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OK, I am in Miami, Florida and I am about to start my first guitar. Obviously I would rather do this in my garage, but the humidity is so high right now (July) that I worry that parts will start warping soon after I cut them out with my CNC.

The wood blanks have been acclimated, as they have been stored in the garage. However, cutting exposes fiber that was once deep inside the block.

Am I worrying needlessly, or is this a legitimate concearn?

I would hate to throw an unknown into the process being that this is my first guitar and that I have a learning curve to deal with already. The last thing I would want is to find out that my newly carved neck is not true to the body.

I know that in other parts of the country this isnt as much of a concearn, but I would be interested to hear from others in Florida or the Gulf Coast or lower East Coast....where we are currently walking out into a steam bath.

Humidity control is important. If you build in tropical conditions, you better keep the guitar in tropical conditions once completed or the change to a much lower humidity could be catastrophic. My advice...get your environment under control at 45% and allow your wood to acclimate for several weeks before starting the project.

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JJ
Napa, CA
http://www.DonohueGuitars.com

So, how does the finish come into play? If I produce in high humidity, I would lock the humidity in. If I produce in 45% humidity, then I would lock that low humidity in as well, right? I am planning to use polymerized linseed oil.

Do instruments produced in low humidity environments get affected in reverse? There are so many outdoor concerts here.

I guess I need an air conditioned environment, and a large stock of wood............since the lumber yards here are not ac environments.

Most builders use the 45% because it is a reasonable average humidity level to work in , which takes into account, if the guitar will be moved to a higher or lower level later .
I built my first with a master , the humidity was between 45% and 55% the whole week , later bringing the guitar to new york , as I began using heat in the fall ( which lowers the humidity level quickly and drasticly ), before I began to hydrate the air . I started to get a buzz from the top moving from the rh change , I quickly corrected the situation by moisturizing the air . in a few days the guitar returned to normal . if I had built the guitar in higher humidity , the problem would have occured sooner , and would require more moisture in the air to correct.in the summer , where our humidity in new york reaches 80% to 90% , the guitar plays fine .
i have a separate room I store my wood in and do my glueing in the summer , if I need to take any parts to a higher humidity area ( the basement where my power tools are ) to work on them . I wait a week or two after returning to the controlled environent before glueing . i hope to convert my garage to a shop soon , but till then , this seems to be working .
Too much moisture in the wood before finishing can cause problems too. Jody

Water vapor can get through pretty much any finish, even if you finish the inside of the box (most folks don't). Finish will slow down the process though.

Humidity control is important for a couple of reasons. One, as mentioned, is dealing with the action going up and down with humidity changes.

The other is structural. Guitars are built contrary to one of the first rules of basic woodworking...don't glue one piece of wood across the grain of another. Solid wood expands and contracts with changes in humidity but the the changes are much greater across the grain than with the grain. So when you glue a piece of wood across the grain of another (or capture it between rigid sides), you have problems when the humidity changes. The worst problems for guitars are when the plates shrink with low humidity. The rigid sides and braces will only allow the plates to shrink a certain amount before the plates split to relieve the stress.

High humidity can also be a problem because of something called compression set. Since the plates are bound by the braces and sides and can't expand freely, they get compressed in periods of high humidity. They are essentially forced to be smaller than they want to be. If this happens for long periods of time or for extremes of humidity, the wood will get "set" in that compressed state and essentially want to remain smaller than it was originally. This will potentially cause them to split sooner than they normally would have in periods of low humidity.

So yes, the standard idea is to build at a good mid point unless you know the guitar will be living at one extreme or the other.

One good way to deal with that is to wall of an area of your garage (draping with plastic works too), that is big enough for gluing operations and wood storage and keep it humidity controlled.

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http://www.chassonguitars.com

What the guys have said is sage advice.

I live in Michigan where I have to humidify in the winter (forced air heat) and dehumidify in the summer. Typically I only get a few days a year, and not in a row either, where I don't have to be doing one or the other to maintain the range that I use which is 42 - 48% RH. On some days, many in fact, I may be running the humidifier in the morning and the dehumidifier in the afternoon. It a real pain in the butt wedge.........

And as the others noted there is no escaping it - just as a surgical environment requires an aseptic environment guitar building, if you want to produce a quality product, requires humidity control. And if you are nuts like me and a clean freak an aseptic environment too......

In addition it's important to get a good hygrometer so you have the ability to monitor the RH in your shop. The vast majority of digital and analog units are crap and can be way off. There are many discussions in the archives on how to calibrate your hygrometer so you know what you have to work with. The Caliber III sold many places including Stew-Mac is very accurate in my experience and I have had 4 now that were dead nuts on in terms of accuracy. Why did I have 4? Because I keep giving them to other builders who need one.

