Official Luthiers Forum!

Hi Everyone,

I figure this is a relatively simple fix, but wanted to make sure I got it right. My top currently has x-brace, UTB's, and Bridgeplate glued on. It is a true flat top. It was braced so far at 44% humidity.

Got home from short vacation and was surprised to see the humidity at 32% and the lower bout between the x-braces legs sunken. So, the top has sunk inwards a good bit. I got the humidity back up in the 40%'s. Now what? Should I flatten it at as well somehow?

Thanks for the advice.
Peter

You might want to put it in the go-bar deck with the higher humidity for a few days then recheck it. It should go back where it was. Then contunue finishing the braces.

Thanks, Mark. So you are saying to put the bars back on it to clamp it down for a few days?

Peter

Happened to me too a couple times. It fixed itself but after a long while. It takes hours to sink, but days or even weeks to return to the initial shape. Once it did not and i shaved the braces and started over. That prompted me to try and brace my following tops at 40% rather than 45.

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Build log

Another example of why it's important to glue up the finished plates to the sides as soon as the voicing is completed. And for whatever reason to not do this, keeping it forced into it's proper radius in your gobar deck until you're ready to glue is the next best practice. Even at 45%, the top and back plates are trying to return to their original flat condition. Gluing them up permanently imprisons them into their new curved condition...until someone decides to store the guitar at extreme conditions.

When I'm working on a top or back, it is always gobar restrained while I complete the brace carving. I only remove the restraint when I'm tapping. Within hours of its completion, I glue it to the side. It's just become a habit begun years ago at the nudging from Mario. I rarely if ever ignore such nudges!

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JJ
Napa, CA
http://www.DonohueGuitars.com

Thanks JJ and Alexandru.

I've got it back in the go bar deck. Hope it straightens back out.

Peter

I disagree - there is no need to hurry and attach a top or back to the rim IF.... you do what it takes to maintain a stable humidity at all times in your shops.... If you don't maintain stable humidity in your shops it is indeed a good idea to glue plates at once.

Many builders including some factories who in all cases maintain a stable humidity will not attach tops at once. In some cases tops are left hanging for many months with no ill effects. Again the caveat here is that stable RH is constantly maintained. I just attached a top last week that had been sitting around unsupported, not clamped for a month. No problem.

Examples of companies that do not attach tops at once are Collings, Huss and Dalton, and when I toured Martin some years ago tops were not attached at once there either.

If you check the archives this myth has been perpetuated for years here on the OLF and Mario did comment that he does not see it mattering provided that constant RH is maintained.

If you don't do what ever it takes for your situation to have a stable RH at all times it will bite you OR worse.... your customers sooner or later.

Most immediate variation is more from the moisture of the glue influencing the top. This can take 24 to 72 hours in most cases to stabilize. The glue will ad moisture to the back and this can make the top appear cupped. I do tend to let in the disk over night . They come back once the moisture balances off .
this is a good testament to RH control in the shop. I like to glue up tops and back at 40% . If you can't control your shop's RH glue on the dry side . I have used tops that were glued up months ahead of time and not had any issues. I did learn early in my building the importance of when to and not to glue up braces.

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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

John,

I think that might be it. I glued up the bridge-plate last and used too much water in cleaning up glue squeeze out. That was last Tuesday. I saw the top deformation when I got back Saturday. According to what you are saying I would not have seen it before I left as that was only about 16 hours after glue-up of the bridge plate.

I assumed it was a dry top of the top, but I think it might have been a wet under side of the top. I have it clamped in the go bar deck now. Hopefully it dries out flat. In the mean time I will work on the rims - to get them ready.

Thanks!
Peter