Pipe clamps are a cheap and easy way to clamp glue-ups, but they only apply pressure on the first few inches near the edge. You can always alternate clamps on the top and bottom to apply more even pressure, but this only works for stock under 5″ thick or so. If you’re putting together an even thicker slab, you should probably make sure you apply pressure to the middle, too.
One way to reach the middle is to use some of WoodCraft’s Big Jaw Pipe Clamps that have a 7″ throat depth. Made from ductile cast iron, the clamps fit onto standard 3/4″ threaded pipe. To make the clamps easy to adjust and release, they have multiple disc clutch plates.
A single Big Jaw Pipe Clamp will cost you $22; if you buy four or more the price drops to $20.