Setting abridge

[Willie]

I was watching a show last night about building a cello and the luthier set the bridge by using a yellow grease pencil, he made a mark along the place where he wanted to place the bridge (between the notches of the F holes)and then pressed down on the bridge and where ever there was yellow grease on the bottom of the bridge that was the only place it was touching the top so he kept scraping the bottom of the bridge until he had a yellow grease mark all over the bridge bottom.....Looks like this would be better than the sandpaper way....Has anyone on here ever used this "trick"....BTW..The yellow grease will wipe right off..Willie

[Bill Snyder]

Several people use this method, but chalk is frequently used instead of a grease pencil.

[Antlurz]

It might be a bit easier if someones eyes have trouble picking up the sanding marks on the bottom of the bridge, but aside from that, I don't see any benefits. Just another of many different methods.
Ron

[Martin Jonas]

Yes, I've fitted several bridges this way, using chalk rather than grease pencil. I've been shown this by a violin maker and found it much easier than using the sandpaper method. Just press the bridge onto the chalked soundboard, then use a very sharp carving knife (I use a curved Swedish one) to scrape away everything that's white.

As far as I can see, there are several advantages to the sandpaper methods: it's easier to see the chalky areas rather than roughed-up sandpaper areas; the bridge sits directly on the soundboard rather than separated by a thickish layer of sandpaper which can slightly alter the curvature; and, probably most importantly, you can get a decent chalk mark without having to move the bridge across the soundboard, so you get the actual curvature at the place where the bridge will sit rather than an average curvature over the length of the sanding track. If you look at the Frank Ford method, even with the short track used by Frank, you still have to move the bridge by at least one centimetre sideways before you can see a good trace.

One caveat: if you have a very delicate finish (such as on many Italian bowlbacks), you better put some low-tack masking tape on the soundboard and put the chalk on the tape rather than on the instrument.

Martin

[Antlurz]

As far as I can see, there are several advantages to the sandpaper methods: the bridge sits directly on the soundboard rather than separated by a thickish layer of sandpaper which can slightly alter the curvature...

************************************************** **

One caveat: if you have a very delicate finish (such as on many Italian bowlbacks), you better put some low-tack masking tape on the soundboard and put the chalk on the tape rather than on the instrument.

.

Six of one, half a dozen of the other?

BTW.. I'm not putting this method down. I just think other ways work fine, as well. I'd be comfortable with either method. The final product is all that counts. If it works for you, do it, providing the results are the same...

Strictly speaking, the only way that really works perfectly is one using the same down pressure as the strings will exert, anyhow.

Ron

[8ch(pl)]

I believe there's a built in inaccuracy caused by the thickness of sandpaper. It could change the radius. The chalk method prevents this.

I fit mine with a layer of epoxy on wax paper. I slip the bridge under the strings and bring them up to pitch. When Hardened, the epoxy forms an exact fit and it is harder than any wood.

[Jerry Byers]

Is the epoxy acoustically transparent?

[Martin Jonas]

Six of one, half a dozen of the other?

Absolutely, yes. If you have to put something between soundboard and bridge, whether sandpaper or masking tape, you lose a little bit of precision fitting. Still, that's better than permanently staining the top of a delicate bowlback with ground-in chalk.

Martin

[8ch(pl)]

I think it is more of a concern with carved tops. If I were doing a flat top Bridge I would likely put fine sandpaper on the top of the table saw. waxed paper will

Don't get me wrong, I am not saying that sandpaper on the top is a really bad idea, I think finer grits with resultant thinner sandpaper will be more accurate, but cut slower.

Epoxy is very hard when cured, andit penetrates only about .010 in into the wood, from what I have read in Wooden Boat Magazine. I have been happy with the bridges I have done with it.

I just use the tube stuff which is not the better grade of epoxy. I don't use 5 minute epoxy, I like the longer working time from the slower cure variety. I let it harden until it is set but not rock hard. This allows easier removal of what squishes out from underneath. That can be trimmed with a knife and the sides sanded.

[Bill Snyder]

FWIW. I believe that it is not uncommon for luthiers to use a combination of both the sandpaper and the chalk methods. For a bridge with feet that are not even close you start with the sandpaper to get the bridge close and then chalk the top and fine tune it by scraping.
I believe the primary arguement in favor of using the chalk and a knife for the final fitting is you do not have the sanding scratches on the bottom of the bridge. Also when sanding any rocking of the bridge can round of the outside edges a bit.
I think if done WELL both methods will give you a good result, but I am just a layman that spends much more time reading about building and drawing up plans than I spend building.

[whistler]

I believe there's a built in inaccuracy caused by the thickness of sandpaper.

side

Another built in inaccuracy of the sandpaper method is that sanding relies on movement. Unless you are fitting it to a perfectly consistent arch, the curve you are sanding the base of the bridge to is constantly changing. So you cannot possibly achieve a perfect fit. And that's notwithstanding the inevitable slight rocking motion (which can be minimized with good technique and/or gadgetry, but not eliminated), that results in a degree of rounding.

Having said that, on the few instruments I have completed to date, I have only ever used the sandpaper method. Whilst it may only ever be a quick-fix solution, it seems to be good enough. I wonder if there'd be any discernible difference in tone with a chalk-fitted bridge.

