Question
Drying a green load of northern 8/4 red oak. Does anyone have a good schedule to use? I have never dried a load of 8/4. Any helpful hints?
Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
There is none better than what is in DRYING HARDWOOD LUMBER and DRYING OAK LUMBER. You using a DH or steam? No.1 Common and Btr? Green means "tree green?"
Drying Hardwood Lumber
Drying Oak Lumber
In any case, correct sampling procedures must be followed, per the book. The schedules in the book, developed over 60 years ago, have been successfully used on billions of BF of red oak. Of course, the schedules are just one part of the overall process. Operator skill is also important. I tried to put all these facts together, plus my 40 years of experiences, when I wrote DRYING OAK LUMBER and also DRYING HARDWOOD LUMBER.
I looked at your website, and you have nice looking kilns. A commercial steam heated kiln is a very powerful tool, so when drying something fragile like heavy oak, you can do some real damage real quick. Drying heavy oak in a conventional kiln is how much of the heavy oak is dried. I use a pre-dryer, but when I dry 12/4 I opt to use only a kiln for the absolute control. Any controller can mislead you from time to time. They are subject to intermittent failure like any piece of equipment. I always back up with thermometers and/or hygrometers.
When drying heavy, I or my assistant go in and look at the lumber and samples every day, even on weekends. In time you develop a pattern for how often you need to weigh them, but I suggest walking into the kiln and looking at the lumber and samples daily. Mark existing checks going in and watch them. Know where your moisture gradient is by doing oven tests, especially before you get close to 115 degrees. When you dry heavy oak for a living you use what you have, make it work, and the end result is your report card. Myself and others I am sure have gone back into the kiln at night because you second guessed yourself and did not feel comfortable with the decision you made. It is part of drying heavy oak.
I consider myself to be a decent operator; I know of others who are better. I am not trying to scare you but I am warning you of just how big a deal it can be. You are talking more money on 8/4 and the potential for degrade goes up almost exponentially. Gene's and other books are a must to start with - I still refer to them regularly - but it goes way beyond that. It is done every day to the tune of hundreds of thousands of board feet, so welcome aboard and good luck. I just cannot overemphasize the need to use extra caution.
So, based on experience, we developed schedules that are to be used along with the drying rate and other factors, as stated in the book. Never would the schedules be used blindly. The drying rate gives precise values of daily moisture loss that should not be exceeded. The schedule gives RH values that cannot be drier and temperatures that cannot be hotter. The schedule suggests using cooler temperatures. Likewise, the daily inspection of samples is suggested with the idea that when checks are seen, the operator slows down the drying using the specified tools.
In the old days, kilns were slow to respond to any changes in temperature or RH and had low air flow. With today's kilns designed to dry maple, poplar and 8/4 oak, they are often running at conditions no longer expected in the schedule.
Handheld hygrometers today and in the past and many remote thermometers in the past can measure to the closest 1 degree F (and sometimes only 2 F in those old brass instruments). Controls were often 1F degree resolution and accuracy. However, today's controls often measure and control to within 0.1 F. So today's controls far exceed most portable instruments. Closer control is essential. Avoid relying on imprecise handheld instruments. A good control system can be trusted.
So, with 50 MBF of 8/4 northern red oak worth $75,000 when done drying, how much risk do we want? Usually, we want little risk, so we should, at the least, make sure we are using modern controls with 0.1 F resolution. We need to have fans that do not have too much air flow (200 fpm might be best). We need proper stacking and loading. We need proper MC samples with daily inspection. And so on. We need to use the correct kiln schedule, modifying the schedule as appropriate, following the instructions in the book. And we need to monitor the daily rate of drying - the wood's response to the kiln's conditions.
As all defects occur at high MCs, we can reduce the risk by using mild conditions initially, such as in a warehouse pre-dryer. Then when we get to the kiln, the risk of developing new quality loss is practically zero.
Finally, if we cannot live with the long drying time and the risks, but possibly low drying costs, we can use contributor D's vacuum kiln. In fact, his kiln is so easy, we could get a second job or even spend time on vacation every week. Contributor D's kiln does work... I've seen the final product.
Contributor D, to say you can walk away after turning you vac kiln on is not accurate either. If I buy one, will you put that into a written guarantee? Gene, if the latter were true, who would need consultants?
I respect the books that are out there and the authors like Gene who wrote them. I know decades of research has been poured into them. I also am impressed with your vac kilns. I think it is an interesting concept and it has its applications, but no mechanical or electrical apparatus is void of failure. That is all I meant. Regarding the thermometers, hygrometers and such, you have to start somewhere for a basis when equipment fails or appears to be inaccurate and this is where I believe in the old school methods. In my years of drying I have had one or two thermometers be off a degree or two, but when I look at three of them at the same location and they equate, I gotta think they are right and the rtd or controller is wrong. Without even opening up one of my drying manuals I know they talk of using such tools.
When I start a kiln, I set the heating ramp rate, chamber pressure, and pressure dead band. That's it. Set and forget. But I do need to add RH control if I'm drying white oak.
