Shopsmith's Double Bar Clamps are hands down the best clamps for edge gluing lumber into panels. For many years I used these clamps weekly to glue-up table tops for classes, and I NEVER had a failure or severe misalignment as I have had with pipe clamps and standard bar clamps.
The bars of these unique clamps are made from poplar, and each bar is milled with a special profile that allows them to provide superior clamping on a full range of widths and stock thicknesses. When gluing pieces edge to edge, these clamps apply pressure from the sides, top and bottom simultaneously.
The secret to the special clamping action is the ingenious (and subtle) curved radius of each hardwood bar. This precision cut radius distributes pressure equally over the entire width of the project; first applying pressure on the center of the panel, then tightening to the edges.
While there have been a few copies of the Shopsmith clamp, none have matched the ease of use or the flawless function of the SSBDLBAR clamps. Your workpiece glues up evenly and tightly, which eliminates the need for tedious surface sanding or planing.
These clamps are still available today from Shopsmith, so make sure you don't get bit-happy. Available in 24", 36" and 48" widths, the new clamps from SS are priced from $57.84-$77.19.
Click link for Shopsmith Double Bar Clamps for Sale on eBay (Very light activity)