Replies

1. 
   Samson | Feb 14, 2009 02:31am | #1

   A 1/16th cup over nearly 22" is not all that bad.  Often such a piece will be pulled flat when joined to other pieces (e.g., other sides of a cabinet; the apron of the table for a top, etc.).

2. 
   JohnWW | Feb 14, 2009 05:35am | #2

   Alternating the ring orientation means the movement of the different boards tends to balance out, but if one board cups slightly more or less than the others (which is almost always the case since no two boards are ever alike), there will still be some overall cupping.

   You can diminish the effect by using narrower boards, and using quarter sawn stock.

   Keeping a top flat is a combination of how you construct the top and then using some structure underneath, such as table aprons, it to further pull it flat.

   John White (Former Expert and retired FWW Shop Manager)

3. 
   Dave45 | Feb 15, 2009 01:29am | #3

   Before you glued up your pieces for the panel, did you lay them on a dead flat surface and check how well the edges matched up?

   I had a similar problem once (yeah, sure, only once - lol) which turned out to be the result of my edge joining not being perpendicular to the board face. When I tightened the clamps, the edges closed up and left me with a slight "cup" in the panel. (For a visual, think barrel staves)

   Most of the local cabinet shops make their panel blanks slightly thicker than their final thickness and run them thru a wide belt sander to flatten them out after they're glued up.

   Another way to eliminate this problem is to run your boards thru the joiner so that any error in the fence adjustment gets cancelled out. The first board goes thru with the front against the fence. The second board has the back against the fence, etc ,etc. When the boards are laid flat, the edges will match up even if they're not perfectly perpendicular to the face.

   If you do this, be careful with your glue up. The boards will want to slip a bit as the clamps are tightened.

   
   

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   Edited 2/14/2009 5:30 pm by Dave45

1. 
   jscharver | Feb 15, 2009 04:43pm | #4

   Thanks for the advice folks. In my naivete I may have experienced a combination of factors which caused the problems. The stock is Southern Yellow Pine (C&BTR), 16'(1x8) purchased from a local lumber yard, not a big-box store.I don't have a jointer so getting a true 90 degree edge was a non-starter for me. However, I did run a few boards through the table saw as follows: I squared the end of the board on a crosscut sled and then used a large framing square to choose which side of the piece appeared "square". That side was placed against the fence and the opposite edge was ripped with a Freud "Glue Line" blade. Sequentially mating pieces (3 total) were each marked with chalk to maintain grain and face orientation. I suppose a little cupping could introduce error here, particularly if the cup was placed down during the cut to produce a less than true 90 degree edge. Such little differences would be cumulative and most evident after glue-up. Correct?

1. 
   Dave45 | Feb 15, 2009 06:57pm | #5

   There's no question that cumulative errors can (and will) bite you in the arse at the worst possible time. Murphy's Law says that "Anything that can go wrong, will go wrong." Many years ago, I developed a corollary which says that "Murphy was an optimist!!" - lolThat technique I described would also work on your TS. Square your blade to the saw table, then run your boards face up, face down, etc, etc. It's the same principal - if your adjustment is a fraction of a degree off, the cutting sequence will make the errors self cancelling when you assemble the pieces.Personally, I don't square the board ends before assembling a panel. I cut them a bit long, and rip them so the glued up panel is a bit wider than what I need. When a panel comes out of the clamps, I scrap/sand it reasonably smooth, then use my TS to rip it to final width, then use my panel cutting jig to square one end and then cut my final length.