Replies to This Discussion

Permalink Reply by Ron "Oily" Sprague on April 30, 2014 at 4:39pm

Tension on each string runs anywhere from 16-25 ft lbs. Bridge pins hold ball end strings in by friction. Think this way: if they work successfully on commercial gits, which are thinner and lighter than many cigar boxes, and also often have 200+ ft-lbs pulling on them, why wouldn't they work on a CBG, with much less tension? You'll be fine using em.

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Permalink Reply by J Lee on April 30, 2014 at 4:53pm

Thanks Ron...I had no idea about those stats!

Merbau and bridge pins it is on the next build......

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Permalink Reply by ChickenboneJohn on April 30, 2014 at 6:49pm

Err.... Ron, not meaning to be pedantic (but I am being pedantic, I know..) but Foot Pounds (or Newton metres in SI) is a measurement of torque or turning moment. Tension on a string is usually given in lbs or kg. Technically speaking thats a pound or kg force - the equivalent of that mass acting under normal gravity..that's really far more theory than anyone needs to know when making a guitar.

It's easier just to imagine a string with a 20lb weight hung on it to get some sense of the actual force involved, so a 3 string neck (and also the bridge) will be resisting 45-60lbs of tensile load....hardly minimal, thats why pin bridges sometimes either distort the guitar top or pull away from it if badly glued.

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Permalink Reply by robert jones on May 1, 2014 at 1:15am

You may want to adjust this particular post for accuracy.

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Permalink Reply by Ron "Oily" Sprague on May 1, 2014 at 7:49am

Sorry, was watching an old episode of Top Gear when I wrote that. They were talking about engine torque. Didn't intend to torque everyone off. Pounds of tension is correct. Reason I brought it up is, you seemed to think there was minimal tension for a three-banger. Not true, exactly - depends on scale length, string material, and string diameter. But it is less than a 6-string git. If you want to use a fixed bridge with bridge pins, there's no one and nothing stopping you, least of all me. The other comments show that doing so could be tricky. But it is not impossible. I encourage you to try, and learn in the process. Have I done it on a CBG? Nope. But I have repaired several old acoustics whose bridges delaminated, due to bad glue joints, and too heavy strings applied to poorly braced tops.

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Permalink Reply by J Lee on May 1, 2014 at 10:54am

Hmmm...food for thought. Thanks again Ron.

I'll let you get back to your Top Gear now...enjoy

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Permalink Reply by robert jones on May 2, 2014 at 1:03am

Force on a pinned bridge guitar top is rotational at the bridge due to the 90 deg. turn made by the strings so Newtons, foot pounds, or "s**t that's really bending the top" are all equally accurate means of measuring the affects of string tension on the CBG top.

(Newtons or foot pounds being simply quantified units of force measurement not force vector.)

Anyway, J Lee,  build a pinned bridge if that's what suits you just plan a little going in and you'll be fine. If the worst happens and the top bellies too much you can revert to a tailpiece and floating bridge design.

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Permalink Reply by The Phrygian Kid on April 30, 2014 at 8:23pm

In my opinion it adds fair bit of complexity compared to a tailpiece and compression type bridge.  It (a martin style pin bridge) exerts pressure on the soundboard in an entirely different way.  I do not recommend it for beginners although I'm certainly not saying it can't be done.  It is also much more difficult to make adjustments to in any dimension (intonating or for string height, action, to defeat fret buzzes etc.)  Anyone who's done repairs for a while knows the pin bridge is a flat top guitar's archives heel.

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Permalink Reply by J Lee on May 1, 2014 at 10:55am

Thanks Phrygian Kid

Seems the last few comments are all suggesting it might just be more trouble than it's worth. Thanks for the heads up.

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Permalink Reply by David McQueen on May 1, 2014 at 1:49am

A standard style acoustic guitar bridge is a precision operation. Typical set up starts with a finished ( laquered) guitar and measuring and marking exactly where the bridge assembly goes. Then, carefully scrape off the finish at that location. The bridge assembly is then glued down to the board using special clamps that reach inside the guitar and miss the internal bracing. So, if the bridge is too close, or too far or not dead square with the rest of the guitar or the glue joint is not perfect, or there is insufficient bracing, the guitar fails.

As for the loads, there are string charts for string tension for 25" scale necks. Roughly, light electric 6 string runs at about 102 lbs. ( d'Angelo lights. I remember that one.) Light acoustic is about 150 lbs. A twelve string rings in at about 240 lb. tension. So your 3 string will come in at 50 to 60 lb. depending on what strings you use.

That is why, when I see those guits with the glued down bridge, I have more than a fair amount of admiration for the builder.

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Permalink Reply by J Lee on May 1, 2014 at 10:56am

Thanks David

Think I might give it a miss after all....was just a thought.

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Permalink Reply by Wichita Sam on May 2, 2014 at 2:01pm

David, I've done 25-30 acoustic style bridges with pins, with only a single fail.  Surface prep and good glue  and ample drying time is the key.  Almost doubles build time on a simple CBG.

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