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Back radius inverted! Need advice.
https://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=42498		 Page 1 of 2
Author:  ZekeM [ Mon Jan 20, 2014 2:27 pm ]
Post subject:  Back radius inverted! Need advice.
So this winter has been crazy with temps goin up and down and the same with the RH. So I've had my current build in a plastic trash bag with some damp paper towels to keep any adverse affects from the RH swings we have been having. Well last week the RH got up to an acceptable level 30% so I took the box out to do a little work on it.

Well I forgot to put it back in its sack and when I came into the shop today the RH was 15%. Apparently this was too much for the back to take. The back radius has inverted and there are now humps along the side where the braces meet the sides.
Image

Do I need to take the back off the guitar and rebrace it? Or is there another way of fixing the issue? I'm just glad the top is unharmed! Also glad this happened here rather than at the future owners house! It'll be a learning experience for sure. Any help is much appreciated.
Author:  fingerstyle1978 [ Mon Jan 20, 2014 2:35 pm ]
Post subject:  Re: Back radius inverted! Need advise.
I've had this happen as well. Alaska can be a real pain. Get your shop back up to 40% ASAP. I have wiped down the I side of the guitar with a moist (not wet) rag as well but I wouldn't recommend doing that unless you have to. Give it a couple days and it should go back to normal unless the wood is flatsawn. You may want to consider shellacking the inside of the box. I have massive humidity issues here and I've found that this helps tremendously.
Author:  ZekeM [ Mon Jan 20, 2014 2:47 pm ]
Post subject:  Re: Back radius inverted! Need advise.
I can't really control the humidity in here that's why I've been keeping the guitar in the trash bag. This shop is much too large plus it has giant size garage doors all along one side that are far from airtight. Hopefully one day I'll have a dedicated wood shop I can control. Until then I have to just build around the RH swings and stop forgetting to put the guitar back in its sack!
Author:  meddlingfool [ Mon Jan 20, 2014 4:43 pm ]
Post subject:  Re: Back radius inverted! Need advise.
15% is insanely low. You need to find an RH solution, even if its just building a box to put your work in. In my experience, wood that has experienced such low levels of RH never really come back to where they were when built, no matter how much humidity you try to add.
Author:  uvh sam [ Mon Jan 20, 2014 7:18 pm ]
Post subject:  Re: Back radius inverted! Need advise.
Even 30% is too low to build guitars. I live in Michigan and it is cold and dry here, without humidifying 15% is probable here too. We have to humidify to stay at between 40-45%, which is ideal for guitar making. You can get a steam generator for about a grand or run a couple of the wicking style humidifiers and fill them every day.
Also I would advise a high quality digital sling psychrometer because cheap ones are often off by 20% rh.
Author:  itswednesday14 [ Mon Jan 20, 2014 7:52 pm ]
Post subject:  Re: Back radius inverted! Need advise.
I read a report that quoted a study done by the Army that discovered Slings were often off 10 - 20% so I dont think the expense and trouble is worth it.
Author:  uvh sam [ Mon Jan 20, 2014 8:22 pm ]
Post subject:  Re: Back radius inverted! Need advise.
I have never checked ours but it is a digital sling psy. Supposedly accurate to +\- 3%. We also have a few radioshack cheapies and they are off by 10 to 20%
Author:  ZekeM [ Mon Jan 20, 2014 8:46 pm ]
Post subject:  Re: Back radius inverted! Need advise.
i dont know how accurate mine is. all i know is that in the summer ive seen it read as high as 60% and i know that the reading was 45% when i braced the back and put it on the build. so even if it is off i am taking the readings from the same hygrometer and therefore i think i have a general idea of what is high and low with it. When i took it out at 30% the box was already complete. the only work i was doing was some pore filling and sanding on it.

