Replies

1. 
   JohnWW | Apr 21, 2006 06:33pm | #1

   Chuck,

   The stiffness in a torsion box comes from the two skins being separated by a fairly great distance while still being rigidly locked together by the filler structure.  The stiffness of the filler can contribute some additional strength but it isn't what primarily makes a torsion box stiff.  This is why you can build very stiff torsion boxes with cores of cardboard or aluminum honeycombs even though the honeycombs by themselves are actually flimsy.

   So the answer is yes, you can build a core lattice from plywood.  You will lose some glue joint strength if you use yellow glue because 50% of the edge of the plywood will be end grain, but the strength of the glue joint will still be adequate because of the large overall surface area of the edges.  To compensate, you could seal the plywood edges with a primer coat of glue. 

   An alternative would be to use a construction adhesive like PL400 which is made for gluing plywood decks to joists.  The thick construction adhesives have good strength even when applied on end grain.  PL400 and similar construction adhesives are applied as a bead with a caulking gun, so they are easy to use, and are available at Home Depots and lumber yards.

   The strength of a torsion box is highly dependent on establishing a good grid to skin glue joint over the entire surface of the grid, so you need to nail or screw the plywood skins to the grid right after applying the glue so that good contact is maintained while the glue sets.

   John White

   
   

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   Edited 4/21/2006 11:35 am ET by JohnWW

1. 
   user-139185 | Apr 21, 2006 07:28pm | #2

   Thank you very much for your insight John. This is exactly the information I was after.
   Have a great weekend,
   Chuck