True Dimensions of 4/4 Green Lumber
The terms "4/4" and "RWRL" take some explaining. Here's the voice of expertise and experience. October 8, 2005
Question
When someone wants green rough lumber that's 4/4, what thickness are they expecting, in inches? Also, when they ask for RWRL, is there a typical minimum length and width?
Forum Responses
(Sawing and Drying Forum)
From contributor A:
Four quarters of one inch, in other words one inch thickness.
From contributor B:
Some saw fresh boards at one and one eighth inch thickness (1-1/8")to compensate for shrinkage.
From contributor C:
To contributor A: Are you sure 4/4 means they are expecting 1" boards? I thought that when green, 4/4 was always 1/8" over 1".
From contributor D:
4/4 green is cut 1-1/8 to allow for shrinkage as previously posted. After kiln drying, we rough surface to 15/16. If it was sawed 1" it would be 7/8" after drying which is useless in our operation.
From contributor E:
As far as random width and length, I think somewhere around 4 inches give or take a quarter inch would be the minimum for width.
As a cabinet/furniture maker, anything less than an eight foot length is undesirable. However, I am sure there are those who would use three or four footers if that’s the way a log sawed out and the stock was nice.
From contributor B:
RWRL is more subjective. It depends on the end use I presume, be it domestic or exotics.
Narrows (3"-4") and shorts (3 to 6 feet long) will often sell for less money per board foot, even in exotics such as Pau Ferro and some others.
From contributor F:
4/4 is quite tricky terminology. To my understanding the grading rules for 4/4 require that after drying and dressing (planing), a true 3/4" is attainable. So for practical application narrower boards can be pushed a bit and sawn right at an inch off of the saw mill. Wider boards may need to be sawn closer to an inch and an eighth to still get 3/4" true, due to cupping tendency of wider boards. The other measures also have requirements for what final thicknesses are attainable and can be "played" with a bit depending on customer needs (optimizing resources).
Hopefully I’m not confusing the issue, but this seems to be a common misunderstanding.
From contributor G:
To contributor C: For RWRL lumber, the width and length comes into play with the grading rules for some species of wood. I just received the latest edition of "CABINETMAKER" and Gene Wengert has an article about grading lumber, and how the dimension of it relates to its grade.
From contributor H:
It sounds like you are cutting hardwood in which case surfaced thickness for 4/4 is 13/16" green and 3/4" kiln dried. If you cut it green at 1" and it shrinks 1/16" in drying, that leaves 3/16" or 3/32 per side to clean up both sides. This is nearly impossible. I cut 1-1/8" to 1-1/16" green with grade hardwood. If the customer is siding a horse stall it means 1" green even in hardwood. In softwood 4/4 is 1" green. The end use is very helpful to know so you are not cutting 1-1/8" when 1" would do.
From Gene Wengert, forum technical advisor
The NHLA grading rules require green or air dried lumber (at the time the lumber is graded) to be at least 1.00 inches thick in the area used to determine the grade of the piece. If thinner, then it is counted as 3/4 and not 4/4. If parts of the area used to determine the grade are over 1.25, it is still a 4/4 piece if some parts are under 1.25. If there is a large variation from the thinnest to the thickest, then the grade is determined, as normal, but then the word "miscut" is added.
Traditionally, green 4/4 hardwood lumber is cut to a thickness of 1-1/16 to 1-1/8 inches AVERAGE. This allows for some variation due to equipment variations without being under 1.00. Mills with little thickness variation can easily cut to 1-1/16 average and the customer can still achieve the required thickness after drying and planing. (Note that kiln dried thickness requirement is less than green thickness.) When I first started in this business, it was common to see a lot more thick and thin variation. Average thicknesses were 1-1/8 plus a little more. But each 1/32 extra thickness is 2% yield loss, so, today the lumber is thinner on the average but still it is not too thin.
From contributor J:
We saw the majority of our hardwood grade lumber 1/8” over – 4/4=1-1/8”.
We started out sawing for one outfit that insisted on 1-1/4”. When I got older and wiser, I guessed that they were using a lot of 5/4 in the product and likely most of our 1-1/4” 4/4 would “clean” to 1 inch for 5/4. So they were getting 20% for free.
We started dealing with another broker that dried and surfaced their own lumber and they said anything over an inch. They didn’t really want it over and 1-1/8” because it just caused them more milling and waste to deal with.
We custom saw some grade lumber from customers from their own logs. If they ask us how thick, we suggest 1-1/8”. But some have their own ideas and ask us to saw their lumber as thick as 1-1/4 and as thin as an inch.
In short, it’s best to get it clear with your customer before you saw.
From the original questioner:
I just wanted to take a moment and thank Gene and all the rest for the helpful information in your responses. I thought it was a basic question, but now I see it's not as "clear cut" as I thought.
From contributor K:
I have noticed that when milling on my Woodmizer, if I go by the 4/4 rule my lumber comes out 15/16ths thick. If I try and saw a full 1 inch, I have to adjust the guide every cut. I’m using the double hard blades.