By the way I don't think that I welcomed you to the OLF yet so welcome to the OLF!

Before I had the humidity under control in my workshop, I would keep the guitar and parts in the house when I wasn't working on it. This was a bit of a pain, but not as bad as hearing a cracking sound as the guitar dried out on a cold dry winter day in the shop.

I have heard of others who built a humidity controlled closet/cabinet to keep their work and wood in while not working on it.

The Hardwood center I go to sometime to get wood has kiln dried stock but it is stored out in a large building that has no humidity/temp control. So what ever I get there won't be used for a while. No matter where you get your wood, I think you should sticker it for good while before use.

It'd be hard to find many places that have much more of a tropical climate than here in Cairns, within an hour's drive of areas with drastically lower relative humidity. I will join the top and back plate out in the garage without worrying about the humidity, but then they are put in a spare bedroom where I have a dehumidifier. It's here that they will get the braces glued on and stay here until I'm ready to carve them. I'll take the plates out to the garage and carve away, hopefully on a day with lower RH, but that's not always possible. Then they go back into the controlled room.

I don't worry about the rims too much, but I do let it sit in the "dry room" for a few days or weeks depending on my schedule before closing up the box. I get the box ready to go and glue top and back on over a weekend. In the same day if all goes well.

My first guitar I built without RH control and it turned into a nightmare of warped plates that I watched turn inside out with swings in humidity from day to night. It took a few weeks waiting for the optimum time that the humidity returned to point that the top and back plates where happy, then I glued them on as fast as possible. That guitar has been together now for 1 1/2 years and seems fine, though I wouldn't want to take it to a really dry climate.

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Allen R. McFarlen
Barron River Guitars & Ukuleles
Facebook
Cairns, Australia

This is going to be a solid body electric upright bass, so I dont have to worry much about thin plates for a sound box. However, it is made from laminated hardwood: Jatoba | Purple Heart | Jatoba.

The body will be cut with a 4-Axes CNC machine, and then I will glue on a Brazilean Rosewood fingerboard onto it.

Humidity in Miami is out of control. You can count on 98% from here onto late November. In other words, twice what it should be.

I read through all the posts and noticed that some people keep the wood in dry, cut in non-humidity control garages, and then glue after it has acclimated again. How long do you feel comfortable taking the wood and cutting and carving it in a non-controlled environment????

I will be laminating the body blank prior to cutting it, so does this mean I can take it to the garage and have it be milled for 6 hours in 98% humidity and then take it back in and let it acclimate before gluing on the fingerboard????

Its either spending money to soundproof the CNC machine............or spending money to put AC in a garage that doesnt belong to me.

I have noticed that taking a braced top from 45% RH on my back deck at 60% RH to do some sanding and the top started to deform in 20 minutes.......... 6 hours at 98% RH would most likely be a problem IMHO.

Also air conditioning is not going to work well in your humidity level. Especially since they switched to the new freon that sucks at dehumidifying and feels like a swam cooler. I really thing that you will need a dehumidifier.

I hate to be the bringer of bad news but again proper RH control is really important.

Bad news would have been to have found this out after making the electric upright!

The good news is that I have 6 weeks before I start cutting. My Caliber III hygrometer is on its way. I guess the best way to soundproof the CNC machine is to put it in its own small room/closet with a dehumidifier and enough space for 2 months of wood.

6 hours , i think , could be a problem , different woods expand at different amounts and rates .... jody

Can anyone recommend a nice quiet dehumidifier that can take the wood dust problem?

My woodworking and wood storage room will be no bigger than 6'x8'

I have a Home Depot Gold Star cheapy dehumidifier and it works great and is quiet too. These days they are all quieter I think but they still are a bit loud but we get used to it. Be advised too that dehumidifiers produce heat so the AC will have to work harder.

I build in a small workshop I’ve set up in an unfinished area of my basement. The humidity level on a given day can be all over the map depending in the time of year, visiting rain storms and the number of doors my kids have left open at any given moment as they charge in and out of the house. I ended up building a small 3’x4’ closet in a corner where I keep my wood stock and in-progress work. I have a 60w bulb in the closet which stays on continuously and keeps the small closet environment at a fairly constant 42% regardless of the general shop humidity levels. Anything I am working on goes back into the closet at the end of the day. I run a dehumifier in the open shop area during the steamy summer months but the RH level never gets much south of 55% I would guess even while under constant attack. A good hygrometer takes the guesswork out of knowing what you are dealing with.

