I recently purchased rocking chair plans from Hal Taylor, and plan to build a chair from them mid-spring. Hal convinced me that I should use stock that’s a bit drier than the 11% MC of air-dried stock in my area. His suggestion was to use 6% MC kiln-dried wood.
I oven-dried some cherry and then let it equilibrate in my house. This exercise indicated that right now 6% MC is right at equilibrium. However, it’s currently unseasonably dry, our summers in Oklahoma tend to be pretty humid, and I wouldn’t be surprised if equilibrium changed by at least a few % seasonally. Joints in a bed I made from air-dried stock suggests this is the case. So, I could either use slightly wetter wood and expect a little shrinkage in the winter, or use 6% and risk swelling in the summer. Because of the sculpted nature of the joints for this chair, movement in either direction would likely be noticeable. So, do you experts out there recommend I go with 6% MC, or should I shoot for 8-10% as a happy medium? Or am I being way too anal-retentive about this?
On a related note, for this project I plan to dry some fresh-cut walnut using a dehumidifier, following methods described on this forum. I plan to take the MC down slowly and allow periodic rest periods to relieve stress in the wood. Suggestions any of you have regarding this process are appreciated.
-Day
Replies
Day,
Your wood should be in equilibrium with your shop conditions, or there will be movement during building. That's no good. If 6% MC is in equilibrium with your shop conditions now, use the wood. But using wood with 6% MC in your shop during the humid summer is going to give you problems and you'll need to let it c ome to equilibrium at those conditions.
The advice, simply to use wood at 6% MC makes no sense.
Whatever you build should be designed to accomodate the ambient moisture changes that it is going to experience.
Rich
Thanks for your response, Rich. I should clarify that Hal's suggestion was to use wood that had been dried to 6%, not necessarily wood that was maintained that that MC.
I have no means of controlling the environment in my shop, so my plan is to keep the parts inside the house except when I'm working on them. There don't seem to be any safeguards factored into the chair design to compensate for wood movement, but then the only wide pieces are in the seat and headrest, so perhaps wood movement is less of a concern than I'm giving it.
Day,
I have seen this recommendation before as though drying wood to 6% MC vs some other value imparts some improved quality. It doesn't.
Wood needs to be dried to between 8-11% MC and used in about that range for quality construction of furniture and similar pieces. It could certainly be taken down to 6% by the ambient conditions in your shop and that would also be fine. But if your shop supports a wood MC higher than 6%, there would be no advantage to using wood that had been dried to 6% MC.
Let's say the ambient conditions in your shop are such that wood of 9% MC would be in equilibrium with the air. If you brought wood into your shop that had just been released from a properly set up drying program and had 9% MC, it would be ready for use. No further drying would be of any benefit. There would be no reason to take it down to 6 % MC and then let it equilibrate to your shop conditions.
Rich
Hi -Day ,
The bottom line is wood can move and good design as Rich mentioned is key with this project for sure .
I have always believed that most hardwood lumber leaves the kiln at 6-9% mc . Regardless if it is 2% or 11% when moved to a different climate the wood will reach it's RH (relative humidity) in its new location .The same is true for a finished piece of furniture in most cases , out in the damp garage a piece may move and suffer differently than in the heated house .
A certain time of year your cabinet doors may have less or more space between split pairs and such .
Most important is that your stock is stable , if 8% is stable for you then use it then .
best of luck dusty
Okay Dusty and Rich, you've convinced me that it doesn't matter whether equilibrium MC is attained by going up or down the concentration gradient, as long as it's attained before working the wood. I really appreciate you both confirming my suspicions, as I'd hate to find out otherwise after the project is complete.
So now to my second question, that regarding drying fresh-sawn lumber. I've mostly worked with air-dried stock, but in the past have had the luxury of it sitting in a covered shed for 15-20 years. For this project, though, time is of the essence, so I plan to set up a box in my basement equipped with an incandescent light on a thermostat to maintain the temperature around 90 F, a small fan to move air, and a dehumidifier built into the side and set to run for a few hours each day. My goal is to have some 8/4 stock ready to use in three months. Does this time frame seem plausible? If necessary, I can select my pieces. from some standing deadwood I cut that should already be a bit drier than the live I harvested at the same time. The dead has been so for about four years, and is a trunk about 16" diameter. I haven't ordered a moisture meter yet, though I plan to soon, so I haven't a good estimate of the initial MC.
-Day
Day,
I don't think your home-grown kiln is going to do the job. It's one thing to air dry lumber. Enough can go wrong with that process alone and case-hardening (too-rapid drying of the outer fibers, locking in a wet core) can happen.
A drying kiln for lumber is as much art as science and it takes experience and a lot of loads to get it "right." Logs for drying should be sawed as soon as possible after felling. I have no idea how 4 y/o logs are going to fare in your drying process.
