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Hi All,

Just wondering your thoughts on joining tops/backs on humid days. It's about 70% humidity today and climbing (gonna rain this afternoon).

I was just wondering about any "Do's and Don'ts" with regards to joining tops on very humid (or for that matter very dry) days.

I ask because I had my first exposure to humidity related changes with a top and back that I jointed about 2 weeks ago, but didn't join. After jointing them, I went out of town and left the top and back on workbench in the garage (instead of inside the house where they would be less affected by the climate). We had a couple of very hot, very dry days while we were away and when I got back the joints were all over the place. Both the top and back had to be re-jointed......I assume because of shrinkage due to loss of moisture.

If I would have let them re-acclimate as the weather cooled and got more humid do you think they would have come back to their original form?

Anyway, now I've got a couple of tops that I jointed this morning and I'd like to join today, but want to make sure I'm not making a mistake by doing so on a humid day.

I'd appreciate any advice you all can offer.

Thanks,

Erik

A bad idea IMO. Quite the job to close a center seem on a finished guitar.

Glueing top or back halves together in less than ideal RH is not a problem with quartersawn wood.
It is only when you lock in the width by installing bracing that you need to worry.

That actually makes a lot of sense.

Thanks Filippo, intuitively I figured that I'd want to do the work in a more consistent Humidity environment, but was "hoping" it would be ok to join these today.

It is an interesting point that Jeff brings up though too. I guess once they are joined there's not much problem with a little shrinking/swelling until the point at which I brace them up.

So it would seem that the key here is to glue up your braces in a stable 35-45% RH environment (and ensure your top/bracewood are both well acclimated to this environment).

Other thoughts?

Erik

I'm with Jeff, just joining (not bracing or gluing to the rim) should be okay. More importantly, why would you joint them, if you don't intend to glue them immediately? In my opinion, you should glue as soon as possible after the joint is planed. Along with movement, waiting too long will cause the jointed surface to oxidize and compromise the joint strength. There is not a lot of gluing surface in a thicknessed top, so you don't want to take chances with a bad joint.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I would glue either the top or back on the ribs at least 1 day after bracing, when you are radiusing your backs and tops to make sure your lateral and longtitudanal curves match, that will give the wood a chance to settle in to it/s new shaped position.. Leaving braces on indefinitely , with swings of varying humidity, can leave your top or back looking like a bent pretzel especially with wildly fluctuating humidity 35% winter 70% summer here in KC.

It also gets pretty humid here in Chicago in the summer. I built a small 3’x4’ closet in one corner or my basement shop. Pretty simple – wood stud framing, drywall on both sides, batt insulation in the stud cavities, Home Depot wood door and frame. Plenty of room for shelves for storing dimensional wood, fretboards, etc. and plenty of room in the lower half of the closet to sticker wood sets. I keep a single 60w bulb on in there 24/7 in the summer and the interior closet RH level never varies outside of 45% to 50% even on the most humid days. I keep my in-progress work in there and take it out only when I’m working on it. A good simple solution to humidity control.

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Doug Mills
Chicago, Illinois

i join my plates, install rosettes, back strips etc then store. they sometimes go through an entire season of humidity changes. sometimes the outside edges curl a bit but bracing shakes that out.

I do strive to brace the plates and assemble the body in three days or less, usually on mild days, but i keep my shop in the 50-60 range consistently, or rather my shop keeps itself there.

i see no problem with it

b

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brendan 3.0 new and improved, with better interpersonal subroutines

Yes
I would, guitars shipped to SoCal, or worse, NM, Arizona and so on, may do funny things.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

good point. however i don't ship any guitars. at least not yet

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brendan 3.0 new and improved, with better interpersonal subroutines

Okay, I know I'm going to touch off a hornet's nest of reaction here, but I see no problem with gluing up a center joint on a top or back in any relative humidity. It's long grain to long grain, and furthermore, it's usually from book-matched pieces. The joint itself will be okay. But you can't do ANYTHING in the way of cross grain gluing, including bracing, when everything including your top and back plates are humid. The real problem here is what happens to the rest of the plate. If you glue on braces when it's humid, you are begging for a crack when things dry out. If you DON'T glue on bracing, and if you leave the plate on a bench top, you are begging it to warp into a "potato chip". So....if you're going to do this, go ahead and join the top or back pieces and then sticker them under weight, and wait for things to dry out before you do anything at all that requires a cross grain glue up. You should be okay. Remember that lots of fine guitars (and fabulous Italian violins, cellos, etc., too) were made when humidity control was nothing more than a dream--but those guys DID know the difference between long grain to long grain, versus long grain to cross grain. John D'Angelico had to work on humid days. So did Antonio Stradivari. So did Guarneri. So did Amati. As far as I know, none of these guys had a de-humidifier in his shop. They built some of the most fabulous instruments the world has ever seen or heard. See what I'm saying? Avoid cross grain glue ups on humid days, and you will be okay.

And now for the hornet-like reactions.....

I would say you have another thing to think about. That is you should glue up your top or back right after you joint it. You want freshly jointed surfaces for glue up. Not a good idea to let them sit. Wood will oxidize, oily wood will seep oil, and you will lose joint integrity. Glue up right after jointing the edges.

As far as the other thing I agree with cphanna.

Link

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Cut to size.....Beat to fit.....Paint to match.

Hi All,

Thanks for all the replies. I ended up deciding to wait for a dry to day to re-joint the tops (since as others have pointed out they will have oxidized) and glue them. I do appreciate what CPhanna and others have said about gluing tops on humid days, but waiting to glue cross braces, etc on dry days.

If I ever "have" to get some plates glued up on a humid day, I don't think I'd be afraid to do so if I keep the plates stickered under weight until things dry out.

Erik

Agree in principal, except that it's a lot easier to flatten two potato-chipped unjoined plates than a single potato chipped joined top or back. But yes, the joint itself is not doing anything bad.

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Jim Kirby
kirby@udel.edu

Point taken about D'Angelico and others who have made instruments through the ages with reasonable results. However, it is hard to compare guitar to violin family instruments. Violins have no cross grain bracing to deal with, only the bass bar which is roughly parallel to the top's grain direction. Seems kind of apples and oranges in that sense.

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Chuck Kish

Point taken about D'Angelico and others who have made instruments through the ages with reasonable results. However, it is hard to compare guitar to violin family instruments. Violins have no cross grain bracing to deal with, only the bass bar which is roughly parallel to the top's grain direction. Seems kind of apples and oranges in that sense.

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Chuck Kish