GRADE DEFECTS IN HARDWOOD TIMBER AND LOGS
GRADE DEFECTS IN HARDWOOD TIMBER AND LOGS
Combining grades: FAS and Select
Our basic philosophy about the FAS and Select grades is to not combine them like our competitors. To understand why, first we have to look at the differences between the grades FAS, Select and #1 common to understand what the grades mean, and why these grades exist.
NHWA Lumber Grading
For all of you out there that have not been through a NHWA grading course or school, and don’t have the grading rules handbook, I will explain the main differences. Once a person understands better the grading rules, you will see why we don’t combine FAS and Select. Not that there’s anything wrong with it, but coming from a woodworking background, why pay for something you don’t need, or get something that you can’t use.
First, let us look at the grades for hardwoods as shown in the rules handbook, and a brief description on how boards are graded. Lumber is graded on appearance. We are looking for the largest areas of a board that are clear, without defects. I won’t get into any definitions about defect in a board. These areas are called cuttings, or clear cuttings. Different grades allow different sizes and amounts of cuttings on the face of a board. The better the grade, the bigger the area of clear wood there is.
The next thing to remember is that a board is graded on both sides, and the worse side determines the final grade. The best grade is called FAS. This stands for Firsts and Seconds. These grades are the best you can get and were combined, or adopted, by the NHWA because the members, who are the people in the lumber industry, voted it in. Firsts required 91 2/3 percent clear area and Seconds required 81 2/3 percent. Now, FAS, which is both Firsts and Seconds combined, requires 83 1/3 percent clear area. Some people think that FAS stands for “face all sides”.
The second best grade is called F1F, or FAS1F, (FAS 1 Face). This grade is not used much here in the Midwest because the trees are not as big as in other parts of the country. F1F is a bit better than Select and graded the same, except the minimum board size is 6 inches wide and 8 foot long.
The next grade is Select, or SEL. This is a combination of FAS on one face and #1 on the other face. Select boards must be 4 inches wide and 6 feet long or bigger. The better face still needs to grade 83 1/3 percent clear for the given area of the board, but it does not have to be as large as FAS graded lumber.
The next grade is #1 Common. This grade requires 66 2/3 percent clear area on the worse face.
Then you have 2A, and 2B at 50 percent, and 3A, and 3B at 33 1/3 percent. Basically, the required clear area drops as you get down to a 3A board.
Choosing the Right Grade For Your Application
Now let us look at two types of applications and what grade one would use. If you were going to build a piece of furniture, like a open bookshelf, and wanted to use clear solid hardwood for the sides, top, and shelves, the best choice would be FAS because of its higher area of clear wood. Because both sides of each board are exposed, you wouldn’t want to spend money on lumber that has knots on one side. You need long pieces of clear lumber, clear on both sides.
If you wanted to build a dresser, or piece of furniture where you only see one side of a given board, you would want to chose a Select grade because the worse side grades a #1 Common, and you don’t see that side.
So back to our way of thinking about keeping the grades separate. Many boards, when they are being milled off a given log, will be clear on one side. As the board is cut and taken off, the backside is exposed and if one or more knots appear on that face, that worse face will determine the grade of that board. So a board with one face that is totally clear of any defect may have one knot on the other face. That knot might be right in the middle or near one end. If you are building bookshelves and you can only buy Select or Better, how much Select are you going to get and how much will be FAS? If half of it grades Select, you have half a pile of wood that won’t work for the sides of the bookcase you are building. You don’t want knots showing up on an exposed side. So you paid for wood that you can’t use. So then you are stuck cutting shelves out of the “Select” graded boards; cutting around that one knot that is on the worse face.
The other side of this is if you are building a dresser and buy Select and Better where half the boards are FAS and clear on both faces. What a waste of a perfect board. There is a big difference between one side of a FAS board and the #1 Common side of a select board. So why pay one price for everything if you don’t need it. And why get narrow Select boards that only have to be 5 inches wide and 6 feet long when you need bigger pieces for a given project.
That’s why we grade and sell the two grades FAS and Select differently. One can see why they combined Firsts and Seconds into one grade because they were so close in appearance. But we feel that there is too big a difference between the grades FAS and Select (with a #1 Common face) to throw them into one group. If all you need is Select, that is all you should pay for. That’s why we sell them separately.
