Q: What is the difference between quartersawn and flatsawn lumber?
A: The basic difference is that the annual rings (when viewed from the end grain of the lumber) run from edge to edge in flatsawn (also called plainsawn or flat grain) and run from face to face in quartersawn (also called riftsawn or vertical grain). It is just a matter of how the log was oriented when the lumber was sawn. According to many texts, when looking at the end grain, if most (80 percent or more) of the annual rings are at an angle to the face of 45 to 90 degrees, then the lumber is quartersawn. But within the industry we can find some slight variations in definitions.
Flatsawn lumber has an angle between the annual rings and the face of the lumber between 0 to 45 degrees, when viewed from the end grain. Riftsawn has an angle of 45 to 70 degrees. Quartersawn is 70 to 90 degrees, although 60 to 90 degrees is sometimes used. These are the most common definitions. However, some people would also argue that quartersawn is a specific type of riftsawn so rift goes from 45 to 90 degrees. True vertical grain would be 90 degrees (that is, the rings are perpendicular to the wide surface).
If you are selling or buying lumber or veneer, my advice is to check with the supplier or customer to make sure that you and the supplier/customer agree on the definition.
When looking at the processing differences, quartersawn has a great deal of figure due to the rays forming many areas called ray flecks. On the other hand, flatsawn has interesting grain due to the annual rings.
Flatsawn shrinks more (percentage-wise) in width than quartersawn, but quartersawn shrinks more than flatsawn in thickness. Knots in flatsawn are small circles, while in quartersawn, knots are longer and slender, often running from edge to edge, and are called spike knots. Sapwood, if present, is typically on one edge and can be easily edged off of quartersawn lumber.
Quartersawn has very little likelihood of surface checking, honeycomb and cup during drying. Flatsawn has a higher risk of raised grain after machining, especially in heavy grained species like Southern pine. Quartersawn is more resistant to liquid movement through the lumber, face to face. Quartersawn holds the paint better when the wood is subjected to wetting and drying. Quartersawn lumber is more expensive than flatsawn because yields from the log are substantially lower.
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