Fitting a bridge when the top isn't smooth

[Jordan S.]

Hi folks. I've got an older mandolin that needs a new bridge. I bought a Cumberland acoustic and have the bridge fitting jig. BUT, the top has some minor indentions from years of a poorly fit bridge, I think. So I guess I'm not sure the jig and back-and-forth sanding method will work. In essence, I need to bridge to fit where the indentations are (perfectly placed for intonation), but I'm not sure how to achieve that. Ideas?

[pops1]

Forget the jug and use the side to side method where the old bridge was. It is helpful if you have a guide to keep the bridge in the correct place while you move it.

[Hendrik Ahrend]

Basically what Popps said. However, I'd use the side to side sanding method mainly to mark where wood needs to be removed. The latter I usually achieve with a sharp narrow chisel and a pocket knife. Then carefully sand again and so on until the bridge fits. The pocket knife I use as a scraper.

[HoGo]

First, I would consider fixing the indentations... Perhaps some steaming or just little lacquer fill would do. Secondly, if they are not major, I would fit the bridge like normally and ignore the small viods as you may sometimes in the future need to move the bridge for intonation. You can change your preferred type of strings, or height of action etc.
If you really want to do the fitting over the indentations, then do the normal fit first and from there chalk fitting will get you where you want.

[Jordan S.]

Ok, thanks for all the tips, guys. I guess I wasn't sure that moving side to side would be any better than moving front to back. Imagine trying to "sand" a board to fit a pothole. No matter which way you slide it, it's going to be rounding off edges.

I suppose there's also a very good chance I'm being too picky here. The indentations are minor; I just want to give it my best shot at a snug fit.

[HoGo]

I prefer moving side to side (meaning bass to treble) if the top has reasonably smooth arch. But I'm moving at most 1/4" in either direction when rough fitting and perhaps 1/8" or so for final fit. I found out 150 or 180 grit yellow aloxide latex coated paper gives me best and fastest results. Use small strip 1x4-1/2" so you can see where your bridge is placed. Dust it often and check progress. You can see where you are removing material and use scraper to remove some wood for rough fitting.
One impoortant thing for me is holding the base. I'm gripping the base by the posts with my thumb and middle finger (pulling them together) and putting pressure in the middle of base with index. This helps pre-flex the base for better fit under pressure of strings (especially on lightly built tops the bridge under pressure may lift the ends of the feet as the top settles)

[Ivan Kelsall]

Jordan - Remove the bridge saddle & sand the base side to side.That way unless your rock the base on it's edges,pretty difficult as you're holding it so close to the top,you won't round them off,
Ivan

[Marty Jacobson]

I've tried all the methods, from pocketknife and carbon paper to complicated jigs and fixtures, and all of them take a fair amount of fiddling with to get it to fit right. And even after all that, there is the odd bridge that looks like it fits perfectly but reveals major gaps once strung up (which definitely weren't there when it was not under tension). So then you get to figure out how to deal with that. Fun times. I don't know that any method or tool is "best".. just work with it and be patient and you'll get it there.

[theCOOP]

I had a Kentucky KM-150 with a terrible 2-footed bring that must not have been fitted properly from the beginning. The onboard edges of the front of the feet had made a mess of the top.

Probably my best approach (should have been) the charm and scraper method. But from my perspective at the time, it was hopeless so I passed it on.