The top of my unassembled cherry trestle table is 75″ by 39″ is butt edge glued using three 8″ boards in the center and two narrow boards on the outside. The lumber is from a log I had sawed at a local mill and air dried in my unheated barn in Vermont for 14 months. The boards are flat sawn with adjacent boards alternating the grain curve up and down. I have built the legs and fitted the stretcher, which measures 50″ from inside the leg to inside the leg, and 3 1/2 by 1 7/8. The base is assembled and is solid on the floor
I diligently tried to square the edges in prep for gluing up each board (which I did one at a time) but the top has a twist., resulting in 2 opposite corners being higher than the other two. When I clamp just one corner of the top to the top of one leg, the base is solid all around on the floor, but the oposite corner is 7/8″ up from the top of the other leg. When the top is clamped to two opposite corners of the base, the stretcher twists and the opposite corner feet have a difference of 3/8″. In other words the table has a rock of 3/8″.
I have tried clamping the high corners to a flat surface, even with a 1/4″ plywood scrap in the middle to overbend, but only for about 48 hours and with little effect. Also tried laying the top on the floor for 24 hours , but with no effect.
Suggestions? I hope I do not have to build a new top.
Thanks, Ryan
Replies
Cherry with a twist
Hi,
I assuming your top is glued up with the grain of all the boards parallel and running the long way.
A couple of questions. Did the top glue up with a twist or was it flat and then twisted after glue up?
if it glued up twisted, you could saw through the joints resquare and reglue, being extra careful that the edges are square to the edge and careful that the clamp pressure is not bending the wood.
If it twisted after glue up, moisture change is likely the culprit (although tension in the wood is a possiblity too). This is more problematic. Were the boards acclimatized to the shop? Even if they were, the Vermont change of seasons will likely cause some movement of the top. Cherry is supposed to be a stable wood, although I have found it prone to twist. It may be because I tend to use #1 because l like the sapwood contrast (and it is cheap). The twist could be caused by a particular board, or it could be cumulative across all boards. If it s a particular board, you may be able to cut it out and replace it with a more stable board.
You don't mention the thickness of the top. If it is too thick, say over 7/8, its moisture based movement may be overpowering the stablizing weight of the base. A trestle table isn't the most rigid base so it can only help so much against twist. Thinning the top, screwed -not glued- battens on the undersides with elongated holes for the screws (flat head sheet metal with oversized washers work good) might help, but no guarantees. A finish will slow the absorption and loss of moisture, but in Vermont, you are going still going to hit the extremes of winter dryness and summer moisture regardless of the finish.
cherry with a twist
Hackmeister,
Thanks very much for your thoughtful reply.
The grain is parellel and thickness is 3/4". I think that most of the twist occured after the glue up, but I was having a very hard time aligning each of the boards as I glued them. The individual boards were not perfectly flat before gluing.
I am going to try the battens with one or two running diagonally, using screws and elongated holes as you suggest.
If yu have further suggestions,I am all ears.
Thanks again.
Cherry twist
Really heavy candelabras might work:)
The not flat prior to assembly part probably didn't help, although it sounds like a combination of twist in the wood and moisture change.
Take heart, gluing up long boards together into a flat top is more difficult than it appears. Wood can bend after glue up, boards can shift under clamp pressure, certain boards can be more susceptible to moisture than others, and not everything can always be quartersawn. I had a workbench top slip under clamp pressure earlier this year to my great annoyance.
A couple possibilities short of cutting the glue joints and reassembling/replacing wood, depending on how quickly you want to get the table done. Do bear in mind though, that it is possible that these particular boards may never behave and lay flat, though.
1. Leave it sit for a couple weeks. It is possible that the twist may get better (or worse), but letting everything stabilize wouldn't hurt.
2. Extend the stretcher, giving more leverage and weight on the ends.
3. Try a diagonal batten with a bow in the opposite direction (OK, this won't get either of us an A in shop class, but there is a chance it might work). Battens across the grain near the ends might work, but only if the twist is pronounced just at the end of the tops. Battens can be C clamped/temporarily screwed to test prior to permanent attachment.
There are some other more ones that would be irresponsible to share (wet the side that you want to stretch, cover it with poly, prop the down edges up with flat 2x4s and put a cinderblock in the middle, but only if you used titlebond II or III, and similar crazy ideas), but the above may work.
Look at it this way, the worst that could happen is that you end up cutting the table top into a set of nice cherry shelves that match your new tabletop, made of carefully flattened and squared boards free of twist:)
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