Darryl Keil Last Activity 2025-09-09 11:09 AM
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Arthur Allen

Posts: 3

Joined: 2007-07-05
Location: Lincoln, NE

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Subject : Unibond for torsion box?
Posted : 2012-06-13 3:17 PM
Post #36661
I am making a torsion box with 1/4" Baltic Birch skins: there is no veneer. I have done this once before using nails, yellow glue, and plywood struts. Unfortunately, my torsion box sagged significantly over time. To reduce this problem, I will increase the width of the struts and use a glue with less creep. Is Unibond 800 the best glue to use for this project? If I use Unibond, is nailing still okay? Nailing is easier, but will my torsion box sag less over time if I use a vacuum bag instead? If so, how thick a platen is necessary given that the skins are 1/4" thick and the struts are about 6” apart? I would much prefer the platens be as thin as practical.

Thanks so much for your help.



 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: Unibond for torsion box?
Posted : 2012-06-13 5:34 PM
Post #36662 - In reply to #36661
Arthur,

The two best things you can do to make your torsion box sag less is to do it in the vacuum bag, (better pressure and more uniform) and to decrease the spacing between ribs to every 3". At 3" you could get away with a 1/2" caul on top for pressing it up.

Unibond 800 being a extremely rigid bond will help the sag factor, but its the flrst two things that will make the biggest difference.

Darryl Keil
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