Here is my plate joining jig.
Here you can see it at use, gluing the back of a viola.
The purpose is to glue the two halves of a top or back plate for a stringed instruments.
These plates can be either flat (for flattop instruments like acoustic guitars for instance) or have the shape of a wedge for carved instruments (bluegrass mandolin, jazz guitar, violin familly..).
The traditional way of doing it is to use the "Spanish method", like can be seen here :
but this method only work well with flat plates.
The jig I use above has the advantage of being suitable for both kinds of instruments.
There is a table, one fixed edge on one side, and above the center line, a kind of wooden bridge made of a round pole (it can be wood or even round steel tubing).
The flat faces of the plates are kept flat on the table thanks to wooden wedges that insert between the plates and the above pole. You put wooden shims as necessary, depending on the plate shape.
Add two big clamps to tighten and you have an easy way to do this strategic job when building an instrument.
The seem must be invisible, so you need quite a bit of pressure.
But you dont want the plates to lift because of the pressure, hence the jig.
I forgot to say that I add a band of waxed paper under the joint to avoid the squeezing glue to stick the workpiece on the table.
That's it !