25 January 2019 at 1:10 pm #554706
I got my 5 pieces cut and ready to glue up for the top. 7 3/4 wide, 1 1/8 thick, 72 long.
My question, I was thinking about making sure all the grain was going the same direction so that any finish planing after they are glued together, the plane would travel all boards the same direction. Is that a good idea, or am I look at possible causing an unforeseen problem such as bowing length wise. I understand that if the boards reverse grain direction they tend to off set bowing like that. Right now all the boards are good, but the future? The Trestle table will be outside under our Gazebo. Protected from rain and sun, but subject to heat and humidity changes more so than if it were inside the house. I plan on finishing it with Varnish, all sides.
I’m thinking the undercarriage would help prevent bowing, but I have learned that wood has the strength of Superman when it wants to bow, twist or expand. Oh almost forgot, I switched from Oak to Cedar for this project as the grain on my cedar was much straighter than the Oak was and I had problems with the Oak curving.25 January 2019 at 3:21 pm #554710
By all means arrange the boards so that any rising grain is all facing the same way; however, what I infer from your question is the fact that some of the boards may ‘cup’ or warp as they acclimatise. This will certainly happen if you change the board’s environment – nothing to be done about this other than let it happen, let it all reach equilibrium and then flatten both sides again. It’s what wood does. Cupping occurs because the heart-side of the board dries slower than the bark side.
One accepted strategy, where a series of boards are arranged edge to edge, is to minimise movement (and any subsequent remedial planing) by aligning the boards in an alternating sequence; heart-side uppermost, then bark-side, then heart-side and so on. This means that even if the top is very slightly corrugated, any cupping cancels itself out across the width. In reality, a cupping of only a couple of millimetres across a 4 inch board is not worth bothering about.
Where boards are edged for a table, I note that you have boards almost 8 ” wide – I would strongly advocate keeping them about 4” – 5” wide – in order to minimise cupping and to assemble the whole thing without glues – especially if it is outdoors. 7-plus inches will give a deeper cup than 4 inches. Ideally Tongued and Groved (or grove and spline) with bread-board ends, fixed with draw-bored pegs. This method may minimise movement, but allow the whole thing to move with the change in seasons and will leave the possibility that if the worst comes to the worst, (it warps badly) you can take the whole thing apart and re-make it.
Here’s a couple of photos of a table top of similar dimensions to yours that I made about 10 years ago using T&G, bread-board ends and draw-bored pegs which illustrates the method I outlined.
You must be logged in to access attached files.25 January 2019 at 11:08 pm #554715
Thank you for all that information. I actually was thinking about doing Tong and Grove. It wouldn’t be that hard with this wood.
Actually the hardest part so far is getting the long edges absolutely straight and square. But I have surprised my self by being able to do it. I plane to what I think is straight & square then let it sit a couple days, then re check it. I’ll keep doing that until the time comes to call it good. I’m at the point with those boards that I have my plane depth set very shallow just taking of a whisper of a shaving each pass and then re checking. Still learning and getting my confidence. OH, and having a great lot of fun doing so.
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