I am quoting on a table project and found some 12/4 x 16′ x 16″ clear Walnut
that I am interested in using for this 108″ x 36″ x 2″ thick table top, and would
be interested in any feedback using air-dried stock that is this thick. I was told
that the current moisture content is about 14%. How much movement can I
expect vs. kiln dried wood and any other feedback would be appreciated.
I will probably have it planed to about 2-1/4″ thick to start and I was also
wondering how long I should wait to continue planing?? Thanks in advance!
Fritz1
Replies
The amount of movement you can expect will depend on the relative humidity of where the finished piece will live. Has nothing to do with air dried or kiln dried. (Though for walnut, air dried sometimes has more vibrant coloring). Also, you seem to imply you have only the one board. You will need a minimum of 3 to make the table you want.
Hello Ben,
I have Three boards 12/4 x 16' x 16". so I have plenty of wood for this project.
Thanks for your help.
Fritz
Hi, Fritz!
While in some ways I agree with much of what has been advised to you, I have a slightly different take on the situation.
First, are the boards currently relatively straight-- no big cups, bows, or twists? If they are really crooked right now, it indicates reaction wood from a leaning trunk, and that wood will be unstable forever with any moisture change, which we have to assume in the real world. If the boards are relatively straight, we can proceed.
Second, are you making this table for a particular customer? If so, what sort of interior environment will the table end up in? If it is a very dry house (dry winter heat and heavily airconditioned in the summer) it is going to lose a lot of moisture when it is in that house. It needs to lose that moisture slowly and evenly and without improper restraint. If the table will be in a house that tends to be very similar to the outdoor environment, then there will be little chance of a problem. Also, moving it into the house in between the dry seasons (in the spring or fall) can help it ease into the dry summer or winter environment, at least a little.
Third, you have a definite advantage working with walnut (mahogany is also unusual in this way) in that these two woods have almost equal percents of shrinkage in the radial and tangential directions. If they start out flat, this leaves them flat when the moisture content changes. If you had wanted to use red oak, there would have been no way in hell you could have restrained 2" thick material from cupping.
Fourth, a few weeks in any non-extreme environment is not going to change the interior moisture content much on 3" thick wood. The one exception to this is the ends, where moisture is lost much more quickly. If your shop is very dry, seal the ends of the boards to keep them from checking. Make sure you provide good finish sealing to the end-grain of the finished table, or the ends may check (or the glue joints fail at the ends) from rapid drying of the last inch or two of the top while the bulk of it stays the same moisture content and hence the same width.
Fifth, as mentioned in another post, use good design for the connection between the top and the base. It is critical to leave adequate room for movement for the top, or it will split itself apart. This top will almost surely shrink across its width in use, and then shrink and swell much less from one season to another in the interior environment. There are tables in books of how much % of shrinkage each species of lumber has with a given percent of moisture loss. You could estimate with them about how much the top will shrink in width as it dries. (Here in the Southeast the interior MC is figured to be in the 6-8% range.) The typical attachment methods are to use slotted screw holes (except for the center one, which is round, and keeps the top centered on the base) or clip blocks and a notch in the base batten.
Sixth, as also mentioned in another post, you want to finish the top and bottom the same so that moisture loss is approximately the same from the top and bottom. If much more is lost (or more rapidly) from one side compared to the other, the top will try to warp. Years ago I saw a table with a thick walnut top that was totally warped, and had pulled the screws out from the base, just because one end sat in the sun every day; the top lost much more moisture and shrank much more rapidly, so the top cupped up seriously.
Seventh, when you are planing down the lumber, try to take off about the same from each side if you have the option. This will give you more likelihood of having a new thinner board that has approx, equal moisture contents on each side.
Eighth, as also pre-posted, you may have much more beautiful color variation than commercially kiln-dried wood, which is steamed before kiln-drying to even out the color, esp. between the heart wood and sap wood. It's actually the steaming process that kills the color, not the kiln drying.
That should be enough for the moment; to me it would be worth the risk to try to make a spectacular table! (I just a year ago finished a 9' walnut table, tho I started out with kiln-dried 8/4 lumber, so the final thickness was about 1.5". Expect it to be heavy! I couldn't pick up the full top by myself to move it. I made this table 12 sided; 2 long sides, 2 ends, and each corner was cut away with 2 sides at 30 degrees instead of one at 45. Gave much more of a feeling of roundedness without being round. I also used the same kind of angle motif on the trestle base. I wish I had pictures, but I made it for my photographer, and it is in his dining room instead of his studio. No telling when I will see pictures of that piece!)
Anyway, there is more but I'll stop here. Any more questions, just ask.
JHarveyB
Awesome!
Your approach to answering the question was exceptional.
