Hi,
I’ve finished cutting the boards to length for the bookcase I’m building but I’ve run into a minor problem. I’ve noticed a warp in one of the shelves. Is there anything you can do to fix a slight cup in a board. (If you place the board on edge and sight down the center you can see it curving to the rt.) I might end up tossing that board out and cutting another piece for one of my shelves.
How can I prevent knotty pine (appearance pine) from warping/cupping/splitting? I just purchased the kiln dried pine boards 6 days ago. It’s not like I stored the boards on an uneven surface. I had them layed over 2 wooden work horses. Are long boards more likely to warp than smaller boards. The ones I bought were 1X 10″X10″ Maybe I should have purchased them in smaller lengths.
It’s no easy task trying to find suitable boards to build a bookcase. It would have been too costly to buy the more expensive clear pine althought those boards would give you a higher yield
Wendy
Replies
Wendy,
You have probably already answered your own question. Tossing that board and cutting another. You may consider using that board for the bottom shelf, it would be the least noticable. Filled with books you may never notice.
I suggest buying your wood only as long as you need it, considering waste of course. Storing with good support through out the length will help, or storing vertically.
Enjoy, Roy
You can't prevent wood from warping. At any given moisture content the board has a certain shape. If you increase or decrease the moisture content it changes. If you restrain the board, not allowing it to change shape, then if the tendency to change shape exceeds the strength of the board, it will split.
Woodworking is all about accepting and working around this characteristic of wood. With changes in moisture content wood will not change in length at all, will change in the radial direction (that is across the tree rings) a fair amount, and in the tangential direction (that is, in line with the tree rings) about twice as much. It is this approximately 2:1 difference between tangential and radial shrinkage that causes the problems.
In your pine board, there is probably a portion of it that came from near the center of the tree. You will always get cupping around this area. Further out, where the tree rings go pretty much straight from one face to another, there will be almost no cupping. If you could mill a board to the exact shape an size you wanted, and then never ever change it's moisture content, it would keep it's shape. But, in the real world that doesn't happen much. You can slow down the change in moisture content with finishes, but you can't stop it. In museums, valuable wooden objects are always kept under constant humidity for this reason. You can often see humidity sensors in the display cases.
So, back to your shelf. If you try to force it flat by bending you'll only crack it. If you plane it flat now, it will be thinner. If the moisture content is pretty close to what it will be in use then it won't warp much further. But, if the room becomes more or less humid the warp will change.
The only way to prevent warping in such a shelf is to not use boards with grain close to the center of the tree. One way is to glue up the shelf from narrower boards, none of which have grain from the center. Or you can glue up narrower boards with grain alternating up and down. This will produce a board with smaller waves instead of one big bend like you have now. Another way is to use veneer plywood for the shelf, and attach solid wood only as an edging to hide the ugly core. If it's not a premium piece of furniture, you really only need to edge the front because that's all that shows, but as you get better as a woodworker that will seem like cutting corners to you.
If you are not yet equipped with tools to do glue ups, and not ready to try, then you can buy wide boards already made of glued up pieces in most home centers. They would be much better for your shelves.
Pine, and especially knotty pine, is more subject to warping than most. Since you bought wide boards, they are virtually guaranteed to contain grain from very near the center of the tree. One reason better furniture costs more is that woods that warp less than pine cost more, and there is more waste because they are cut in such a way as to avoid the center of the tree. Pine is a good wood to learn on because it shows the challenging character of working with wood more clearly, and it's cheap.
The length of the boards makes no difference to how much they cup.
I hope I answered your question without being long winded.
Edited 5/16/2004 10:46 pm ET by WAYNEL5
Welcome to the world of woodworking. You are in the process of paying your dues. Using #2 or worse pine is perfect for beginning projects but as you see, expect a waste factor. Don't figure your jobs down to the last inch, get some extra for waste, oops, set up and practicing. Once your skills develop you will see the value of the time and resources you will commit to projects. Premium lumber is a joy to work with and you pay for it. You don't have to have premium lumber to do premium work.
When you buy boards from the local lumber yard chances are good that the moisture content is rather high even if they are kild dried. Take the boards home and stack them with stickers in between each board 2 or 3 feet apart. Keep the stickers in line with each other. This will allow the air to circulate on all sides of each board and may help one side from drying faster and causing warp. When you select your boards, sight down them to check for bows, warps, crooks, etc. After some experience you will be able to see potential trouble. If you find a bunch of nice 10 footers then buy them but if you only need 4' check out the shorts too. Most of us are not afraid to poke through every stack of lumber we can. If we run into something particularly nice we grab it. Everybody is out there looking for the best so you have to be a competitive shopper and expand your sources. Selecting lumber is one of the most important parts of woodworking, learning to do it well takes practice.
I gather from your post that the board had been flat and that it warped since you started to work on it. If that is the case, it suggests to me that it either picked up moisture or dried out unevenly. How did you have it stored? Was the air free to move around all four sides?
If you think the warp developed after you worked on it, I suggest trying the old "grass" trick. Put it out in your yard with the concave side down for a few hours. The moisture from the grass will enter the concave side and then sun and air will dry the convex side. It should make it a lot flatter. Once you get it flat, make sure you are very, very careful about how you store it. It should be stickered so that there is good air circulation around all sides.
Good Luck,
Bill
This forum post is now archived. Commenting has been disabled