Dan
Flat sawn is not less stable than quarter sawn - remember that a flat sawn piece is quarter sawn when flipped 90 degrees and quarter sawn is flat sawn when flipped 90 degrees.
Where the difference in "stability" comes in - first, wood will swell and shrink with humidity more perpendicular to the grain, so a neck with the flat sawn face showing up will get taller and shorter, whereas a neck with the flat sawn face to the sides will get wider and narrower (tiny amounts here).
The second way the necks differ in stability is that many woods will be stronger along the vertical grains. So a neck that has the flat sawn faces on the side will be potentially more rigid and stable than one with the flat sawn faces on top (again, tiny amounts).
Both of those neck blanks are both vertical and flat sawn depending on which face is up.
In boat building, the hull planks have vertical grain so they get thicker and thinner with humidity and water, not wider and narrower, which would tear the boat apart.
It's all good
Ed Minch
flatsawn black cherry necks
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ruby@magpage.com
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Dan Bombliss
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Re: flatsawn black cherry necks
After rereading what I had written the first time, and rereading the initial question of this post, I wanted to shed some light on some of the real life science of wood movement and stability concerns opposed to hear say and personal opinion so that you can take in the information and decide for yourself. Everyone is different.
I mentioned that I couldn't remember the exact movement rates so I did refer to some of my wood info to get accurate information.
Wood is hygroscopic, which means it takes on and gives off excess humidity. That is the reason why it's important to give wood time to acclimate to your shop before working with it.
RH is Relative Humidity, which is the level of humidity in the air, aka the environment the wood is in.
MC is moisture content, which is the level of moisture in the wood.
The relationship between the two is the EMC, the equilibrium moisture content. The EMC is the point to where the wood's MC matches the RH.
When RH goes up, the MC goes up and the wood swells. When RH goes down, MC goes down, and wood shrinks. If you put a dry board in a very humid room, it will take some time for moisture content to raise to match the higher RH. When the moisture content of the wood does equal out to the same moisture of the RH, that is what is called the equilibrium moisture content. It's the balance between the two.
A chart showing examples of the relationship between RH and MC read:
RH MC
0% 0%
25% 5% (This figure is why we shoot for a range of 35-50% (depending where you are) The ideal
50% 9% moisture content is around 6-8%, which according to this chart is higher than 25% (5% MC) 75% 14% and lower than (or maximum of) 50% RH (9% MC))
99% 23-30%
If you constantly control your shops humidity at a dead set 40% all year round, you can expect your wood to be at the 6-8% moisture content. As soon as your piece of wood (or guitar) leaves that shop or environment, and goes to say 75% RH (A regular summer in the midwest, if not even higher) That piece of wood (or guitar) is going to continue to acclimate and expand (take on moisture) until it reaches the matching 14% moisture content to the environments 75% RH. Again when that piece of wood reaches the 14% MC that relates to the 75% RH, that is what is called the equilibrium moisture content.
Cool, a page full of numbers, but what do they mean? How does that moisture affect your guitar or project? Well, the science in those numbers is there to accurately estimate how much your wood is going to move. This is when the slab cut piece of wood is less stable than the quarter sawn. Stable meaning as little movement as possible. By no means does "less" stable mean "not" stable, but less is less, which is the equivalent to "less" desirable. Also one of the reasons why flat sawn necks are frowned upon; there's a better option.
Now, species of wood does affect the rates, as some move more or less than others, there's a general rule on predicting wood movement. Also quarter sawn moves roughly half of the figure flat sawn does.
Most flat grain species of wood - For each 4% change in moisture content (MC) the board will shrink or expand 1%. So in the figure of having an acclimated board to 35% RH (6% MC or so) and then a move to 75% RH (14% MC) That's a spike of 8% moisture content, which according to these figures is movement of 2% of the size of your board across grain.
Now take that figure of 2% movement and apply it towards a 3" thick neck. That's 1/16" movement on a flat sawn board. Because quartered is roughly half the movement of flat sawn, you're looking at 1/32" movement for 3" board.
(THIS INFORMATION IS THE MATH AND SCIENCE USED TO ACCURATELY PREDICT WOOD MOVEMENT IN LARGE QUANTITIES. IT'S EXTREMELY ACCURATE WITH APPLICATIONS OF WOOD FLOORING AND SUCH, AS OVER THE WIDE LAY OF THE FLOOR, IS AVERAGE OF THIS MATH IS SHOWN TRIED AND TRUE. EVERY INDIVIDUAL PIECE OF WOOD IS DIFFERENT SO THIS EXACT WOOD MOVEMENT IS NOT A PROMISE.)
So one other thing to point out with stability of necks, is if you have a fingerboard glued down restricting the movement of the wood, the wood has to move somewhere. That's when you would potentially find more twisting patterns of flat sawn necks versus quartered.
So to some this up, I will stand by the statement that flat sawn IS less stable than quarter sawn, because the science says so. The reason why people can build with flat sawn necks and that they work is because the rules of RH are generally followed. If the piece of wood you are about to build with, despite the orientation of the grain, is completely acclimated and stable with a moisture content of 8%, and this neck never leaves an environment where the EMC is 8%, in theory that piece of wood would never move due to moisture.
