Table-Top Glue-Up Tips

      A discussion of whether to use biscuits or alternate board grain alignment when gluing up table tops. December 6, 2008

Question
I'm having a little back and forth with my shop foreman. We are doing a white oak desk top 36 x 68 x 1.25. He believes in biscuiting 3" strips, reversing each strip, and he wiggles on the glue. I, on the other hand, like not to use biscuits and spread the glue evenly on all surfaces. Anybody want to weight in on this debate?

Forum Responses
(Architectural Woodworking Forum)
From contributor T:
While biscuit joints will not add any strength to the top, they will aid in alignment of the boards, which may in turn save you some time in planing/sanding the surface. With 3" wide boards, you are going to have a lot of gluing to do.



From contributor G:
How will the ends be finished? If breadboard style I would run the strips in a glue joint cutter. If exposed end grain, I would use 1/2 inch dowels.


From contributor P:
I would go with the glue joint also, it really speeds up the glue-up and sanding process. The biscuits take way too much time.


From contributor M:
We do tops all the time and never use biscuits. I still strongly believe in alternating the grain on every board to prevent warping. 3.5" strips work nice but we end up with anywhere from 2"- 4.5" wide, otherwise we have far too much waste. Just face joint each board and plane to same thickness. You will have no problems with lining them up.


From contributor A:
It all depends on what kind of material you start with. Yesterday I had to throw together a 3/4" x 32" x 10' qtr sawn white oak. The 4/4 boards started less than 1". In that length I was able to end up at 13/16" with rough spots on the back side. They were 6" boards. I elected to biscuit every 12" for alignment only. No glue on the biscuits. It took me 10 minutes to cut the slots. I could have hit the top with 100 grit with a random orbit, but I'll run it once at 150 through the Timesaver. If you've got plenty of meat to grind off, then the biscuits are a waste of time.


From the original questioner:
Thanks to all who have jumped in here. End grain is open on this top, so bread board doesn't apply. I'm with contributor M on this. That's the way I do it. The top did curl up and we are fixing it. I do think the biscuits change the dynamics of the wood joint and uneven gluing are the culprits. My guy disagrees. We'll do the next one my way.


From contributor H:
Forget the biscuits. Aside from alignment they provide little more strength than just using glue. Biscuits swell after being inserted. On thin stock, 3/4" or less, they actually raise the surface where they are located. When you sand the top, you sand off these high spots. Then the biscuits shrink, leaving small divots wherever they are located. You will notice this more on tight grained wood with glossier finishes. If the wood fails before the glue joint, then again, what purpose do the biscuits have aside from alignment? When we glue wood tops, we take our time and use caul blocks to flatten and keep the joints aligned.


From Professor Gene Wengert, forum technical advisor:
I agree with the use and uselessness of biscuits. It is interesting that the idea of reversing the strips continues to persist. If the MC is appropriate for the product, such reversing is not needed.


From the original questioner:
Reversing the cupping of the grain was promoted by Jerry Metz, who wrote a column for the furniture industry. It was called Metz rules. But that was always a rule even when I started in this business in 1979. I think it is a good idea regardless of MC. My shop isn't climate controlled. Anything I can do to put the odds in my favor is worth the effort.


From Professor Gene Wengert, forum technical advisor:
The point about flipping or reversing the grain is that you would be much further ahead spending time to get the MC correct. The effect of flipping is impossible to measure when the MC is correct and it is also hard to measure even when the MC is slightly off. If the MC is way off, do not use the lumber.

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