Fan-Shaped Table Top Glue-Up
A discussion of how wood movement may affect a table top assembled from thin pie-slices, assembled in a radial pattern. January 19, 2012
Question
I'm trying to research the best way to produce a radial lamination. I basically want to glue together a number of pie slices of 1 1/2" walnut and end up with a radial fan effect. This will become a table top. Final thickness: 1 1/4".
Forum Responses
(Laminate and Solid Surface Forum)
From contributor D:
This will not work with solid wood, since wood moves with changes in humidity. This is why this type of radial lamination is always done only with veneers. Beyond those two statements, things can get pretty complex, and a very good working knowledge of wood and its behavior is needed to go any further.
From the original questioner:
Okay, so it's a no go. What makes the radial lamination different from a butcher block? Both are composites of joined wood. Would this scheme work if there was a kind of cross support under the radial lamination to compensate for the bending due to humidity?
From contributor J:
I disagree with contributor D. It wouldn't work for a full circle, but for a quarter circle it would be fine. The top would change shape with humidity fluctuations, but it wouldn't self-destruct. This is basically a multi-stage gluing and clamping challenge.
Moisture from gluing the parts together could deform the thin ends of the wedges, so it might be necessary to glue on one piece, then machine the outer edge flat before adding the next piece. It'll be a tedious process, and ultimately you'll end up with a top that needs to be smoothed and flattened after all the gluing is over. I hope you're either proficient with hand planes or have access to a big wide-belt sander.
From the original questioner:
That is encouraging. I'm aware that all the things you say will have to happen: gluing pieces in pairs and build up to the full surface, plane it after. How would you join the pieces? Dowels? Biscuits? I've been told that a good way is to use a hardwood joint of a slightly less hard hardwood than walnut (the table top material). This will somehow compensate for swelling of the wood by the glue. Thoughts?
From contributor J:
The only reason to use dowels or biscuits in this situation is to help align the parts during glue-up. That may or may not be helpful, but it probably depends on the particular clamping arrangement you come up with. I can't comment on your hardwood joint idea because I don't understand what you mean.
From the original questioner:
Beyond alignment of parts, is there a method (biscuit or dowels) that will help to avoid splitting or warping more than others? Or are they all more or less the same?
From contributor J:
Wood movement is caused by changes in the moisture content of the wood. Dowels and biscuits have nothing to do with it. The wood should be properly dried before assembly. After that, the wood only moves with humidity changes. Keep in mind that this top will change shape considerably during normal seasonal humidity fluctuations, so make sure it's attached to the base in such a way that it can move without damaging anything.
From contributor G:
Why do wood floor medallions work at 5/8" thickness with grain moving in various directions? Many of these designs incorporate pie-shaped wedges revolving around a central axis...