As far as monitoring the condensate is concerned, there is normally no monitoring until the last day or two to verify that the wood is equalized. And that is done by a glance at the computer, not checking samples.
Unfortunately, some drying equipment manufacturers must cut corners to be cost competitive. Some customers buy the lowest priced units rather than the best drying quality. In these cases, control systems often suffer. As one example, I convinced a client of mine in MO to change his 6/4 red oak predryer controls from conventional to Lignomat. He was, with new controls, measuring the air conditions just before the air entered the stacks rather than up near the ceiling. Measurements were very accurate with EMC values being within at least 1/2%. The first thing noted was that the temperature and EMC conditions in the predryer became very steady. Next, they noted much less degrade... Significant indeed, as a manufacturing plant is not geared to measure quality, so only big changes will be noted. He also had more sensing points. He had a large error checking routine. Finally, with the computer that was part of the system, the operator could check the conditions in the pre-dryer from any remote computer including the one at home at any time, day or night.
Contributor D, I like your son's controllers. They seem very practical as does he. I just have not decided yet on a system. We are talking apples and you're talking oranges pertaining to the quantity of lumber we are required to dry. Your vac kilns are a great concept but they do not fit all applications.
Here are the three things you need to dry lumber effectively:
1) Hygrometer
2) Oven tests
3) Common sense
CONTROLLERS: Technology has pushed itself past the point where it is fully utilizable. I could care less if I can determine what the temperature is to 1/10th of a degree. In Gene's own words, his schedules were used "effectively" even with the old gas tube control/record units, so wad up your thinkin' that the fancier the control looks, the better it is. I've got a whole wall full of the latest and greatest, and I still go into the kiln every day to take readings from a $100 hygrometer. That's a number that I'll rely on.
SCHEDULES: Contributor K spent a lot of effort explaining how an operator should read and react to the lumber at hand, not what the good book says. Oven tested samples will give you a starting basis, and be your guide through the whole run. The schedules should be guides, and be considered speed limits for drying. I have never started up 8/4 oak anywhere close to the book, and would never consider it. As for working off a probe system to give you a hint of where your drying MC and rates are, good luck, and back up the firewood truck.
Keep in mind that the schedules of today were developed back when there were limitations on heating capacity, airflow capability, and venting capability. Things have changed. Also, lumber quality was much better back then. We are now drying lumber that used to be made into railroad ties, and the acceptable amount of degrade was much higher back then than it is now.
COMMON SENSE: After doing all of the above, keep detailed records and learn from every loading. Experience plus luck does not equal quality.
Contributor D, I've been down the vacuum path, and have two huge problems:
1) Stress relief
2) Consistency of moisture content.
Because you go the Easy-bake-oven route, you have no true handle on your variability. But boy, it sure was easy!
Can you give us the model number and manufacturer of your $100 instrument? Also, if you still have the book, can you give us any of the four items? Similarly, can you do the same for your control instrument? It would be usual to see a $100 instrument accurate to within 2 or 3 F and no better than 5% RH.
As I visit many dry kiln operations every year, I have yet to find schedules that deviate far, if any, from the book. Having worked well for 50 years, I am sure the book schedules are still good guides indeed.
