Bridge Lift: Common on Acoustics?

[redir]

Nice experiment there Wilcox. The biggest reason why the bridge lifts, aside from what John mentioned above that cheaper guitars glue to the finish, is the distortion that happens the top right under the bridge. Particularly if the X-Brace is loose under the bridge wings and or if the X-Brace is not under the bridge wings. That allows the top to distort, and bridge plate, so much that it breaks the bridge glue joint. A failing bridge plate can cause this too.

So in your experiment if you thinned that top or let it sit for many years you would see more lifting there I think.

[Otterhound]

Originally Posted by Peter Wilcox

Disclaimer - I am a hobbyist luthier and repairman. I'm sure there will be great disagreement with what I post, but as with many things in life you have your facts and I have mine.

Years ago I did a mockup of a guitar top and pinned bridge. Briefly, with the bridge sitting on the top (not glued), no pins, and the bridge slotted with the ball ends snugged against the bridge plate, the bridge pulled forward (toward the nut) a couple of mm, and the back lifted a mm or so. With pins in, which acted as stops to keep the bridge from sliding forward, the back lifted a mm or so. This again was without the bridge being glued down.



My take home lesson from this is if the strings are properly installed, with the ball ends snugged against an intact bridge plate, that even if the bridge to top glue joint is failing, the tail end of the bridge might lift a little, but it will never fail completely and probably won't progress significantly over time.

Do you still have this mockup ?
If you do I want to ask you to not use pins , place a piece of 1/8" Lexan under the bridge plate as the place to anchor the ball ends and place a stop at the front of the bridge to prevent forward motion and then post the result .
Oh yeah , one last thing , if you will . Thin the bridge down to about 1/8" in thickness where the strings emerge from it before the saddle .

[John Arnold]

If you do I want to ask you to not use pins , place a piece of 1/8" Lexan under the bridge plate as the place to anchor the ball ends and place a stop at the front of the bridge to prevent forward motion and then post the result.

Removing the pins and using Lexan under there will make no difference, since you have not changed anything of consequence.

[Larrydez]

Guys and Gals, I apologize for my ignorance about the term "bridge lift".
Thanks to all of you I now know it is the bridge itself actually lifting off the body. My bridge is solidly attached to the top. As I so poorly described in my inital post, I used an envelope perpendicular just below the bridge and noticed I was able to rock the envelope slightly East and West. Thinking that the envelope should not be rocking atr all, I figured the bridge was "lifting" the body ever so slightly. I had no idea that the body has a radius as well as the neck. My whole takeaway here is that in spite of vague, misinforming information, you reached out to me to try to help, and for that, I thank you. As I visit this site from here on out I'll have more questions than comments or answers, but to all of you, you have made me feel welcomed and I appreciate that!