This is a technique shown to me by a friend that is a luthier (someone who makes or repairs string instruments).  Often they work with thin pieces that are bookmatched for the faces of guitars, lutes, violins, etc.

If you just use bar clamps, it's difficult to keep them from buckling up and hard to get them to glue flush.  Since you don't have a lot of thickness to play with, you can't just plane off a lot more.

The method uses large tapered pieces, some cauls, and some cord.  Wrap the cord in a figure-8 over the pieces and around the cauls underneath.  Then insert the wedge underneath, repeat several more times down the length.  Alternate the tapers' direction.  Once you're all set up, drive the wedges in deeper a bit at a time.   the downward pressure will push the pieces down against the cauls and together at the glue joint.

Let the glue set up, then pound the wedges back out.

 

Now that's neat!

That is a cool idea

I had never given any thought as to how guitar makers glued up their panels.  Thanks for the how-to.