Official Luthiers Forum!

Hi - I have a set of Brazilian which is slightly curved, I want to use the the other side for the outside of the back which is would effectively be the concave face if it were glued together.

Will prolonged storage under pressure flatten these curves out or if I glue it against the natural curvature cause any problems ?

See pic

I'm assuming the back will be radiused, right? I'd put that puppy in a radius dish as glue 'er up, myself. Doesn't look like much curve to me. The most critical thing is to be sure the RH is under control before bracing. This movement could be the result of a humidity shift. Still doesn't look major to me.

_________________
Wes McMillian
Santo, TX
http://www.wesmcmillian.com

In the past I've ironed pieces like this through a slightly damp hand towel.
This "steams" the wood which you can then clamp flat between two pieces of plywoood (1/2"+) and allow to dry.
Usually the bracing will stabilize pieces with a slight cup.

Hi Wes

Thanks for the reply, yes it will have radius, its just that the natural curve is is going the wrong way from the side I want to use for the outside. I would have to force it to radius the other way.

I assume you men RH = Humidity - I don't think it is much an issue over here in the UK.

Thanks

John

Hi David

Do you actually use a hot iron of is that just a term of phrase ?

Would you get it to final thickness first or do it before ?

John

John: I concur with Wes,if this is your biggest problem,you are laughing. Quite often plates will have a bit of cupping,especially backs.Mostly due to internal stresses causing the wood to move after being cut and during drying process.If well seasoned and at the right RH for gluing I don't think you will have any problem.Good Luck.
Tom.

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

Perhaps we need to start a new thread on the correct RH for gluing, I am not sure it is much of an issue in our European climate but I would be gald to listen to some advice?

JC

For glue-up i always keep the RH between 40 and 50%.I monitor it always when building the box.And find it easier to build in the winter here in Michigan.I build my electrics in the summer and my acoustics in the winter for RH reasons.It is easier for me to control that way.

John

Humidity can definitely be a problem over here in the UK. I had two guitar bodies sink badly last winter. Luckily Rod True from the OLF was on hand to give me some advice and I got these bodies back on track
Always check the humidity before glueing. I keep two hygrometers in my shop now and control the RH accordingly. Like Mark says, I always glue up between 40 - 50%. I also try to brace the top & back, voice, and glue up the body within the shortest timescale possible - say a weekend, all within this humidity range.

Mat

Thanks, a Hygrometer is the next item on my shopping list - can you recommend a model and source ?

John

I like the Abbeon and I believe a lot of others do too. Look around for a better price. I think I found one for about $145 or so. Sometimes used ones show up on ebay; they can always be sent back for repair/calibration. In fact if you get a used one you will want to get it recalibrated anyway.
https://www.abbeon.com/store/item.cfm?code=1565

_________________
Steve Smith
"Music is what feelings sound like"