Bridge Bolts/Screws

Edgar Poe · #1 07-18-2018, 11:52 AM

I have read many times that it is not good to bolt or screw the bridge to the soundboard.
I'm sure the experts have logical reasons for not doing that.
However, If the bridge is solidly glued to the soundboard, and you add two bolts, one at each end of the bridge, how does this effect anything if in fact the bridge is securely glued to the soundboard. It woulds seem to me all you are doing is preventing the bridge from lifting in the future, I see no reason that the screws or bolts would effect performance. It not that much added weight. I would think a very minimal effect if any. About along the lines of changing bridge pins to heavier ones.
Someone please explain that to me.
I added these small bolts to my Harmony H1260, and one online H1260 expert says it's a bad idea. I just don't see why ?

Ed

Tico · #2 07-18-2018, 11:58 AM

Maybe the small weight does matter.
Maybe the higher density of the metal, compared to that of the wood, affects how the bridge can vibrate.
Maybe the exact location of that weight is also matters.

I'm no luthier, but I respect it as a complex field so I'm looking forward to answers from the experts.

JonWint · #3 07-18-2018, 12:09 PM

If bridge lifts in the future, reglue it.

Such modifications degrade instrument originality and usually reduce value.

OTOH, it's yours, do what you want.

Judson · #4 07-18-2018, 01:49 PM

Good idea or not ... certainly up for debate ... but hasn't Gibson used two bolts to help hold the glued bridges to their acoustics on many occasions over the years?

tomiv9 · #5 07-18-2018, 02:02 PM

Not trying to be harsh, but these are the reasons I have for not putting bolts on a guitar:

1. It doesn't look good aesthetically
2. It makes the guitar look poorly made/cheap
3. Probably devalues the instrument if reselling
4. Probably voids any warranty
5. Adds weight, could affect sound
6. Not easily reversible
7. Doesn't really add any benefit - a well glued bridge should last a very, very long time. If the bridge does start to lift, reglueing is a pretty easy fix.

Truckjohn · #6 07-18-2018, 05:09 PM

The weight of bridge bolts acts like a "low pass" filter... And it accentuates bass...

Why is this important? Well - heavily built factory guitars tend to be quite stiff and very very bright/trebley.... And the extra weight on the bridge brings out some bass without the warranty concerns with a more lightly built instrument.

That's why you see two big heavy 2 1/2" long #12 machine screws with 1/2" thick brass nuts on them when they could use 1" #8 screws with a washer and an itty bitty nut and save well over half the weight... Reducing the weight is not the point though....

While bridge bolts can be looked at as a bit of extra insurance - they really aren't a big insurance policy. Most every luthier has seen guitars with bolts pulled completely thru the top - a royal mess...

RRuskin · #7 07-18-2018, 06:51 PM

Quote:

Originally Posted by Judson

Good idea or not ... certainly up for debate ... but hasn't Gibson used two bolts to help hold the glued bridges to their acoustics on many occasions over the years?

You run the risk of cracks radiating from the bolts when the glue starts to let go. I've seen this quite often on Gibsons.

M Hayden · #8 07-18-2018, 07:21 PM

Let alone all the other reasons why bolts are a bad idea, the washers beneath the bolts on the bottom of the soundboard can seldom be large enough to distribute the torque load so that the spruce doesn't deform, causing further damage that is difficult to remediate.

TBman · #9 07-18-2018, 07:41 PM

Bolts don't have to be made from metal.

AZLiberty · #10 07-18-2018, 07:44 PM

Rainsong bolts and epoxies their bridges to the soundboard.

the 12-strings have five bolts, the 6's only three.

Edgar Poe · #11 07-19-2018, 11:51 AM

Quote:

Originally Posted by M Hayden

Let alone all the other reasons why bolts are a bad idea, the washers beneath the bolts on the bottom of the soundboard can seldom be large enough to distribute the torque load so that the spruce doesn't deform, causing further damage that is difficult to remediate.

Every guitar I've looked into, has a rather hefty Bridge block behind the soundboard to support the stress of the bridge.

Ed

Edgar Poe · #12 07-19-2018, 11:56 AM

Quote:

Originally Posted by RRuskin

You run the risk of cracks radiating from the bolts when the glue starts to let go. I've seen this quite often on Gibsons.

Like I mentioned to M Hayden The bridge itself and the internal bridge block sandwiches the soundboard quite well between the two. Plus the glue, and the added screws, would make that assembly pretty much a single unit, I highly doubt the bolts are going to cause any distortion.

JMHO

Ed

Edgar Poe · #13 07-19-2018, 12:00 PM

[QUOTE=Truckjohn;5786995

While bridge bolts can be looked at as a bit of extra insurance - they really aren't a big insurance policy. Most every luthier has seen guitars with bolts pulled completely thru the top - a royal mess...[/QUOTE]

Like explained above,
I would like to see a photo where this actually happened, I find it extremely hard to believe that the bolts pulled through, BEFORE the entire soundboard area AROUND the Bridge would not break out. Unless you are talking about bolts used in another area, and not at the bridge, I can't see it. You have the Bridge backing block, the soundboard, the bridge, all glued together, plus the added bolts, I just can't see that failing before the soundboard itself gave way around the bridge and it's supporting block. IF it does happen someone please post a photo.

Ed

stringjunky · #14 07-19-2018, 12:35 PM

Quote:

Originally Posted by Edgar Poe

Like explained above,
I would like to see a photo where this actually happened, I find it extremely hard to believe that the bolts pulled through, BEFORE the entire soundboard area AROUND the Bridge would not break out. Unless you are talking about bolts used in another area, and not at the bridge, I can't see it. You have the Bridge backing block, the soundboard, the bridge, all glued together, plus the added bolts, I just can't see that failing before the soundboard itself gave way around the bridge and it's supporting block. IF it does happen someone please post a photo.

Ed

If the bridge glue separates, even with bolts in, the guitar's probably going to sound not very good from loss of uniform contact. I think the bolts function is superfluous, besides adding mass. It's a solution looking for a problem really because it's pretty rare for bridges to come flying off and if it does come away, you've got the bolts to undo as well as reglue the bridge and then put them back on.

Alan Carruth · #15 07-19-2018, 07:53 PM

Bridges and tops are made of wood, which has a certain amount of 'give', and also tends to 'cold creep'. That is, wood under stress deforms permanently over time, even when the stress is not large enough to cause a short term failure. Bolts don't work like that. The material has a much higher Yong's modulus, and so deforms much less under a given load, and it doesn't cold creep.

So, over time the bridge, top, and bridge plate, all start to move, but the bolts stay the same. More and more of the load gets transferred to the bolts, which makes the rate of creep around them higher. Eventually the bridge starts to peel up, the top gets very highly distroted in the area around the bolts, and, given enough time and neglect, they do pull through. As Truckjohn says, everybody who has done more than a little repair has seen this one. I never took any pictures, though.

Any time you use hardware in a wooden structure you're asking for trouble unless your detail design is really good. And even then... Just ask the FAA.