Darryl Keil Last Activity 2025-09-09 11:09 AM
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lkasdorf

Posts: 3

Joined: 2009-05-17
Location: Waterford, VA

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Subject : torsion box- must I apply backer to each skin?
Posted : 2009-05-17 10:31 PM
Post #35418
I am building something like this:

http://barncattech.com/projects/coffeetable/boke_table_1a.jpg

I want to make the top as a torsion box- 4' x 4' x 2.5".

THE BIG QUESTION IS:
Do I need to apply backer to the inside surface of each skin? Or, do I simply need to apply backer to the underside of the completed torsion box?

I have some folks telling me that if I do not put backer on each skin, that it will warp from the face veneer. This makes intuitive sense to me, but I hear of lots of folks making torsion boxes, putting face veneer on top, backer on the bottom, and it all works out.

This is driving me crazy- I need to get on with the project!



 
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craig tufankjian

Posts: 308

Joined: 2004-02-01
Location: syracuse ny 13208

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Subject : RE: torsion box- must I apply backer to each skin?
Posted : 2009-05-18 7:18 AM
Post #35421 - In reply to #35418
Ikasdorf,

I see no need to veneer the backsides prior to assembly. Make sure that your skins are glued to the whatever you use on the inside of the box.

assemble you torsion box and veneer both sides, should be fine.


Craig


 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: torsion box- must I apply backer to each skin?
Posted : 2009-05-18 9:42 AM
Post #35422 - In reply to #35418
Ikasdorf,

I agree with Craig, no need to veneer the inside of the skins. Think of it this way, any lay up should be balanced in the number of glue lines and the materials used, from the center out. If you added a veneer to the inside of one of the skins but not the other, that would be unbalanced, an extra glue line. If one of the skins was 1/4" plywood and the other 3/8" MDF then that would be unbalanced as well, different thicknesses and different materials.

Darryl


 
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dana

Posts: 1

Joined: 2009-05-29

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Subject : RE: torsion box- must I apply backer to each skin?
Posted : 2009-05-29 10:33 AM
Post #35449 - In reply to #35422
I disagree (unless you've already done it then it's ok) and think that both sides should be skinned. If your inner frames are 8" apart that leaves 8" of unsupported material vulnerable to the stresses of veneering one side just as if it was 8'. It may not be noticeable at a certain spacing of frames, or a certain stiffness of material, or a certain sheen of finish, but the risk is there.


 
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BigRob777

Posts: 142

Joined: 2008-05-26
Location: Newark, DE

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Subject : RE: torsion box- must I apply backer to each skin?
Posted : 2009-05-29 11:34 AM
Post #35452 - In reply to #35449
Dana,
Very impressive web site, you have there. You do amazing work. Welcome to the forum. I look forward to your future insights.
Rob (beginner)


 
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Brian Gray

Posts: 339

Joined: 2004-01-21
Location: Sandusky, OH

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Subject : RE: torsion box- must I apply backer to each skin?
Posted : 2009-05-29 2:25 PM
Post #35453 - In reply to #35418
I say go ahead.

Just out of curiosity, what is the spacing of your struts that make up the torsion box? The smaller the spacing, the sturdier, and this will also help with stability of a veneered panel that my want to move.

But when it comes to veneering, balancing the stack is the rule. Even in the application of this torsion box, you are still balanced regardless of the torsion box being there.

Should be fine.


 
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lkasdorf

Posts: 3

Joined: 2009-05-17
Location: Waterford, VA

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Subject : RE: torsion box- must I apply backer to each skin?
Posted : 2009-07-17 9:13 AM
Post #35644 - In reply to #35418
Just for closure, I wanted to mention that my project worked out fine and the customer loves it.

Here is the torsion box sandwich that was created:

macassar ebony veneer
1/2" mdf
1" honeycomb
1/8" plywood
1" honeycomb
1/2" mdf
junk veneer for backer

It was in my shop for 2 months after the torsion box glueup and it appears to be totally stable. So, indeed, it seems that when you make a torsion box like this, you can think of it as a single panel. Balance the glue lines and materials and it all works out.
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