Replies

1. 
   jvs | Jan 21, 2004 05:07am | #1

   How were they stored? If they were flat with no circulation on one side, it is likely that they just lost moisture on the exposed surface and will un-cup if left alone or left up on a couple of 2x4s or -6s for a few days. Worth trying before planing it into veneer for your *new* tops.... :)

   /jvs

2. 
   HowardAcheson | Jan 21, 2004 05:54am | #2

   In addition to jvs's comments and suggestions, you may not have to get the tops flat.

   How are the tops to be mounted and how cupped are they? If the tops will be mounted in a way that the cup can pullled flat, then that is the way out. Try this. If you can flatten the panels by pressing down in the center with a little force, then the mounting may be able to get the tops flat.

1. 
   toddhunter | Jan 21, 2004 07:35am | #3

   They cupped while sitting on the mdf ping pong table in the basement (where the wood was stored then cut).  I am hesitant to press down too hard or to draw the ends down, as the cupping is at least 1/8" at the sides.  The ends curve up.  Tonight on one, I planed off some of the center from the bottom surface, and already it doesn't rock so much.  How much cupping would be amenable to mechanical manipulation?  Todd

1. 
   joinerswork | Jan 21, 2004 08:09am | #4

   Todd,

   How thick are the tops?  How wide?

   1/8" doesn't sound like too much to pull down, but I'd turn them over on the ping pong table and monitor them for a day or two before doing much else.  They may straighten themselves out; if they do, then stack them with stickers between to allow for air circulation on both sides till you get them in place.

   Cheers,

   Ray

2. 
   HowardAcheson | Jan 21, 2004 10:06pm | #8

   As you have already learned, you never lay a panel down totally on another surface. Air needs to be able to freely get to both sides at all times or the panel will warp. If you must store a panel, do so completely on an edge or sticker it with weights on top if you must lay it on a flat surface. Don't lean it against a wall either.

   In most cases, you can just sticker it so it is off a surface by an inch or so and it will almost completely flatten as long as it has not be cupped too long.

3. 
   wop | Jan 23, 2004 01:06am | #11

      Set them propped up in the sun convex side up and keep an eye on them for a few hours if it is a question of uneqaul drying this can flatten them somewhat. Make sure that when you bring them in out of the sun that you stick and weight them and leave them sitting until the temp of the piece is uniform(even a couple of days). Then consider planing flat if the cup is still too bad.

                                    Philip

3. 
   3fingers | Jan 21, 2004 04:15pm | #5

   I wonder how long was your stock stored indoors before working ?

   sometimes even if klin dried, the wood needs to acclumate to the humitity level in your shop.

1. 
   toddhunter | Jan 21, 2004 08:45pm | #6

   I'll give all suggestions a try.  BTW, the wood is 3/4 and 18x18, four pieces each top.  Thanks, Todd

4. 
   forestgirl | Jan 21, 2004 09:07pm | #7

   Todd, I've fixed cupped tables in the past by re-balancing the moisture content.  It's easier in the summer than the winter, 'cause the sun shines here sometimes in the summer <g>.  In the summer, I lay some newsprint or tissue paper out on the lawn, put the boards concave side down in the sun (Northwest, the sun doesn't get too hot usually) and leave them there until the boards flatten out.  They I put them in the shade with circulation all around, and check many hours later to see how they're doing.  If they have re-cupped some, they I do it again, but I take the board every so slightly past flat.  Then back in the shade, check again later.  They usually get flat within 2 treatments, but 3 or 4 might be necessary.

   To duplicate this in the winter, I do it inside with a damp (not wet!) towel and a heat lamp.  Main thing is to not make anything too hot or too wet. 

   forestgirl Another proud member of the  "I Rocked With ToolDoc Club" .... :>)  you can take the girl out of the forest, but you can't take the forest out of the girl ;-)

5. 
   JohnWW | Jan 21, 2004 11:24pm | #9

   Todd,

   A board will cup for two reasons:

   1.  A flat sawn board will cup when it loses moisture and flatten out when it gains moisture.  This will occur whether or not the board was kiln dried, whether not it was finished, and will occur even if both faces are equally exposed to the air and heat and gain and lose moisture equally.  The only way to avoid this completely is to use quarter sawn wood which is more stable.    

   A quick way to tell which way the board will go is to look at the end of the board, the growth rings will straighten out as the board dries out, they will curve tighter if the board gains moisture. 

   If all the growth rings on a glued up top face the same way, the top will cup upward or down as it gains and loses moisture.  If the growth ring's orientation is alternated, face up and face down from board to board, the top will ripple but overall stay relatively flat as it dries.  There are two schools of thought as to which is the right way to orient the growth rings when putting a top together.

   A board that has cupped because it has gained or lost moisture equally throughout its thickness will only be flat when it goes back to the original moisture content it had when it was first flattened. 

   2.  A board will also cup if one face gains or loses more moisture than the other side of the board.  In this case the board will cup towards the drier side. 

   The unequal moisture gain or loss can occur when only one side of the board is exposed to sun or air circulation or when one side of the board has a different type or amount of finish than on the other side. 

   A board that has cupped because it has dried out unequally will flatten out when the moisture content of the two faces is brought back in balance.

   John W.

    

   
   

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   Edited 1/21/2004 3:31:54 PM ET by JohnW

1. 
   toddhunter | Jan 22, 2004 11:28pm | #10

   I'll try flipping them.  When joining I went with the school that says use the best looking side up, and if it's not too big a piece, hold it down mechanically.  Since I've waited so long, it got ahead of me.  Thanks, Todd