Question
When sawing cherry, what are the dimensions I want to cut my boards? If someone asks for 4/4, 6/4, or 8/4, what do I actually need to mill them to? If someone asks for 4/4 (1"), should I cut them to 1 1/8"? When selling 4/4, and milling them to 1 1/8" thick, do I charge for the 1" or the 1 1/8" thickness?
Forum Responses
(Sawing and Drying Forum)
From contributor S:
I contract cut for a local hardwood mill and they request that 4/4 be cut 1 1/8" for a finished size of 15/16". I believe that 4/4 (and under) is sold as 1" when calculating board feet, whereas 5/4 is 20% more. Not real sure on that, as hardwood is not a big thing where I live and work on the left coast, where everybody's thinking is stuck in softwoods.
Some of the big western mills that are into big box store sales are providing hardwoods 1" nominal (3/4" actual) that are selling as if they were 4/4. Widths are also nominal, e.g. 6" is actually 5 1/2". Within the rule book but kind of a rip-off to the unknowing. And much of the oak boards are glue-ups to provide wider boards - rip-off times two.
Sawing thinner may make an extra board, but if you lose a board for being too thin, it is not worth the money or time. If you are sawing and drying for your own wood, then take the chance because you can sell the thinner stock.
However, if you are air drying the lumber first and then selling, the minimum thickness requirement is still 1.00", but you may have 1/16" thickness shrinkage in air drying on some pieces (many will be closer to 1/32"). So, then you need to cut 1-1/8" to assure 1.00" after air drying on all pieces.
Note that each 1/32" of added thickness is roughly 3% in yield, so cutting 1-1/8" when 1-1/16" is acceptable for the customer, will cost you 6% in yield, or 6% in value. Stated another way, someone that wants 1-1/8" should be paying about 6% more for that lumber compared to 1-1/16" thickness average. If they do not pay more, then you are losing 6%, as your yield will be 6% less.
If you are selling wholesale and the buyers are real picky, then you run the risk of having your whole load rejected because of a few thin boards. You need to run your lumber business with enough margin that you don't have to worry about 1/16" of thickness.
If I saw pine siding, I'll drop down 1" and the boards will be about 7/8"+. If the customer wants to plane these boards smooth, though, he'll have to go below 3/4" when it's all dressed.
2. How many more cuts do I need to make on a face to gain a board if my blade is 0.055 thick and set at 0.022?
3. I buy hardwood logs down to 10 inch tops, and say the average log size would be 16 inches in a daily average (large butt logs over 20" are quartersawn). So what is your average log size?
4. If with a good 16" log I make a 6x8 tie, how many boards will I make at 1 1/8th? At 1 1/16th?
I ask this not to be a smart aleck, but to let you know that when the blade hits the wood out here at the mill, things do not figure the same as they do on paper. I get 13 to 14 boards either way, just slabs 3/16th thicker and a bit wider face on the boards of the 1 1/16th cut.
Now on stock that you are going to dry and plane, you may look at it like this. There will be one less pass in the planer and any board that is too thin may be sold as thinner stock. The slightly wider faces may look better, but the board will edge out the same after planing since you are just removing the wood at a later date. Wood chips are selling good right now. Just something to think about while you are eating sawdust.
Note that to cut 1-1/16", a mill needs to have very little variation in thickness. Indeed, many of today's mills do have much less variation in thickness than the older mills had. In fact, it is indeed possible that the 10% thinnest pieces with a modern mill cutting 1-1/16" will actually be thicker than a mill cutting 1-1/8" with wider variation. So, at 1-1/16" from a modern mill, the customer will find that the thinnest pieces are actually thicker than in the past or from a poorer mill.
The shrinkage in drying to 12% MC (softwoods) is on the order of 4% or just over 1/132". For hardwoods, drying to 7% MC, the shrinkage is on the order of 1/16". These numbers are for quartersawn lumber which shrinks nearly twice as much as flatsawn. So for a flatsawn mill, the thickness will be even greater after drying.
Bottom line: On a modern mill, it would be worthwhile exploring a thinner average target size due to the potential increased yield... 3% increase for each 1/32" thinner.
