hickory would be fine. Just make sure you have a large dimension in the clamping force plane. For example, given two I-beams of equal weight, one with narrow flanges and a wide web will be stiffer in the plane of the web than the one with a narrow web with wide flanges.

I bet you're going to need to make it quite wide to provide a lot of clamping force at three feet.

You might check out wooden boatbuilding web sites for examples of long- reach wooden clamps. These are frequently used in clamping planking, usually shop-built from plywood.