either way i know the rh dropped way lower than when the guitar was braced, resulting in this problem. Ive tried doing a little bit of rehydrating today and have it back in the safety of the garbage bag. we shall see if joeys idea of hydration and waiting will fix it. If not it looks like ill be removing the back and rebracing since i havent heard any other solutions
Author:  uvh sam [ Mon Jan 20, 2014 8:57 pm ]
Post subject:  Re: Back radius inverted! Need advice.
That is what I would do zeke. You may find that the back is permanently shrunk, so you may have to widen your purfling scheme on the back
Author:  Clay S. [ Mon Jan 20, 2014 9:21 pm ]
Post subject:  Re: Back radius inverted! Need advice.
What is the outdoor RH where you are? You may be better off storing your work in a cold unheated area where the RH will be higher than using a plastic bag. When I'm not in the process of gluing something up I'll store my parts in a cooler part of the shop.
Author:  ZekeM [ Mon Jan 20, 2014 9:30 pm ]
Post subject:  Re: Back radius inverted! Need advice.
I'm not sure what the outside RH is. I'll have to check that
Author:  uvh sam [ Mon Jan 20, 2014 10:58 pm ]
Post subject:  Re: Back radius inverted! Need advice.
It may sound weird but I can tell if the rh is right by how it feels when you breathe. In winter, outside really feels dry in my lungs, so when I walk in the shop first thing, I take a deep breath and if it feels "right" I still might check, but not with urgency. If it doesn't feel much different than outside I am running to check the rh and checking to see why the humidifier isn't working!
Author:  grumpy [ Tue Jan 21, 2014 12:11 am ]
Post subject:  Re: Back radius inverted! Need advice.
If you can't control the humidity, consider taking-up a new hobby.

Seriously.
Author:  ZekeM [ Tue Jan 21, 2014 8:33 am ]
Post subject:  Re: Back radius inverted! Need advice.
grumpy wrote:
If you can't control the humidity, consider taking-up a new hobby.

Seriously.

I don't know about all that. I mean what did luthiers do before they had ways of controlling humidity like we do today? I mean maybe they had their methods if keeping things stable but I think I can work around it. I'm just taking this as a learning experience. I think I'm gonna go Fillipo's route and brace at lower RH levels. Hopefully I'll be able to arrange a better shop once I move later this year.
Author:  Goodin [ Tue Jan 21, 2014 8:42 am ]
Post subject:  Re: Back radius inverted! Need advice.
Zeke you should probably go to Lowes and get a humidifier today. It's supposed to get down to 9 degrees tonight. Put it as close as you can to your work and crank it up. Even though your shop is big and drafty, it will help a bunch if you have a humidifier near the work.
Author:  ZekeM [ Tue Jan 21, 2014 9:17 am ]
Post subject:  Re: Back radius inverted! Need advice.
I've got a humidifier at the house just never thought it would do much good in the shop so i never have gotten one here. Maybe I'll just take it home with me till things settle out a bit. I'm ready for these cold spells to be over. They are just a pain! Winter is far from over and I'm already tired of breaking ice so the horses have water!
Author:  ernie [ Tue Jan 21, 2014 9:27 am ]
Post subject:  Re: Back radius inverted! Need advice.
I reglued back bracing a40 45 percent humidity

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Author:  Clay S. [ Tue Jan 21, 2014 9:41 am ]
Post subject:  Re: Back radius inverted! Need advice.
The actual humidity is generally lower in the winter (because cold air can't hold as much water), but the relative humidity out of doors can be in the same ranges as during the summer. It is when we heat the cold air that it becomes "dry", because the warmed air can now hold so much more water. Similar to "wind chill" drawing the heat out of warmer bodies, "relative humidity" draws the moisture out of things that are at a higher moisture percent.
I've read that some makers would warm their parts over a stove before doing cross grain glueups. This would dry them out during times of higher humidity as well as give a bit more open time for hot hide glue. Some waited for the conditions to be right for gluing things together.
Author:  arie [ Tue Jan 21, 2014 3:14 pm ]
Post subject:  Re: Back radius inverted! Need advice.
ZekeM wrote:
I've got a humidifier at the house just never thought it would do much good in the shop so i never have gotten one here. Maybe I'll just take it home with me till things settle out a bit. I'm ready for these cold spells to be over. They are just a pain! Winter is far from over and I'm already tired of breaking ice so the horses have water!