[nelson_luthier]

I like old fashioned carbon paper for final fit myself. It's very thin and technically will change the shape of the foot by just that much, but my scraper in hand is not [/U]that[U] accurate anyway. #When the hard maple presses down into the soft spruce top won't that make up any difference anyway? #

When I was taught how to set fiddle bridges I was told to wet the feet (ok, I was told to spit on them) just prior to final installation. It is supposed to help fit the feet to the top and vise versa. Does anyone else do this?

I have only built one Mandolin so far, but when it came to fitting the bridge the one I had needed significant shaping before I could even start to fit it. Faced with a whole lot of tedious sanding I came up with this little jig to speed the job up.



Should be self explanitory.

Greg

[Antlurz]

That's quite interesting. I'd think the overall movement by the sander would be far less that doing the same thing by hand, so the bridge foot shouldn't encounter the variations it is exposed to by pushing and pulling it around by hand.

I'd think one would want to keep the bridge as close to the center of the axis as possible.

Ron

[Willie]

Glen...I have been trying to think of a way to use epoxy but never gave wax paper a thought...Thanks for the idea...Thanks to all of you for your ideas, I have never been able to get a "perfect" fit with sandpaper because of the rocking of the bridge when doing it be hand but it does get it close and the final tweeking is the important part as far as I am concerned....Thanks....Willie

[Frank Ford]

Nelson -

That is indeed a clever solution to the problem!

Here's a more traditional method:

Fitting Bridge Feet

Cheers,

Frank Ford
FRETS.COM
Gryphon Stringed Instruments
My Home Shop Pages

[ErikAitch]

May I point out that the bridge fitting in question (assuming it's the same one I saw) was for a Luis and Clark carbon fiber cello? Episode 108 of the Science Channel's "How It's Made".

While it was nothing new to me, tech-wise (I used to build radio control slope racers), it was still fascinating.

http://www.vidly.net/collection-how-its-made.html has some of the How It's Made videos, including one of the Taylor factory, but the L&C isn't there yet.

[buddyellis]

The cello how it's made was quite interesting. Highly recommended.

-b

[Willie]

Yes, that was it on "how it`s made"...I was impressed...Willie

[bryce]

I make my own bridges so I get to pick the starting arch. I use a tool I like for fitting wood moulding to set my arch. Its a bar with about 100 small wires running through it. Don't know its proper name. Pressing it down on your mandolin at the bridge position will give you the exact arch. Transfer this to my bridge bass and trim very close. Then holding my bridge with one hand I pull 3/4" strips of sand paper out from under each foot. One at a time. The bridge never leaves its location. Working through higher grits as I go. I do this in the white to get a early set up. After the finish is applied I have very little if any to scrape using carbon paper.
David

[david blair]

I've been thinking about a tool like that lately, lots of little nails in a sort of mould. I've seen them for measuring curves and such.
There's been speculation that some of the great violins were carved inside first, and many of them have small nail marks in the wood. Sometimes many nail marks. Anyway, if one were to attempt to shape the perfect bell or arch just like another one this could be a sort of template.
Has anyone tried carving the inside first?

[Jerry Byers]

They are called a contour gauge. They come in metal and plastic. The plastic ones are a bit easier on the finish.

[Willie]

I have used a contour gauge but when the bridge is shaped to the mandolin top without any pressure the bridge base ends will not be touching when strung up to pitch due to the top compressing slightly, I guess thats why doing the chalk while under pressure is a good idea...Willie

[Bob Denton]

I believe there's a built in inaccuracy caused by the thickness of sandpaper. It could change the radius. The chalk method prevents this.

I fit mine with a layer of epoxy on wax paper. #I slip the bridge under the strings and bring them up to pitch. #When Hardened, the epoxy forms an exact fit and it is harder than any wood.

I am not a luthier and all my tools are in storage, so I have limited facilities. I usually work at my desk in my office in between phone calls.

My attempts at fitting bridges has been less than satisfactory. I made a tool, ala Siminof, but it didn't work all that well, and I didn't want to spring for the Stwmac tool.

I tried the method on two mandolins, first my Kentucky 380S and then my Gibson F5-L.

For the 380 I used a piece of silicone paper from a sheet of labels. I applied the epoxy, then the paper and positioned the bridge on the mando and tuned up to pitch.

The results were good, but after the epoxy had set, and the strings were removed, the fit was looked no better that my sanding attempts.

There was, however, an improvement in tone and volume.

For the F5, I also used silicone paper, courtesy USPS, and this time put only light tension on 1/2 the strings. Enough to make solid contact with the top but not enough to deform the bridge or top during the curing process.

The results were excellent. I removed the bridge after a couple of hours when the epoxy was still supple and trimmed the excess off with a knife, then back for antoher few hours.

I removed the paper and tuned up to pitch. The results were excellent! During the following hours I could heard changes in the higher frequencies as the epoxy hardend. This morning, afer 18 hours or so of curing the results are dramatic. The Gibson is like a new mandolin, lively with great top ends and resonant bass.

Thanks for the tip!