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Bridge shape
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TerryT
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February 19, 2012 - 3:00 pm
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My bridge popped out earlier and I have successfully replaced it.

On closer inspection, looking at it from the side view it seems to have a different profile on one side to the other.
One side is definitely flat whilst the other side has a slightly convex form.
Is this a design? And if so does it matter if it flat-side toward the fingerboard or vice versa?

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Sofia Leo
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The bridge is generally planed on the fingerboard side to a slight angle, but the side toward the tailpiece (where the logo or stamp is) is left perfectly flat. It should not be curved on either side - this may be a sign that it's warping and will need to be replaced soon.

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TerryT
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Thanks Cat, I'll get a spare in readiness. Should I plane/sand the new one to the same size as my current bridge! (before it breaks!)

facepalm

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cdennyb
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IMG_20120218_210004comp.jpgImage EnlargerIMG_20120218_210041comp.jpgImage EnlargerIMG_20120218_205827.jpgImage EnlargerIMG_20120218_210148comp.jpgImage EnlargerMy luthier has instructed me as follows on cutting and positioning the bridge i relationship to the fingerboard. Hope this helps.

The bridge has a shape that forces the E string to be something like 3 mm above the fingerboard at the end closest to the bridge. The G string is 5 mm above it. I made a small board as seen in the pics that is taped to that exact height as measured with a pair of calipers. Making a small mark on the bridge at the required locations allowed me to sand it down to that gentle curve which allows room between the strings for bowing. Using a sanding block I was able to taper the bridge to 1-1.5 mm in cross section (The distance across the bridge where the string is touching the wood) leaving the center section thickest above the cutouts.

Once cut to the correct height, higher is better than too low... I used a small welders tip cleaner file set to cut a rounded groove into the top of the bridge. File it square with the world and only deep enough to allow the string to fit flush with the top of the wood. Using a knife to cut a "V" shape will only allow the string under tension to spread the wood and eventually possibly split the bridge, then you start all over from square 1.

 

Place the bridge with the straight side facing the tailpiece and the tapered side towards the fingerboard. Using a piece of 320 sandpaper laying rough side up on the top, you can very gently (keeping the bridge perpendicular to the top surface more or less)  slide it back and orth on the sandpaper causing it to conform to the top shape thus keeping as much in contact with the top surface as possible for max sound vibration transmission.

Hope this helps. 

"If you practice with your hands you must practice all day. Practice with your mind and you can accomplish the same amount in minutes." Nathan Milstein

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Sofia Leo
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Terry said

Thanks Cat, I'll get a spare in readiness. Should I plane/sand the new one to the same size as my current bridge! (before it breaks!)

facepalm

That's what I did on the fiddle I recently refurbished. The bridge was badly warped, but the string clearance was correct and the top arch made playing very easy. I first trimmed down the feet and then matched the top arch. Works pretty well, even if I say it myself smile

You'll need to verify the proper string clearance with the old bridge first, but this can vary a bit - if you find it easy to play, then it's right for you even if it doesn't quite meet Traditional Specs.

Use a very sharp knife and do be careful not to cut yourself - ask me how I know yell

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Oliver
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@cdennyb    I just became aware of the "law" from an expert that a proper bridge will be able to stand alone and vertical if the feet are done right.

I tried it and only achieved a shorter bridge and never the balance.  smile

When you come to a fork in the road, take it.

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TerryT
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Thanks guys, this is all great advice. I do find (as a beginner) that I have a problem playing the A string. The profile of the bridge is quite flat where it supports this string and whilst eventually I want to play Celtic music with my sailing buddies, so this profile would be easier for double stops I guess but at the moment it's a pain!
So I might experiment with a 'slightly' more pronounced curve, giving me just one or two degrees more bow clearance from the D and E strings.
Whaddya reckon?

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TerryT
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Lol at you Oliver, good one laugh

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Oliver
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What is your problem playing the "A" string ?  Just bad string crossings ?

When you come to a fork in the road, take it.

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cdennyb
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Terry said

Thanks guys, this is all great advice. I do find (as a beginner) that I have a problem playing the A string. The profile of the bridge is quite flat where it supports this string and whilst eventually I want to play Celtic music with my sailing buddies, so this profile would be easier for double stops I guess but at the moment it's a pain!
So I might experiment with a 'slightly' more pronounced curve, giving me just one or two degrees more bow clearance from the D and E strings.
Whaddya reckon?

The distance between the strings, double stops vs single string notes is a function of the curve with no doubt. Also, the difference in height between the G & E strings above the fingerboard allows a more steep curve without getting the center strings too far away from the fingerboard. With the strings off tension, stand the bridge up where it kinda goes and sight down the fingerboard from the peg end. The curve should almost perfectly follow the same curve shape as the fingerboard, (I think the radius is something like 42 mm) but if the E string is closer than the G string to the board you can get more seperation between the strings and thus hit single notes very easy.

