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I have been asked by an impatient friend to make a Nakashima style table from a 2in slab of African Mahogany that fell in a storm. The flitch is 8ftx2.4ft and will probably take 2yrs to dry since it is still green. I am considering doing the following..
1. Sealing the ends with varnish.
2. Planing or sanding it flat. Keeping the heart side up.
3. Routing parallel channels in the underside to aid drying
4. Screwing ( thru sloted holes ) 2×4 beams to the underside to hold it flat.
5. Taking it back after a year to flatten and finish it.
Questions.
a) Will this keep the bow within 1/4in?
b) If the answer to a) is yes, could I do it with a 4in slab?
c) Will the routed parallel channels prevent twisting while it dries?
Thanks
Shane
Replies
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Who knows?
Shane, it's impossible to predict how much your slab is going to want to move. I think you have a good plan as long as both you and your impatient client understand that anything could happen. The slab could dry beautifully, it could check in several places or pull those screws loose and twist itself into a pretzel.
Drying rate may be a problem if the table is going to be exposed to very dry air.
You must leave room for shrinkage when you use the screws, I'd suggest at least 1/4" lag screws in elongated holes.
Is the slab already dry enough to hold the varnish on the ends? If not a wax emulsion would work better.
Lee
*Shane, I'll second Lee's opinion and just offer some shrinkage stats on African mahogany.Average volumetric shrinkage, green to ovendry = 8.8%; radial = 2.5%; trangential = 4.5%; T/R ratio = 1.80 to 1.Luckily you are working with a very stable wood (not quite as stable as American mahogany, but nonetheless very good in this respect.)...But still, making greenwood table tops ranks right up there with nude skydiving when it comes to risk based thrills.
*Jon,i "nude skydiving," you say. And contributing to the thrill I might add, i 'probably without a parachute too!'b I think I'd be keen to pass on this job unless I got it all in writing that the client bears all the responsibility, but even that won't protect your reputation if things go badly pear shaped, perhaps literally, ha, ha. Shane, that is seriously risky woodworking. Slainte, RJ.
*Yup Sgian, to qualify for what they call the "Delux Trip" ("DTs" for short) you gotta pay in advance and leave the 'chute at the airport...I'm surprised you'd pass on a sport like this. Even at your age, you'd have a shot at the gold; the Olympic record so far is only one jump...but then I guess staying home and doing free hand rips on the table saw is just as exciting....And by the way, thanks for that illustrated explanation of the merits of a short rip fence you posted on that other thread. It's crystal clear to me now...Seems when you blow all that money on fancy power tools, all you can afford is half a rip fence...Did I get the point?
*"Hitting the chute" might take on a new meaning for nude skydivers, recon? Especially if it's a male that happens to get the harness on wrong!
*I thought I had heard about some companies using microwave kilns, Id be inclined to try and find one.cheersbake
*Jon, Free hand ripping is a lot less exciting than people think.You got the point regarding short fences. I can only afford a half one, not really worth using at all------ see first sentence. Slainte, RJ.
*Thanks for all your responses. I was away for the w/e and only could read them just now. My impatient client/friend is willing to try it ( no, not nude skydiving...) since the wood was obtained cheaply ( transport and milling only ) so I will probably give it a go. I dont know of a microwave kiln but I might send a flitch through a steam drying kiln. Thanks again,Shane
*No one mentioned this, so I will. If you place the "heart side up" and channel the bottom, wouldn't this increase the chances of it cuping upward in the center? During the drying process there will be lots of shrinkage (across the grain). By placing the heart side up, there will be more growth rings coming out on the top side than on the bottom. This will enduce pressures that will tend to push the sides downward. Having channels on the bottom would lessen the resistance to cupping. Seems to me that you should place the heart side down and make the channels on that side.Or, am I all wet here?? ps - I observed a piece of wet Sassafras in my shop recently that cupped badly. I was a 3/4" thick piece that had been slabbed just to the side of the center of the log. There were probably three times as many growth rings coming out on the heart side than on the bark side. The sides cupped away from the center of the tree. That's why quarter sawn lumber has less propensity to cup - same number of growth rings coming out on both sides.
*Mike, My intention in channeling the bottom was to reduce the effective thickness of the wood while retaining the look of a thick tabletop. I agree that the top will crown ( convex curve on top ) but to me its aesthetically better than a curve the other way. I hope that if I make 1in deep channels in the 2in slab then the crosswise beams will be able to hold the curvature to a minimum. You might be right in thinking that I should put the heart side down...but I am worried that the tendency for the wood to curve toward the heartside will overcome the different drying rates of top and bottom. A little cupping is worse than some crowning...let me think about it...Thanks for your insight
*i "...but I am worried that the tendency for the wood to curve toward the heartside will......"Are you sure about that Shane? Slip of the tongue maybe? ;-) Slainte, RJ.
*Sgian, You got me there. A slip of the fingers...I should have typed " away from the heartside". I looked up 'Sgian Dubh' ...a Scottish dagger? Is the design particular to your clan like the tartan pattern or are they they similar across Scotland?Shane
*Several variations of the general pattern are known as sgian dubh. I'm not aware that any are clan specific, but I could be wrong. Slainte, RJ.
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