Replies

1. 
   johnhardy | Nov 21, 2002 07:56pm | #1

   I can think of lots of things that can aggravate something like this. Here's a few items to think about.

   Are you clamping up the table top with pipe clamps? If all the clamps are underneath the top you may be bowing the top because the clamps flex. Try putting clamps on both the top and the bottom of the glue-up, and it wouldn't hurt to put several cauls across the glue-up to keep it flat.

   What sort of edge do you have on the boards? If you're using a sawn edge, your blade may not be perfectly square to the table. If it's off, say a half degree, and you cut both sides of a board on the saw, the amount you're off for that one board is 1 degree (2 edges). If you glue up 6 boards, you've got a total error of about 6 degrees. For a sawn edge, one way to fix this is to cut one edge, flip the board to that the top is now on the bottom, and saw the other edge. The two edges are now parallel planes and the glue-up wouldn't have this error.

   If your boards are flat sawn, the growth rings will look like a smiley face or a frown (looking at the end of the board). If you glue up all of the boards with the growth rings in the same position, you're asking for a compound cup (IMO). Alternate the boards so that you have an up/down/up/down/up ... pattern. This should minimize any problems related to growth rings pattern.

   John

1. 
   jondee41 | Nov 22, 2002 02:51am | #5

   Hi John

   Thanks for all the info.  I will try your suggestions and hopefully the problems will go away.  Thanks again

   Jon

1. 
   fiddlebench | Nov 22, 2002 06:17pm | #6

   John

   this may be obvious, but are you face jointing your boards on the jointer to flatten them to begin with. The only other way is to flatten a board with a hand plane. Remember planers do not flatten boards. Planers only parallel an already flat board.

   After the faces are true then use the jointer on the edge of the board to true the edge then tablesaw the board parallel. I then joint the sawn edge.

   I would also dry clamp to determine if you have a flat assembly of boards.

   You may want to review an article in FW on stock preparation. There is more to it then I can cover in this post.

2. 
   johnhardy | Nov 22, 2002 07:35pm | #7

   Jon,

   One more thing. It wasn't clear from your original description if the problem was before or after finishing.

   If you do not finish all sides of the top it's more likely to have future problems.

   And you need to remember that when you attach the table top you need to use a fastening technique that allows the top to move seasonally.

   John

2. 
   BenM | Nov 21, 2002 09:21pm | #2

   Is the wood properly conditioned?  Are the individual boards flat, straight and out of winding?  Is your glue-up work area flat, level and out of winding?

3. 
   BHerman | Nov 21, 2002 10:10pm | #3

   I used to have this problem from time to time - found that cauls top and bottom (typically I use old 2x2) across the planks with clamps on both ends helps alot. I put one pair on each end and 1-3 in the middle, depending on panel length.

1. 
   jondee41 | Nov 22, 2002 02:49am | #4

   Hi Ben

   Thanks for your reply.  I will try your suggestions.  Hopefully my problems will go away.

   Jon