[OP]
Member
For a 32” wide by 43” long coffee table I would like to use flatsawn lumber for aesthetic purposes. Clearly, if this were a relatively thin board say, 5/8”, cupping would be a problem. But it will be 1 ½” thick. The use of breadboards for stability will not be available with this design. Alternating grain patterns I have read is really not all that useful in the long run either. At 1 ½” do I need to be concerned?
Member
I'm not sure the thickness of the board is relevant. As long as the raw material is machined/prepared and mounted to the frame correctly and in a similar environment to the destination, and there are no large changes due to seasonality you should be good to go. I've always alternated grain in panel glue ups.
Member
What is the wood? Is it really dry or framing lumber dry from a Big Box store? Can it be ripped into 2-4" wide strips and then glued together? No one can provide a good answer to your questions without knowing how dry the wood is and what kind of wood it is. Where it came from is important too. Most lumber is flat sawn. Have you seen quarter sawn? Narrower strips with alternating grain will bow less, but if the wood isn't dry enough to begin with it will change shape as it continues to dry after you have built something from it.
Charley
Alternating the grain can help to some degree, but I tend to match boards for grain pattern appearance. What I have learned from the coffee tables with 3/4" thick tops, I have made that it is important to start out with lumber at about 7% mc. Then let it acclimate in your shop while stacked and stickered for at least a month. Cut you pieces to rough size and glue them up. Make sure you allow air to get to both sides while the pieces are clamped up. Remove the piece from the clamps and continue your shaping and trimming and at no point leave it leaving against a wall or sitting flat on a bench over night. When you get to staining and finishing, apply equal amounts to each side, flipping the piece after each face has had a coat of finish applied. Make your frame so that you can mount the top so it can move with seasonal moisture changes. Applying finish to oth sides will insure that the underside doesn't absorb more moisture than the top side.
Lee Schierer
USNA '71
Go Navy!
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Moderator
I agree with Andy - depending on several factors the thickness may not stop the cupping. I have some 1.5" and 2" persimmon that cupped badly. (Persimmon is bad for that) I've even had 3" thick dogwood cup a little and it was just 12" wide. Some woods don't seem to cup much - I have 1.5" walnut slabs that didn't cup at all after being stickered, weighted, and air dried then brought inside. Making sure it is properly dried and sealing both sides after it is surfaced might help. But sorry, I have no experience with using a single slab as a table top.Originally Posted by Alan Kalker
JKJ
Contributor
ive never stickered and weighted any material and wouldnt. Id machine the boards some amount over final thickness put them on their edges so air gets around them leave them some days then see what you have re machine them straight. Most will probably still be straight. Never understood why people want to force hold stuff flat then make it into something. Id want to get the tension out of the material not leave it in.
Contributor
Alan,
OK, back to basics. If the lumber is properly dried and acclimated, as recommended earlier, warping will be the result of differences in moisture content on opposite surfaces. Moisture content will change as the result of relative humidity changes in the ambient air. The greatest changes usually occur from summer to winter. Indoor air is much drier in winter, when the interior of a building is heated, than in summer. So, if the top surface dries much faster than the bottom surface it will shrink and the panel will become convex. The thickness of the lumber will not affect cupping, except in the sense that thicker lumber may take longer to dry and acclimate to your shop. The key to avoiding warping, cupping, etc is to control moisture penetration equally on both sides of the panel. I don't know how you plan to finish the table. but however you do that, finish both sides the same.
No finish is a complete barrier to atmospheric moisture, but some finishes will slow down changes more than others. I like film-forming finishes like shellac and varnish. I always finish both side of a wide panel equally, or, if I am applying more than four coats to the top, I apply at least three coats to the bottom. Shellac is a very effective barrier to atmospheric moisture. The point is, if you can slow down moisture penetration enough, seasonal fluctuations may have little or no effect.
I do not believe that alternating bark side/heart side will accomplish much. If the boards are going to cup, you will get a "washboard" effect from that as they cup in opposite directions. More important, IMO, is to make sure that the grain direction (rising and falling) is uniform so that you can surface the panel without too much tear-out. If you have "cathedral" shapes on your flatsawn surfaces, they should point in the same direction.
