Guitar Bridge Plate
Source: Guitar Building Articles/The Guitar Top

The guitar bridge plate is a plate or a thin layer of wood, often a bit thicker than the top plate of the guitar. This plate offers additional structural support directly beneath the guitar bridge and give the top additional structural support to help distribute the tension of the strings. The bridge plates for a classical guitar are vastly different from the bridge plate of an acoustic guitar. Most of this difference is a result of the differing string tension for the two instruments.

The Classical Guitar Bridge Plate:
The plate normally is about 3 to 4mm thick. It usually approximates the shape of the tie bridge that is mounted above it and usually the sides of the plate taper or are curved inward at the ends of the plate. Different luthiers shape them in different ways. Some construct them as a flat plate with the edges knocked off. Other round the plate from a high point in the middle and gradually taper to the top wood.

The wood used on most instruments either matches the top tonewood or the bracing used for the top. More often than not, the plate is fashioned from an unused portion of the top plate. When the plate is installed, it is glued with the grain running 90 degrees to the top tonewood. The top plate is held in place solely by adhesives as no strings penetrate the top. Usually this plate is the first thing installed on the classical guitar top. The fan braces are fit OVER the bridge plate – in other words they are notched to receive the bridge plate.

The Acoustic Guitar Bridge Plate:
As important as the classical guitar plate is in resisting force from the strings, the acoustic guitar bridge plate plays an even more important role is maintaining the structural integrity of the top. The acoustic guitar bridge plate does not resemble the bridge shape in any manner at all. The plate is fit between the X-Braces and the acoustic tone bridges, which give it a rather odd shape.

Differences Between Bridge Plates

One of the significant differences from the acoustic guitar bridge plate to that of the classical is the materials that are used in it’s makeup. The acoustic plate is made from a hardwood, such as walnut, rosewood, maple or other back tonewood. I always make my acoustic bridge plates from the same wood as the back/side materials, before I mill it to thickness. The grain of the wood should run at 90 degrees to the top wood.

The acoustic guitar bridge plate is much thicker than the classical guitar plate. The plates are usually around 5mm, based of the strength of the wood being used.

The strings from the acoustic guitar bridge extend through the bridge pin holes and are wedged against the bridge plate by the bridge pins. So another critical function of the plate is to prevent the string balls or ends from ripping through the bridge plate and they form a wedging action against the top.

Lastly, the classical guitar bridge plate is the first gluing operation on the top plate, where the acoustic guitar top plate is, or nearly is the last gluing operation on the guitar top.

Fitting and Gluing the Plate In Place:

Rough cut and shape the bridge plate. If you decide to curve the top of the classical guitar plate, it is probably best to do that after the plate is glued in place.

Carefully mark the location of the plate off your Guitar Building Plans. Make a gluing caul that is the same shape as the bridge plate profile, except make the caul about 1/8″ smaller in all directions so you can observe the clamping.

Spread a small amount of Titebond glue (2-Part Epoxy for exotic woods) over the surface of the bridge plate and onto the guitar top. Place the bridge plate in place and put the caul on the bridge plate and apply pressure with a couple of wood cam clamps. Be sure to protect the top tonewood at all times and if you use metal clamps, be careful not to use too much pressure.

Perform a glue cleanup as described in our article Gluing Tips for great ways to cleanup every bit of glue residue quickly and easily.

Tags: acoustic guitar top, guitr bridge plate, how to build a guitar

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