Question
Recently I purchased 450 bf of 4/4 #1 common red oak, R1E and S2S (ripped 1 edge and surfaced on 2 sides) from a regional sawmill. I'm using it for oak plank flooring in my woodshop (now under construction). I'm sorting the boards (random widths and lengths) by rough width, and grouping lengths together to get approximately 28.5' of usable length (accounting for knots, and grade variations, etc.). I then rip each group of boards to the finished width of the board having the smallest width (trying to minimize waste). I then lay each group of boards lengthwise, end to end, and arrange them for best joint overlap and look, and then trim to their combined finished length. In general, how much finished square footage should 450bf yield? Or, put another way, what amount of bf is needed to cover 370 square feet?
Forum Responses
(Sawing and Drying Forum)
From contributor R:
That is entirely dependent on how much waste you have from ripping to width and culling knots and undesirable areas from each board. A board foot is a 1 inch thick board 12 inches wide and 12 inches long. Exactly the same as 1 square foot.
In a formula:
370' /.75=493'
493'+ 35% waste=666bf
With the last number that came up, I might avoid this project altogether! Maybe round up to 700bf so you don't spook the supplier :)
My guess is:
a) Board length X average board width/144 = N.nn bf.
b) Somebody at their facility then builds/assembles enough boards to equal my order.
c) Then my order was R1E'ed and planed.
If correct, at this point, in theory, the 450bf order is now about 405bf (accounting for 10% loss due to ripping one edge). This should then yield an average of 75% usable stock based on the #1C grading yield. Then I should apply the average waste percentage calculation.
Which is the biggest area of "shrink," 1) the mill's initial estimation of total bf, or 2) the loss due to ripping one edge? I realize that my orders are small stuff/mice nuts compared with other orders. However, being informed and understanding what is customary helps me do a better job of planning and buying.
Now when dried, there will be 6% shrinkage, but the industry uses 7%. The footage green is therefore reduced by 7% after drying. However, some folks add 7% back to the dry footage to obtain an estimate of the green footage. This is an illegal practice since 1977. The actual footage at the time of sale of KD lumber is called the net board footage. If you add 7%, then you have the gross footage. (In the terminology of contributor O above, it is illegal to sell lumber based on the pre-kiln-drying footage.)
The grade of No. 1 Common guarantees that there will be one or more (the number depending on lumber size) large clear rectangular areas (on the worst side of rough lumber) whose area totals 2/3 (67%) of the area of the lumber. For example, with a 4/4 piece of lumber that is 7-1/8" wide and 8 feet 10" long, you have 5 BF and are permitted to have one or two clear areas, each clear area being at least 4" x 2' or 3" x 3'. The area of these two clear cuttings must be 480 square inches. (As a variation, you can also have three clear areas that total 75% of the lumber's surface or 540 square inches.)
So, with this restriction on clear areas, and because this 67% is the minimum, and most lumber pieces will therefore have more clear area, it is easy to see why the actual yield when cutting small furniture parts, cabinet parts or flooring will potentially be quite a bit higher than 67%.
Note that when grading planed lumber, the clear area is judged from the best face. If I rip lumber on one edge and if the saw kerf is 1/8" and I remove 1/8" strip of wood, then this 1/4" loss on a 6" wide piece of lumber is 4%. A 10% ripping one edge loss is excessive on 6" wide lumber pieces.
