Official Luthiers Forum!

How do you feel about it?

My thinking is that theoretically, since there is no cross grain structure glued on, it should be ok.

Right now, my jointing room is at 48%, my glue up room at 42%. I'm thinking I can just go ahead and not worry about cluttering to glue room floor with the clamping racks, and that joining a few panels at 48% should be harmless...

I'd say you're fine to join panels at the higher RH, but the bigger danger is gluing braces at the higher RH. Locking in the dimensions of the wood by gluing down bracing at Higher RH can cause problems when it tries to shrink down under dryer conditions.

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Chris Alvarado
www.ChrisAlvaradoLive.com
www.Driftwood-Guitars.com

I think you're fine

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Jim Watts
http://jameswattsguitars.com

Ed: In general I think you will be OK...........but a while back I glued EIR panels that had a slightly curved grain pattern. It was coming together at either end of the glued panels. The panel was thinned and put away for building in the winter when RH dropped. When the build started the back had a slight propeller twist to it. You could flip it back and forth with the twist one way and then the other and was very reluctant to stay flat. What to do.......? I thought about taking it apart and relieving the stress but figured during the large RH swings on the East coast it would be in the panel at a fair portion of the year no matter what I did. So I braced it ,installed it and it has been OK for about a year and a half. And I'm keeping my fingers crossed. Not sure it proves anything but certain grain figures may give a problem. But my sense is that straight grain will not be a problem.
Tom

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A person who has never made a mistake has never made anything!!!

Yep, that's my thought as well. Straight grain is totally fine, but curved grain is questionable. Assuming the plate is reasonably thin, the braces should generally be able to hold a squirrely back in shape.

Another potential problem is the growth ring angle. If the rings at the joining edge change rapidly from flatsawn to quartersawn (usually near the center of the tree), the edge of the piece will curl outward in one or the other extreme and peel the joint open. I have two that do it, and with the center reinforcement it really doesn't cause any problem other than visual, but it would be better to inlay a center strip at half thickness to reinforce the joint (and remove some of the wood that's causing the problem in the first place).

Also, 48% is definitely not enough to start worrying about minor things like this. Just no cross grain gluing like rosettes/braces/bridges...

once upon a time the target humidity range for gluing was 45- 50 % R.H. Has this changed?

I wouldn't hesitate to join the plates, either. The thing our beginning lurkers must remember (so I'll say it again) is that it is not safe to do cross grain glue ups in periods of higher humidity. All that said, 48% RH does not strike me as a high relative humidity. It is, of course, higher than 42%.

Glue the panels together in either room. Then move the plates to the lower RH before adding braces.

I shall proceed with the procedure!

Yes Bye! Sher my humidity goes up and down that much when I open and
close the door. Glue on.
Ken