Mandolin

In a mandolin, the bridge is one of the most crucial pieces. It is the avenue by which the vibrations are transmitted from the strings to the sound chamber. So it needs to be the correct height, make good contact with the top, stop the strings cleanly, and be made of something that transmits the vibrations well. When they break, are ill fitting, or replaced by something else, the mandolin performs much less well. So what is to be done if we have a problem with the bridge? Well, there are various answers to that, mainly because there are various bridge types, and a variety of different problems. First of all there are essentially 2 bridge types found on traditional mandolins; the simple or plain bridge (with in-built or even no saddle) and the shelf bridge (where any saddle, usually bone or brass, sits on a small shelf). Secondly, there are problems specific to each, and others common to both. I will try and out-line these below. Note, I have not included the bluegrass style split bridge with height adjustment wheels here, as you don't see this on traditional mandolins. You occasionally see a small early type in metal, with small wheels, but the feet of these tends to be very small, and pressure on the top often damages it.
		Shown here are some typical problems with old German and Italian traditional style mandolin bridges.... some show one problem, others a combination.

Anatomy of a bridge
Shelf bridge		Simple Bridge
		(May come with inbuilt or top-mounted bone/plastic saddle)
Typical Problems
Broken off wings	It is possible to glue wings back on but not easy, even if you have the piece. They break where they are weakest so there is often too little gluing surface.
Slots cut too deep	Once the slots are too deep, the easiest way to remedy this is to add additional material to the foot.
Warped	When mandolin tops sink, the bridge often warps with the top under the string pressure.... once this happens it is not really feasible to restore the bridge to its former shape.
Broken string separators	Replacement bits can be glued in here using superglue, but they are inclined to be weak thereafter . A more complex repair can be achieved by cutting out a section below the missing separator, and installing a new piece with the grain running vertically, though this is difficult and fiddly.
Insufficient height	With a shelf bridge, you have 2 options. First increase the thickness of the saddle, or second, add material to the foot.
Insufficient height	With a simple bridge, you can add material to the foot. If it has an integral saddle, it is sometimes possible to replace this.

Repairing a string separator When I repair original bridges, to keep an instrument as authentic as possible, this is the repair I do most often.

Above you can see a bridge where several string separators has been knocked out. They are inherently weak because the grain runs laterally.	Using a small square needle file, make sure the bottom of the slot is flat and level....

From a small piece of ebony, cut a small section the right height for the slot, then split it to fit the size of the missing separator front to back.....	Using a small dab of superglue, glue it into the slot....
	This one has gone in slightly crooked, but if that happens, its easy enough to tap it out and start again. Also, I have used ebony to repair a rosewood bridge, so it is more visible. Normally I would use the same wood as the bridge.
...if it survives, with a little careful sanding, necessary to level it off with the surrounding wood, it should last a while....

Adding height to a bridge If the bridge is fine, but just too low, especially as a result of successful repair work, there are some things that can be done instead of making/buying a new bridge, with all its attendant fitting problems. With a shelf bridge it may be possible to add a sliver of veneer beneath the saddle, or exchange for a new saddle, i.e. thicker bone, or chunkier brass. With both it is also possible to add a little wood to the foot as below.
1.	2.
Edging strips usually come in a fairly regular thickness, 2mm, 1mm, 0.5mm and this is what I use to augment the height of bridges. Here again I have used ebony just for visibility.	Choose a suitable thickness to provide the desired height, and cut a piece to length. If it is not as wide as the bridge, two strips side by side will need to be used.
3.	4.
After making sure the foot of the bridge is smooth and clean, glue the edging strip to the bottom of the bridge. I used Titebond.	You will find there are various bits that need to be cut away.
5.	6.
I cut away with a chisel or craft knife, or against a rotary sander, depending on the extent of the section to be removed.	The slots I finish off with a round file. Once this is done, a good sanding/polishing session helps to blend the two woods together. If you have a curved foot, be prepared to have lost a certain amount of the curvature in clamping up. Then you need to sit with sandpaper on the top, and refit the foot of the bridge to the curvature.