I started making a table out of pine. Project will be 6 feet by 4 feet. Anyhow, I purchased pine that was already pre-glued to make 20 inches and 16 inches wide pannels (by 4 feet). I have 2 of each for a total of 6 feet. My problem is that after sanding with 120 and then with 220 sandpaper… the wood warped. It looked u-shaped when I came in the room the next day to continue the project…
I had not left the wood on it’s flat side, rather siting against a wall with the 4 feet section pointing up…
Now it’s really dry here at the moment… ranging from 20 to 30% humidity. My guess is that is what caused the problem. I took a water bottle with a spray gun and applied a minute amount of water on each side of the board using fine spray. I put the planks donw with the U shape part receiving pressure from the planks on top of it. Now it seems back to normal but I am affraid this will happen again when the table is assemble and the wood will crack…
Anyone ever experienced something like this? Anyone know how to prevent it and why it happened?
Any comments will be welcome.
Replies
Calendyr,
I am having a very hard time understanding the dimensions and construction of your table top. Is the table 6' long x 4 ' wide? (that's a big table). What is its thickness?
Did you bring the wood in from the outside to your low-humidity situation just before working on it? If so, the wood warped as it began aclimating to the workshop. It would eventually have returned to its flat condition.
Did you sand the panels on one side only? If so, you increased moisture movement from that side to room air while the unsanded side didn't exchange as much.
Don't sprinkle water on the wood. Allow it to equilibrate with the drier air of your shop for a week or so. Let it rest horizontally, not vertically and lift it from the surface on which it's resting by a few pieces of 1x2s so the air can circulate over both surfaces.
Have you considered breadbord ends for the construction of this table? That large top is going to move quite a bit and will need something to stabilize the warping forces.
VL
Hello Venicia,
Yes you are right about dimensions. The planks are 11/16 of an inch thick. It is a big table ;) One of the reasons I am making it myself actually.
I brought the wood inside about a week ago, but it was sealed in plastic. So humidity did not change. I removed the plastic to sand it this week. And yes I only sanded 1 side. No use spending hours sanding a side that will no even be visible right ;) So should I sand the other side too then ? And what about finishing... I looked at many tables sold on the market and they are not finished at all underneat... won't that create a problem since varnishes prevent moisture exchange...
I am not sure what you mean by breadboard ends... I am new at this... A friend of mine explained I should not bolt the top to the frame using corner hardware pieces. He suggested I use a special clip designed for that purpose that allows the wood to move. He said to use along the side only, not at the ends. I could not find the clip he suggested and got something similar, it's designed to hold mirrors up, it will screw in the top pannels and slide in a groove I made on both side planks... you probably know what I mean...
Thanks for the help btw ;)
Dan
>I am having a very hard time understanding the dimensions and
>construction of your table top. Is the table 6' long x 4 ' wide?
>(that's a big table). What is its thickness?
>Did you bring the wood in from the outside to your low-humidity
>situation just before working on it? If so, the wood warped as it
>began aclimating to the workshop. It would eventually have returned
>to its flat condition.
>Did you sand the panels on one side only? If so, you increased
>moisture movement from that side to room air while the unsanded side
>didn't exchange as much.
>Don't sprinkle water on the wood. Allow it to equilibrate with the
>drier air of your shop for a week or so. Let it rest horizontally,
>not vertically and lift it from the surface on which it's resting by
>a few pieces of 1x2s so the air can circulate over both surfaces.
>Have you considered breadbord ends for the construction of this
>table? That large top is going to move quite a bit and will need
>something to stabilize the warping forces.
calendyr,
Personally, I'm having a heck of a time with this dryness. I have been hand planing and resawing maple, cherry, oak that has been in my shop for about two years...and nearly every piece is warping after the resawing. About 5 weeks ago I bought a band saw and have been practicing...some of the pieces stay flat but many/most do not. So I think with this dryness all the usual rules just don't work.
As Venicia suggested, breadboard ends would probably be smart for your table top. I have a coffee table with a 48x22x5/4 ash top...that is expanding and contracting about 1/2" this year. The breadboard ends helps keep all the boards flat ...and makes the expansion/contraction fairly unnoticable.
Calendyr,
I used to use those plastic wrapped panels from the big-box store before I had any tools or equipment to speak of (just a skill saw and an electric drill). Found that they were seldom dried properly, especially the pine. Only solution I can suggest, if you have to use them again, is to bring them indoors several months early, stack them in stickers, weight them down, and let them dry.
Probably a good idea to let them sit the way you have them now for a month or so. Should help.
Jeff
Along with these suggestions, you should alternate growth rings (visible on the ends) as you glue up your panel. This is important to promote stability.
