Official Luthiers Forum!

Pondering some important questions on this labor day ??????? mostly I have sought out quartered stuff but there seems to be a lot of highly figured wood out with the grain running this way then that way, sapwood, beetles running rampant,etc......kinda wondering what everyone's thought are on the subject.

_________________
MK5acoustics.com

I've only got 5 guitars together so far, but have accumulated over 60 back and side sets of all descriptions (about 40 species). I'm an addict, I'll admit it. I like it all, quartered and figured with sapwood and beetles. Right now, I've bent sides of Ambrosia maple (with no plans to fill the holes) and leopard wood for the next two, and have thinned some imbula and padauk sides and glued the backs for two others. The imbula and ambrosia are not quartered; most of my sets aren't. Looking at book matched figured wood is a lot like cloud watching or Rorschach plots for me; just like what I see there.

Quarter-sawn wood does not expand and contract across the grain with temperature and humidity changes as much as flat-sawn does. For that reason, most guitars are made with quarter-sawn material.

It's been relatively recently that flat-sawn wood has been more commonly used but if you take a look at most esteemed builders instruments, you'll see that their guitars are made from quarter-sawn wood.

If you build at controlled RH levels and always keep your guitar at about the same RH as when built, you can probably get away with using flat sawn but it's still riskier. However, bending flat-sawn for the sides can still be problematic.

Cor blimey! You need to start building 5 at a time. Unless you're planning on building an ark with it all

Quartercut will actually expand and contract across the plate width more than flatsawn, otherwise everyone would be wanting flatsawn tops. A spruce top 16" wide can shrink as much as 3/8" just going from 80% RH to 45% RH. If quartercut does crack, it will be in a straight line along the grain and relatively easy to repair. With flatsawn and/or many figured woods, if there's a crack, it will follow the wild, figured grain, and could be a nightmare to try and repair. Some woods are a lot more stable than others,, and I'd decide on a case to case basis.

Brent

3/8"? That's more than I expected... You say from 80-45% RH. I'm still unclear, how does dew point enter the equation here?

Not sure about the dew point. Years ago I tried bracing an Engeman top in the early fall. My apartment at the time was electric heat and no AC. I'm guessing it was 80% RH when braced. When winter came, the dry heat caused my top to go from slightly domed (3/16") to severely concave. All my Sitka braces were warped backward by a lot. I was too upset at the time to even measure.

Brent

Anyone building at 80% RH deserves what they get. The results will be pretty predictable. Flatsawn wood doesn't bother me. If the sides stay flat after bending you are good to go. Last week I bent two sets of quartered EIR that rippled badly. They cleaned up, but you never know what wood is going to do until you try it.

Where did you get that? All the data is represented as T/R (transverse over radial) and the numbers are always greater than 1.

Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

It's this aspect regarding dew point that I'm trying to understand. There can be a big difference between the actual amount of vapour in the air at 80% RH depending on dew point and temperature. How does that relate to guitar building environments?

Since you've make a statement here contrary to what I've always understood to be a fact, I'd appreciate some evidence.

Don't worry about dew point, leave it to the weatherfolks. 80% RH is dangerous under any condition as far as guitar building is concerned. Its Relative Humidity.
Relative to the temperature. If you can control shop temp but not the humidity, cease building when the RH gets out of the happy zone, 40-50%. But that's only a general rule if your instruments are going to travel. If you build at 80% and the instrument will always live at 80% (just to pick a figure), you'll be home free. But not much of American real estate is that consistent.

It doesn't. The moisture content of wood is driven by relative humidity, not absolute humidity.
I just think of dew point in relative terms....the closer the dew point is to the air temperature, the higher the relative humidity. For a given mass of air, the higher the temperature, the lower the relative humidity. The reverse is also true. Lower the air temperature to the dew point, and the RH becomes 100%, which is when condensation (dew) occurs.

I have built guitars from slab, quartered and rift sawn wood, and the only thing you know for certain is that it is from a tree. I have also had severe ripples from bending quartered sides, and no issues from bending sides that are slab or rift. Certainly there can be more problems with some slab-cut wood, but it is by no means universal.
I do like quartered sides, but that is more about the appearance than the workability. The straight lines of straight grain, QS wood just look better on the sides, which have square edges. The back is a different story, since the edges are curved. This philosophy makes sense from the conservation aspect as well, since a small tree is more likely to yield quartered sides than quartered two-piece backs.

_________________
John

Great, clear answers from the two Johns!
Many thanks!

For what it is worth, the dew-point is the temperature at which the air will reach 100% humidity (and produce dew).

Bob

_________________
MK5acoustics.com

I don't have much to add, but just to say welcome to John Calkin. I've enjoyed reading you articles in the GAL rag over the years.

_________________
Jim Watts
http://jameswattsguitars.com

My experience with the Engelman top was in the 1970's, and there was not much info around. I had worked with different woods in the cabinet business and had never seen the same thing happen. Some warpage, but not the same type of shrinkage. Thank you guys for the info. I'm learning new things every day.

Brent

Yup, live and learn. I knew better than to store some projects in a room that actually reached 80% in the summer. They went nuts. Bindings popped loose, as did tops and backs. Even the plywood reso bodies freaked out. They all ended up in the landfill.

Thanks, Jim. You're very kind.

Quarter sawn wood will, indeed, expand and contract with humidity changes. However, it tends to get thicker and thinner as it moves. This is not to say that it won't expand and contract across its width, but its lateral movement will be LESS than a flat sawn plate of the same species. I can't agree with the assertion that it will move more than flat sawn wood across its width. Of course, an uncured plate cut in ANY orientation will shrink as it dries--across its width and in its thickness.

Ditto here. Glad to see you posting, John. Your articles are the ones I read first when American Lutherie arrives at my door.

Pat

_________________
formerly known around here as burbank
_________________

http://www.patfosterguitars.com

I have to agree with cphanna on this. I've done a lot of cabinetry with QS wood, and when sufficiently dry, doesn't move in width as much as flat sawn of the same specie, and stays flatter with RH rise or fall. It does change more in thickness, but when you are dealing with plates that are .07" - .125", it isn't going to be too critical.

Alex

_________________
"Indecision is the key to flexibility" .... Bumper sticker

John, what temps did that room get up to? What kind of glue was it?

_________________
Pat

It's not about temperature within reason. My first couple of guitars were built in a shop that was regularly above 90*F, during the summer Months, but the humidity was controlled to 45% or below. It was a "dry heat", like in Arizona! Good for the sinuses! Also, I have played my guitars in temps from below freezing up to the 90's with little issue, and in humidity from the 30% to 90% range outdoors during the Fall of the year. Also with no issues, except for the 4 weekends I played in the rain, and put my guitar in the gig bag and sat it in the corner when I got home. It took 4 more weeks in my shop for it to dry out. That guitar, my 2nd, is still my player.

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars