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Nice explanation, Darryl.

What I'm curious about is how this effects the load (deflection) on the top. There is a pivot point where the saddle meets the bridge and the moment arm extends some distance forward and back from there (from an engineering standpoint, I'm guessing that is considered the same arm, not 2 arms?) If you make the bridge wider in either direction, you increase the length of the arm and, like with the cheater bar, reduce the force required to resist the torque. (and since this is already complicated enough, let's assume the bridge is perfectly rigid)

So how do you express the effect of that change on the top? The ft/lbs of torque has not changed but it's effect on the top has because less force is required to resist the torque.

And how is the load distributed to the top when the pivot point is not in the middle of the moment arm? If the bridge stayed the same width but you moved the saddle further back, I assume the top will show greater upward deflection and less downward deflection?

Whew...

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http://www.chassonguitars.com

I find this topic very interesting. Todd Stock and Alan Cartuth are on the money. In building guitars , the stresses must be understood. What surprises me is how many use opinion to decide what to do. I believe that an investment into a few books , one is the machinist's handbook , this is a great tool. In it you can learn about loads and forces and how they apply to what you are doing.
The pocket ref book is also a useful tool . Keep a building log and see what happens over time. Nothing can be more frustrating over time than thinking you are doing it right , when you are actually doing things wrong.
We don't know what we don't know . till we know it. Thanks Alan and Todd for sharing information
john

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I might be expounding on the blatantly obvious here. It wouldn't be the first time.

I think one of the keys here is that the gross forces on either the "front" or the" back" of the bridge are essentially the same. That is, the compressive force on the front must equal the peeling force on the back or you'll have motion. We can't reduce these forces by changing bridge dimensions. What we can change though is the load per unit area, or how large of an area those loads are distributed over (poor writing, I know). From this model we could intuit that a larger glue area can be more effective by spreading the forces involved over a larger area, not by reducing them.

The reverse belly could reduce the per unit of area load on the back of the bridge, but I think it's an inefficient way to do that. Seems it would make more sense to add area at the back, reducing the per area force. Maybe there were some tonal issues taken into consideration when belly bridges were developed, adding mass for bass and sustain?

Much of the construction of stringed instruments— speaking here with respect to resisting string force—seems to have been based on the premise that they have a rigid structure, which of course is not true. Many schemes for keeping bridges in place would work much better if this were true. In the case of the reverse belly, we more often see failures on the bridge, cracking where the saddle pushes down. On the "normal" belly, we see the failure at the back, with the bridge being pulled up by the string ends, causing top/bridge plate to peel away from the bridge. I think this particular problem is addressed quite elegantly by the Yairi design.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

Kent and Pat, your explanations are more intuitive than mine, thanks. Kent, I think you have a good point that we are using static analysis to analyze dynamic circumstances. While I was typing my response I realized the moment arm probably isn't constant when the string is stuck. When the front of the bridge rotates down, I'm guessing you are correct that the center of rotation changes. I would guess (please don't take this as fact) that the center of rotation moves more toward the front of the bridge the further the bridge rotates forward. It's probably all a compromise, the larger bridge creates more glue surface area (which lowers the loading on the glue) and the tradeoff is a large, stiff brace in the center of the guitar and it's affect on the sound (good or bad).

I'm not familiar with the Yari design.......could somebody post pictures?

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Formerly known as Adaboy.......

Todd, do you hate to see this bridge?

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Darryl,

See Michael's post near the top of the thread. The pin block if you will has a flange that sits under the top. The block is installed from inside, and pokes up through the top, sort of like an elongated T-nut with six holes.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

Elegant though the Yairi bridge might look, cutting that big a hole in the top in a key sound transmission area to stick a lump of ebony through probably wouldn't be my choice.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Hmmmmm.......You've got a point there, Dave.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

Gotcha, Todd. Thanks for your feedback.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

I think what John was saying about keeping a log is a great way to improve building in the future.Maby that's what Gibson has done to Justify useing the backwards bridge.They have been doing it for fourty some years and still do.So there must be a good reason why they still reverse the bridges on some of they're guitars.They have done it on alot of different models in the last fourty years.But why? Even some of the epiphone guitars built in kallamazoo back in the sixties had backward bridges as well.They must know something learned over time to be still doing it.But why? I have noticed that alot of lg & j models had them reversed mostly.I know they are still doing it on the j-185 guitars today.But Why?

I bet a pair of wool mittens that the reason they do it backwards, is so it looks different from other bridges and identify the instrument as a Gibson. No other reason.

I think if that was the case,it would be done on all gibsons.It has to be something else. Maby type of tone produced. They seem to be done on the same kind of models.I think it's ugly,but maby i'm just use to the regular way.I have also noticed that the grain on most run towards the end block on them.Seems they are using the same blanks that would be used the regular way.They don't seem to have much concern for grain orientation on them.