I'm building walnut table tops 48"x 78" x 3/4". Useing 12" stock...4 pcs per top.
Shop humidity is high. Their living environment is heated and air conditioned.
What kind of precautions would you take?
Bob
Fritz,
As the first poster said, whether or not the wood was kiln dried makes little or no difference to its movement.
Also the current moisture content makes little difference provided you allow the wood sufficient time to acclimate to your shop, if you don't do that, you will definitely have trouble as you work with the wood. Given the thickness of the wood, the boards will probably need to be stickered for at least a few months in a heated shop space before they stabilize at what will likely be a lower moisture content, but this will depend on local conditions.
Since you have no way of controlling the climate that the table will be used in, and where it might be moved to in the future, that also will make no difference, you simply design the table for large seasonal moisture changes using standard design details to allow for wood movement. The finish on the wood won't change the need for good design. Properly designed, the table should be able to be moved from the tropics to a bone dry arctic climate without joint failure or uncontrolled warping.
Planks that wide are almost certain to contain broad expanses of flatsawn wood that will probably cup significantly between times of high moisture content and low. If it important to the client that the table stays reasonably flat, you won't be able to use the planks as is for making the top.
As always, I highly recommend "Understanding Wood" by Bruce Hoadley as a must read for anyone who intends to be a cabinetmaker.
John W.
I would prep the edges and glue it up now. DO NOT plane to finish thickness but skim plane both sides. Move the slab into your house for at least three weeks. Obviously, you can build the base during this amount of time.
Hopefully, any significant contortion will happen during the three week 'house sitting' period and can be planed out when you're working the slab to finished dimensions. When it's sitting in your house, the slab needs to be leaned against the wall as upright as possible (long dimension on the floor).
You want to challenge this slab to move. Putting it in the house will do just that. Normal cross grain movement is to be expected and you should know how to construct for that eventuality. What you're trying to flush out during the three week wait is significant twist/bow/cup and all that crap.
cstan,I'm curious why you would glue up the panal before allowing the wood to come to equillibrium. Wouldn't you want the boards to go through their contortions first, so that you could plane square edges before glue up?Tom
You want to evaluate the movement of the slab as a unit , but yes you should put the lumber in your shop for few weeks before gluing up (I thought you'd had your stock for a while). While the movement of the individual boards is academically interesting it doesn't have a ton of bearing on the delivered job sitting in your client's home. Misbehavior of the top after it's glued is your main concern. The single most glaring defect in a table is a bad top. You might have a hairline gap at a leg-to-rail joint or any number of other problems that are minor by comparison. But if the top starts curling your client is going to call hollering.
In your case, think about this as a three-stage process - shop acclimation/glue-up/indoors acclimation. You don't want that top to look like the roof on a Chinese Pagoda a few months down the road. Patience will be rewarded. Don't finish mill the top until you are ready to mount it. Then when you do mount it get the finish on it (finish the bottom before mounting and get a coat of finish on the top the same day). It would be great if you could move it to a climate controlled area for finishing.
Quote lead time generously to give yourself room to breathe.
Edited 1/20/2005 4:07 pm ET by cstan
You've got the information you need on drying & wood movement. This is just anecdotal information.
My benchtop is 2 1/4 thick walnut. It doesn't seem to move much at all! Prior to assembly, the walnut sat in the shop wood piles for ten years. Obviously you don't need to wait that long...
Have fun...I love the smell of planed walnut in the morning
Fritz
I work with air dried slabs almost exclusively in my shop for 20 years now. If you build a table top out of these slabs at 14% MC, you are asking for trouble. You need to let it get down under 10% before doing anything. Unless this client of yours lives in the tropics with a very high humidity in the house without air conditioning, the wood will acclimitize to a lower MC (moisture content), and your beatiful air dried walnut is going to turn into a banana slide.
I saw my own logs. With 8/4 and 12/4 cherry and walnut (pretty similar drying characteristics, but not exactly) I let them sit for 3 years before even bringing them into the shop to get acclimated, which can take another month or so.
If you want to take a flyer and risk all with your customer, build it now. If you want good results that will protect your good name in your area as a business person, then you'd better wait. They're not ready yet at 14% MC.
Just my .02, and good luck. Air dried walnut is extremely beatiful to look at, as well as work with.
Jeff
If the air in the shop is at 70 degrees Fahrenheit and 50 % relative humidity, then the moisture content of the wood will drop to 9.2 percent. This is from commonly available charts based, almost always, on USDA handbook information which was rigorously researched.
At this time of the year, in the northern tier of states those conditions would be considered blessedly humid. In my shop, in Connecticut I'm looking at a relative humidity of 30% and wood with a moisture content of 6% and it may still go lower. In places where the outdoor temperatures are going sub sub-zero, woodworkers are probably looking at 4% moisture content at equilibrium.