I hope this helps
Doug
Moderator
Perhaps you don't have a sawmill. Perhaps I wasn't clear. The stickering and weighting is needed when the boards are dripping wet directly off the sawmill. This is not the same procedure for managing KD wood purchased for a project.
Without stickering and weighting the stack of wet wood, boards from many species would curl into firewood in short order, especially if flatsawn. Without stickering for air circulation nearly all boards would also start to degrade in a few days from stain, mold and then rot. Try air drying red oak, cherry, or even tulip poplar without stickering and weighting. If I don't add a few concrete blocks for weight the top few layers may not dry flat but the rest of the stack will since it is has the weight of the boards above.
Properly stickered and dried the wood has a good chance of being useful. This shows a log over 24" in diameter sawn about 2" thick, stickered for drying (for maybe a year, ERC drys quickly):
cedar_P9064287es.jpg
(I have a Woodmizer behind the barn.)
In this part of the country air dried wood reaches no lower than about 12-15% EMC (moisture content at equilibrium.) Before making something the boards are best brought indoors to acclimate for months, or even longer for thick stock. I still sticker or stand upright to allow free air circulation. During this final drying boards will still sometimes slightly cup, twist, bow, etc. due to additional shrinkage as the moisture decreases but usually not much. (except for persimmon, at least the persimmon from one log I sawed!) Mill flat after acclimating and the stock will be pretty stable, especially if sealed, some more than others as mentioned.
As the OP asked, I don't think the thickness alone will guarantee the long term flatness a particular slab of a certain species at a given moisture content .
JKJ
Contributor
dont own a sawmill and dont see a thing mentioned about it I dont see a thing about wet wood. ive hand picked from fresh lifts of top quality material for many years and machined tons, my views on wood are based on how it behaves machining it, the changes in tension that occur as you are removing material.
Ive seen enough of the moisture is diff both sides or case hardening or " warping is a result of diff moisture contents both sides" it comes down to I have a board am I going to use it or not if so what machining do I need to do to make it straight, then stick it on its side for a few days then make it straight again if need be.
Id machine the boards twice get the tension out put the best side up usually the heart side and it usually takes the finish better as well.
Moderator
You are right, I should have been more explicit when I wrote "I have 1.5" walnut slabs that didn't cup at all after being stickered, weighted, and air dried then brought inside."
The next time I'll try to write something like "I have 1.5" walnut slabs that didn't cup at all after being stickered, weighted, and air dried from wet to EMC then brought inside to acclimate to conditioned spaces.".
That's probably a good illustration why a technical writing career might not be best for me.
JKJ
Member
Make sure it is dry to a moisture content suitable for your climate, alternate the growth rings make sure your glued edges are machined square and polish both sides. Breadboards are fashion, not structure so don't worry about not using them. Alternating the orientation of the growth rings does matter, speaking from extensive experience. Cheers
Contributor
Tag Frid was the first guy i saw say he doesnt alternate boards, his reason was that on a large top it is held down anyway. More important and not mentioned is you can make cuts on the bottom of your boards. Flooring is relieved on the bottom. If I looked at any furniture with solid tops the old guy made even down to a small end table there were a number of saw cuts in the bottom of the boards, they stop before the ends of course, he called this breaking the back. and it took away the strength for the boards to do what they want later down the road.
Do that put your best side up finish both sides the same and fasten your top so it is held down but can expand and contract and you will not have issues. We all have our ways, ive got lots of time into this, the old guy way more and learned where I wish I could have learned.
Wayne you said polish both sides did you mean finish both sides?
Member
Yes polish means finish. To me, finish means sit down and have a beer
Cheers!
Member
A board of any thickness can cup it all depends on how seasoned it is.
Flat sawn lumber is the most prone to cupping.
An issue with alternating boards is you can have grain reversal which be a major PITA unless you use a wide belt sander.
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