Arching a bridge base

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MarTay6

Posts: 69
Joined: Jul. 10 2011

Arching a bridge base

I understand that a soundboard has an arch in it- and that glueing a flat bridge to an arched top would be counterproductive- bending the bridge or flattening the top in theory. In the practical building world, how is this dealt with? Is the bottom of the bridge sanded to conform to the arch? If so, how is this typically done?
Wes

REPORT THIS POST AS INAPPROPRIATE | Date Aug. 8 2011 12:36:14

Sean

Posts: 672
Joined: Jan. 20 2011
From: Canada

RE: Arching a bridge base (in reply to MarTay6)

Cabinet scraper and sandpaper, I don't recommend a file to a beginner. There are flat tops, compound domed and conical domed tops, the bridge can be fitted to the top or the top can be pulled up into the bridge to increase its dome. I recommend you purchase a set of plans so we can answer more specifically based on the building style used by that maker.

REPORT THIS POST AS INAPPROPRIATE | Date Aug. 8 2011 14:46:22

Stephen Eden

Posts: 914
Joined: Apr. 12 2008
From: UK

RE: Arching a bridge base (in reply to MarTay6)

I use a piece of sand paper double sided taped to a bit of wood that conforms to the shape of the dish I use for doming. Using a scraper to start out does make the job alot faster.

_____________________________

Classical and Flamenco Guitars www.EdenGuitars.co.uk

REPORT THIS POST AS INAPPROPRIATE | Date Aug. 8 2011 15:36:51

MarTay6

Posts: 69
Joined: Jul. 10 2011

RE: Arching a bridge base (in reply to Sean)

quote:

I recommend you purchase a set of plans so we can answer more specifically based on the building style used by that maker.

Sean- I am considering purchasing a plan or two to further study the construction of a guitar. As a bit of background, I have built a couple of steel-string guitars, and am fairly competent at getting things right with one of them- and have also built a couple of other instruments. To my untrained mind, the flamenco guitar is somewhat specialized in that light construction and bracing make major contributions to the sound of the finished instrument, as well as tension in the guitar- or lack of it. In my mind there can be two schools of thought about a flat bridge against a domed top- 1) That it puts more tension into the top- which could be deemed good- or 2) That tension in the top by forcing one part to fit against another dissimilarly shaped part is bad.
I am unfamilar enough with the different makers guitars to even know which set of plans to choose, so I am open to any suggestions or comments as to advantages or disadvantages of the different makers- and differences between their instruments. I do know that I like the very bright, dry sound that a very lightly guitar brings. At least this is the sound I conceptually have in my mind.
If I decide to continue pursuing the idea of building one, I want to go into it having as much understanding as possible. I noted mention of at least one book on building a flamenco guitar, I would certainly like to gather any material I can.
Wes

REPORT THIS POST AS INAPPROPRIATE | Date Aug. 8 2011 15:40:43

Sean

Posts: 672
Joined: Jan. 20 2011
From: Canada

RE: Arching a bridge base (in reply to MarTay6)

A tension free top does not exist nor ever has, although I do remember some misguided individuals who were sanding their fan braces in an attempt to defy the laws of physics. Fan struts are glued down like springs which puts tension in the top, the bridges different expansion rate with humidity alone puts tension in the top and tightening the strings puts tension into the top. The only unrecommended way is doming a top and forcing a flat bridge on to it because this makes no sense. Archtop guitars are as close to tension free as you can get, that is until you string it up.
No tension in a top equals no sound produced

REPORT THIS POST AS INAPPROPRIATE | Date Aug. 8 2011 23:15:30

jshelton5040

Posts: 1500
Joined: Jan. 17 2005

RE: Arching a bridge base (in reply to Sean)

quote:

ORIGINAL: Sean

A tension free top does not exist nor ever has, although I do remember some misguided individuals who were sanding their fan braces in an attempt to defy the laws of physics. Fan struts are glued down like springs which puts tension in the top, the bridges different expansion rate with humidity alone puts tension in the top and tightening the strings puts tension into the top.

Well yes Sean but some of us feel that the top should be glued to the sides as gently as possible so as not to undo the intended built-in top tension. It's functionally impossible but one tries none the less.

_____________________________

John Shelton - www.sheltonfarrettaguitars.com

REPORT THIS POST AS INAPPROPRIATE | Date Aug. 8 2011 23:43:38

Sean

Posts: 672
Joined: Jan. 20 2011
From: Canada

RE: Arching a bridge base (in reply to jshelton5040)

quote:

ORIGINAL: jshelton5040

Well yes Sean but some of us feel that the top should be glued to the sides as gently as possible so as not to undo the intended built-in top tension. It's functionally impossible but one tries none the less.

Yes and I totally agree with you there, what I was referring to was someone pressing the soundboard into a radius dish then sanding the fan struts to fit the concave curve.
What they were missing was that the top was once flat and when they unclamp it after glue up it wants to return to being flat, thus ending up under tension. The only thing this accomplished was cutting long grain fibers in the struts, like bad runout. This was about 5yrs ago and the classical maker claimed it increased volume and sustain.

REPORT THIS POST AS INAPPROPRIATE | Date Aug. 9 2011 3:50:29