Acoustic Guitar Construction in the small shop -- Kenneth Michael Guitars LLC

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The purpose of this forum site is to provide a means for acoustic guitar makers at all skill levels to forward information, share experience and ask questions if project obstacles are encountered. We ask that egos be left at the door – the highest levels of courtesy and respect are to be shown to all. Posts containing disparaging comments will be removed. The “Acoustic Guitar Construction Forum” is owned by Kenneth Michael Guitars and is copy protected. Direct links to luthier suppliers are not permitted and will be edited.



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 Post subject: My take on humidity.
PostPosted: Tue Oct 29, 2013 9:48 am 
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Joined: Mon Apr 15, 2013 5:32 am
Posts: 15
Well, I've read the articles and seen the videos and then I've gone out and looked at the large tongue and grooved shed that is my workshop, sitting happily in a tree lined garden and exposed to the weather.
I have considered the articles and the videos and studied the currently available humidifiers and de-humidifiers and I am now using the best humidity detection device available. While I was working on the last guitar I noticed that during periods of high humidity a ridge on the top of the joined and unfinished soundboard would rise up. Having trimmed the soundboard a large section of this ridge is nailed to the wall. When it rises up I take anything delicate indoors. If it is lying flat I leave the stuff out. I must confess that I am not a qualified scientist, but was humidity as an instrument builders problem discovered sometime around the sale of the first electric de-humidifiers? I mean, how did Andrea Amati (1505-1577) live without one? And how do you get the buyer of a humidity controlled guitar to maintain that perfect humidity?


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 Post subject: Re: My take on humidity.
PostPosted: Tue Oct 29, 2013 9:56 am 
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Joined: Tue Dec 13, 2011 7:44 pm
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Welcome to the Forum, Dave!
I have not even humidified my own body with coffee yet this morning...someone will answer you fairly quickly I think.
Again welcome!

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 Post subject: Re: My take on humidity.
PostPosted: Tue Oct 29, 2013 1:48 pm 
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Joined: Tue Nov 27, 2012 8:01 pm
Posts: 756
Location: Kalamazoo, MI
Hi Dave (both of you),

Buyers do what they damn well please most of the time, and it is not limited to just humidity. Don Teeter tells the story of a guy who took his Martin with him on a high altitude sky dive, then wanted all the cracks the dive created fixed under the terms of Martin's lifetime warranty.

One solution for back and side cracks is to laminate those parts. This is controversial as many poor sounding cheap guitars were and are made this way. Yet the legendary Selmer-Maccaferri jazz guitars - not cheap these days by any measure - featured laminated back and sides. Dave Bagwill has considerable experience laminating sides and might be willing to offer more insight into that possibility. Cracks in solid sides are harder to fix than cracks in a flat plate, my opinion anyway, formed from fixing both. The one laminated back I have resonates at a much lower pitch than any of the solid backs I have. I have not used it yet, so I can't say how this will translate into the sound of a finished instrument.

But the top is a different matter. There is little support for using laminated wood for this, the most crucial part of the instrument. True, less expensive archtop electrics have laminated tops, but the general view is they gain consistency and resistance to feedback at the expense of volume and perhaps tone. But being amplified, there are ways to offset these developments that are not available to an acoustic instrument.

I will be interested in Dave's response after he hydrates. He works in what I consider to be quite a humid environment. (It grows the juiciest pears in the world, though.)

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 Post subject: Re: My take on humidity.
PostPosted: Wed Oct 30, 2013 8:02 am 
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I believe you can find tid bits of documentation that the ancient makers dried the air in their shops with open fires. Also, plates and bracing was placed in direct sun prior to gluing.

I agree that we make too big a deal out of this -- especially if the instrument is going to spend its life in the location where it was built. However, making sure the plates and braces are at their smallest dimensions prior to glue up is very important -- having the shop at a constant low RH, not so much, but a good practice so assembly/construction can take place at anytime.

