Fitting the bridge

[Guitdolin]

I another post I described my attempt at fitting my bridge as being like a bad haircut: a little more....a little more....Oh! Too much!

I finally got a flush fit, but I removed way more wood than I should have.

What is the secret to getting perfect fit? 99% patience, 1% knowing the right method and 0% power tools, I'm sure.

I tried "digging" out the middle to leave the edges high enough to contact the sandpaper I had on the top. I couldn't keep from rocking the bridge slightly though as I moved it back and forth across the sandpaper. I've seen a jig in Stew Mac with a wheel that is supposed to hold the bridge straight up. Another thing I thought of though is that the top is arched, and as I was rubbing the bridge across the top it was moving across different arcs. Should I "grind" sideways rather than from headstock to tailpiece?

I would appreciate any advice I could get from all of you that know what you're doing. I did finally get a good fit along with MUCH better tone, but I'd like to leave a little more wood on the bridge next time! http://www.mandolincafe.net/iB_html/non-cgi/emoticons/laugh.gif Thanks for your help.

[misifus]

The advice I've seen before is to only pull or push in one direction. What worked for me was to patiently hold the bridge firmly and pull toward me (at the tail piece). Then, lift and move back to starting point and pull again. This is taking very small movements, keeping the bridge quite close to it's final position.

Periodically, I lift the bridge and blow the dust off of it and the sand paper. I used the pattern of saw dust on the sandpaper to judge how much of the bridge was in contact with the surface of the top. Once it looked even, I gave it several more pulls just to be sure.

This took several applications each of at least a half hour. You just can't rush it.

FWIW, Kathy Wingert told me to get a scraper, because it's very difficult to sand it true without rolling the edges. I think it can be done, but not in a hurry.

-Raf

[Fretbear]

Just in case you don't have enough grief yet, Mike Compton was talking on the GOTW about fitting the bridge at a slight angle, back towards the tailpiece, to drive the top more, as seen on fiddles. I am going to try to incorporate that the next time I fit a bridge.

[Michael Lewis]

The method I use incorporates a holder I made of plate aluminum, holes to let the adjuster posts through and put the nuts on and tighten them. The thing is shaped like a big "T" with the bridge attached to the top of the "t' and the tail of the T is the handle. This just keeps tha bridge from rocking. Hold the bridge in it's proper position on the sand paper, and move the whole thing back and forth along a path about 1/4" long. Just a few strokes and you can see where it touches, then use a scraper to take down the high spots. Repete this until it fits. It takes me about 1/2 hour, and my bridges are mostly continuous contact all the way across.

[peterbc]

Do you start with low grit and move up? What grit do you end up on? My bridge isn't in complete contact on the bass side and I need to fix that.

Thanks,
Peter

[french guy]

One time I have trouble for fiting a bridge on a A sigma mandolin. When the bridge was ajusted and when I string up, every time the contact was not perfect.
I use the method as follow:
1- let the string attached , but just remove the tailpiece ready to be quickly replaced.
2- put a plastic film on the top.
3- cut a part of a two part plumber's epoxy
4- After kneading it a while, I form the epoxy a little worm about as big around as a pencil
5- Put it between the top and the bridge
6- replace the tailpiece , and quickly retend the strings
7- When the epoxy become hard ( 1/2 hour ) , I distend the strings , and sand the excess of opoxy.
8- Then I use a permanent pencil to make a tint on the gray epoxy to imitate the ebony wood of the bridge.
9- remove the plastic film of the top and string up again.
Hope everybody understand what I write , not easy for me to explain in english what I think in french !!

[John Zimm]

Hope everybody understand what I write , not easy for me to explain in english what I think in french !!
Je comprende tout vos mots, mon ami francais. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif C'est une bonne idea.

-Monsieur Buckley.

[Guitdolin]

Just in case you don't have enough grief yet, Mike Compton was talking on the GOTW about fitting the bridge at a slight angle, back towards the tailpiece, to drive the top more, as seen on fiddles.
I did try to angle mine back just enough to make it perpendicular to the strings rather than to the top. I don't know if that's correct or not, but it seemed like how it ought to be to me. I think using a scraper rather than a Dremel with an abrasive "drum" bit would definitely be the way to go. I thought I'd make it faster with the power tool, but it still took me at least 30 minutes. One thing I did like about the Dremel was the curved shape of the bit rather than a straight edge. If I'd have slowed the speed and used a finer grit along with the curve, it would have been better. The top, of course, is curved--both directions. Patience was my biggest missing ingredient.

