Clamp two handscrews to a sawhorse or tabletop so their jaws are lined up. Slide the workpiece into the jaws and tighten the handscrews. Medium-size handscrews have 5/8 in. of usable jaw surface ...
[Mgx3d] has done that by designing 3D printable bar clamp jaws with a quick release mechanism that can be used with standard T-slot aluminum extrusion. This allows you to create ad-hoc bar clamps ...