Dead-flat surface - Woodworking Talk - Woodworkers Forum
 
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post #1 of 9 Old 05-30-2009, 02:56 PM Thread Starter
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Dead-flat surface

Hi gang! I'm new to the group any have been trying to find the answer to a seemingly simple question with little luck.

I'm trying to create a torsion-box type structure which needs to be dead-flat. I have read that a jointer is used to get all the interior support elements of the box flat and even. The problem is I don't have a jointer. These are the tools I have at my disposal:

1) Table saw whose fence I do not trust.
2) A hand-held power planer.
3) Jigsaw
4) Belt sander

Using these, how can I make sure that the dimensional lumber (2x4 and 2x6 douglas fir) I am using for the structure is flat and level?

Thanks for any help you can provide.
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post #2 of 9 Old 05-30-2009, 03:14 PM
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#1. Get a good fence and true up your saw. There should be some good tutorials on that on this site.

#2. Lose the doug fir. Chances are it has a high moisture content and will move even if you get it straight.

#3. Cut your pieces out of mdf after you are sure your saw is set up properly. Mdf is a stable product and will work great for this application.

I am sure you will get some more great input but that is my 2 cents worth... I hope it helps.
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post #3 of 9 Old 05-30-2009, 08:22 PM
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yeah, every "how to" I've seen for a torsion box has been using mdf for both the top/bottom AND the honeycomb internals
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post #4 of 9 Old 06-01-2009, 09:04 AM
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What's a "torsion box?"
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post #5 of 9 Old 06-01-2009, 03:22 PM
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This will probably explain it better than I can...

http://www.diynetwork.com/diy/ww_mat...278181,00.html
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post #6 of 9 Old 06-02-2009, 06:31 AM
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"Tables built in the torsion box style are known to carry great weight and are resistant to twisting and bending. "

This statement in the referenced article explains where the word "torsion" comes from.

G
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post #7 of 9 Old 06-02-2009, 07:09 AM
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Dead flat as I understand it is impossible with wood. I used to work in a machine shop next to the room where they did testing. They had a granite table that was "dead flat and level" to 6-10 decimal figures. Wood breathes considerably more than thousandths, more like 1/8-1/2 over a season.
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post #8 of 9 Old 06-02-2009, 07:43 AM
where's my table saw?
 
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Dead Flat is Relative

Woodworking of course does not require "dead flat" to the same tolerances as a machine shop. MDF or plywood was suggested because it is a structured material, not a natural wood that will vary considerably in different moisture environments. The construction method and the depth of the box greatly limit the flexing of the top surface against the bottom surface, since for one to move in one direction the other must move in the same direction. The internal ribs act as triangulation members to the opposite surfaces to prevent this movement. Hey, it's only a work/glue up surface, not a surface plate. The old expression "We're not building a watch here applies" bill

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #9 of 9 Old 06-02-2009, 08:18 AM
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I now understand what a torsion box is and what it's used for.

As usual, great info on this forum.

Thanks!

Kevin H.
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