Gluing Bridges

     I was asked about what clamps to use to glue a bridge on. I don't have an instrument in that part of the process right now, so I'll have to fake the photos a bit. Next time I glue a bridge I'll post a proper write-up
     I have tried all kinds of ways to do this, including vacuum clamping, making my own clamps, modifying commercial clamps, etc. I have settled on this process and it works for me. To begin with, the bridge must very closely match the top, which is usually slightly convex. If the top is concave, you have a problem with the construction of the instrument. If the wings of the bridge do not touch the convex top without using clamps, you need to sand/scrape the bottom until it fits. Some builders tape a piece of sandpaper on the top and slide the bridge back and forth on it to get the same curvature on the bridge as is on the top. I just use a sharp scraper blade instead. Once the bridge underside curve matches the top, I then scrape a few thousandths more off the bridge center so that the wings touch and there is a very slight gap in the middle of the bridge. This allows me to use just 1 clamp in the middle of the bridge. If the wings are floating free and not touching the top, the bridge will most likely come off or you will distort the top. You can't just clamp the wings down with force. It generally does not work.
     I use a simple shop made jig and a single 6" cam clamp that has been bandsaw to clear the braces.Nothing elegant about the jig. I made it sometime ago, thinking I would make a nicer version, but it works and I just keep using it.The one I use is the funky little wooden one on the right. You can make it in a few minutes from a piece of hardwood, 2 T-nuts, and a couple of knobs with threaded shafts to fit the T-nuts or you could use hardware store bolts just as well. The extra holes in the top are for the 1/16" brass rod pins the go through the saddle slot to hold the bridge in place while gluing. The extra cork on the bottom is to raise the jig up to make glue clean-up easier. The 2 little squares of wood are padded with leather and will go on top of the wings. I have ground the threaded shaft ends into a cone shape and the ends will go into the shadow drilled holes on top of the wing caul squares. That holds them in place.

I'm just using a Plexiglas template as a mock bridge here

Here is the 6" cam clamp that has been modified to fit over the top braces.

Here is the jig in action. Camp the center cam clamp securely and then just lightly tighten down the wing clamps until you see a little glue squeeze out. This works for me every time. Good luck!--Bob