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I've been tasked with building a round 60" rustic oak table. I have a stash of 4/4 oak, and I was thinking about doubling up the top with two obviously separate layers (both 60"). The top will need to be one solid piece for practicality. I was thinking about alternating the grain of the two levels for strength and just using screws to connect the layers, but a 90 degree cross grain probably wouldn't work to allow for movement. What would be an acceptable angle the alternate the grain of the two layers to add strength (to reduce cupping) but not restrict any movement? 20-30 degrees?
I would just build up the edge, not the entire top. If the wood is dried correctly, you won't have any warping problems. Use quarter sawn if you want more stability.
I agree with just doubling the edge. You won't gain anything with a full thickness, and may actually create more problems.
Perhaps a couple of stretchers where the base attaches........
Building the edge up will not allow wood movement and has a better than average chance of failing because the end grain would be trapped by the edge build up . The best would be to use 6 or 8/4 lumber to start with .
I would laminate the boards you have if you insist on using them face to face to create thicker stock then glue your table top up.You could select an edge detail that can hide the line between the 2 boards maybe .
So long as we all agree...
But seriously, I think I can rule out any sort of cross grain approach. The customer's father works for a power company, and she suggested something similar to a large wire spool. The flanges on those things have a 2 layered cross grain construction. I was thinking of emulating that.
I do prefer a uniform thick slab over building up the edge. I want to have the weight of using thicker boards. I want it to look the part in a log cabin. I was leaning toward just getting some 8/4, if I can find some.
A whole lot depends on your budget. Emulating a wire spool would be better using a double layer approach you initially talked about, but I would use reclaimed oak to bring the look together. Depending on where you're located, there is a large market for reclaimed materials and oak is rather plentiful. Thicker boards in 8/4 and 10/4 are not unusual at all and would work well to keep the rustic appearance while maintaining a single layer. If you look to the new materials, finding 8/4 shouldn't be an issue at all.
D brown, sure built up edges will let the wood move. You just need to glue up solid stock and cut an oversized donut and glue that under the top. Then flush trim the buildup to the top and profile if required.
Whatever you do don't use cross grain construction, or any other angle except parallel if you decide to use a built up construction. That is a sure recipe for future problems.
Oak is a high movement wood when the humidity changes. Some oak species shrink of swell 1% in size with a 3% MC change. The environment in homes and offices often changes more than 3% throughout the year. So, we do need to plan on a moisture change. In any case, make sure the MC at the time of manufacturing matches the MC in use.
Note that quartersawn shrinks half or less than flatsawn.
As soon as you get the grain of two layers at an angle, stress develops because of the difference in shrinkage (lengthwise is zero mostly), so you are asking for trouble.
If both top and bottom take on or lose the same amount of moisture, cupping is minimized. So, use identical, vapor resistant finishes, and also make sure nothing restricts the bottom from moving...screws in slotted holes work only if the screws are not real tight.
Finally,I repeat... make sure nothing restricts the movement of the bottom.