Again much of what is being discussed and recommended here is based on a poor understanding of how wood and moisture and the climate interact. It does not matter what the final moisture content is, what counts is that the moisture content of the wood is in equilibrium with the air in the shop when precision cutting and fitting is done.
If the wood is rapidly gaining or losing moisture it will be unstable and hard to work with because it will be changing dimensions. If the planks lose a lot of moisture because the shop is quite dry, they are almost certainly going to cup and possibly twist or bow, it makes sense to know this before the wood is made into a table top rather than after, especially before the customer gets it.
It also does not matter where the piece of furniture is intended to go when it is first delivered. Tomorrow it could be delivered to Florida and settle into a fairly steady MC of around 16%, but five years from now the table's owner could move to New Hampshire and the woods MC will be down to 5% by winters end. (If the table being discussed here was exposed to these conditions it would shrink a full inch during the first winter it spent in the Granite State. It would also expand a full inch that following spring.)
I regularly see nicely made, but poorly designed furniture literally disintegrate when it is moved from one climate zone to another and it doesn't have to happen. There are hundreds of design details available to a knowledgeable furniture maker that will allow him or her to build furniture that can handle all extremes of environmental conditions.
I take some pride in the fact that, whatever else its failings may be, my furniture isn't going to come unglued, or warp, or crack, or bind no matter where it it may end up. I hope and expect that some of my pieces will still be around centuries from now. That will only be possible if it is designed to stay together no matter what climate it is in, and that really isn't all that hard to do once you understand how wood reacts to moisture changes.
John W.
Edited 1/21/2005 5:54 pm ET by JohnW
Edited 1/21/2005 5:55 pm ET by JohnW
There are so many variables involved, I would be afraid to make a piece for a paying customer with wood that has not been kiln dried. Some of it depends on the part of the country you live in and other factors involve how the customer's house is heated. Down here we have real humid Summer conditions where we just cannot air dry anything to satisfaction (ever) and then when winter comes it is bone dry to an extreme. You have to understand your materials 100% and be able to control circumstances somewhat.
I think the thickness of this wood could be a problem for you. Several posters have suggested you let the wood season in your shop and I agree if it were 4/4, but 12/4? I don't think it will stabilize in a short period of time, it may take a long while. I also wonder how accurate a reading you are getting on that thick stock. This will also affect it's stability over the long haul.
Proceed carefully.
Edited 1/22/2005 1:31 am ET by el papa
Another "woodworking myth", that kiln dried wood is more stable than air dried.
Kiln drying is a faster way to get a stack of wood dried out but it does a nothing to make the wood more stable in the long run. If poorly done, kiln drying can create more problems than it solves, but the same is true of air drying, it must be done right.
As always, all this information, and a lot more can be found in "Understanding Wood" or Lee Valley's "Wood Movement Reference Guide" and other publications.
John W.
Edited 1/22/2005 12:09 pm ET by JohnW
Not a myth, a fact. Another reason we kiln dry wood is to be certain it is completely dry, all of it...not just the edges. I like books too but they seldom cover all possible situations. I think this situation has to many variables to throw out some random bits of wisdom from a book and hope all is well. He should be real careful with this situation if he wants to ensure success. Maybe he should read the book and decide for himself and he should get his own moisture meter.
I frequently see pieces of so-called air dried walnut in my part of the world that have been cut and in-the-dry for 25-30 years that have a moisture content of %20. And that, Brother, is not covered in the book. And it may be a variable for this poster, we just don't know. He should be careful.
If you had kiln dried some walnut in the same sizes 30 years ago and stored it under identical conditions for 30 years, what would its moisture content be today?20% MC implies an average relative humidity of 90% Where is your part of the world?
East Tennessee, you have to live it to believe it. The worst part is in the Fall and Spring when it is too warm for the heat and too cold for the AC to run. Mold grows on everything. Then when our short Winter comes it gets so dry that nice wooden furniture cracks and splits so loud you can hear it all over the house.
If you read books and articles on air drying they will usually say "in most parts of the country". Even kiln dried stock has a shelf life under these circumstances, it will pick up moisture then you are faced with the next scenario...is your dry season long enough to dry it out? And how even will it dry? It is not a one size fits all world. I don't see better then 15-18% MC when air drying which limits what I can do.
A side note: my supplier argues with customers (hobbyists) all day long who don't think they need kiln dried lumber. They simply won't sell it because they cannot guarantee satisfaction in our difficult climate.
I didn't throw out "random bits", I said in my first posting that he should do some reading so he would understand about how wood responds to moisture changes, then he will be able to make the right choices.
