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Hello all, can you please help?
I'm making a acoustic guitar for a friend from a stewmac kit, Now I got the ribs glued on the back and the sound board, all going well looking good, didn't get the chance to go and work on them for a couple of weeks but last week went the do some work and the top is flat (as in not curved) and the lower part of the back is bending the wrong way as in convexed, it has been hot around 85-90 with a high humidity but my workshop is still the coolest place to be in(concrete floor ect) am I totaly stuffed or can these be saved with out planing off the ribs and starting again. I did wet and clamp the back in the one curved brace I got but is sprung back with in a couple of days, I haven't got a radius dish or the like to try to re bend them.
any help please as these are for a realy great bloke who goes out of of his way to help anybody and this was a small way to say thanks.
many thanks
HeathHeath38903.7413194444

Heath,

1st, don't panic, it will not help.

I put together the Stew-Mac kit also, so I do understand what you are working with. Did you radius, or put a dome in the back or top by radiusing the braces and using a curved piece to clamp them with? If you did, and the dome has collapsed, the humidity must have dropped significantly and the top and back have shrunk. So, you need to humidify them asap. Do you know what the humidity was when you braced the top and back?

Jeff

I cant say for sure what the hunidity was when you braced and all, but remember that if its hot with high RH outside, going into a cooler area like a basement the RH goes UP, not down (cold air holds less moisture as a percent, so 80% at 90 degrees goes up when you drop the temp - think beer glass on a hot day, it sweats)- thats where things like to grow mold ... you need to get humidity out when building in areas like this - 40-42 % is what I aim for.

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

What do you mean by ribs? Do you mean the braces, or the guitar sides (which are sometimes called ribs). If what we are talking about is just a braced top and back, which side was facing up?

I would expect the cause to be too high relative humidity (take warm humid air, cool it and you'll raise it's RH). Were they sitting on a benchtop brace side facing up? In a high humidity environment the side that is exposed to air is going to swell. As a first step I would just stand them on end and lean them against something so that air can get to both sides fairly easily, come back in a couple of days to see if they've moved back.

I believe what he did was brace the tops and backs then let them sit for a couple of weeks. If you ever read Cumpiano book this is a no no. In his book he states once the top and back are braced and the glue is dry your ready to join them to the sides. Which should have been done first if you already didn't do it. Somewhere on his website he responds to someone with the same problem with the answer that you have to chisel off the braces and start over. One the glue is cured waste no time joining them to the side. Once glued this will help them maintain there correct radius even if the humidity changes. I would also get a hygrometer for checking the humidity and a humidifier or a dehumidifer depending on if its high or low. Below is a link to the question and answer from Cumpiano site.
Potato Chip Top

Heath,

If youre ging to brace a top or back and then leave it for some time (not
really a good idea) you need to either have a humidity controlled
workshop or store the top/back in a light box or hot water cylinder
cupboard (if you have such things where you are).

A light box is simply a ply box with a light bulb inside to add a bit of
warmth and keep humidity down.



kiwigeo38903.8431944444

Ditto on what Michael Shaw said.

My shop is temp and humidity controled, however, I follow the Cumpiano recommendation and when the glue is dry, it is time to join. I would probably remove the braces, place the top and the back on a flat surface and flatten using a work board weighted down. Leave it overnight or a couple days. Check your braces to make sure they still have the correct radius and did not warp out, sand back to right or call and order some new ones.

I glue my back to the sides first, so I would do the back bracing first and join to the sides, let it set for several hours or overnight. Clean up any squeeze out. Then brace up the top, let the glue dry and join to the sides, let it set a day.

My 2 cents worth

Mike
White Oak, Texas

Thank you for all your help, yeah I hadn't glued the top or back on, DOH!
this acoustic making is very different from the electrics I build, I lot to learn, but with a bit effort and help from good people like all of you I hope to get through this mine field.
thanks again
HeathHeath38905.7862384259

[QUOTE=Michael Shaw] I believe what he did was brace the tops and backs then let them sit for a couple of weeks. If you ever read Cumpiano book this is a no no. In his book he states once the top and back are braced and the glue is dry your ready to join them to the sides. Which should have been done first if you already didn't do it. Somewhere on his website he responds to someone with the same problem with the answer that you have to chisel off the braces and start over. One the glue is cured waste no time joining them to the side. Once glued this will help them maintain there correct radius even if the humidity changes. I would also get a hygrometer for checking the humidity and a humidifier or a dehumidifer depending on if its high or low. Below is a link to the question and answer from Cumpiano site.
Potato Chip Top[/QUOTE]

I have made this mistake. I removed the braces (chiseled off) made new braces flattend the top by placing between 2 sheet of MDF for a few days (a couple days before makeing the new braces) rebraced and all was fine. If you are going to need to leave a brased plate un attached for any length of time you can keep it clamped in a stable radius bowl. use go-bars at the ends of brace and on large open areas of the plate. use spruce cauls where needed.MichaelP38905.5921527778

[QUOTE=Heath] Thank you for all your help, yeah I hadn't glued the top or back on, DOH!
this acoustic making is very different from the electrics I build, I lot to learn, but with a effort and help from good people like all of you I hope to get through this mime field.
thanks again
Heath[/QUOTE]
Heath it's a totaly different animal then electrics. I think everyone on here has made mistakes like this one time or another. Just learn from this mistake and keep going. Don't give up. In the end everything will work out.