View Full Version : Sanding bridge feet
My 2006 Epiphone F-5 has the (seemingly) standard factory adjustable bridge. I suppose it can be defined as a two foot bridge, as there is a very small gap in the center between the bridge and the mandolin top (less than a 1 millimeter). This being said, I was wondering if it would be wise to sand down the bottom of the bridge to make it a truly full contact bridge(I have sanding experience and I know the pitfalls of sanding too much too quickly). I have heard positive and negative things about taking such a step. I have also heard that having a bridge with as little mass as possible is a good idea. Mind you, my mandolin has no internal bracing, with maple sides and a spruce top. Any advice?
I don't believe the (very slightly reduced) mass is a large factor in the single vs. two foot bridge base. Whether you will like the effect on your instrument can only be known by trying it. I personally prefer a single-foot bridge base, but also feel that choosing a high-quality adjustable ebony bridge like a Cumberland Acoustic is more important than whether it has one foot or two. I also have a theory that in conjunction with the internal tone bars, a full-foot bridge forms a kind of continuous modified "H" bracing, similar but different to "X" bracing.
Lot's off differant opinions on this here. Some of the luhiiers will be chiming in I expect and can give you several insights of pros vs. cons. There has been a ton of discussion on this, if I could I would point you in the right direction to read some former things on it, but I simply don't know how to do that.
If it's a question of precisely matching the bridge to the top, better than the factory In Asia Did,
[rather than some esoteric discussion of improving your tone significantly in the process ] ...
Sandpaper, face up, painter's taped to the top, works.
60 then 120 grit a reasonable pick
be careful it's not rocking as you move your bridge over the sandpaper, as that will defeat your purpose.
probably don't need to move more than a half to an inch back and forth.. over the grit.
keeping it square to the surface, most important.
Another thing that will help is the bridge fitting jig that Stew-Mac sells. If you have those you can get one dead on, and they don't cost too much. I've had mine for a couple of years and it has already payed for itself X three.
My guess is that fitting a bridge perfectly is probably more important that all the other variables combined.
Whether one elects to fit the bridge all the way across or just under the posts, a perfect fit is what is important. My personal preference is all the way across for the simple reason that it distributes the string load across more surface area and hence does not dent the top finish as much.
I would go to finer grits than those mentioned. The reason for this is because the method itself is not as precise to fit a bridge to the top, as some may think. The thickness of the sandpaper prevents the inside arch on the bridge from exactly matching the outside arch of the top. The finer the grit, the thinner the sandpaper and the closer the 2 parts will match.
Having 2 feet will also allow some flex in matching the bottom of the bridge with the top. I always use epoxy on the bottom of the bridge, with a piece of waxed paper taped to the top. I slip the bridge (with the epoxy) under the strings and bring them up to tension. The epoxy will not adhere to the waxed paper. After it hardens, I remove the excess epoxy. The epoxy will fill any gaps and it is hard enough to noy affect sound.
For what it's worth, I did the epoxy thing that 8ch(pl) describes on my cheapo beater mando and was surprised at how easy it was and how much better it sounded compared to the mando with its poorly fitted bridge.
Might not do it with my better instruments though.
Red Henry did some experiments with 2 feet vs full contact bases. His conclusion favored 2 feet. Info is on his website. YMMV.
The idea is to still get it carved as close to the arch as possible. I have never tried masking tape on the sides of the bridge, cut to the edges, to reduce the epoxy appearing on the bridge. Epoxy will penetrate the wood, I read in a Boat Magazine that it generally only goes in about 1/100th of an inch. Masking tape will probably aid it. There is a time when the epoxy is not quite set when it can be carefully scraped from the sides of the bridge with a sharp knife. Then it can be finished with sandpaper. I usually knock it off with a drum sander in the drillpress and finish sand it by han on sandpaper that is taped to a flat surface, sheet of glass, table saw table etc.
Something I don't understand here about the epoxy method, or allowing for string tension. I have fitted bridges to 7 mandolins now using the Stew=mac jig. They are all dead on next to the sound board even with string tension. I've read that you have to compensate for the string tension, but in the ones I've did, I've found this not to be true. I have acess to all the mandolins I've did, see them from time to time, and the bridge fits the top like a glove, no cracks towards the end of the feet. So I'm thinking that if you have a small crack at the end of the feet when tuned up to tension, then something was not right to begin with. Again I can not stess more how the Stew-mac jig will solve all bridge fitting problems. I think it cost around $45, small price to pay for as close to perfection as you can get. I have fitted bridges to mandolins before having this jig, and it was hard to do, the jig takes the difficult part away. But again I'm not a luthier, but only stating here what I find that has worked.
I believe that there is a bit of flex involved, a lot of this process is subjective. The top will move somewhat to adjust to the contour of the bridge. If the bridge has 2 feet, it probably flexes a bit to adjust as well. A single foot maybe less so. I have messed around with my Samick A, carved bridges to fit, put the old bridge back on, made newer ones, used epoxy etc.
The latest 1 piece, 2 foot bridge, made of beech, with a very thin layer of epoxy is the best of my efforts on this instrument so far. I have made some in the Red Henry pattern, this new one is modeled after the bridge on my Mid Missouri, but slightly longer.
If you know what a contour gauge is it will take a lot of the guess work out of fitting a bridge...I place a piece of masking tape across the top where I want the bridge to be and then press down on the contour gauge and it takes the shape of the arc of the top, then I use that to mark the bridge feet and sand them down ( I have used a belt sander if there is a lot to be removed)to the marks and I have always had good luck with this method...I find that there is very little "give" in either the top or the bridge feet, if there is, just a little sanding will correct it pretty easily....Willie