sorry about the guitar. you need to get a humidifier going quick. i had a darkroom in my apartment when i was younger and shooting film and i made it light tight with that black adhesive weatherstripping foam they sell at hardware stores. i lined all the door gaps in a spare closet with the stuff. very light tight and airtight too. good way to make a "humidty controlled environment"

might wanna try it in one of your closets along with something to make some moisture in there. those vicks vaporizer things sold at target and walmart will work in small spaces. get a hygrometer and a calibration kit as well.

you have horses? that's cool!
Author:  ZekeM [ Tue Jan 21, 2014 4:50 pm ]
Post subject:  Re: Back radius inverted! Need advice.
Thanks arie I'll give that a try. Maybe just seal up one of the rooms here and see what that does. Have a storage area for my projects anyhow when things get out of control like they are currently.

And the horses belong to my girlfriend, but you know how that is..."honey it's cold out will you feed and water the horses....and dogs....and rabbits....." Lol
Author:  ZekeM [ Tue Feb 04, 2014 5:29 pm ]
Post subject:  Re: Back radius inverted! Need advice.
Ok with the rain we have had lately coupled with slightly warmer temps the RH got to a manageable level. I took the back off and rebraced it. So now we are all good. Well almost. It looks like I'm going to need to put some purfling around the back when i originally had none. I'm probably going to need something around .06"-.08" wide in order to get everything nice and flush with no gaps. I was thinking of doing a maple/irw purf with the curly maple binding. It would look like this but the inside maple and rw would be slightly thinner.

Image

What do y'all think? Any other suggestions of what would look good. Design is not my strong point.
Author:  LarryH [ Tue Feb 04, 2014 6:28 pm ]
Post subject:  Re: Back radius inverted! Need advice.
Plastic bag with damp towels - humidity minimum 85%. Then into 15% humidity? Bye Bye to almost any wood. We have wild swings here in San Diego as well. I've seen a true 5% during a Santa Ana and watched wood simply curl up. It all came back OK with more RH though and one time I wet the concrete garage floor and it raised the humidity pretty well.
Author:  Guitarbuilder195 [ Fri Feb 07, 2014 3:28 pm ]
Post subject:  Re: Back radius inverted! Need advice.
Zeke,

I'm also working out of a garage. For telecasters I never had much trouble with swings in RH. I've recently started on acoustics and got pretty serious about climate control. Here's what I did: scour the whole garage, find every spot where you can either see daylight or feel air circulating (I could actually feel it coming through my closed windows). Next you'll want to chink all these areas with insulation. I bought a roll of yellow insulation at Home Depot or Lowes, put a strip in each window, shut them on the insulation AND lock them, this pushes the window down further and creates a better seal. Check around the doors as well, if the vinyl seal is away from the door or you can see sunlight from the inside, either nail the vinyl back in place or shove some insulation in the hole. It took me a couple days to find everything but it amazed me how much this helped. I then bought a humidifier from Sears (Kenmore 8-gallon, good for 1700 square feet) plugged it in and kept it filled. It ran constantly for 4 or 5 days, but it's keeping my shop between 42-45% RH and only comes on when the RH drops below 43. Helped my allergies a ton too. Hope this helps some
Author:  ZekeM [ Fri Feb 07, 2014 5:40 pm ]
Post subject:  Re: Back radius inverted! Need advice.
Problem is I'm working out of my machine shop. It's about a 15,000 sq ft building. Not a lot I can do to control humidity in that amount of space.
Author:  Shaw [ Sun Feb 09, 2014 12:29 am ]
Post subject:  Re: Back radius inverted! Need advice.
Zeke I would think of setting up a little room in there just for guitar building if possible. Maybe build a room off in a corner. Doesn't really need to be that big. Just somewhere you can work and store some guitar woods. Put a humidifier in there and you are set...Mike
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