Understanding Hardwood Lumber Grading
Reprinted with permission from the Feb/March 98 issue of Independent Sawmill & Woodlot Magazine
Today, NHLA grading rules are not only the dominant grading system for hardwood lumber in the United States, but also form the basis for much of the international trade in hardwoods.
Most hardwood lumber produced in this country is graded using the rules developed and maintained by the National Hardwood Lumber Association (NHLA). In 1897, hardwood lumber producers and users formed the NHLA to standardize the grading of hardwood lumber. Prior to that time, individual mills had their own grading systems for their local markets. The original NHLA grading rules were based on the number and size of defects as the major criteria. This changed in the early 1930's to grading rules based on the amount and size of clear cuttings. Other than slight modifications every once and awhile, the rules have been relatively stable since that time.
There are eight hardwood lumber grades in widespread use today. FAS is the highest and No. 3B Common is the lowest. In short, the higher grades of lumber have more large clear area than the lower grades. The basic concept of grading is that the grade of all lumber is determined from the poorest face or side of the lumber, with a few cases considering the better face as well. Lumber thickness (4/4, 6/4, etc.) is not considered when grading hardwood; the grades are based on the two faces alone.
A brief description of the basic grades are:
* FAS, which was years ago short-hand for the grade of "First and Seconds," which in turn originated from a combination of the very old grade of "Firsts" and the grade of "Seconds," is the highest grade of hardwood lumber. Most FAS lumber is exported rather than cut in the U.S. as its value, kiln-dried, is often more than $2 per board foot on the wholesale market.
* FAS 1-Face (F1F abbreviation) is a Select piece of lumber that is 6 inches and wider.
* Select is a No. 1 Common piece of lumber (the poorer side grades No. 1 Common) and the reverse side (the better side) grades FAS. The price of Selects and 1-Face is usually the same as FAS. Much of this grade is also exported, but if exceptionally long, wide, and clear on both faces, cuttings are required, then Select lumber is often used. Often, Select grade lumber is used in the Northern U.S., while 1-Face is used in the South.
* No. 1 Common (often called Common or just No. 1) is the standard furniture grade lumber, and provides a good selection of long, medium length, and short cuttings at a reasonable price.
* No. 2A Common (often just called No. 2 Common) has become the standard grade for cabinets, millwork, and other uses requiring medium to short cuttings. Often current prices favor using No. 2 Common instead of No. 1 common for furniture, even though yields are lower with No. 2.
* No. 2B Common is the same as No. 2A Common, except that stain and other sound defects are admitted in the clear cuttings. It is an excellent paint grade.
* No. 3A Common (which is often combined with No. 3B Common and the combination is sold as No. 3 Common) is widely used for flooring and pallets.
* No. 3B Common is graded on the basis of sound cuttings rather than clear cuttings. It is widely used for pallets and crating.
When cutting hardwood lumber into a usable piece of wood, often referred to as parts, the ratio of the volume of parts to the volume of lumber is called yield, and is usually expressed in percentages. In general, the higher the grade of lumber, the higher the yield. However, Select and 1-Face lumber usually have a yield (clear on both faces) that is the same as No. 1 Common lumber.
Unlike softwood lumber, where the grade reflects the strength and therefore the load carrying capacity and safety of a particular piece when used in construction, hardwood lumber grading does not require a certified or licensed grader. Anyone can grade; however, a trained grader will probably be more accurate and quicker than an untrained grader.
Also, unlike softwood lumber, hardwood lumber is not marked with a uniform system of symbols or stamps indicating the grade, although there may be some crayon marks that make sense to a grader or a particular mill.
The grading rules are quite complex and require study. Some of the basic concepts and grading requirements or rules are given in Table 1. The steps for grading a piece of lumber are straightforward. For example, consider a piece of lumber that is 6 and 7/16 inches wide and 10 feet 9 inches long (Figure 1).
Step 1. Determine the species. Some species have special rules that must be considered.
Step 2. Determine the surface measure (SM) of the lumber. SM is the width, in inches and fractions, times the standard length in feet with no fractions or rounding, and then divided by 12, and this answer rounded to the closest whole number. For our example, SM=(6-7/16 x 10)/12=5.36=5 feet.
Step 3. Determine the poor face, which is the side with the lowest grade, or if both sides are the same, the face with the least clear area when grading.
Step 4. Assume a trial grade for the piece of lumber and then see if all the conditions for that grade are met. For our example, assume No. 1 Common.
Step 5. Determine if the lumber size requirements-length and width-are met for the chosen grade. For our example, the minimum lumber size of 3 inches x 4 feet is met.
Step 6. Determine the number of clear cuttings (or sound cuttings for No. 2B and 3B Common and certain other cases) that are permitted. Note that often you can take an extra cutting, but then the yield requirement is increased. Always drop any fractions; do not round up. In our example, the number of cuttings permitted is (5+1)/3=2 at 66 2/3 percent yield. You can take 3 cuttings if you increase the yield to 75 percent.
Step 7. Determine the cutting yield required by multiplying the SM by 10 (FAS), 8 (No. 1), 6 (No. 2), 4 (No. 3A), or 3 (No. 3B). These numbers increase to 11, 9, and 8 for FAS, No. 1 and No. 2 respectively, if you take an extra cutting. The yield required is expressed in cutting units. A cutting unit is 1 inch wide by 1 foot long. In our example, the cutting units required is SMx8=5x8=40 units in two cuttings or 5x9=45 units in three cuttings.
Step 8. Locate cuttings to obtain the maximum area; then, calculate the cutting area. Make sure the cuttings' sizes are not below the minimum size for the trial grade. A cutting that is 5-1/2 inches wide and 4-1/3 feet long is 6-1/2x4-1/3=28-1/6 cutting units. Measure cutting width using inches and fractions, and length using feet and fractions. Do not round the answer, but keep the fractions. In our example, there are two large cuttings; both meet the minimum cutting sizes of 4 inches x 2 feet or 3 inches x 3 feet. The first is 6-7/16 inches x 4 feet, which gives 25-3/4 cutting units. The second is 5 inches x 4 feet, which gives 20 cutting units. The total for these two cuttings is 45-3/4 cutting units which is greater than the 40 required for No. 1 Common. There is no need to take an extra cutting.
Step 9. When the piece grades No. 1 common, check the reverse side to see if the reverse is FAS grade. If so, and if a few other requirements are satisfied, then the piece is Select or FAS 1-Face.
Step 10. Check to make sure that the piece qualifies for the anticipated grade in all other respects, which include the amount of wane (1/2 the length for FAS, for example), the amount of pitch outside the cuttings, and so on.
Clear cuttings are rectangular shaped areas, parallel to the edges of the lumber (not diagonal) that are free of knots on the grading face, and free of rot, pith, shake, and wane throughout the entire cutting as it is projected to the opposite face. The various cuttings cannot overlap each other. Mineral stain is admitted.
Sound cuttings are identical to clear cuttings except sound defects (such as knots, small holes, some discolorations, etc.) are admitted.
Table 1. Simplified Hardwood Grades.
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