I work frequently with one mill that is nearby and they cut over 3 million BF a year at 1-1/16", and their lumber is highly regarded. In fact, in this economic downturn, they are still doing very well.
It is people like contributor H that end up eating that 50 bdft because it did not plane out. Now is where the problem comes. After a while he figures out I am the reason he is eating 50+ bdft a day (250 a week) and no longer takes my lumber. Now I have lost a market for my gain of just $250 a week and have to figure out where to go with that 25mbdft of lumber. Can not afford to lose a market right now, and contributor S can not eat that much fiber.
For in-house market I may take the gamble, but for my wholesale markets I do not. I like having wholesalers calling me wanting more lumber every week.
Finally, in most, if not all cases, the customer is worried about the thinnest pieces and not the average thickness. It is therefore impossible to come up with an average thickness if one does not know the thinnest piece that can be used by the customer.
When we measure the thickness of lumber coming off of a particular machine, we get a variety of thicknesses. If we plot the thicknesses on a histogram (or frequency graph), we see that the thicknesses form a bell-shaped curve (called a normal distribution). The average (or actual target thickness) will be the peak of the curve. If, in addition to calculating the average thickness, we calculate the standard deviation (SD, done with the push of one button on a $20 calculator), then we can determine the spread of the data. The average thickness plus one SD, minus one SD, will make an interval that will include roughly 2/3 of the thicknesses. Plus or minus two SD will include 95%. A typical SD on a good mill is 0.015. So, if the average thickness is 1.063", then two-thirds of the thicknesses will be between 1.048 to 1.078". Ninety-five percent will between 1.033 to 1.093". And virtually all will be between 3 SD, or 1.018 to 1.108".
From the calculations above, we can determine if the thinnest or thinner pieces are too thin. For example, in the data above, 2-1/2% of the pieces will be between 1.018" and 1.033" (roughly 1-1/64" to 1-1/32"). Also, we can ask ourselves if we can afford to be 100% perfect. Sometimes it is better to make a few thin pieces (thin by a few 1/1000") and give the customer a refund than to make every piece overly thick.
Note that by measuring the thicknesses in a particular order, we can also determine if the leading end of the lumber, the middle, or the tailing edge is often thin. We can also determine if the lumber has wedging or bevel, if the saw itself is causing the variation in thickness, or if it's the log that is moving (or a combination of both).
Also, note that many of today's band mills (such as the Wood-Mizer LT-40HD) produce lumber with a very smooth surface. Such lumber requires less planing after drying, as the wood is already quite smooth. This means that the target thickness at the sawmill can be reduced slightly. Also, we are seeing more knife planers with opposite heads that remove equal amounts off of both top and bottom surfaces, so a thinner piece will have a good chance of cleaning up on both faces.
As a final comment, one might think that cutting lumber 1/32" too thick just costs 3% in profits. But it is well to remember that it is also costing 3% more timber harvesting (do we really want to waste our resource?), as well as the fuel and energy used for manufacturing. Our forest resource is just too valuable to waste (and not just money value).
Bottom line is, why take the chance? So you cut at or under 1-1/16 for your customer, and he brings the wood to me for kiln drying and planing. We can't get all the boards to clean up at 3/4. Whose reputation is at risk, yours or mine? It's me, because I handled it last. Did we do anything wrong? No, but the customer thinks we did. So I'll say it till I die, thinner cut wood sucks!
Gene, I do respect you and the work you do for the industry, so don't take it personal.
This is more than "on paper," as the US Forest Service has done hundreds of sawmill improvement studies and has documented the results and the improvements in target size. It is certainly possible that your mill cannot cut a smaller average thickness, but many mills can be improved so their variation is reduced and target is safely decreased.
A stumbling block to accomplishing this is that sometimes a customer says they want 1-1/8" lumber; however, a check with them shows that it is the thinnest pieces they are concerned about and not the average (which is also what you indicated in your last post). So, the real key is not to indicate an average size but rather to indicate the minimum thickness (or maybe the minimum thickness for 99% or 98% of the pieces).
Not only have I done many sawmill thickness studies and helped many of the mills improve, I also managed a mill for several years, so I appreciate the reality of sawmilling too.
