Guitar construction:
Quarter sawn and other types of saw technique.
Talking about solid wood for acoustic guitar, there is deeper subject to follow up; how the wood/ board is cut or sawn. There are several terms that are being used both by (mill) sawyer and (guitar) builder. There are: quarter sawn, rift sawn, and plain sawn (many also use the term: flat sawn).
Which type of sawn wood is best for acoustic guitars? First, let’s distinguish what is quarter sawn, rift sawn and plain sawn.
Cutting method from the sawyer (mill) perspective.
Plain-sawn cutting method, also know as flat-sawn cutting methode. No wood is wasted with this method of sawing.
This second section is called the ‘quarter sawn’ method. But four methods can be distinguished within this category, namely:
- Top left: common quarter sawing
- Top-right: triple-cut quarter sawing
- Botom-left: Alternate quarter sawing
- Botom-right: Rift-sawn, also known as Radial quarter sawing
At Homestead we only use wood that has been radially quartersawn.
Grain Pattern on the board from the perspective of (guitar) builder/ luthier
A. Plain-Sawn
B. Quarter-Sawn
C. Rift-Sawn
As you can see in the above picture, a sawyer has different definitions than a builder. This is based on how the sawyer sees the ‘cutting pattern’, while the builder sees the grain pattern of the wood.
When a sawyer cuts a log using the quarter sawn cutting pattern method, it produces some quarter sawn-grain patterned wood and many rift sawn-grain patterned wood. While if a sawyer cut a log using a rift-sawn cutting pattern method, it will produce only quarter-sawn-grain patterned wood.
From this point forward we will use the term plain-sawn, quarter-sawn, and rift-sawn based on the grain pattern definition, from the builders’ perspective. (unless otherwise mentioned).
As you can see from the picture, quarter-sawn wood is produced in less quantity when using the plain-sawn- and quarter-sawn- cutting method. When using rift-sawn-cutting method, it only produces quarter-sawn wood, but it also generates more waste. This is why quarter-sawn wood is more expensive than other type of sawn wood.
Stability of sawn wood
Wood product is highly affected by the humidity. Before being used as guitar materials, each wood part need to be dried to 6% – 9% EMC (Equilibrium Moisture Content), the point at which a wood board neither gains nor loses moisture. In a place with a lot of seasonal change, the EMC will change with the season. That is why it is important that the humidity of the environment where the acoustic guitar is be maintained between 45% to 55% RH (Relative Humidity).
Quarter-sawn wood (B) has the most stability than other types of sawn wood because quarter-sawn wood has even sections between grains. Those sections will react to humidity more uniformly than the diverse sections of plain-sawn wood (A). A rift-sawn wood (C) will have fewer diverse sections between grain, but a quarter-sawn will still has the most uniform sections between grains.
See the picture below of how different types of cut can change wood’s shape and warp when humidity changes:
As seen on the picture, shape of quarter-sawn wood changes uniformly when it shrinks. Still, the best way to maintain your guitar is to have it or store it in an ideal environment, i.e. 45%-55% Relative Humidity and 17˚ – 20˚ C, then the wood on your guitar will not shrink nor expand.
The Strength of Sawn Wood
In comparing the strength of different types of sawn wood, we also need to look at how the wood is being used. For acoustic guitar materials, the top wood receives pull force from the strings from the head side of the guitar to the tail side. Sawn wood with straight grains running parallel to the strings is the strongest wood for this usage. The more slanted a grain in respect of the string’s direction, the weaker it is. With plain-sawn wood, the grains are asymmetrical and crosses with the string direction. This makes plain-sawn wood weaker than the quarter-sawn wood.
For the side wood, the wood will be curved into the contour of the guitar body model. For a wood to be able to be curved, the wood will be moisturized with water and will be pressed by heated plate on both side or by bending rod on one side into the desired form.
A quarter-sawn wood with straight grain will be easier to bend and is less susceptible to break during the bending process, while other type of sawn wood (rift and plain-sawn) is less easy to bend and have a higher chance to break.
For the back of a guitar body, the wood will be bent a bit, but further, there will be not much force that will stress the back of the guitar body. Because of this, the back of an acoustic guitar is more friendly for figured wood that usually comes from rift or plain-sawn. But regarding strength, since the stress point of a back wood is situated on the bent, between heel and tail, a wood with straight grain is stronger than plain-sawn wood.
The Sound of Quarter-sawn, Rift-sawn, Plain-sawn wood
A quarter-sawn wood has the most uniform density due to the even sections between grains, followed by rift-sawn, while plain-sawn wood has the least uniform density. The more uniform the density of a tone wood, the better it vibrates, which is important as a top tone wood. While for the side and back, tone wood needs to project the sounds created by the strings and from the vibration of the top wood. Density uniformity does not make much difference in wood as projector/ amplifier. The wood density itself (hard or soft wood) determines the sound of tone wood as projector/ amplifier.
Conclusie:
Quarter-sawn wood is the best wood as acoustic guitar tonewood. It provides the strongest and the most stable wood for the guitar body. As top wood, a quarter-sawn wood is a must to provide the best open sound of a guitar. Homestead guitar uses only quarter sawn wood for its top, side, and back of our guitars.