Replies

1. 
   rslatm | Nov 11, 2003 10:22pm | #1

   Get some 6/4 Oak!  Sounds like a perfect recipe for failure if you go with your plan.  The oak will move so you do not want to glue it to a substrate.    The oak must be allowed to expand and contract for seasonal movement.    Biscuits are not necessary to edge join boards.  If you want to use a substrate use veneers and make sure you use a veneer on the bottom for balanced construction.  Read more books on how to construct furniture and on the properties of wood.  Hoadley's books on understanding wood are great not to mention Ernest Joyce's book on furniture making.  You could rip strips of 1-1/2" and glue it up butcher block style.

   
   

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   Edited 11/11/2003 2:27:57 PM ET by Rick at Arch. Timber and Millwork

2. 
   BobSmalser | Nov 11, 2003 10:40pm | #2

   Rick is spot on...as the wood moves seasonally, and oak moves a bit...either your glue joints will fail or the wood will crack.

   A 7/8" top is pretty heavy all by it's lonesome...why not just do that?  No biscuits or dowels or other doodads needed, joint the boards, lay them out for a pleasing figure, flip every other "cup" (endgrain) is you like, and saw up some precise clamping pads so the clamp pressure falls dead center on the edgegrain.  Clamp it all dry before you reach for the glue.  Hide glue, aliphatic, casein, poly...joint and clamp those boards correctly and the layup glue don't much matter.

   Ya can make that top look more massive by adding an apron.  Just make sure the apron...and any base, slide mechanisms or mounting cleats....is mounted with slotted screwholes to allow the top wood movement across the grain.

   
   

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   Edited 11/11/2003 3:44:05 PM ET by Bob

3. 
   SgianDubh | Nov 12, 2003 03:42am | #3

   As Rick and Bob have said, your plan is something of a train wreck waiting to happen. The oak will expand and contract at a different rate to any man made board grounding you use. It'll break up into matchsticks in almost no time.

   You could increase the visual weight by doubling up the thickness of the solid wood at the edges, using traditional and reliable solid wood edge joining techniques that go back quite while. Rick suggested two first class heavyweight books on the topic. Both would be a good purchase if you are seriously interested in learning about woodworking.

   Joyce by the way has just been updated by Alan Peters (again) to include such things as CNC routing, etc., since it was first published thirty odd years back. A seriously masterful tome on the subject that I can't imagine any furnituremaker would be without. Which reminds me-- my copy is almost thirty years old, so maybe I ought dig out the £20 or so needed for a new paperback copy. Slainte.

   Website

4. 
   4DThinker | Nov 12, 2003 06:43am | #4

   I've had one student make a thick top by layering hardwood atop a piece of Baltic birch plywood.  He did this mainly because of the complicated design of the table's base.  He could screw down through the plywood to connect the top to it, then cover the plywood with hardwood.  The trick we used was to not glue the hardwood to the plywood.  We actually cut dovetail slots across the grain on the bottom of the hardwood, and in the same direction and location on the top of the plywood. With some calculation we figured out how narrow the hardwood might shrink to at that extreme, and cut the plywood that dimension. The two layers were connected by long dovetail "butterfly" keys. A few screws along the centerline (from the underside) kept the hardwood centered on the plywood.  The keys were High-Density plastic, and had a teflon-like slipperiness against the wood. A thick apron covered the plywood edge, and the end-grain apron was actually cut from the ends of the top, then miter-folded down. 

   It turned out amazingly well.  In a wet spring there opens up as much as 3/8" between the hardwood edge and the plywood.  In a dry winter the gap is paper-thin.  The only feedback I've had from that student came in an email a year or two after he graduated.  He commented that the table would make interesting noises for a short period each year between air-conditioning and heating seasons.  Apparently as the hardwood expanded or shrank it would slide across the plywood with a subtle oscillation (noise). 

   4DThinker

5. 
   DaveHeinlein | Nov 13, 2003 01:20am | #5

   In your case I would glue up the top, Thicken the edges as already suggested, and either attach(not glue) cleats across the bottom, or make bread board ends.

   When thickening the edges at the ends of the top, do not use a long-grain piece to thicken with, use end grain. The fact that the wood is quarter-sawn means you don't need to worry about which way the annular rings go.