Dowels Aid Clamps on Cast-Iron Table Ribs
To get a good bearing surface for the lower jaw of your handscrew clamps on ribbed tables, build a pair of the clamping pads shown at top. Here's how.
Make the length of the 1⁄4 " plywood piece about 1" shorter than the distance from the front edge of your handscrew jaws to the first screw. This gives you some latitude in positioning the pad.
Size the width of the plywood so that you can position the four 1⁄4 " dowels in the corners to fit snugly over the jaw of the handscrew. Position the 3⁄4 " dowel about 1⁄2 " back from the front of the plywood and cut the dowel about 3⁄8 " longer than the width of the ribs on your table.
—Tom Ryan, Fredericksburg, Texas