This is exactly why we are told to shoot for 40-50% RH year round, and it is so that your wood that is acclimated to 8% moisture content stays that way, and stays stable.
I haven't found a source with the exact information pertaining to old wood, as far as WHY it's more stable, but I have told it has something to do with the constant movements back and fourth as it expands and shrinks which over time gives it stability, and makes it less susceptible to movement. That would explain why instrument builders seek 50+ year old wood. You'll also find if you resaw veneers out of a 2 year old board opposed to a reclaimed board from a very old piece, that even with both acclimated, the new wood will move drastically more than the old. Potato chips anyone?
-Dan
I mentioned that I couldn't remember the exact movement rates so I did refer to some of my wood info to get accurate information.
Wood is hygroscopic, which means it takes on and gives off excess humidity. That is the reason why it's important to give wood time to acclimate to your shop before working with it.
RH is Relative Humidity, which is the level of humidity in the air, aka the environment the wood is in.
MC is moisture content, which is the level of moisture in the wood.
The relationship between the two is the EMC, the equilibrium moisture content. The EMC is the point to where the wood's MC matches the RH.
When RH goes up, the MC goes up and the wood swells. When RH goes down, MC goes down, and wood shrinks. If you put a dry board in a very humid room, it will take some time for moisture content to raise to match the higher RH. When the moisture content of the wood does equal out to the same moisture of the RH, that is what is called the equilibrium moisture content. It's the balance between the two.
A chart showing examples of the relationship between RH and MC read:
RH MC
0% 0%
25% 5% (This figure is why we shoot for a range of 35-50% (depending where you are) The ideal
50% 9% moisture content is around 6-8%, which according to this chart is higher than 25% (5% MC) 75% 14% and lower than (or maximum of) 50% RH (9% MC))
99% 23-30%
If you constantly control your shops humidity at a dead set 40% all year round, you can expect your wood to be at the 6-8% moisture content. As soon as your piece of wood (or guitar) leaves that shop or environment, and goes to say 75% RH (A regular summer in the midwest, if not even higher) That piece of wood (or guitar) is going to continue to acclimate and expand (take on moisture) until it reaches the matching 14% moisture content to the environments 75% RH. Again when that piece of wood reaches the 14% MC that relates to the 75% RH, that is what is called the equilibrium moisture content.
Cool, a page full of numbers, but what do they mean? How does that moisture affect your guitar or project? Well, the science in those numbers is there to accurately estimate how much your wood is going to move. This is when the slab cut piece of wood is less stable than the quarter sawn. Stable meaning as little movement as possible. By no means does "less" stable mean "not" stable, but less is less, which is the equivalent to "less" desirable. Also one of the reasons why flat sawn necks are frowned upon; there's a better option.
Now, species of wood does affect the rates, as some move more or less than others, there's a general rule on predicting wood movement. Also quarter sawn moves roughly half of the figure flat sawn does.
Most flat grain species of wood - For each 4% change in moisture content (MC) the board will shrink or expand 1%. So in the figure of having an acclimated board to 35% RH (6% MC or so) and then a move to 75% RH (14% MC) That's a spike of 8% moisture content, which according to these figures is movement of 2% of the size of your board across grain.
Now take that figure of 2% movement and apply it towards a 3" thick neck. That's 1/16" movement on a flat sawn board. Because quartered is roughly half the movement of flat sawn, you're looking at 1/32" movement for 3" board.
(THIS INFORMATION IS THE MATH AND SCIENCE USED TO ACCURATELY PREDICT WOOD MOVEMENT IN LARGE QUANTITIES. IT'S EXTREMELY ACCURATE WITH APPLICATIONS OF WOOD FLOORING AND SUCH, AS OVER THE WIDE LAY OF THE FLOOR, IS AVERAGE OF THIS MATH IS SHOWN TRIED AND TRUE. EVERY INDIVIDUAL PIECE OF WOOD IS DIFFERENT SO THIS EXACT WOOD MOVEMENT IS NOT A PROMISE.)
So one other thing to point out with stability of necks, is if you have a fingerboard glued down restricting the movement of the wood, the wood has to move somewhere. That's when you would potentially find more twisting patterns of flat sawn necks versus quartered.
So to some this up, I will stand by the statement that flat sawn IS less stable than quarter sawn, because the science says so. The reason why people can build with flat sawn necks and that they work is because the rules of RH are generally followed. If the piece of wood you are about to build with, despite the orientation of the grain, is completely acclimated and stable with a moisture content of 8%, and this neck never leaves an environment where the EMC is 8%, in theory that piece of wood would never move due to moisture.
This is exactly why we are told to shoot for 40-50% RH year round, and it is so that your wood that is acclimated to 8% moisture content stays that way, and stays stable.
I haven't found a source with the exact information pertaining to old wood, as far as WHY it's more stable, but I have told it has something to do with the constant movements back and fourth as it expands and shrinks which over time gives it stability, and makes it less susceptible to movement. That would explain why instrument builders seek 50+ year old wood. You'll also find if you resaw veneers out of a 2 year old board opposed to a reclaimed board from a very old piece, that even with both acclimated, the new wood will move drastically more than the old. Potato chips anyone?
-Dan