Calendyr,
Respectfully sir, I question the wisdom of building a 4' wide table top out of 3/4" pine all glued up as one panel. In my opinion, this design is inviting substaintial and difficult wood movement. Your time would be well spent considering how to break up this vast table top into panels or something to allow movement of the pieces.
However, if you're anything like me (hardheaded) and you've already decided to do it, then you'll proceed irregardless of what I'm saying, so go for it. The finished table top is going to expand and contract substaintially in the cross grain direction. I think light sanding and sealing the bottom surface would be beneficial to your piece and tend toward stabilizing it. It would be less effected by sudden moisture changes caused by heating systems, etc. I know I would take the time, and that doesn't need to be "hours" as you put it.
If you opt for bread board ends, they need to be properly mortised and tennoned onto the main top so the top can move relative to the ends or else you'll just have a mess likely causing splitting of your top. There was an article in FWW a while back on how to do this. Only the middle tennon is fixed, and the outboard tennons float in wide mortises with sloted peg holes. I've used bread board (or I like to call them "bisquit" board in the memory of a few elements of my youth) ends on a few table tops like this because I like the look. They would be a fair amount of work and I disagree that they are necessary.
I guess I'm just desagreeable this morning because I also disagree about alternating the grain of every other board. I've seen many articles written on how to do it and while in theory it's probably sound, in practice I find it's not necessary. I guess I just don't have the same experience with wood as those authors do. While it may help, I haven't found that it does. Put the prettiest side up. I bet you can take one of those thin pine boards and lay it out on your worktable, and stand on it and flatten out the cupping with the weight of your body - or even less weight. Just bind them down to the skirt boards, but allowing for the movement. Wax between the two surfaces will help them slide against each other.
The mirror clips you talk about are plastic? I doubt they would work very well. There are several ways a creative person can bind down the top, but the easiest is with table clips. I mail ordered some a while back for I think $2.50 per dozen. Took just a few days for them the arrive. Another way is to use those ell clips you mentioned with the horizontal leg being held off the bottom surface of the table about a half inch or more to allow a portion of the screw shaft to be exposed between the clip and the bottom surface of the table top. This allows the screw to move with the table top. Get the reinforced kind of clip, or ones with short legs so you can really put some pressure on them. The longer leg ones will just bend.
Another way to allow for movement is using wooden blocks with long screws, with the hole in the block being oversize for about 2/3's of it's length allowing the screw to move around in the hole. Anything that will allow movement. In that soft, thin wood though, plan on plenty of screws and be careful not to strip them out installing them.
Another thing you can do to minimize the cupping, or to help battle it, is to back relieve the boards by ripping some slots in the underside. The slots don't have to run out the ends - just approach the ends. Frequency and depth of slots depends on the stiffness of the lumber and severity of the cupping. Experiment. Be sure to seal the underside after backrelieving.
Good luck with your project.
jdg
Edited 2/9/2004 11:12:59 AM ET by jdg
To Everyone,
The answers to this question, and dozens of others like it that I've read on this site in the past year, show an amazing lack of understanding by most woodworkers, both amateur and professional, on the the way wood responds to changes in moisture.
If you are going to invest large amounts of time and money into making furniture, you must understand the material you are working with. There is nothing mysterious or magical or upredictable about wood movement, absolutely, totally nothing unpredictable. Once you understand how wood moves, you will be well on your way to never having a piece of furniture warp or crack or distort ever again.
Two hours spent reading a few magazine articles, or a chapter of a book on the subject of wood movement, would be the best two hours a beginning woodworker will ever spend in learning the basics of the craft.
John W.
Lots of things, hope I won't forget any ;)
The mirror clips are metal, not plastic.
Who said it would be 1 large glued up plank? I plan on having 4 planks, like they are now. A bit like old tables where made. I will sand the edges off a bit on the part that will touch to show they are separate planks but not enough to create a problem with stuff getting stuck between the planks. I was planing on using something flexible between the planks to allow for wood movement... felt, rubber, silicon?
I am pressed for time (coffee break only). I will make a more detailed answer tonight ;) Thanks for the answers
If you have dry winters and moist summers where you live the table top will expand and contract more than 1 1/2 inches.
John W.
All right home at last ;)
I think adding some finish to the underside is not a bad idea at all. I was thinking about doing it when I read this article about the various finishes and their effects on humidity transfer. Only thing that blows my mind is that none of the tables I have seen sold commercially are finished underneat and they don't warp or bend. Even more disturbing is that most are bolted directly to the frame and don't warp or crack. There must be a trick to this but I just fail to see it.
