View Full Version : sanding the bridge

Eric Hanson
Apr-11-2010, 11:54pm
Today I took it upon myself to sand a bridge to shape on my Johnson A. I have been wanting to slowly get into luthiery and thought this might be a good starting point.
I put the sandpaper grit side up and used a method described on this forum.

Reason: I have friend that is interested in learning to play and is shy on funds. I am planning on loaning it out to him on extended loan.

Result: I could not have expected a better outcome. For the small amount that was paid for this mando ( it was a gift ), and the plywood construction, I was very pleased with the outcome. My wife on walking up to the house thought I was playing my solid wood "Click". She doesn't have a trained ear, but is sensitive to the sound. ( I have been known to wake her up at night with my late-night playing ). Thus she definitely thinks it is louder.

The reason for this post: Thanks goes out to all who continue to lend their advise and encouragement to all of us neophytes to the luthier world.
Hmmmmm. What is my next project for which my wife will ask, "What's he building in
there?". - Tom Waits

Apr-13-2010, 2:16pm
I am teetering ever closer to doing so on my entry-level Kentucky that I now realize was never set up at the store... It doesn't sit quite right, and I think I'd be getting better volume and having a lot easier time with intonation, I think there's a tiny amount of wobble on the treble side that keeps it from staying put.

Apr-13-2010, 9:58pm
A while back I wanted to fit the bridge better to the top of my old cheap clunker mando. I tried the usual sanding with sandpaper taped to the mando top, but since I don't have one of the Stewmac thingys, I kept getting rounded edges and even with scraping with a knife blade, I just couldn't get the base to fit perfectly.
In desperation, I remembered someone's suggestion from months ago. So I taped some aluminum foil to the mando top where the bridge should sit, applied a thick coat of 5-minute epoxy to the bridge base and positioned the bridge exactly where I wanted it to be on the top (on top of the foil), with the angle I wanted. I carefully put the strings into position on the saddle and tightened to maybe half tension. Enough to hold the bridge FIRMLY against the top. I double checked the position and angle. After 5 minutes or so, I removed the strings from the saddle, took the bridge off, scraped the ooze out of epoxy from the edges.
The hard epoxy formed a perfect match with the mando top. I even left the aluminum on the surface of the epoxy but trimmed it so it doesn't show.
Voila! Perfectly fitted bridge! I sure wouldn't do this with any of my nice mandos, but the clunker sounds better now than ever.

Apr-14-2010, 5:28am
I've been using this method for years. I use waxed paper as a release surface, normal epoxy rather than the 5 minute and I bring the strings up to full tension.

I would use this for any mandolin. The perfect fit is the object and the hardness of the epoxy transmits sound very well.

Rob Gerety
Apr-14-2010, 6:21am
If I can work up the courage I may try something like this -

Ivan Kelsall
Apr-16-2010, 1:48am
If anybody wants to fit a bridge to the top of a Mandolin as well as it can be done,try sanding the base by pushing the bridge across the top from side to side rather than from top to bottom as is usually done.That way you don't get any rocking of the bridge thence no 'rounded edges' .I've only ever fitted one bridge & i took care to think it through & did an excellent job. One of our best builder 'Cafe members on here,Gail Hester, also uses this method. It's a "the same only different" way of doing it & it works well,
especially if you mark the exact bridge location on either side & push the bridge back & forth between those 2 points,

Lefty Luthier
Apr-16-2010, 9:26am
Add a bit of powdered glass (epoxy filler available at boat stores) to add rigidity to the epoxy. I always leave the aluminum foil in place since it is easier on the finish than bare epoxy. I have taken a number of quantitative spectrum measurements before and after this treatment and found that it does increase acoustic response above 400 Hz a bit and generally raises overall output as well.