Official Luthiers Forum!

The hygrometer thread got me going on this.

Letting your shop environment change humidity levels is good!!!!!!!! Once
the instrument is assembled from all the parts they will continue to
change or try to change as well. There is no way around this unless you
keep it in your cigar humidor or in your continuously constant shop.

Once my wood is thoroughly dry, and seasoned, I let my parts cycle
through the seasons and changes in humidity and temp. I watch the parts
move a little. I don't clamp my plates down and restrict movement to
keep them flat. If I see something troubling like a warping back or side, I
might discard it or brace it differently.

I don't have a big volume of guitars, bass violins flying out of here so I do
have this luxury. This is a big part of my building process.

Understanding how much and which way wood moves is a big part of
mastering the craft. Which I haven't done yet.

Here's what's silly, to keep your shop at a constant humidity level. It is
expensive and unnecessary!!!!!!!! .

But for all newbees and anyone selling or giving away a guitar, keep in
mind that any cross grain glue operation has to be controled and
performed in a low humidity state. Crank the duhumidifier for a couple of
days before bracing, and keep all parts out in the room to acclimate for a
a few days or a week. Keep both sides exposed to air and make sure the
air is dehumidified to a reasonable level. If you want to measure it, go
ahead, but it just needs to be dry. As to how dry, that totally depends on
where the instrument will live. Arizona is not worse than Boston as some
might think. A guitar braced at 45% RH going to Boston might reach 15 or
10% in the winter when the heater is cranking. And the back will want to
cave in.

Hedging for these extreme events is all about what makes you successful
and the instrument live a long life. Design proper bracing cross grain glue
only in a dry state.

Fingerboards should be kept at low humidity for longer since the dense
wood takes longer to acclimate.

Here are some large maple slices ready to be thickness sanded for bass
violin sides. This plan is for a "guitar" shaped bass and the sides are 50
inches long and 10 inch wide.

Then a couple pieces are sanded and ready to bend and look like this after a
few months.

One note is that the sides were throughly dry even before resawing.

Now look at a side that was bent months ago and now looks like this. I
will need to bend it again to get it fine tuned and take care of the spring
back. There is a problem that I can see though that worries me and needs to
be addressed when I put the sides in the mold. I will need to brace across
the sides in some places since there is some natural waviness in a few
places. That is what the wood wants to do, and I now know it. I will decide if
it will be okay to cross brace it without inducing a crack years down the
road.

KenMcKay38900.5084027778

The bass will eventually have this shape.
This is the rough sawn back ready to thickness. I am keeping this on the
shelf with both sides exposed to air. It is staying pretty stable,but I will make
further judgement when it is thin ...7-8 mm.
KenMcKay38900.5133333333

This is the thickness now of the back maple, It is coated on the end with wax
so it doesn't crack.

As you can see the wood is not quartersawn. Some makers would not even
use wood like this. I have seen lots of big bass viol type instruments with flat
sawn wood that are hundreds of years old. I like the character of the wood
and take this as a challenge to make it work.

So...throw open those shop doors and get some fresh air into that shop.
Take a deep breath...breathe out...breathe in...

Yes Hesh that is why It felt it was important to post my approach. There are
may different ways to set up your method of making instruments but a
closed shop is too much like a factory for me.

Think about the luthiers of past...in the great book about Antonio de Torres
by Romanillos, there is a great description of how Torres approaced the
humidity and bracing problem. Although his world was different, since his
guitars were mostly kept on Spain and there was no central heating and all
that. He used a humidity stick to judge the right and wrong time to brace
the back. It was said that he could tell by the winds blowing from the west or
some romantic notion like that. I forget exactly, but I highly recommend that
bool!

Thanks for a really interesting point of view Ken, i like your thoughts on how wood behaves, i also agree on opening up the doors to let the fresh air and wind in the shop.

Ken,

Good information. The seasons changing must season and prestress the wood, much like many do by putting thier top woods in the oven for an hour at about 200 degrees I think it is. Puts maximum stress on them so they probably will not ever encounter that type of stress in the real world. I have not baked a top yet, but I am going to try it. Have you done that, or considered it?