Almost all sawmills purchase logs based on both log volume and log quality. Processing high quality, large logs costs less per board foot of lumber produced, and yields a larger percentage of high grade lumber, than does processing smaller or lower quality logs. Higher grade lumber with lower costs means higher returns; thus, a mill can afford to pay more per board foot of volume for larger and/or higher quality logs than for smaller or lower quality logs.
The log grades presented here were developed nearly 50 years ago by the USDA Forest Service (USFS). The three log grades in the USFS grading system are No.1, No.2 and No.3 – sometimes called F1, F2 and F3, with “F” standing for factory. Most logs will fall into one of these three grades. Two additional “qualities” are also often encountered: a higher grade called “veneer” and a lower grade, “cull.” Neither is included in the USFS factory log grading system nor are they discussed here. The USFS factory log grades – No. 1, No.2 and No.3 – are quite close to the individualized, independently developed, log grades used in many mills in Wisconsin and throughout the East and South. USFS grades, however, offer several distinct advantages to the sawmill: 1. The grades separate logs of the same size by at least 20% in value.
2. The grades allow easy estimation of lumber volume yield by NHLA grade, based upon log size and USFS grade. 3. With price information, value yields for different log sizes and USFS grades are easily computable. 4. The USFS grades provide a basis for a mill to compare its yields from different sizes and grades of logs to actual industry standards. This paper further explains the potential benefits which can be realized using the USFS hardwood grading rules. The rules are described and illustrated, and grading procedures are explained in detail, including the definitions and treatment of log defects. IMPORTANCE OF USFS GRADING RULES The primary intent of developing the USFS grades was to provide at least a 20% value separation between logs of equal size but different grades. This value separation allows the buyer a certain confidence in knowing what to pay for logs. In other words, the buyer knows that a No.1 log is at least 20% more valuable than a No.2 log, which is at least 20% more valuable than a No.3 log. The value separation arises because different grades of logs produce different grades of lumber. For example, consider a red oak log 16 inches in diameter and 16 feet long (Table 1). Regardless of its grade, the log will produce roughly the same total volume of lumber. However, the volume of lumber in each grade, and therefore the total value of lumber produced, will vary with the log grade.
GRADING HARDWOOD LOGS Mastering the USFS log grading system is not difficult, and close adherence to the following guidelines will ensure that grading is accurate. The key to accurate grading is determining which externally visible bark anomalies, or “defect indicators,” are signs of underlying defects and which can be ignored. Note that grading defects are often NOT related to scaling defects. Scaling defects are those defects that reduce the volume of sound wood; grading defects, on the other hand, take away from the appearance or limit the usefulness of the wood. Clear Cutting Area The log grading system is based on clear areas called cuttings. To begin grading, the log is divided into four equal sections or faces. Each face is one quarter of the circumference, extending the full length of the log. The faces do not overlap each other; hence, the four faces completely cover the log’s exterior surface. The faces can be rotated into the most advantageous position. Usually this means that the faces are rotated into a position that concentrates as many defects as possible into one face. This “worst face” is not considered in grading. Likewise, the best and second best faces are not considered, other than to assure that they are of equal or better quality than the third best face. It is the third best face that is used to establish the grade. (However, often all faces must be inspected to establish which face is actually the third best grading face.)
The grade of a face is based on the clear areas, or clear cuttings, of the face. A clear cutting is an area that is the full width of the face (that is, one quarter of the log’s circumference) and as long as possible without including any defect indicators. The grading rules establish minimum lengths of clear cuttings for each log grade, and maximum number of cuttings permitted on a face (Table 3). Each log grade requires the cuttings to occupy a minimum percentage of the scaled length (Table 3). (Note: The entire log length can be used for the cuttings, even though the scaling length may be shorter.) The proportions for various log lengths are calculated in Table 4. As a short cut, remember this: For a No.1 log, “log length (in feet) times two” gives the inches that can be lost while maintaining 5/6 of the yield; for a No.2 log, “length times four” equals the allowable loss (in inches) to maintain 2/3 yield. The USFS clear cuffing requirements for a No.1 face are quite similar to the rules for clear cuttings in FAS lumber grades-minimum length of 7 feet for a clear cutting and clear cuttings occupying 10/12 (or 5/6) of the surface area. Therefore, a No.1 face can be expected to produce FAS (or perhaps Select or FAS-1 face) lumber when sawing begins on this face. For a No.2 face, the rules for clear cuttings are similar to No.1 Common lumber rules – 3-foot minimum length and clear cuttings occupying 8/12 (or 2/3); therefore, a No.2 face will likely initially produce No. 1 Common lumber. Finally, a No.3 face has rules similar to No.2 Common lumber – 2-foot minimum length and clear areas occupying 6/12 of the surface; No.3 faces will produce No.2 Common lumber initially.
