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Back material slightly curved
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=23890		 Page 1 of 1
Author:  segovia [ Wed Sep 23, 2009 7:54 am ]
Post subject:  Back material slightly curved
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
Author:  Wes McMillian [ Wed Sep 23, 2009 8:36 am ]
Post subject:  Re: Back material slightly curved
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.
Author:  David LaPlante [ Wed Sep 23, 2009 8:41 am ]
Post subject:  Re: Back material slightly curved
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.
Author:  segovia [ Wed Sep 23, 2009 9:00 am ]
Post subject:  Re: Back material slightly curved
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
Author:  segovia [ Wed Sep 23, 2009 9:04 am ]
Post subject:  Re: Back material slightly curved
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
Author:  Tom West [ Wed Sep 23, 2009 9:36 am ]
Post subject:  Re: Back material slightly curved
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.
Author:  segovia [ Wed Sep 23, 2009 10:17 am ]
Post subject:  Re: Back material slightly curved
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
Author:  Mark Groza [ Wed Sep 23, 2009 10:41 am ]
Post subject:  Re: Back material slightly curved
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.
Author:  Matthew Jenkins [ Wed Sep 23, 2009 11:47 am ]
Post subject:  Re: Back material slightly curved
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 [:Y:]
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
Author:  segovia [ Wed Sep 23, 2009 1:06 pm ]
Post subject:  Re: Back material slightly curved
Thanks, a Hygrometer is the next item on my shopping list - can you recommend a model and source ?

John
Author:  SteveSmith [ Thu Sep 24, 2009 4:02 pm ]
Post subject:  Re: Back material slightly curved
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
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