I want to make a 1.5″ thick table top from two .75″ previously glued up boards, “A” and “B”. Board “A” (the original top) is a 40″ x 16″ solid rectangle. Board “B” is a frame with a 6″ wide perimeter, that’s also 40″ x 16″ (a rectangle with a 28″ x 6″ hole in it).
I thought this was I good idea when I agreed to “thicken” the original top (“A”) with the frame (“B”), but when I started to set up the clamps it occurred to me that there’s a lot of square inches of glued surface to squeeze (452), and only 112″ perimeter inches to get the clamps on. It’s not just the total si’s that is concerning me, it’s also the total distance the glue must travel (at least 3″) to squeeze out. I have nightmare visions of glue being trapped in pockets, lurking, only to be discovered when I finish the edges as a #$%! glue void by my router (I don’t think I’ll be able to sleep tonight if I think about this any longer !!).
Part of the original plan was to use 2″ x 6″ cauls top and bottom to allow the clamp pressure to radiate to the entire glued surface. When I got around to doing the detailed clamp layout I realized that I need a minimum of 24 large (3″ throat) clamps (spacing 4.5″). This does present an opportunity to double my clamp collection, but I’m not confident even the 24 will be able to apply enough pressure for that 6″ wide perimeter (“B”) to make a tight joint with the old top (“A”).
The material is maple, the joint edge between the two is to be routed and will be visible.
Suggestions ? Ambien ?
Tom
Replies
I'd use a vacuum press.
Greg
•••••••
Exo 35:30-35
Have you considered using screws, driven in from underneath, to clamp the boards? Tighten from the centre outwards and remove the screws when the glue has dried.
I glued up a bench top from 2 x 19mm x 85cm x 200cm sheets of pine laminated boards and where I have drilled dogholes the boards are snug against each other. Alternatively would you consider bevelling the edges to 45 deg and applying a triangular edging. This would have the advantage that the table edge would not show a joint. Like this if my ASCII art works:
_ _ _ _ _ _
|
| Tabletop
|___ _ _ _
^
Edging
Remember that it is only the line that will be the edge of the top when a profile is routed on the edge that has to be thoroughly clamped, not the full 6" deep surface. That means that just about any clamp that will handle the total thickness will do--you don't have to have them reach all the way to the middle of the boards. This brings your bar clamps and other shallower reach clamps into the count. If the new edge line, and and just an inch inward from it, is solidly glued, the rest of the 6" that remains will be plenty firmly attached even if it were only "tacked" a few places with a deeper reach clamp.
Tom,In addition to what Steve said, if you started out with flat boards where are these pockets of glue gonna come from? When I do what your doing I plane and scrape and then hit it with 100,150,220 long strokes, and a final scrape. Also, I usually oversize the glue up and use the waste to double the thickness of the top....better color and grain match.
As another poster mentioned, screws. If that's not desirable, long-wise cauls and 3 or 4 clamps per side will do the trick. You have a lot of glue area so you won't need to develop maximum glue strength -- just "good enough". You're overthinking this.
One thing that could pop up to bite you, though -- is the grain on the "frame" (board "B") all going the same direction as the grain on board "A"? If not, you have a movement differential issue to address.
Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.
To All,
Thanks for the advise all.
I glued the top this afternoon. 24 clamps, 2x6 cauls top and bottom, and a pint of Titebond I. I appreciate all the suggestions. The one that hit home was the "overthinking" one. Sometimes you "gotta just do it".Tom
Tom, Your description does not make any reference to the grain direction on the end of the frame. If you are running the grain 90ยบ to the other layer across the end, you are not going to like where this path is likely to lead.
Keith,
All grain runs in same direction.
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