As for not understanding wood, you are perfectly right. This is my first project and the only thing I know about wood is that it moves around depending on humidity. I plan to read on the subject, many people suggested I purchase a book called Understanding Wood ;) I found the other book from the same author : Understanding wood finishes but not the prior one. I will most likelly order it.
1 and 1/2 inch is a lot. I am not sure how to plan for that... I think that I will leave a bit more room than I intended between the planks. I will have 4 planks so that is 3 spaces or 1/2 inch... that's a lot! I can't leave that much space, it will look completelly ridiculous and it will not be practical. Well this is my first project so if it fails I will start over, the frame will still be good... Have to learn some way and I used pine so that it would not cost an arm and a leg if I made a mistake ;)
Next time I think I will buy a big plank of plywood 6' X 4' will save a lot of troubles ;)
A friend gave me some website to order speciality items, thank you for the advice, I will order what I need from now on, much easier.
Calendyr,
Your lack of understanding the behavior of wood and that of table construction principles is so great as to make advising you an exercise in futility.
There are many ways to learn. One is to make mistakes. You will not lack from opportunities in your project. But I'll doubt you'll learn much except frustration.
A better way to learn is to study advice from others. It's also necesary to learn basics, in small increments and to build on those. Crawling before running a marathon is not only a good idea, it's the way the universe is put together. Your table project is already out of control and beyond your absolutely inadequate level of preparation. Your project already violates the basics and requires significant bending of the rules to pull off.
It's ok to be innovative. But innovation stands firmly on sound understanding of principle. I have no idea on what kind of tables you are basing your observations, but you are misunderstanding the furniture design and construction.
I have no doubt that an experienced craftsman could take glued up boards like yours and turn out a beautiful table. And you might conclude, watching him work that he used exactly your intended plan. But nothing could be further from the truth.
This is NOT meant to demean, or to discourage you, rather to encourage you to acquire at least some "book learning" if not personal instruction before you go any further.
It's fun here for those of us who have done a little more than you, to help out someone who has questions. But to try to, first, convince someone in your situation to put on the brakes, to listen to advice, and then, to teach every fundamental, then intermediate, then advanced skill via forum messages, is a bit much.
VL
To know what was the cause I would need more information. How long did it take for the boards to warp? If it was basically immediately it was do to internal drying stresses that were not removed during the drying process. Since the boards were wrapped in plastic I can only assume the moisture distribution through the board was uniform and it was not caused by a moisture gradient that was partially removed during sanding. Unless there was a finish on the surfaces originally saning one side would not make that side loss or gain moisture any quicker than the other. The loss of moisture from a flatsawn board will cause cupping and this would occur over a period of time , like over night. Flipping the boards such that the grain alternates does not reduce the warping: only the appearent warping. It will cause a washboard effect by many alternating cups. While some people prefer the appearance of flatsawn board with the cathedral shaped grain raidally sawn boards are more stable and will not cup ( radially sawn boards have only straight grain).
If you allow the board to acclimate to the environment and it still is cupped you may spray the convex side with water liberally. Then as it dries it will flatten out. This is not an axact science and the results will vary in degree of success.
Calendyr!
Well, you're getting all kinds of advice, so I thought I'd jump in here too. Listen to John W, as you already know, that top is going to move. Where beginning woodworkers go wrong is in trying to prevent wood movement. While I personally think 1 1/2" might be a bit more than a pine panel 6' wide will move, you can certainly make allowance for that by using the table clips as recommended already. Why not glue the separate panels together? Then anchor the top firmly to the apron in the center, and as you go toward each end use the clips in grooves so they can move. It won't matter how much movement takes place, it'll be divided in half toward each end. I've built several extension tables 6' wide, up to 8'wide, using this technique. One of the 8 footers went from VA (humid climate) to Colo (dry ), and back again without problems.
One of the posters would have you refrain from building until you've educated yourself. Hey it's only wood. No need to genuflect before the altar of the all knowing before you get your hands dirty. I started woodworking because I wanted to create, how about you? The 1st glue joints I made were for a blanket chest I built in my dorm room in college. I didn't have a plane, much less a jointer. I used a sanding block and SHOE POLISH to find the high spots and bring them down. My girlfriend (now wife) thought that her hope chest was terrific. 34 years later, I walk past it every morning in our bedroom, those glue lines are still holding fine, thank you. (I would'nt use that technique now!) My point is, if you want to build, go for it, learn as you go. If you wait til you have sufficient knowledge, you'll never have the confidence. My 2 cents.
Ray
LOL! I know I have to learn, I have every intention of doing so and since the planks warped I put the project on hold. The warping happened overnight. I sanded and the next morning the planks were all warped. Now after a few days laying flat the warping is gone.
I took a list of the books that people recommanded. I intend to start with Woodworking for dummies then get Understanding Wood.