Thanks for the replies! Michael, I like your holder idea. Does yours have a wheel on the handle end of the T or do you regulate the height/angle by hand?

[8ch(pl)]

I do the same thing as French guy, using normal Lepage's Epoxy and waxed paper between the bridge and top. I leave the strings on and use them to tighten the bridge blank down, spreding them to their approximate location on the bridge. I wait abut 3 hours and trim the excess epoxy off the sides of the bridge with a pocket knife before the epoxy gets rock hard.

The sanding is done to a pencil line from the old bridge on a spindle sander with 120 or so grit. I try to keep the outside of the line at the ends and go inside the line in the center. This ensures that the ends have good contact and keps things true for the adhesive to harden.

I made the last one of Beech, harder than Maple. I am pleased with the results. I have always thought that an adjustable bridge robs sound, since it has to travel down the 2 screws. When summer arrives with it's humidity I will make another bridge if needed to compensate for movement.

I am also of the opinion that the thickness of sandpaper between the bridge and the top does not render a true contour. the epoxy is dead on and I don't even sand the bottom, except to remove the excess.

Like I said, i am happy with it.

[Chris Baird]

That is an interesting technique. Epoxy, though, is generally considered a dampener. Perhaps there isn't enough on the the bridge to do any signigicant dampening.

[Gavin Baird]

Chris,
There are epoxies and there are epoxies. The thing is to select the correct one. It seems to me that the selection of a suitable one in conjunction with the incorporation of ebony dust would make a good combination for doing this sort of operation. I would do the prelinary sanding as previously stated and do the final fitting using the epoxy/ebony proceedure. What do you think?....G

[Chris Baird]

Certainly sounds like a worthy experiment.

[Gavin Baird]

Chris,
I forgot to add something that I am certain everyone knows. The relief in the centre of the bridge serves a critical purpose. What it does is to allow the two sides of the bridge to exert pressure on the two sides of the top. In other words, as the pressure of the downward force of the strings comes to bare on the saddle, the force is transferred to each side of the bridge and the bridge tends to become more tight fitting to the shape of the top. It is important that there is enough flexability in that centre area of the bridge to allow this to happen....G

[Chris Baird]

I believe that the two footed bridge also works well in a tone bar braced mandolin because it directs the strings energy further out away from the thicker center seam and also transfers the energy in a more lateral way. A well built top will be much stiffer along the grain than across it. I hypothesize if the bridge is in full contact it will be trying to drive the top more along the grain than against it and perhaps will have the effect of lesser volume and a more trebley response. Don't know though, haven't done any experimentation with alternative bridges.

[Fretbear]

Maybe I am missing something, but is the basic gist that there are spaces left between the the top and the bridge foot and that they are now filled up with epoxy? How does that sound?

[Luthier Vandross]

I build bridges, and there is a touch of angle built into a proper base.

Let me see if I can describe how I fit a bridge, with text.

I place the bridge on the top, hold it down with my left hand, and starting at the point were it doesn't touch the top, on each side, I draw a line, that matches the top curve, file that close, then holding the instrument in my lap, in a playing position, I hold the outsides of the base, and sand it, as normal.

Yeah, I understood that!

In my opinion, an adjustable bridge doesn't harm the sound, it's just a component of the sound. You could argue, just as much, that the screws act to cut the humpy low frequencies, that clutter an already complex sound.

M

[8ch(pl)]

If you try epoxy, do not use the 5 minute stuff, it does not harden like the normal kit epoxy. In my experience it is a bit "rubber like".

I try to sand as close as possible to the contour, but don't bother getting it perfect, the epoxy is applied in a thin coat and fills up the very small gap that is left. I also don't use too fine a sandpaper, the epoxy adheres well to a rougher surface. With the waxed paper as a release barrier it comes out glass smooth. The strings to tighten it all down are an effective clamping setup.

The important part is to slip it under the strings (loosened of course) and onto the correct area of the top without moving the bridge to much from side to side.

[GTison]

this may be dumb but..... why couldn't you make a jig to hold the bridge WITH an electric sander and just press it down on the top to match the curvature. I've never heard of anyone doing that but I looks like it would work esp. if you had to do it alot.