Ken, you said, "keep in
mind that any cross grain glue operation has to be controled and
performed in a low humidity state." My assumption is that it is better to have wood expand after bracing rather than shrink after bracing, is that correct? Shrinking would contribute to cracks developing, but could over expansion pop the braces loose?

Jeff

"All categorical statements are false"

I think you really have to assess your circumstances before you can make a decision on this. Sometimes you'd like to have some humidity cycling, and other times it's the kiss of death.

All wood has some built-in stress, and it is pretty likely that humidity cycling helps to relieve this. It has also been shown that humidity cycling contributes to the breakdfown of hemicellulose, which is the part of wood that absorbs moisture from the air, so over time wood that's stored in a place where the humidity can vary will become more stable, and a bit lighter, too.

OTOH, when you're actually working with parts I think it's better to keep the R.H. pretty well controlled. This is particularly true of the top and back plates after you've started to glue on the bracing, and before you close the box. Small changes in plate width in either direction can put a lot of stress on the glue lines between the braces and the plates, and cause them to peel up. Of course, it takes time for wood brought into the shop to acclimate to the humidity level as well, and it needs to do so before yuo start to work on it, as this can cause it move around as you mill it.

Probably the ideal situation, then, is to have some sort of roofed structure for long-term storage, where the wood gets exposed to seasonal changes but is protected from getting wet. Move the wood into the humidity controlled shop a few weeks or months before you start to build with it, depending on the size and variety, and how well seasoned it is to begin with.

A lot will depend on whether you're building things to sell, how many instruments and of what type you make, where you live, and where you ship, if at all. I'm in New England; guitar hell. The R.H. varies from about 20% to 100%, and the weather changes so fast and so often that stuff is always moving in all seasons. I'm shipping stuff all over the place, and need to know that it's not going to fall apart when it gets there. I've always got stuff in the works, at different stages of construction, both my own instruments and those of my students. Without humidity control I'd be sunk. Yeah, it's expensive, but if it keeps me working year 'round it's a no-brainer. YMMV.

[QUOTE=Alan Carruth] I'm in New England; guitar hell. The R.H. varies from about 20% to 100%, and the weather changes so fast and so often that stuff is always moving in all seasons. [/QUOTE]
It's the same here in Michigan. I think in today's world, every instrument should be built with the expectation of those extremes.

I think you are right-on there, with both assumptions Jeff. That is why you
kinda need to know where you are humidity wise. I don't need to know the
exact RH to know when it is time to brace and if I had a good hygrometer I
would use it, but for me the Radio Shack digital is working and proven to
work. I personally don't worry about getting the shop humidity too low.
That only happens in the winter if I keep the shop heated for a long time.

I can truely say that I build my instruments in a humidity controlled
environment and pass a lie detector test. I guess I should add that my shop
walls are (mostly) plastic enclosed and it only takes a short while to get the
RH to where I do gluing. And I agree with Alan in that if I had a guitar in a
mold, ready for a back, I would probably keep the shop dehumidified until I
finished and closed up the box.

My shop stays at a constant 45% humidity year around. Outside humidity
ranges from 20 to 95% through the year. My basic rule is a guitar gets
built in an environment less humid then the one its going to. Better
having wood swell a bit rather than shrink and crack.

Many of the older instruments made by the spanish makers seem to be
more stable than modern day instruements but that could be because
better wood was available at the time and I imagine Spain has a generally
drier climate than many parts of America and certainly here in the
Adelaide Hills Australia (Sth Australia supposed to be the driest state in
Australia!).

Im sure many of the old spanish luthiers employed climate control simply
by not carrying out certain tasks at certain times of the year. if
dehumidifiers had been available at the time Im sure many of these guys
would have used them.

Just my ten cents worth



kiwigeo38900.8481134259

The problem where I live is it's already very humid and when it rains the humidity in my work area skyrockets up to the mid sixties. When this happens I put the air conditioner on and it brings it back down to the 40 to 50 range.

Ken, what you're suggesting is called 'seasoning the wood', which is the norm for most woodworkers and luthiers. It's why we store our new(or green) wood in a different building or room, seperate from our shop, or main assembly area. An unheated attic or shed is ideal.       