But yes I want to do it to have fun and learn. I got plenty of advices to avoid the major errors, if I make some minor ones well I will have 4 very nice planks for shelves ;) Don't worry I am aware of the dangers but that's part of the learning procces.
John,
If you are going to lecture on the seasonal movements of wood, please validate your responses with sources. An 1 1/2" movement per season is ludicrious. Depending on species of pine, on a six foot long slab, the movement you'll see will be more like 1/4". Here is a great source of usable information:
http://www.woodbin.com/calcs/shrinkulator.htm
Steve
Edited 2/11/2004 1:46:26 AM ET by Dirt Stirrer
Dirt Stirrer,
The figure of 1-1/2" that JohnW mentioned is large but not at all ludicrous. The movement is going to be greatest across the width of the table, not the 6' length. The length will not change appreciably. (assuming the length is the long-grain direction of the panel - I can't tell from the description).
The wood shrinkage and expansion calculator link you posted predicts movements in the vicinity of 1" for maples and pines subjected to relative humidity changes of 50% (10% to 60% differential). That kind of change and more is not at all difficult to achieve in many areas of the US.
My son lives in Minneapolis. A 30" wide breadboard maple table I made him shows almost 3/4" of movement from the humid summer months to the dead of winter when the heated indoor air is bone dry. You can actually hear the top move in the first few weeks of October after the furnace gets used a lot.
I made the table in Hawaii where it must have been about 40-50% RH. So the breadboard ends overhang the table width in winter and the table overhangs the ends in summer. That's a lot of movement, but not at all that unusual.
VL
I just used the calculator you highlighted and it produced a wood movement of 2.03 inches of movement, so I guess I was being conservative if anything.
These are the values I entered: Pine, western white, moisture content going from 4% in winter to 14% in summer which is fairly typical in much of the world. The dimension was 72 inches, the table top is going to be built with the grain going crosswise to the long dimension so the expansion and contraction is going to occur over the six foot length of the table.
Running these numbers, the calculator shows that the final dimension would be 74.03 inches for a top made of tangentially sawn wood. I'm presuming that Home Depot isn't gluing up panels from quarter sawn stock.
The only way I could come up with your numbers was to set the calculator for a 4% to 14% change in relative humidity and use the calculation for radially sawn wood. However using a 4% to 14% change in relative humidity would mean the environment was desert dry year round. If you are going to use relative humidity, the values should range from 20% to 75%.
The calculator I used is an inexpensive, but very effective, card stock device made by Lee Valley.
Hope this helps you to understand how the calculation was made. If I've left anything unclear, feel free to ask further questions.
John W.
Well here in Montreal, winters are very dry. This winter I had a few days with humidity in the below 20% range. In summer it's the oppposite, we have long periods where humidity will be over 80% and some days it can go to almost 100%. So I am expecting a lot of wood movement. I know it takes a while for humidity to change in the wood. I am planning to use 6 coats of water based varnish on the tabletop and 3 coats on the table frame. I am not overly concerned about the frame. As for the top, I think it will take a very hours for humidity content to start changing... I saw a table somewhere on Taunton's site but I can't remember where... I will have to print it, very useful info giving detailed info about the effect of each type of finishes, and they effect of hudity transfer depending on the number of coats applied.
The U.S. Forest Products Laboratory evaluated finishes for their resistance to moisture transfer and those results are often quoted. The information is presented in a fairly technical form that can be hard to sort out, but the basic fact you come away with after studying their data is that no finish does a really good job of preventing moisture transfer.
Even the best of them with multiple coats would still only slow down the process to the point that it would take a month or so for the moisture to move in or out of the wood until it was again at the level of untreated wood. The net result is that since seasonal humidity levels stay steadily dry or moist for months at a stretch, the long term effect of any finish is negligible and that designs should accommodate the full range of expected wood movement.
John W.
Calendyr,
Welcome to Knots. This is a great source of info for us all. Newbies and experts alike. None of us know everything, and people who make judgments about your capabilities due to their "superior" knowledge should be ashamed.
Here is a good source of info on wood movement:
http://www.woodbin.com/calcs/shrinkulator.htm
or find the "Fine Woodworking" issue #165, from Oct. 2003, as it has a helpful article about wood movement in it.
My first project had some issues, but my second one was better. That's how we learn. If you think you can do something, try it. If it fails, find out why, and fix it on your next one.
Wood moves tiny amounts with moisture changes, not inches. If you don't allow for those movements, sure it may crack or warp, but chances are it will still work. Just keep the grain going parallel when possible, and when not, allow for a little slippage. There a gazillion ways to do it, that's part of the fun. Contrary to some peoples beliefs, it's simple to deal with. Have a good evening,
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