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Doug Mills
Chicago, Illinois

Why is it that woodworking projects always turn into MORE woodworking projects????? I started off building a bass guitar....now I am building an addition to my apartment....with advanced climate controls.

OK, this is a custom CNC machine. It is only 12" wide x's 64" long. I am thinking I can do storage on the bottom, for all the 64" long skinny pieces of wood.....humidifier on top.

I think I can get away with a 4' x 8' space or 6'x8'.

Since you are making solid body instruments, you should know the rule of thumb that lumber stablizes in an environment at the rate of one inch thickness per year. Yup, you got a ways to go. And solid body guitars are no less prone to humidity problems than acoustics. Watching your neck laminates warp before you can get them glued up is not a secure feeling.

The biggest reason to control the RH in your shop is maintaining a stable environment. wood swells and contracts with the amount of moisture available. Rapid changes can be a big issue no mater dealing with acoustics or solid body guitars. a fine fit joint at 40%rh will be too tight at 10% and too loose at 75%. Controlling rh is the key to controlling fit up and allowable shrinkage and expansion.

40-50% is preferred to allow for life in varied environments once completed but it also is a median point on the rh scale which allows for the largest amount of fluctuation with the least amount of affect on the wood during fabrication.

It is the big and rapid rh swings that are the killers

There is a world of difference between building solid body and acoustic guitars wrt humidity control
With an acoustic top and back in particular, you are breaking normal woodworking practice by gluing braces across the grain of a flat plate. It is very important to have an appropriate moisture content in the wood because you are locking in the relationship between braces and plates at this point.
Solid body- thick timbers, no cross grain gluing -totally different
IMHO dont worry as long as you are using well dried timber

I agree for the most part but non the less if you cut a fine fit pocket in a solid body at 60% rh and you have a drop in RH to lets say 20% if you check the fit on that pocket you will find it is now narrower than it was at 60% rh. Proportionally not as sever as if dealing with thinner pieces of wood but it still has contracted due to the drop in rh.

I did not mean to imply that he could not continue and I did not make such a statement. I only explaining the reasoning for controlling RH

Could you expand on this observation? It seems like a lot for wood bought from a fine wood yard, and not a construction lumber place. I cant imagine a piece of Jatoba shrinking 1" over 12 months.

All grain will be running parrallel in my designs. Electric Upright Bass arent very wide. They are mostly "walking stick" style designs, so I cant imagine the need for a member that has grain going perpendicular to the rest of the body. I dont have any pieces to my current design that dont have the grain running along the length of the instrument.

Jatoba | Purple Heart | Jatoba

I will be using carbon fiber rods in the neck, and the neck will be laminated pieces......all of relatively dense woods.

One thing I have always wanted to know is why laminating makes a neck stronger and less prone to warping. It would seem that wood tends to shrink and expand in different rates according to the different densities of species. Why would using two different species of wood not cause more warpage (due to humidity variations) since the two different species will expand/contract at different rates?

Would I be better off with a single piece neck........considering that I am building in a tropical climate with extreme humidity conditions?

[quote="MichaelP
I agree for the most part but non the less if you cut a fine fit pocket in a solid body at 60% rh and you have a drop in RH to lets say 20% if you check the fit on that pocket you will find it is now narrower than it was at 60% rh. Proportionally not as sever as if dealing with thinner pieces of wood but it still has contracted due to the drop in rh.

I did not mean to imply that he could not continue and I did not make such a statement. I only explaining the reasoning for controlling RH[/quote]

I agree there is some movement Michael, but the neck pocket is the only place with a potential for an issue to arise and even there, both the neck and the pocket should be moving in the same direction and at similar rates.
The other area that can give a problem is the fretboard, which if fretted too wet can give fret sprout if moved to a dry climate.

When you laminate you do not run the grain exactly parallel for best strength and warp resistance. Even a 2 degree variance gives large increase strength. the combination of the two help counteract each other. Just like with plywood the lamination of two or more pieces is vastly stronger than an equal thickness and length of a solid of the same species.

I studied Architecture.....and understood that laminate wood beams and plywood is stronger because the wood is mostly fill. The strength of the glue is what makes for strength. The mass of glue to the mass of wood in a guitar is much different than in a piece of plywood or laminate wood beam. I.E.........concrete is stronger than concrete block....the block is just fill, which adds strenght and stability.....but nowhere near as much as the poured concrete members....

Wow! That 2 degree sounds like an interesting thing to investigate.

Isnt all lumber subject to that variation......since the wood fiber rarely grows perfectly perpendicular to the centerline of the original trunk???

How much variation is there between the different exotic hardwoods when it comes to expansion and contraction due to humidity?