Maintaining a constant RH in your build area is critical to building long lasting, stable instruments. If you were to assemble a guitar this week, at 80%RH, it will crack come winter at 20%RH. The frets will stick out from the fretboard, action will drop horribly, etc...
If you assemble at 20%, when it suddenly finds itself at 80%, braces will pop loose, action will rise, the neck will take a backbow, etc...

Not to mention what the above situations do to the tone; the dry one will be stressed to the point of breaking, sounding tight and nasely, while the wet one will be swollen and fat, sounding suddenly muddy,lacking clarity.

There's a good reason the instrument making industry has adopted 42-47% a it's normal RH range.

Your wood can season as long as it wants and needs, and doing so is good, and is old hand, but where you build must be controlled, and the wood you build with today must be acclimated to that environment, or prepare for a rude awakening.

'tis not silly, 'tis smart.Mario38901.006875

The "silly" statement was provocative and really just a suggestion for
myself. I carried it over from the hygrometer thread when that word came
up. I am just thinking how silly I would be if I were to run my dehumidifier
full time and keep asking my two young boys to CLOSE THE DOOR! And
how my accountant (wife) would ask me to decide between dry air and dry
cloths...

Al said it well " you really have to assess your circumstances before you
can make a decision on this".

I am going to be assembling that bass sometime in the winter, in the
meantime I am making parts for guitars, building cabinets, planing wood
with the door open. Once the parts are made, I can assemble in the winter
(hopefully) when humidity is low. This would be totally impractical and
silly for some.

I would worry about the long term integrety of my bass if I didn't let the
wood cycle through the seasons. This is an extreme case, my sides are 10
inches wide and 50 inches long! There are no books written on the
subject. I would be afraid to see what would happen if I kept all my parts
at a constant 45%, built the thing and shipped it out. When it comes time
to assemble it I will make sure the RH is low 45% approximately.

It's just another approach.

When it comes time

I see; you sounded like you were saying you weren't going to control the environment at all. I know most of you don't build full-time, but I think most of you are in the shop a few times per week, at which point, keeping it controlled all the time is required. But if you don't plan on being in there for a month, yes, let it go "au naturel". Even my shop's environment wasn't controlled when I was gone on vacation to the acoustic camps, but then again, it was still 68?f and 48%RH when I returned(there are -some- good reasons for living up here <g>)

I keep a hygrometer and thermometer ourtside the shop as well, as when the outdoor numbers are within spes, my door is open, also, which means most of the summer. Quite often, when I hear the dehumidifier start up, I'll glance at the outside hygrometer, and will simply open the door to dry up the shop, instead of burning kilowatts.

Now... where am I going to put those cross braces on the sides, how many
and how big?

Hey Al, what about that big bass from the New Family Octet, are there cross
braces on that? As I recall, the sides aren't very deep on the big bass.

I have never cross braced my sides so I am new to this kinda thing. KenMcKay38901.7176273148

The big bass is built like any violin, only bigger! The only 'brace' is the bassbar, and that runs more or less along the grain. The relatively shallow ribs put a lot of stress on the neck joint with the button, of course, owing to the leverage of the high overstand. They have the same problem at the other end of the scale, with the Treble, which also has very shallow ribs.

Alan Carruth / Luthier

[QUOTE=Mario]

I keep a hygrometer and thermometer ourtside the shop as well, as when the outdoor numbers are within spes, my door is open, also, which means most of the summer. Quite often, when I hear the dehumidifier start up, I'll glance at the outside hygrometer, and will simply open the door to dry up the shop, instead of burning kilowatts.[/QUOTE]

Hey, now THERE'S a good idea!   

_________________
Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

I do the same thing, it is nice to finally get some fresh air into that dusty shop! It is one of the nice things about living this far north I guess, the humidity swings are not that dramatic.

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Rian Gitar og Mandolin

Man, i wish i had windows like most of you guys have!

Hi Serge, good to see you, it sure is quiet around here today! Is everybody sleeping in or what?! <checking calendar> Oh, I see...

Happy Independence Day all Americans!

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Rian Gitar og Mandolin