My bench has only one vise, so it needs to be versatile. The jaws on my vise can be positioned to hold objects flat on the bench or cantilevered off the end. In addition, the clamp is removable, so I can still use it for regular clamping jobs.
My vise is based on an ordinary 3/4-in. pipe clamp with one modification: The pipe is threaded 1-3/4 in. (extra long) for mounting.
I used scraps of 1/2-in. Baltic birch for the brackets. I got everything else, including the clamp, at a hardware store for about $25.
1. Drill holes in the brackets for the screws and pipe (Fig. A). Enlarge the 1-in.-dia. holes with a file to make the pipe fit.
2. Mount the brackets and install the clamp with its jaws positioned vertically. Fasten the clamp to the front bracket by threading on two 3/4-in. electrical conduit lock nuts.
3. Drill a 1/4-in. hole through the bracket and the clamp head for the positioning pin (a 1/4-in. quick-release pin from the hardware store).
4. Loosen the nuts, rotate the clamp head 90 degrees and retighten the nuts. Use the hole in the clamp head as a guide while you drill the second positioning hole in the bracket. 5. Install the positioning pin.
To change the jaw's position, remove the pin, loosen the nuts and rotate the clamp head. Then reset the pin and tighten the nuts.