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 Post subject: Re: My take on humidity.
PostPosted: Wed Oct 30, 2013 9:54 am 
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Hi there new Dave!
Humidity is definitely an issue that needs to be considered when building. Build at a high RH and then take the finished guitar to a low RH environment and you will likely get cracks somewhere. Probably in the top and back plate. My solution to this is to build when RH is quite low. I live in NY city and the RH gets nice and low in the winter time. So that is when I brace my tops and back and when I glue them onto the rim. The only issue I have had is that the action gets high in the summer and low in the winter, but my guitars don't need to be stored in constant RH environments to avoid cracks. My solution to the action issue is to have two saddles for the guitar. When the owner changes the strings in the spring, they install a lower, "Summer Saddle". When they change the strings in the fall, I have them put the "Winter Saddle" back in. It is easy to do when the strings are off and so far, people are happy to do it to maintain low action all year. I mark the saddle so they know which way to install it. My brother keeps his guitar on a stand all year. It is never in a case. He has had no cracks at all.

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 Post subject: Re: My take on humidity.
PostPosted: Wed Oct 30, 2013 1:09 pm 
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Joined: Tue Dec 04, 2012 5:37 am
Posts: 334
Location: UK
I've been drying my 'Shop' (err, living room) With an open fire. I must be an old master luthier.


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 Post subject: Re: My take on humidity.
PostPosted: Fri Nov 01, 2013 1:41 pm 
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Posts: 15
I have top say that I think a constant humidity, even if it is high, is ok. I certainly don't seem to have cracks appearing all over the solid wood I'm using, and the Sapele I'm using at the moment is rather ancient and very brittle as it was part of a job lot from a house clearance, probably from some cabinet maker who is now deceased. I can see there would be problems taking a guitar from my workshop to somewhere extremely dry, or very cold. In all honesty I've seen two guitars that were suffering from humidity troubles; one had been hung over a radiator and the other had been left in a freezing horse trailer for months on end at sub zero temperatures. They both came back to more or less normal with some proper care. In England, where I am, the humidity tends to change gradually through the seasons. I doubt if that stresses the wood so much.
I've included a picture of Sapele build; it's an experiment as it's the first scratch build I've done, and I also wanted to install a piezo pickup and reinforce the side to accept the controls. The wood wasn't quarter sawn, but it still seems to have good tone. It really is extremely brittle, though. I originally thought I would use it to practice side bending on my new machine but the results were so good I carried on.


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 Post subject: Re: My take on humidity.
PostPosted: Fri Nov 01, 2013 2:37 pm 
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On the other hand here in the USA I have personally seen hundreds of guitars damaged by low humidity -- our major vintage dealer here in MI Elderly (and many others) have nice profit centers, just repairing such damage. Its really not the RH you hear on the weather reports that is the problem -- its the RH in the room or building where the completed instrument is stored, used, displayed. As an example in some Shopping Malls the air conditioners pull off so much mositure the RH can be in the 20's -- as a matter of fact one high end dealer in a Madison Heights MI Mall (this was a while back) saw damage on much of their solid wood guitar inventory before they took the impact of the central air make up into consideration.

And a simple forced air furnace, common in American homes can do exactly the same thing -- thus, that is why we makers and all the major manufacturers (even though we build in about 45% RH) stress the importance of the need to use a basic case humidifier.

Back to the original post -- unless the instument will never be exposed to low RH (it does not matter how slowly it occurs) for most of us its less of a gamble to construct the guitar in an RH that is much lower then it will be exposed to on average. $.02

Also Dave, if you still believe this is a contrived notion circulated by the guitar making industry, you may want out check out the subject of RH and material moisture loss and gain in the general wood working publications, in particular text books. I can tell you in advance you'll see the very same warnings

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 Post subject: Re: My take on humidity.
PostPosted: Fri Nov 01, 2013 3:30 pm 
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Joined: Fri Dec 23, 2011 8:33 pm
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Location: Seattle
In Seattle Washington we have relatively consistent humidity the RH swings outside morning to afternoon relative to the temperature. One really does not even have to think about humidity control. With no control the RH inside is usually around 50-55%

When living in Indiana I experienced swings from almost no humidity inside during the winter to 99% RH in the summer. I would sure hate to build there in the summer without humidity control and have it experience a week of -30C where without added humidity the air is virtually without any moisture and the RH approached zero when the air is heated. Bad stuff happens.

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 Post subject: Re: My take on humidity.
PostPosted: Wed Nov 06, 2013 1:09 pm 
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I think I made the point that it was probably the humidifier industry, not the guitar industry? All the guitar builders and luthiers I've discussed things with are honest in their opinions. I think John Parchem echoes my point; the humidity here is constant, usually, and only changes slowly, so I'm not going to worry about it. I have enough worries about neck angles.


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