Why ?

[Otterhound]

Is this bridge securely located and not even close to wanting to roll forward ?
Please note the use of the word roll .



Thank you .

[Brucebubs]

Sorry I can't answer that - I need to wash my eyes after looking at those pictures.

[Otterhound]

Originally Posted by Brucebubs

Sorry I can't answer that - I need to wash my eyes after looking at those pictures.

It is a simple test mule and was never considered to be a functional instrument .
Thanks anyway mate .

[Brucebubs]

Apologies, I didn't mean to offend - it just reminded me of an oversized Bo Diddley guitar.

[John Arnold]

Strings anchored underneath? If that is the case, the only force on the bridge is at the saddle, which is downward.

[David Eastwood]

Originally Posted by Otterhound

Is this bridge securely located and not even close to wanting to roll forward ?
Please note the use of the word roll .
Thank you .

Where’s the rolling moment? Maybe a little from the contact point of the string over the saddle, but the strings coming through the holes in the back of the bridge plate are what’s holding everything down. I think you could take the block of wood in front of the bridge away, and still nothing would move.

[Otterhound]

Originally Posted by Brucebubs

Apologies, I didn't mean to offend - it just reminded me of an oversized Bo Diddley guitar.

Yeah , I had thought that as well . Very oversized . I just couldn't bring myself to cut down a perfectly usable piece of 1 1/2" plywood for this .

[JCave]

Originally Posted by Otterhound

I just couldn't bring myself to cut down a perfectly usable piece of 1 1/2" plywood for this .

I also have more respect for plywood. But hey, add a pickup, plug it in and rock on

[Otterhound]

Originally Posted by JCave

I also have more respect for plywood. But hey, add a pickup, plug it in and rock on

It also serves as a spacer of my homemade GoBar deck . Not destined for a musical instrument , particularly when I have so much real wood available . You know , non plywood .

[John Arnold]

I think you could take the block of wood in front of the bridge away, and still nothing would move.

Depending on the friction coefficient, it might slide forward a little, because the force is not exactly perpendicular. The force vector bisects the angle that the strings make across the saddle. In other words, if the string break angle is 20 degrees, then the force vector is 10 degrees off vertical.
Essentially, what you have here is the same as the bridge and tailpiece arrangement on an archtop. The string tension is borne by the mostly rigid solid block of plywood, so the only force on the bridge is that generated by the bending of the string across the saddle.
Two rules of statics:
The sum of all forces on a system is zero.
The sum of all torque on a system is zero.

https://en.wikipedia.org/wiki/Statics

[Otterhound]

Originally Posted by John Arnold

Depending on the friction coefficient, it might slide forward a little, because the force is not exactly perpendicular. The force vector bisects the angle that the strings make across the saddle. In other words, if the string break angle is 20 degrees, then the force vector is 10 degrees off vertical.
Essentially, what you have here is the same as the bridge and tailpiece arrangement on an archtop. The string tension is borne by the mostly rigid solid block of plywood, so the only force on the bridge is that generated by the bending of the string across the saddle.
Two rules of statics:
The sum of all forces on a system is zero.
The sum of all torque on a system is zero.

https://en.wikipedia.org/wiki/Statics

So there is no force loading into the bridge assembly at the point where the strings emerge through the bridge after they leave the plywood .

[Rudy4]

Originally Posted by Otterhound

So there is no force loading into the bridge assembly at the point where the strings emerge through the bridge after they leave the plywood .

Yes, there is, but not enough to overcome the inherent strength of the plywood. Do the same experiment on a piece of 1/8" plywood and you'll see the results of the force vectors.

[redir]

As a geologist I had to take some engineering courses at the Uni and this stuff always amazed me. If anything it taught me that your intuition is your own worst enemy.

[Otterhound]

Originally Posted by Rudy4

Yes, there is, but not enough to overcome the inherent strength of the plywood. Do the same experiment on a piece of 1/8" plywood and you'll see the results of the force vectors.

Am I permitted to add bracing to the plywood ?

[John Arnold]

So there is no force loading into the bridge assembly at the point where the strings emerge through the bridge after they leave the plywood

Force is a vector. It has amplitude and direction. The force on the bridge assembly where the strings exit is downward. Just like my example of the force on the saddles, the force at that location is at an angle bisecting the angle the string makes.
If you were to attach the strings to the back of the bridge, then you have a different situation. You would have a force pulling up on the bridge, causing it to lift from the back edge. Right now, the upward force is borne by the thick plywood.
Like so many of these situations, a simple diagram of the forces would surely help.