Hard maple is a wonderful, expensive, nearly white wood used for almost every application imaginable both today and even prior to the colonization of the U.S. Uses include cabinets, furniture, bowls, bowling alleys, bowling pins, flooring, piano frames, dulcimers, spinning wheels, cutting boards, tool handles, veneer, pallets, particleboard, paper, firewood, and even railroad ties. What is this ubiquitous wood that we call maple?
Hard maple lumber, which is also called sugar maple, sweet maple, black maple and rock maple, comes from two species. Most lumber comes from sugar maple (Acer saccharum) and a small amount from black maple (Acer nigrum). Once hard maple lumber is manufactured, it is impossible, even under magnification, to separate the lumber into the two individual species. The name "hard" actually means that the lumber is substantially harder than the other maples, including the grouping called soft maple.
What person hasn’t had pancakes topped with wonderful, sweet maple syrup? Sugar maple is the tree that produces maple syrup. Although the other maple species have sweet sap that can be boiled down into syrup, the sugar maple has the highest (twice as much) sugar content in the sap, as well as is the best tasting. A grove of producing sugar maple trees is called the sugar bush. Also, did you know that it takes about 40 gallons of sap to make a gallon of syrup?
Certainly, the white color is the primary characteristic of hard maple that makes it so desirable, Yet, achieving this color is not automatic. Logs must be freshly harvested; lumber must be promptly sawn, especially in warm weather; and drying must be done correctly to achieve the best whiteness. Within the tree itself, there can be brown colored heartwood that is not highly desired in manufacturing. For trees that are younger than 75 years old, it is not common to have much brown heartwood, unless the tree has been injured, such as by tapping for syrup, previous logging, or even by woodpeckers and sapsuckers. Such injury causes the tree to form brown heartwood at the injured site and lowers the grade of any lumber produced.
After drying to 7 percent MC and planing to 13/16 inch, maple weighs 3-1/3 pounds per board foot. Black maple is slightly lighter. Hard maple is one of the heavier hardwoods.
Maple is subject to blue staining and also chemical staining if not dried promptly and aggressively. Chemical staining occurs when the starches and sugars oxidize to pink or gray colors.
For whitest color, maple must be stacked promptly after sawing using dry stickers. Protect the stacked lumber from rain and snow. The best control of color is achieved by kiln drying immediately after sawing. Initial kiln conditions must be fairly dry; the humidity should be no higher than 72 percent RH. Avoid temperatures over 120 F while the lumber is above 30 percent RH; avoid going over 160 F at any time, except for stress relief.
Maple is not exceptionally stable. Therefore, the final moisture content when the lumber leaves the kiln must be very close to the in-use moisture content. For most uses, 6.5 percent MC is the ideal final target, with almost all pieces being within + or – 1 percent MC.
Gluing and Machining
Being a dense wood, maple requires surfaces to be glued to be freshly prepared and perfectly flat. Small errors will result in low strength joints.
Because the grain in maple swirls quite a bit, planing and other machining operations will frequently be planing against the grain. To avoid chip out and torn grain, knives must be very sharp. Avoid over-drying the lumber (under 5.5 percent MC is over-dried), as brittleness and poor machining will be increased.
Hard maple changes width and thickness when the RH changes...about 1 percent size change running parallel with the rings (tangentially) when there is a 3 percent MC change, and 1 percent change across the rings (radially) when there is a 6 percent MC change.
Sugar maple is a little (10 percent) stronger, stiffer and harder than black maple. The bending strength is 15,800 psi, stiffness 1.83 million psi and hardness is 1450 pounds. This is similar to red oak.
Color and Grain
Maple is a wonderful, nearly white wood. Unfortunately, there is no definition of "how white is white" so different suppliers will have different whiteness. Developing a close understanding with lumber suppliers is essential if very white color is required.
Most markets also only use No.1 Common and higher grades. In addition to the standard grades, some markets will also ask for "No.1 white", which means that both edges and faces must be all sapwood (no brown heart). "No.2 white" means that one face and both edges will be sapwood. (For example, the specification might be 500 BF of 4/4 No.2 white, No.1 Common hard maple.)
The hard maples frequently develop small little burls or curls in the wood, which we call bird’s eye. Bird’s eye maple is quite attractive and valuable, especially to the smaller craftsperson market. The hard maples also develop grain deviation called fiddle back, which again is quite desirable. The causes of such growth features is unknown.
A troublesome growth defect is called mineral. These are small spots are often greenish in color and lenticular shaped (several inches long in the vertical, long direction) within the wood. These streaks are not defects in the standard grading rules, but may be defects for the ultimate customers. High mineral content logs will be common in a particular geographic site, for reasons unknown. I have seen more mineral in sites that have also been grazed by cattle.
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