When I teach woodworking, the first thing on the agenda is wood movement, if the student doesn't understand that, he doesn't understand the material he is working with and nothing done with the wood will turn out well except by sheer luck.
Once again, the only correct moisture level for a board is the level that is in balance with the air in the shop. How is anyone going to work with a board that is changing shape as they work with it? If the board at 14% MC is in equilibrium with the relative humidity in his shop then he could start tomorrow on building the table. In my first post I said it was entirely dependent on local conditions.
If the table top is going to be exposed to large swings of humidity after it is built, unless it is an especially stable batch of quarter sawn, it will cup and possibly twist to some degree no matter how the wood is processed or restrained. Personally I wouldn't build a large slab table top unless I was very sure that the customer understood very clearly that some wood movement was inevitable.
John W.
Edited 1/23/2005 3:21 pm ET by JohnW
Edited 1/23/2005 8:06 pm ET by JohnW
I see a lot of confidence in your posts regarding his situation whereas I would urge him to read the book, procede with caution and size up his own situation. Lots of variables ya' know.
Once again, the only correct moisture level for a board is the level that is in balance with the air in the shop.
Except for a slab top for a table. I'd much rather mount a top that has acclimated to the environment that it will be moved into very soon (presumably a home or office). No way I'm going to mount a thick tabletop sitting at 14% EMC (or drier on the other end of the spectrum) and then move it into my home (or a client's home or office) two or three days later. No way.
Construction methods should be implemented to allow for movement but why take chances with a tabletop?
Maybe I'm a fool.
Edited 1/24/2005 12:45 pm ET by cstan
cstan and el papa,
John has, as usual, correctly described the situation.
Kiln drying achieves nothing that imaprts any inherent stability to wood. Except this: If the drying is done correctly, moisture is added near the end of the drying process to prevent case hardening. Case hardening can occur with either air drying or kiln drying because the outer layers of wood, once drier than the interior can trap the intererior from further coming to equilibrium.
The condition cannot be corrected in air drying, simply because the process is inherently non- mechanized. But done incorrectly, kiln-dried lumber can also be case hardened, and case-hardened wood will warp no matter what. It is essentially a "defective" product good for little other than firewood.
It might be safe to say that one can assume with a higher degree of confidence that kiln-dried is free of case hardening than is air dried and in THAT sense "kiln dried wood is more stable." But that degree of confidence is far from 100%.
Air-dried wood can be free of case hardening, and if it is, then it is as stable as is wood properly kiln-dried. Once both have been brought to whatever equilibrium condition is the goal, both will give up and absorb small amounts of moisture from the atmosphere as that changes. And both will move exactly the same. And that movement must be accommodated in all construction methods.
Once that is done, It really doesn't matter where the piece lives or is shipped, it should not self-destruct.
I live in the tropics. El papa, I can't imagine that your humidity conditions are any worse than I contend with. I make furniture for my family. They live in San Francisco, Minneapolis, Salt Lake City, Miami and Denver. I have never had a piece fail moving from this climate to one of those, or going through the considerable humidity changes that occur during the year in those places.
Cstan, I can't imagine working on a table top that is at equilibrium for the environment for which it is destined, but not for my shop. How does one work on it fast enough and get it out the door, bound for its "correct" environment before it moves?
Rich
Edited 1/24/2005 4:10 pm ET by Rich14
Here's my routine when I build a big(ish) table for a customer:
Glue tabletop from skim planed, rough stock. I usually glue up a big top at least four weeks before starting the base. Top glued from stock that has been in shop for several weeks. Move top to a centrally heated and cooled environment. Good news here - I'm moving into a space with central heat and air soon so won't have to move big tops around much. No more kerosene heaters and window unit air conditioners.
Build the table base.
At this point, the top has been glued and sitting in a centrally heated/cooled room for around five to six weeks - plenty of time to contort if it's going to.
Move top back into shop, plane to thickness, smooth, and cut to finished length and width. First coats of finish on both sides of top. Top in shop only one day for this work, maximum of two.
Move base and top to climate controlled room to complete finish job. Piece delivered a week later, assuming all is well.
See, no big deal. I'm able to work on big panels well in advance as my work is scheduled well in advance. I always have a few days built into the schedule for gluing up the next commission's big panels.
While my technique doesn't guarantee that the top was stored in an environment exactly like the one it will live in, I can usually assume that the piece will be in a centrally heated and cooled home or office.
I don't have a dog in the fight about air dried vs. kiln dried. Doesn't matter much to me, however I don't currently have a source for air dried stock.
As I said in my earlier post, I don't take chances with table tops. Problems with these stand out like a goat's #### going up hill.
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