Hello All ! I have 3 pieces of mahogany 37 X 13 X 3/4 which I have noticed they have a slight cup on one side near the end. what is the best way to handle this. Is it best that I rip each of these boards into 3 parts and use biscuit and glue then back to geother. Or is their some way I could use clamps to force them back into being straight.
Jack Griffin Brighton, Ontario
Edited 8/29/2008 10:54 pm ET by sparky 2006
Replies
Jack , what your proposing, in my opinion, is heading towards heartache.
first, what are you doing with the boards?
how thick do they need to be?
do you have a jointer and planner?
You must surface the cupped side flat and then plane the other side parallel to have any kind of furniture quality board. I hate to think of ripping a 13" board into 3 pieces to make it useable (but I have had to rip them in two before and always regret it), it will never look as good as it does whole.
If you have just a planner there are ways to use a sled to surface your boards in it with out a jointer (FW should have on web site).
I have had some boards get flatter under pressure , usually a sheet of mdf with weight, but it takes a long time and some seasonal changes to do it and its never very flat.
again, it depends on what you want to do with the wood - but do try to keep it whole if at all possible, or resaw and use it as a veneer.
good luck steve
Steve !! Thanks for the information, Yes I do have a jointer and a planer.
I making a circular table top, 2 half moons each one is 17 inches across by 35 inches long. Maybe just maybe, I would better to cut the cup off ( the cup is only at one side of the board and them add 6 or 7 inches as I will have to add something to it anyway.
Jack From Brighton, Ontario
P.S. what did you mean about the headache !
Edited 8/26/2008 8:50 am ET by sparky 2006
It is possible to do what you suggested in your original post, though it isn't as easy or straightforward as ripping the stock into pieces, straightening it, and re-gluing it.
In much the same way as it's possible to put extreme bends into wood by steaming it, you can use differential moisture absorption to your advantage to straighten slightly cupped boards.
To do this, it's helpful to have your project mostly completed except for attachment of the top. Rip and crosscut the top to its rough dimensions, then place the concave side of the cup down on your bench on top of moist (not wringing wet) towels. Apply heat through the use of a hair dryer, heat lamps, or whatever method is handy to the convex side of the cup. The moisture adsorption on the concave side will expand the wood, while the application of heat on the other side will dry the wood out and cause it to shrink.
You have to monitor this process closely - your goal is to catch the right moment when the top is pretty close to flat. At that point, remove the top from the adsorption setup, finish plane/sand, and attach it to the table aprons with buttons, metal brackets, or whatever method you choose. As the wood returns to equilibrium moisture levels on both sides of the board, one of two things will happen - it will either take the "set" of the flat orientation of the table aprons, or it may crack along the length of the grain. In my personal experience, #2 rarely happens as long as the wood is relatively thin, the degree of initial cup was relatively slight, and the wood is not excessively brittle (as with some exotics like ebony).
dkell, while I'm not terribly optimistic the re-moisturize technique will work for this poster, I have used it on small old tables that have cupped, so I'm offering a slightly different take. Just "my experience" type comments.
One: The cycle can be performed two or three times. I've never slapped a finish on the minute the wood gets flat, rather I've taken the wood away from the grass or damp towels, let it stand with air circulating on all sides, and checked a few hours later to see what happens. Then tossed it back onto the grass or damp towels if the cup returned.
Two: With the most stubborn specimen, I let the wood go just barely past flat with the slightest hint of a cup in the other direction, then let it settle back down.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Jack , HEARTACHE, my woodworking friend, that's what I said about ripping a wide board and regluing to help flatten.
I still would advise to find a way to keep your boards whole while attempting to get the cup out. If you need the stock to be close to 3/4 thick then I would suggest using battens in your design for the table.
Basically a batten is just a stable piece of stock fairly thick and wide that is screwed under the top towards the ends to help keep the top flat. A search on any web site should give you info on this.
Since you say your top will be a circle the cup could be effectively lessened by the cup orientation to the board and your lay out of same.
good luck Jack
steve
Slit cup? Slight cup! You will never force it back with clamps. Let the wood move and then deal with it.The wood will always win. You could rip it into pieces and glue it back. No need to use biscuits in my 35 years of gluing. Waste of time and does nothiong for strength. Curved cauls are more useful for aligning.
Buy wood oversized and allow for milling. Sticker and wait a few weeks before milling. Longer for air dried.
This just gave me an idea... I'm going to carve the image of a coffee cup, in deep relief, into a thick piece of mahogany. Hence, "Cup in Mahogany"
Edited 8/27/2008 2:01 pm ET by BossCrunk
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