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I have just acquired 84" rails for my tablesaw and constructed a new outfeed table that spans the whole width. Now I want to build a filler table at the side of the table to continue cast iron top surface between the rails (approx 27" x 36"). I have some 3/4" MDF in the shop, but it appears to have some warp and twist (about 1/4" corner to opposite corner). I have enough MDF to make the top two layers thick and have clearance below to add deeper wood supports to help keep the top flat. When I tried dry fitting the two top panels with clamps I still show a little twist. Before I try laminating the top pieces together I want to be sure I am not missing some simple tricks to flatten the surfaces permanently. Can the warp in these panels be permanently removed or is the material beyond hope in creating a surface flat enough for a tablesaw table?

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    Personally I'd get fresh MDF and use the warped stuff for something where the warp doesn't matter (eg where it is used in smaller pieces, since the warp per piece may be negligible.) – keshlam Mar 5 '16 at 19:16
  • Totally off topic, but how did the MDF warp in the first place? I have this problem where none of my MDF stays straight, and it frustrates me because all I hear about is how stable MDF is. – Jason C Mar 6 '16 at 4:57
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    The piece was stored vertically and had leaned a bit in the storage rack causing a slight twist. – Ashlar Mar 6 '16 at 15:34
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    What kehslam said! :-) "Can the warp in these panels be permanently removed?" possibly, but many variables (minor warping can be removed just by fixing a board to stiff framing, but not always). "is the material beyond hope in creating a surface flat enough for a tablesaw table?" just how flat does the table need to be? A 1/4" deflection more than 6 feet from the blade doesn't sound like it would actually be a problem... – Graphus Mar 6 '16 at 19:51
  • no good can come from MDF. it is basically bleached mulch with glue. one spilled cup of coffee and it is done. – SkipBerne Mar 15 '16 at 18:07
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Rather than laminating two pieces of MDF together which is not guaranteed to remove the warp you see I recommend you build a torsion-box style lattice structure out of straight stock and skin it on each side with your MDF. The lattice structure is incredibly rigid and because you are building it with solid wood you can mill it to ensure consistency and flatness. Once you fasten the MDF on top and bottom of it (glue should be sufficient) it should overcome your warping.

I am assuming you are trying to make use of what you have in the shop, otherwise I maintain my recommendation but would use thinner MDF for the skin.

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All I do whenever I have a warped MDF board is put it down on a flat surface and weigh it down and leave it. For me that works every time.

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