Defects, as indicated by bark anomalies or indicators, cannot be included in clear areas. The following guidelines for identifying defects or their indicators are standard: ● A distortion of the bark clearly indicating an overgrown knot is a defect. ● A slight distortion of the bark that is believed to indicate a defect that extends into the wood for a depth of 15% or more of the log diameter is graded as a defect. ● A small distortion of the bark, not clearly an overgrown knot, is not a defect in 15-inch or larger logs. ● Grub holes or other insect holes are defects, with the following exceptions: Logs 16 to 19 inches in diam., disregard every 6th hole Logs 20 to 23 inches, disregard every 5th hole Logs 24 to 27 inches, every 4th hole Logs 28 inches and over, every 3rd hole ● Bird peck is ignored in grade 3 logs. Fresh bird peck (the hole is open and not occluded) is ignored in all grades. Bird peck is a defect in Grade 1 and 2 logs when there are more than four pecks per square foot. ● Bumps are a defect if their height is greater than 1/12 their length (i.e. height to length ratios (H:L) are greater than 1:12). Low bumps have a H:L of 1:12 to 1:6; medium bumps, 1:6 to 1:3; high bumps, 1:3 or greater. Clear cuttings can include 1/4 of the length of a low bump on each end, or 1/8 of a medium bump. ● An adventitious branch 3/8 inch or less in diameter is a defect in logs under 14 inches in diameter. On larger logs, only every other adventitious branch is considered a defect. For soft hardwoods, adventitious branches are not a defect in Grade 3 logs. ● Straight seams, frost cracks, and splits are ignored if they are on the line dividing two faces. Surface seams, cracks and splits are ignored if their depth is less than 15% of the log diameter. Deep seams, not included in the above cases, are defects as follows: If full length, they are a defect. If not, one-third of the length can be included in a clear cutting (but not at the end of a log); if not showing at the end, one-fourth of each end of the seam can be included in a clear cutting. ● Spiral seams, spiral frost cracks, and spiral splits deeper than 15% of the log diameter are defects. End Defects End defects are disregarded if they are in the heart center, the central 40% of the log diameter. The remainder of the log end is divided into two concentric, ring-shaped areas, each of a thickness equal to 15% of the log diameter, called the inner and outer quality zones (Figure 1). Disregard rot, heart check and ring shake that extend into only one quality zone and are within one quadrant. If the defect extends into both outer and inner quality zones, consider it as a defect as follows: If the defect extends full length, it is a full length defect; if it extends partially along a log, one third of the defect (at the end where the defects tapers out) can be included in a clear cutting. ● Holes, bird peck, bark pockets, grub holes, and gum spots are ignored in grade 3 logs. In grade 1 and 2 logs, when the affected area extends more than half the width of a quality zone, and is also present in three quadrants at one end, or two quadrants on both ends, lower the log grade one grade. ● Stain is ignored in grade 3 logs. In grade 1 and 2 logs, stain, including stain in the heart center, is only a defect if the stained area has an effective diameter greater than one-half of the log diameter.
Other Considerations Total allowable sweep and crook are limited according to the rules in Table 3. To assist in calculation of sweep and crook deductions, consult Table 5. There are also allowable total scaling deduction limits, including sweep and crook, permitted (Table 3). Log Grading Procedures There are four steps to determining log grade: 1. Measure the average small-end diameter, inside the bark. For oval shapes, average two diameter measurements taken at tight angles to each other – the same procedure as in log scaling. Estimate the diameter of abnormal shapes or sizes. Measure the log length; any fractional footage is dropped, not rounded up or down. That is, a 12′ 10″ length is recorded as 12 feet. 2. Establish the location of the four faces, and choose the third best face. (Note: Occasionally, several faces may have to be graded (as in Step 3) to determine which face is the third best.) 3. “Grade” the third best face based on the log size and the clearcutting requirements (Table 3). 4. Adjust the grade determined in Step 3, as necessary, for end defects, excessive sweep and crook, or large scaling deductions (Tables 3 & 5).
LOGS SHOWING EVIDENCE OF METAL WILL BE SEPARATED AND CHECKED WITH OUR METAL DETECTOR.