Bridge Placement Question

[baumgrenze]

My little sister found this Angelo Mannello bowl mandolin for me in a pawn shop just south of the Loop in Chicago in around 1955. It was in need of restoration. All of the mother-of-pearl binding was missing and had been replaced by Plastic Wood. There was a serious crack in the lower part of the top under the tailpiece. The tailpiece had crushed its way into the top, probably through overzealous tuning, pulling the bottom of the bowl with it. I made the cosmetic repairs you see about 15 years ago.I placed a small patch of spruce in the lower top and rebraced the area beneath the tailpiece. I obtained the spruce from Gryphon Stringed Instruments in Palo Alto, CA. I cleaned are reglued all of the pearl and tortoiseshell inlay scratch-plate. The tortoiseshell is clearly celluloid. I cut and polished pieces of abalone shell to restore the binding and made replacement ‘tortoiseshell’ parts from an old comb of an appropriate color. I French polished the top to incorporate the patch. I am dissatisfied with the placement of the bridge. I left it where I found it because the two buttons at the ends of the bridge are clearly glued to the top and more or less define its ‘intended’ placement. It would be nice to restore it to playing order. If close-up photos of any part of the instrument would help someone to understand my problems, I will try to add them.

The measured distance from the nut to the 12th fret (to the center of the fret) is 166.5 mm. The distance from the nut to the cant point on the sound-board is 329 mm. If I use the standard rule-of-thumb and double 166.5, my scale length should be 333 mm. This puts the bridge just below the cant point. Should I move the bridge to the lower portion of the soundboard, below the cant? Do I need to worry about bracing? The neck looks to be straight. The current clearance at the 12th fret is very close to 3 mm; a 1/8” drill bit just lifts the string a hair.

I’ve read that Mannello sold a lot of factory made bowl mandolins for the trade in the years around 1900 – 1920. This one looks a bit nicer (but not as nice as the ones in the Metropolitan Museum) than some I have seen on the web.

I would appreciate expert advice about what to do next.

Thanks,

baumgrenze



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[Tavy]

First off - really nice work so far!

Re bridge placement, ideally it should go forward of the cant (neck side) and not aft of it (tailpiece side). But judging by your measurements you appear to have a problem! The overarching issue though, is does it play in tune? So I would move it backwards the smallest amount I could get away with 'til it plays in tune, possibly compromising the position so it only plays in tune for the first 10 frets or so if that's all I could achieve without "falling over the abiss". BTW if the bridge ends up more or less right on top of the cant, that's OK too. Oh and you'll want to bring that action down if you can too....

HTH, John.

[Jim Garber]

I don't think that yours is a factory model. For one thing it looks more upscale than the plain ones I have seen and also has that Italian style neck construction which would prob indicate a better model. Nice work on the restoration.

John has some good advice above. I would try using an electronic tuner and see where the bridge ends up when the notes play true. What kind of strings do you have on it? Also, was the nut replaced and were the nut slots properly angled. That could make a few mm difference as well.

[baumgrenze]

John and Jim, thank you for your helpful comments and questions.

It does not play in tune. That is why I asked about bridge placement. I checked the strings with my micrometer and read 10.5, 14, 25, and 40. I can no longer remember if I put new ones on when I did the restoration work. If so, I would have purchased them at Gryphon. Perhaps I would be better served with even lighter strings. I read here today that bowl mandolins sound better with light strings.

The nut is original, unless it was replaced before I was given the instrument.

In other posts, I've seen mention of 'canting' the bridge. I gather this means setting it so that it is not quite at right angles to the strings. I can see where this might help with a non-compensated bridge.

Thanks for the compliments on my workmanship.

I opened the tailpiece to photograph the repair in the soundboard and discovered that I'd had the 'craftsmanship' to put a note on the inside documenting the repair's completion on 11/25/85. It also revealed that I could have done a bit better with the purfling patch I created from scrap rosewood and maple I had at hand. A good luthier would have made a perfect match, even though it is under the tailpiece. The patch is 5/16" wide and runs from the tailpiece to the cant, just to the treble side of the seam down the center of the soundboard.

I will try to schedule time to work on the bridge, but retirement is busy this time of year. I promise to report back.

Should this instrument also be on "Post a picture of your mandolin" or is such cross-posting considered inappropriate?

Here's a photo of the repaired region of the soundboard.

[Michael Lewis]

Is it possible for the neck or fingerboard to have moved slightly? The neck attachment area seems to be a common trouble area in many instruments and certainly bowl back mandolins are not excepted. If the fingerboard had come loose and been re-glued slightly closer to the bridge could be a reason for the misalignment of the bridge ends. In short, the way to fix the intonation would be to remove the fingerboard and move it toward the headstock a small bit.

Lighter strings will help with intonation a bit as they are more flexible and require less compensation. Lighter strings are better for the structure too.

[Tavy]

10.5 to 40 strings are seriously heavy for a bowlback - normally recomended are the GHS ultra lights which are 9-32 - if you want the instrument to last any length of time a change of strings is definitely in order! You may find both intonation and action improves somewhat with lighter strings as well (less string pull distorting the neck forward).

[baumgrenze]

Thank you John and Michael for further input.

I ordered a set of GHS Ultra Lights this morning. I think I will wait with the bridge placement until they arrive.

I have a 'theoretical' question. Shouldn't the 12th fret contact point and the half wavelength or octave overtone node point coincide? If so, could I mark the contact point (this should not change with scale length) with a pen like a white Sakura Permapaque and then try to set the bridge so that the octave overtone node is in the same place? I envision using a dowel, pointed using a pencil sharpener, as the tool for finding the node.

Thanks again,

baumgrenze

[baumgrenze]

I should have searched before I asked. The question is addressed here:

http://www.co-bw.com/Audio_string_harmonics.htm

See the comments under "Complications with harmonic tuning" which bring up the stretching of the string when it is fretted (this varies with the fret placement, at least a little) through dirt on the strings from the player's fingers. "Cum grano salum" but the points are well taken.

baumgrenze

[Jim Baker]

I worked on a bowlback with a canted top and found a similar problem with bridge placement. In order to get near perfect intonation the bridge needed to be set back of the cant and on an angle. It didn't look right but played just fine and caused no problems otherwise. I strung it with light strings.