Bridge Mystery

[Pete Jenner]

Can anyone shed some light on the following mystery?

Yesterday I spent many hours filing down the string slots on my home mad ebony one piece bridge. I used nut and fret files that were as close to the string gauges as possible. I filed the slots one at a time and tuned back to pitch as I finished each string.

Some files were slightly narrower than strings and in those cases I rocked the file from side to side to widen the slot.

While filing, I frequently stopped to check string height above the 12th fret and tuned up to check for fret buzz. All the slots were kept clear of dust.

I managed to get the E sting down to .042 inches above the 12th fret and the G string to a .060 (using the StewMac feeler gauges - otherwise I would have measured in metric). No fret buzz and a beautiful easy action. I tuned up and played for a while.

I then removed the bridge and sanded away the excess wood from the top. When the slots were just right, I slipped the bridge under the strings and place it exactly where it had been. To my dismay, the strings were sitting on the fretboard. Luckily I have a couple of spare bridges but before I do the same thing to them, can anyone tell me where I went wrong?

Thanks in advance.

[Paul Hostetter]

Keep at it! This is all part of a necessary learning curve. There may be some info here that'll help you.

It is always easier to lower action a bit more (in a fixed bridge) than to raise it. I think the big lesson here is that you jumped the gun a bit. Adjust, test, correct. Et cetera.

[Eric Hanson]

Just a guess.
Could the neck tension have changed with the removal of the bridge?
Prior to your removal of he strings how long had the mandolin been strung up?
Have you allowed the mandolin to remain strung for a period of time? If so, has there been any change in the string height?

[Pete Jenner]

Just a guess.
Could the neck tension have changed with the removal of the bridge?
Prior to your removal of he strings how long had the mandolin been strung up?
Have you allowed the mandolin to remain strung for a period of time? If so, has there been any change in the string height?

Yes Eric - the mandolin had been stung up for 2 weeks. No noticeable change in neck relief. The nut was still in place. I didn't notice any change in string height.

Paul thanks for that link - from a quick glance, I think I have adhered to the basics there but I'll have a closer look at it.

[Pete Jenner]

Here is the offending article.

[almeriastrings]

On many instruments, when you remove or re-apply full string tension/pressure it is not only the neck that moves, but the top. How much is happens can vary, from insignificant to very considerable. Also, if you thin the saddle down too much, you can get a bend there as the pressure goes on. I fit the bridge to the top first, then go very slowly when finalising the saddle and nut slots, working on one string at a time, with full tension on the rest. I also allow "settling time" after removing and replacing the bridge before doing anything irreversible.

[Pete Jenner]

On many instruments, when you remove or re-apply full string tension/pressure it is not only the neck that moves, but the top. How much is happens can vary, from insignificant to very considerable. Also, if you thin the saddle down too much, you can get a bend there as the pressure goes on. I fit the bridge to the top first, then go very slowly when finalising the saddle and nut slots, working on one string at a time, with full tension on the rest. I also allow "settling time" after removing and replacing the bridge before doing anything irreversible.

Yes that's exactly how I did it.
The soundboard deflection is minimal anyway. I carved it pretty thick and it's graduated from 6.5mm in the centre to 3.5 mm at the recurve then out to 5mm at the edges. The Xbrace is extremely well fitted and sturdy.

However, I didn't bring the strings up to full tension after I replaced the bridge. Maybe the neck WAS bending under full string tension - I'll get back to you on that one. Meanwhile thanks very much for all the advice.

[Michael Lewis]

Check for unevenness in the shiny surfaces by using low angle light and look at the reflections in the finish. Also look at reflections in the finish from a distance of several feet or more. Any distortions from failing structure should show up. Inspect all glue joints you can find, see if any are opening. To be thorough you might go through this both with and without string tension, and compare findings.

You can glue more wood to the top of the bridge you have, and re-cut the intonation and string spacing.

[Pete Jenner]

Thanks Michael. I did as you suggested and there is absolutely no deviation anywhere in on the soundboard. The soundboard and I have been inseparable since it arrived in the post from America 8 months ago as 2 spruce wedges (is that weird?). I know every contour and curve intimately (ok so now it's starting to sound weird but at least I've stopped sleeping with it).

I've strung it back up to approximate full tension and will give it a few hours to settle. If the strings rise from the fretboard, I'll know it is a neck bending issue. If not I'll just go ahead with my #2 bridge.

[Pete Jenner]

Keep at it! This is all part of a necessary learning curve.

Never a truer word was spoke Paul. I learned a big one today.

Mystery solved and I'm both pleased and amazed!


Eric - you were right about the neck. I put the old bridge back on and tuned back up to pitch - voila - the neck bent and the strings rose up from the fretboard. The action is restored to pre-bridge removal specs.

Thanks again to the Manolin Cafe community for helping me solve it.

[Dick Hutchings]

Are you saying you hadn't tuned to pitch when you found the strings lying on the fret-board? That makes sense to me.

[Pete Jenner]

Yes Richard - didn't occur to me that there would be that much bend in the neck. They were tensioned but not to pitch.
I didn't make the neck - just the soundboard and bindings etc.

When I do make a neck it will have a carbon fibre rod in it.

[Big Joe]

You may have had the bridge backwards when you tried to put it back on. I know that sounds impossible, but we see that a LOT in the instruments we work on. I would have done a full contact on a one piece bridge as well. That won't affect the issue at hand, but if you don't like the results, try fitting for full contact and see if that helps.

[Eric Hanson]

Glad to know it wasn't anything drastic. Happy to be of help where I can be.
Just sharing knowledge gained from all the fine folks here.

PS: We would love to see your build. Please post pictures when you can.

[Pete Jenner]

I posted it here Eric.
http://www.mandolincafe.com/forum/sh...erie-Concludes

[Pete Jenner]

Big Joe, I thought of that but it is impossible to put that bridge on backwards. I used a profile gauge and traced the shape onto a paper template I drew on the computer. Then I fitted it using the chalk and scraper method. The arch drops away more on the bass side than the treble.

I chose a two footed bridge after reading everything I could find about Mandolin bridges on the Internet (that's a lot of reading).
Haven't seen a full contact bridge on an arch top anywhere.

It must be ok because the Mandolin sounds better than any other I have played.

Cheers,