"If you practice with your hands you must practice all day. Practice with your mind and you can accomplish the same amount in minutes." Nathan Milstein

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cdennyb
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Oliver said

@cdennyb    I just became aware of the "law" from an expert that a proper bridge will be able to stand alone and vertical if the feet are done right.

I tried it and only achieved a shorter bridge and never the balance.  smile

@ Mr Oliver... I didn't know of any "law" but the properties of acoustics pretty much dictate that if max transmission of a particular vibrational freq is required then max surface area contact is best. Any voids, air spaces or dis-similiar areas of contact will attentuate the sound transmission. This would explain some strings sounding incredible and then another one (usually furthest from the first one) is flat or muted sounding. This can sometimes be traced to inadequate surface area contact of the bridge on either the E or G string side. Equal and complete contact is almost impossible to achieve.

A trick my luthier uses is some old school "carbon paper" which he places under the bridge (It's really thin stuff you know) and puts a little string tension on it and lides it back and forth once or twice then looks at the contact patch and sands accordingly.

"If you practice with your hands you must practice all day. Practice with your mind and you can accomplish the same amount in minutes." Nathan Milstein

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TerryT
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Oliver said

What is your problem playing the "A" string ?  Just bad string crossings ?

If you mean moving from one string to the other, yeh! I'm not too bad on the others, just that d**n A string. Maybe its slot in the bridge is a little deeper, as the bridge profile matches the fingerboard when viewed longitudinally from the tailpiece end (although the bridge was 3-4mm offset, which is why it jumped out originally as i was 'gently' coaxing it back in line)

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cdennyb
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Si853555comp.jpgImage EnlargerHere's a look down my fingerboard. Does yours look the same?

 

Maybe it'll help to get the shape right on your next bridge build.

See the major seperation between the strings? especially the center two?

 

This is for the spacing recommended for synthetic core strings (Which I ordered from FM last week and should have by next week.)

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TerryT
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cdennyb said

Si853555comp.jpgImage EnlargerHere's a look down my fingerboard. Does yours look the same?

 

Maybe it'll help to get the shape right on your next bridge build.

See the major seperation between the strings? especially the center two?

 

This is for the spacing recommended for synthetic core strings (Which I ordered from FM last week and should have by next week.)

Mine is slightly different. More like the profile of a wing, or a sail looked at from above. A more pronounced curve at the G and D, then flatter between D and E.
I'll see if I can upload a picture of it.
I have some Zyex strings on order from Fiddlerman so might adopt this shape bridge when I fit them.

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cdennyb
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Good deal. Those are the same strings I have coming too!

thumbs-up

 

Remember to fit the feet first, then the top.

"If you practice with your hands you must practice all day. Practice with your mind and you can accomplish the same amount in minutes." Nathan Milstein

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TerryT
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cdennyb said

Good deal. Those are the same strings I have coming too!

thumbs-up

 

Remember to fit the feet first, then the top.

here's mine

Bridge1.JPGImage EnlargerBridge2.JPGImage Enlarger

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Oliver
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The problem with all this theory is that it is tempting to do all kinds of tricks at the bridge BUT that's not where most music is played.  Most of the geometric tricks are dissipated by the time one reachs the nut.  Gone !

(Those viola guys got it easy!)

coffee2

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cdennyb
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Si853555compw-dims.jpgImage EnlargerIt's difficult for me to say positivly but I see all the strings shifted to the E string side. It does not appear they are 'centered' on the fingerboard. That's an issue. The bridge appears to be a "blank", or one to use to begin your fitting process to your instrument.

The bridge appears to be 'very tall' and when you go to the new strings I would suggest using the following dimensions to shape it. Using the curve of mine as shown above use a distance above the fingerboard as I showed in the first post of this thread and keep the spacing as shown here.

 

That's what I would do to begin with but maybe another on here that has more experience than i do would suggest different.

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cdennyb
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Oliver said

The problem with all this theory is that it is tempting to do all kinds of tricks at the bridge BUT that's not where most music is played.  Most of the geometric tricks are dissipated by the time by the time one reachs the nut.  Gone !

(Those viola guys got it easy!)

coffee2

Here's an article from years ago about the physics and vibrational relationships of strings and bridges. If you're just kickin back and relaxin on a Sunday afternoon, it makes for some great reading.

 

"If you practice with your hands you must practice all day. Practice with your mind and you can accomplish the same amount in minutes." Nathan Milstein

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TerryT
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Oliver said

The problem with all this theory is that it is tempting to do all kinds of tricks at the bridge BUT that's not where most music is played.  Most of the geometric tricks are dissipated by the time one reachs the nut.  Gone !

(Those viola guys got it easy!)

coffee2

haha, which nut? the one at the scroll? or the one on the frog end of the bow?

I was born with nothing,
and to my surprise I still have most of it left!

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