And last but certainly not least, when "time is of the essence" in a project, things invariably go wrong. Sometimes they can be foreseen, sometimes not, but the outcome is seldom good. "Rush drying" of 8/4 stock in a home-brew kiln? Not likely.
Rich
Rich,
Your skepticism is no doubt well-founded, as much of what I've read suggests that drying thick walnut is tricky business. And you can add my inexperience with drying as another potentially important source of problems. But let me explain my guarded optism for this endeavor.
First, from what I've read regarding kiln drying 8/4 walnut, water should not be removed faster than 3.3% per day, and a rate closer to 2% is a lot safer, especially early in the process. A drying schedule lasting 45-50 days seems typical for experienced kiln operators (based on a limited search on-line). For the purposes of this project, I can live with a drying time 2-3 times longer.
Second, I'm pretty confident of the condition of the 4-year-old dead wood. The sapwood has rotted off, but the heart wood looks excellent. The condition of this wood is likely to be superior to slash, as it hasn't been lying on the ground, and I know several people that have salvaged excellent stock from long-dead downed trees.
Third, I think I can control the environment reasonably well in my homemade box. It's located in a fairly humid basement, so I can open it up to retard drying, and close it up and run the dehumidifier at intervals to pull water out slowly. My plan is to simulate a daily cycle similar to what might be experienced in a solar kiln. I plan to keep careful records of the drying schedule and of MC via regular weighing and moisture meter readings. I also plan to calibrate the moisture meter by oven drying a sample to calculate true initial MC.
Lastly, I'm going to perform this experiment with a subset of the wood, with samples from both the live and dead logs, and sticker the rest outdoors to air dry. I hope I don't ruin the wood in my experiment, but if I do the loss will be minimal.
So that's the plan. I'll be pleased to receive more comments, criticism, or suggestions.
-Day
Well, knowing the possibilities, go for it!
If this little experiment actually works, I'll post the results on the forum.
-Day
Post either way.
-Day ,
Unless there is an emotional reason or value to the fresh sawn lumber (like your Grand Father planted the trees) why not use dry stock ?
My thought is if lumber could be dried in less time and still be stable , it would be being done . I'm not saying you can't BUT ,,, maybe you need to take the time restraint away and let the wood dry properly .
3 cents worth regards dusty
Dusty,
You nailed it on the head--there is a sentimental reason to use this wood instead of going out and buying some dry stuff. I'm building the rocker for my wife who is due to bear our first kid in July, and I'd really like to build it from wood I just harvested off the old farm in southern Oklahoma that's been in my family for several generations. I built our bed out of stock from the farm that was cut when I was 8 years old, and because of the source of the wood and the fact that I took it from logs to furniture myself, it has tremendous sentimental value to my wife and I.
If my drying experiment fails I'll either break down and buy some walnut or use some cherry I have on hand.
-Day
- Day ,
First off , congratulations on the new arrival .
Some hardwoods such as Eastern White Oak get air dried for several years before being kiln dried , I'm certainly not an expert on drying lumber , more of an expert on cutting big boards into small pieces and then gluing them back together ( makes little sense ). I think you would be bi - passing or taking shortcuts on your method of drying .
I have had time while making my own sawdust at work today and this evening to think more about your situation and I realize I'll be taking a risk by making this suggestion to you but what the heck , here goes !
By all means make your wife the chair , but how about making the chair out of stable ( store bought ) wood .
Dry your personal stock of farm wood slowly and properly and make your child a chair from it , perhaps the same design scaled down . This will give you several years more time before the little bundle of joy can actually use the chair that's just like Mommies .
Then you will have created two potential family heirlooms and many memories that will go along with the twin chairs ,,, oops I didn't mean you will have twins , but hey who knows .
again congratulations and best of luck to you and your wife
dusty
Hi Dusty,
Thanks for your thoughtful response. Your idea to save the wood and make a mini-chair down the road is an excellent one. The more I read about the early stages of drying wood without initial air-drying, the more complicated it gets.
That said, I think I'm going to give it a shot anyway. I'm certainly not an advocate of wasting good lumber, but I plan to do the trial run with around 50 bf--a small proportion of the estimated 850 bf I have. Based on what I've read, it seems that the trick early on when the wood is wet and weak is to keep water loss rates low, and increase it as the wood dries. So I plan to start the process with circulating air but no dehumidifier, a scenario not too different from what would be experienced in air drying. Obviously, my hope is that my schedule will be conservative enough to shorten the drying time significantly without damaging the wood. I hope the result is drying time somewhere between that expected from traditional and solar kilns.
If I don't have sufficiently dry wood by, say, April, I'll break down and buy some lumber. I'll keep you posted on how it goes.
-Day
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