Acoustic Guitar Construction

Hi guys,

I think I need some support. My last built suffered the damp of the Québec's summer quite a bit. I built it in wintertime while my house is heaten with a wood stove and now the summer is very humid. The contrast is drastic and the guitar's top has swollen which caused the string action to be stupidly high (0.17 at 12th fret for both treble and bass). Adjusting the truss rod didn't help so I think my last course of action is to lower the saddle.

But first I want to make sure I measure the action correctly. I looked at different sources and some people put a capo at the first fret and others put a pick underneath it... I don't get that and I'm confused. Can anyone enlighten me please?

Hee Geo,

When checking the action, I put my left index finger on the first fret and my right hand pinky on the 14th.
Then I check with my right hand index finger the space below the 7th fret. A tiny space is ok.
I check by eye, but my guess is around 0.004-0.008".
Humidity is a thing. I once made a top at 60%. When the humidity dropped, it completely imploded. And discarted

Herman wrote: ↑Sun Jul 28, 2024 9:52 am Hee Geo,

When checking the action, I put my left index finger on the first fret and my right hand pinky on the 14th.
Then I check with my right hand index finger the space below the 7th fret. A tiny space is ok.
I check by eye, but my guess is around 0.004-0.008".
Humidity is a thing. I once made a top at 60%. When the humidity dropped, it completely imploded. And discarted

Herman you are accurately describing relief not action. Geo part of the confusion is that a truss should only be used for relief (slight forward bow of the neck) not action. It is true that too much relief could raise the action but with humidity the issue is with the body of the guitar not the neck. One should set relief as Herman describes before setting the action.

Action is the height of an open string over a fret (usually measured at the 12th) So no need for a capo at the first fret or a pick. You can figure out how much you need to lower the saddle by subtracting the action you want from the action you have and multiplying the result by 2. For example if you want .1" on the bass side:
(.17" - .1") x 2 = .14" a little over 3.5 mm.

Thanks for your quick and relevant replies!

@John, I did this calculation and it ends up that the saddle height should be flush with the bridge on the treble side. I guess I'm gonna have to live with higher action. How much can I lower the saddle in relation to the bridge? Also, is it a good idea to keep this saddle as it is and make another one so I have one for winter and one for summer?

Ya John, My bad. As a foreigner I always have to switch. Thanks for correcting this one.
Herman

Geo, I often make a new saddle. If I am doing a setup for someone else's guitar I always make a new saddle. You can get pretty close to the bridge as long as you are getting a clean break on the saddle. The bridge pin slots are more important with a low saddle to get a break on the saddle.