Lumber Grading School
This summer I have been out at the sawmill trying to understand how the process all works. I’ve spent a decent amount of time with my brother, Jake, and the other lumber grader watching them flip the board and scribble some marking on it after quickly measuring with a ruler stick. Little did I know everything they had to consider for each board before making that mark and all in just a matter of seconds!
I signed up for the National Hardwood Lumber Association (NHLA) lumber grading short course, which is a weeklong class as an introduction to lumber grading. The complete course which my brother, dad and grandpa all attended is a 12 week long class for Dad & Jake, and back in grandpa’s day it was 6 months long!
During the start of the first day of class we did cross multiplication of whole numbers and fractions, without calculators, for hours! We learned how find the surface measure of a board & board feet.
After so many of examples you start to get the feel of it, and maybe even catch on to a few shortcuts which are very helpful. There is a lot of math that has to be done, quickly, in your head.
Surface Measure = (width (inches) x length (ft)) / 12
BF = SM x thickness
We start talking about the different grades of lumber…
There are 9 standard grades, each has their own set of rules for board size, minimum “cutting” size, basic yield, what the Surface Measure is needed and additional yield needed for each grade in order to take an extra “cutting” to try and get a better board. Then there are Special Yields on top of all that. Then there are sound and unsound cuttings AND you have exceptions for each grade depending on the species of wood. HOLY FRIOJLES! This all needs to be memorized!
This class reminded me of my first couple weeks in Costa Rica taking classes when I didn’t know a word of Spanish. My mind was going in circles trying to remember this new language and from doing so much math in my head. I was fried by the first day!
We also had to memorize, word for word some very important definitions, here are some excerpts for examples…
Cutting – … portion of a board or plank obtained by crosscutting or ripping or by both. In common grades, cutting shall be flat enough to surface two sides to standard surface thickness after it has been removed from the board. In the grades of Selects and Better the entire board must be flat enough to surface sides to standard surface thickness…
Clear – Face Cutting: Cutting having one clear face (ordinary season checks are admitted) and the reverse side sound as defined in sound cutting. The clear face of the cutting shall be on the poor side of the board except when otherwise specified…
Sound Cutting – cutting free from rot, pith, shake and wane. Texture is not considered. It will admit sound knots, bird pecks, stain, streaks or their equivalent, season checks not materially impairing the strength of a cutting, pin, shot and spot worm holes. Other holes 1/4” or larger are admitted but shall be limited as follows: one 1/4” in average diameter in each cutting of less than 12 units; two 1/4” or one ½” to each 12 units and on one side only of a cutting…
So you get the idea, lots of specific details and numbers to remember. Then a lot of the rules have exceptions that will cross reference other rules and paragraphs, something like … such and such 10% is allowed expect as admitted in paragraph 36 or with a minimum width in all grades may be 1/4” scant in width and the10% admitted in paragraph 10.
I feel like I’m studying the constitution in law school! And every rule and exception and 1/4” measurement can make or break the difference in a grade of lumber, which can make a big difference in the value of a board (it varies a lot depending on species but could be around 30% difference in price.)
Understanding the value of each grade of each species and grade is important as well. You have to know if it’s worth actually chopping off a certain amount of wood in order to upgrade the board.
We start going over each of the standard grades in detail after getting a general feel for grading. So I’m going to do my best to summarize what lumber grading is all about without too much detail.
Ultimate Goal in lumber grading –
finding the most value in a board, which would be your best grade possible to sell.
This is determined by the amount of clear wood in the board.
Each grade has a percentage of clear it has to have to fit the grade.
FAS 83 1/3% clear
1 com 66 2/3% clear
2 com 50 % clear
The grader has to figure all this out in his head and mark it in a matter of seconds. In order to determine this percentage you make “cuts” in the board around the knots and other defects. This is where I was confused. The “cuts” the grader makes are just imaginary for the grader. They are not physically cut out in the board (at this stage anyways). So for each grade depending on the board size (surface measure) you are allowed so many “cuts” to get the % of clear wood. There are certain circumstances when it’s permitted to take an extra cut, but then the total amount of clear wood needed also increases.
When you look at a board there are some steps to follow to help you from forgetting,
- Determine the Surface Measure of the Board
- Determine the Poor Face of the Board – (side with the lower grade or if both have same grade it’s the side with the least amount of cutting units)
- Take an educated guess on the % of clear wood on the board (guess the grade)
- Prove the grade
- Is the board big enough (length & width) to fit grade?
- Find the “cuts” & are the large enough to fit the grade?
- How many cuttings are allowed for this surface measure?
- Are you allowed an extra cutting, if needed? (depends on SM for grade)
- How many cutting units (% of clear wood) do you need for this surface measure & grade?
- Are any of the defects too large for the assumed grade?
- What grade have you proven?
- Check the Thickness of the cuttings and the board.
A good grader can grade a board in one second, and has to factor in all of these questions and know all the rules like instinct. As well as understanding what the defects characteristics and limitations are for each species. It’s really impressive to watch someone grading lumber quickly now after having a better understanding of what they go have to consider.
Basically it’s a puzzle. You have to know what the defects are, what’s allowed, and how you can work the board to get as much clear wood as possible. I promise it’ll give your mind a work out trying to figure it all out!