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I have a top that was braced at a 28' radius back in February and I haven't gotten around to closing up the box yet due to my kids activities. I went in my shop today to check on things and noticed that the top (and back also) were at a tighter radius that it was braced at. Is this an issue? The humidity when it was braced was low 30's/upper 20's. My shop is currently running around 50%. I could turn on the dehumidifier but I am afraid it would curl even more. Am I ok or what should I do?

Thanks,
Scott

Higher humidity will tighten the radius as you are observing. Go ahead and reduce it to what you braced it at, and it will probably conform to its previous shape. The higher humidity increases the width of the top (cross grain) more than the length of the braces (along the grain). This forces more of a bow into the top.
Mike

Perfectly normal, nothing to worry about. Many people brace too wet and then have it turn inside out, but this is a sign that you braced at a good level so that won't happen.

Ideally it should be dried until it gets back to its original radius before you glue it onto the rim, but most likely it would be fine if you just force it in its current condition.

Yep - agree. This is a better situation that bracing when wet and then having it turn flat, or inside out, when it dries. It is amazing how a fluctuation of +/- 20% in RH can affect a thin plate of wood, glued to a few more bits of wood. But we all learn this lesson the hard way. You will probably be OK to use it now, but if you can get the RH down to the same as when you braced it you will have an easier time of the next steps. Will your dehumidifier get it that low (mine can't), or was it central heating in the winter that made it so dry?

An important question is what conditions this instrument is likely to experience during its lifetime. If you close the box now at RH 50% - then the guitar lives in your house and dries out to 20% with the furnace on in winter - it might be a problem. OTOH, here in Sydney we rarely go below RH 50% at any time so I have little need to get it lower than that when building. But there are plenty of times when I find it hard to work because the RH is constantly >80.

Thanks guys! I feel better now. I am traveling for work this week so i'll fire up the dehumidifier while I'm gone and and let them dry out.

As far as winter goes, I normally run my humidiefier but didn't this winter when I was bracing the top and back. I also use Humidipaks in my guitars in the winter and keep them in their case when not being played.

Scott

One of the first things I learned is build your rims first so the top and back can be attached forthright. My second guitar top tuned into a potato chip by the time I got around to making the rims.


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