Common Lumber Name | A | B | C |
Hardwoods | |||
Alder, Red | 9.9 | 19.2 | 2506 |
Apple | 10.9 | 31.7 | 4132 |
Ash, Black | 9.3 | 23.4 | 4132 |
Ash, Green | 14.3 | 27.6 | 3590 |
Aspen, Bigtooth | 10.3 | 18.7 | 2439 |
Aspen, Quaking | 10.3 | 18.2 | 2373 |
Basswood | 6.2 | 16.6 | 2174 |
Beech, American | 8.9 | 29.1 | 3793 |
Birch, Paper | 8.8 | 25.0 | 3260 |
Birch, Sweet | 11.9 | 31.2 | 4065 |
Birch, Yellow | 9.2 | 28.6 | 3723 |
Buckeye | 8.9 | 17.2 | 2235 |
Butternut | 11.3 | 18.7 | 2440 |
Cherry | 13.8 | 24.4 | 3184 |
Chesnut, American | 11.6 | 20.8 | 2708 |
Cottonwood | 8.5 | 16.1 | 2102 |
Dogwood | 6.8 | 33.3 | 4331 |
Elm, American | 10.2 | 23.9 | 3116 |
Elm, Rock | 12.2 | 29.6 | 3860 |
Elm, slippery | 11.5 | 25.0 | 3251 |
Hackberry | 11.8 | 25.5 | 3319 |
Hickory, Bitternut (Pecan) | 14.7 | 31.2 | 4062 |
Hickory (True) | |||
Hickory, Mockernut | 9.1 | 33.3 | 4332 |
Hickory, Pignut | 9.3 | 34.3 | 4332 |
Hickory, Shagbark | 10.9 | 33.3 | 4333 |
Hickory, Shellbark | 6.6 | 32.2 | 4195 |
Holly, American | 8.3 | 26.0 | 3387 |
Hophornbeam, Eastern | 7.9 | 32.8 | 4266 |
Laurel, California | 15.1 | 26.5 | 3456 |
Locust, Black | 21.2 | 34.3 | 4470 |
Madrone, Pacific | 7.8 | 30.2 | 3925 |
Maple (Soft) | |||
Maple, Bigleaf | 12.8 | 22.9 | 2980 |
Maple, Red | 13.1 | 25.5 | 3318 |
Maple, Silver | 12.4 | 22.9 | 2981 |
Maple (Hard) | |||
Maple, Black | 12.3 | 27.0 | 3523 |
Maple, Sugar | 12.3 | 29.1 | 3793 |
Oak (Red) | |||
Oak, Black | 11.7 | 29.1 | 3792 |
Oak, California black | 16.4 | 26.5 | 3455 |
Oak, Laurel | 6.3 | 29.1 | 3791 |
Oak, Northern red | 13.6 | 29.1 | 3793 |
Oak, Pin | 13.0 | 30.2 | 3928 |
Oak, Scarlet | 13.2 | 31.2 | 4065 |
Oak, Southern red | 9.6 | 27.0 | 3520 |
Oak, Water | 10.4 | 29.1 | 3793 |
Oak, Willow | 6.4 | 29.1 | 3790 |
Oak (White) | |||
Oak, Bur | 15.4 | 30.2 | 3928 |
Oak, Chestnut | 10.1 | 29.6 | 3858 |
Oak, Live | 17.5 | 41.6 | 5417 |
Oak, Overcup | 10.7 | 29.6 | 3860 |
Oak, Post | 11.0 | 31.2 | 4063 |
Oak, Swamp chestnut | 10.7 | 31.2 | 4063 |
Oak, White | 10.8 | 31.2 | 4062 |
Persimmon | 7.0 | 33.3 | 4332 |
Sweetgum | 8.9 | 23.9 | 3115 |
Sycamore | 10.7 | 23.9 | 3115 |
Tanoak | 9.0 | 30.2 | 3926 |
Tupelo, Black | 10.4 | 23.9 | 3116 |
Tupelo, Water | 12.4 | 23.9 | 3115 |
Walnut | 13.4 | 26.5 | 3454 |
Willow, Black | 8.6 | 18.7 | 2438 |
Yellow-poplar | 10.6 | 20.8 | 2708 |
Common Lumber Name | A | B | C |
Softwoods | |||
Baldcypress | 13.2 | 21.9 | 2844 |
Cedar, Alaska | 14.4 | 21.9 | 2844 |
Cedar, Atlantic white | 10.9 | 16.1 | 2100 |
Cedar, eastern red | 16.4 | 22.9 | 2981 |
Cedar, Incense | 13.1 | 18.2 | 2371 |
Cedar, Northern white | 11.1 | 15.1 | 1964 |
Cedar, Port-Orford | 12.6 | 20.2 | 2641 |
Cedar, Western red | 12.2 | 16.1 | 2100 |
Douglas-fir, Coast type | 12.3 | 23.4 | 3049 |
Douglas-fir, Interior west | 13.2 | 23.9 | 3116 |
Douglas-fir, Interior north | 14.0 | 23.4 | 3048 |
Fir, Balsam | 9.9 | 17.2 | 2236 |
Fir, California red | 10.6 | 18.7 | 2437 |
Fir, Grand | 10.7 | 18.2 | 2371 |
Fir, Noble | 10.1 | 19.2 | 2507 |
Fir, Pacific silver | 10.4 | 20.8 | 2711 |
Fir, Subalpine | 10.5 | 16.1 | 2101 |
Fir, White | 12.2 | 19.2 | 2506 |
Hemlock, Eastern | 12.6 | 19.8 | 2573 |
Hemlock, Western | 11.5 | 21.8 | 2847 |
Larch, Western | 11.3 | 25.0 | 3251 |
Pine, Eastern white | 12.3 | 17.7 | 2303 |
Pine, Lodgepole | 11.5 | 19.8 | 2576 |
Pine, Ponderosa | 12.6 | 19.8 | 2573 |
Pine, Red | 12.2 | 21.3 | 2777 |
Southern yellow group | |||
Pine, Loblolly | 12.9 | 24.4 | 3183 |
Pine, Longleaf | 15.0 | 28.1 | 3658 |
Pine, Shortleaf | 12.9 | 24.4 | 3183 |
Pine, Sugar | 12.6 | 17.7 | 2302 |
Pine, Western white | 10.0 | 18.2 | 2370 |
Redwood, Old growth | 14.9 | 19.8 | 2573 |
Redwood, Second growth | 13.2 | 17.7 | 2302 |
Spruce, Black | 11.3 | 19.8 | 2575 |
Spruce, Engelmann | 10.0 | 17.2 | 2234 |
Spruce, Red | 10.6 | 19.2 | 2506 |
Spruce, Sitka | 10.8 | 19.2 | 2506 |
Tamarack | 12.0 | 25.5 | 3318 |