Shims - how to size?

constantine

Hi I need to shim my bridge..should the shim be the size of the bridge foot or some other dimension?
What is the highest a shim should be , like 2.0 mm?

thanks - Dean

crookedpinky

I usually shim mine with a hardwood veneer - mahogany or oak - I picked up a marquetry kit from a charity shop as it had a whole load of different veneers. The veneer is about 0.8mm thick and I usually cut a couple of pieces just wider and longer than each foot of the bridge then place as many as I need under each foot until I reach the required height and maybe a 1mm over.

I then glue the shims to the bridge feet using Titebond and masking tape to get a bit of pressure on the join. Once it's dried I trim off the excess so it's all flush with the sides of the bridge and then file the ends and cut back any excess from the inside of the feet.

Then you can sand the shims down a bit if needed and - if it's a new bridge - cut string slots ( hence the 1mm over I mentioned earlier ). You can of course do it without gluing the shims but if you're pretty happy with the height I just think you're as well to glue it all together for structural integrity.

Cheers, good luck
Alan

constantine

nice, thanks Alan!

Craig Bumgarner

I don't think there is a limit to how thick a shim should be, at least within the practicalities of the instrument. I once used 4mm shims to make a used bigtone bridge work, seemed to work fine. I confine the shim to the same size as the feet that contact the guitar top. Most any hard material will do. Popsicle sticks, cut up credit cards, old picks. I prefer one shim per foot, not multiples, so sometimes you have to cut your own. I have a little block of rosewood that I cut shims from using a sharp table saw. If I'm careful, I can get them pretty accurate. Because I am not always accurate, I have a box of left over shims so it is not often I have to cut new ones anymore. I don't usually glue shims, but it probably does help a little tonally and for appearance.

Whether glued or not, a good fit is the main thing. If the original bridge fit the top well and the shim surfaces are perfectly parallel, no problem. But if in the end, the bridge doesn't fit the top perfectly, all kinds of problems ensue: Bad overtones, reduced volume, thin tone, etc. If you have to refit the bridge, then gluing the shims is probably the better option as it can be next to impossible to fine tune a shim.

CB

klaatu

A good rule of thumb for the thickness of the shim is that 1mm of shim will raise the action at the 12th fret by .5mm.