Darryl Keil Last Activity 2025-09-09 11:09 AM
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Jeff Roltgen

Posts: 4

Joined: 2008-06-04
Location: Rapid City, SD

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Subject : Torsion Box telegraph issue
Posted : 2009-06-11 8:04 PM
Post #35490
I've been asked to make some more furniture using torsion box method, incorporating the resin impregnated honeycomb. On past projects, I've noticed the outline of my solid wood perimeter frame, and wondering how to eliminate this "telegraphing". Basically, a slight dip develops over the field of area occupied by the honeycomb core. I've been exacting about matching thickness of solid stock to honeycomb. I use 1/4" MDF core plywood, saving the labor of veneering. Assembly is placed in bag on melamine platform with vaccuum channels scored - top is simply layered with evacunet. I put "face" side of panel down on the melamine platform in order to avoid the bag being the culprit in case of excessive vaccuum pull. I can normally pull less HG of vac than the book indicates, due to elevation. In lite of this, I set my press at approx 10HG to get just enough pull to clamp it all snug. Should I mill hardwood frame thinner to allow slight compression of honeycomb to counteract this? Has anyone else experienced this issue?


 
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Enrico Konig

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Joined: 2006-01-06
Location: Vancouver, BC

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Subject : RE: Torsion Box telegraph issue
Posted : 2009-06-11 8:16 PM
Post #35491 - In reply to #35490
I use the honeycomb quite a bit and have also had this problem. I know that one needs to set the press at a lower pull for the pressing of the skins, and this last one I did was below 10HG but still had the slight dip on the side facing up. Bottom side is always dead flat. Putting this flat side up for the veneering of the torsion box at full vacuum never affects this surface and it remains flat. Like you, I am also exact about the thickness of the wood framing. So I also wonder what to do about this.

enrico konig


 
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Brian Gray

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

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Subject : RE: Torsion Box telegraph issue
Posted : 2009-06-11 9:49 PM
Post #35492 - In reply to #35490
What is the thickness of your top, the thickness of the members that make up your torsion structure, and what is the spacing between them?


 
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Enrico Konig

Posts: 74

Joined: 2006-01-06
Location: Vancouver, BC

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Subject : RE: Torsion Box telegraph issue
Posted : 2009-06-11 10:44 PM
Post #35495 - In reply to #35492
I've only used 1/4" mdf skins. But I think Darryl in one of his videos pointed out you can use thinner skins than that, it's just that the box will sound hollow. I've made torsion boxes in many different thicknesses: 1" thick (1/2" honeycomb with 1/4" skins) up to 2 3/4" thick (2 layers of 1" honeycomb with 1/4" skins and 1/4" mdf between the honeycomb layers). Doesn't seem to affect whether there is deflection on the side facing up. I'm assuming I'm just drawing too much vacuum at even 8-10 HG and this is causing the honeycomb to compress. But it seems difficult to set it much lower than that.
The way I understand it, it doesn't matter how much wood framing you do or do not put in your torsion box when you're using honeycomb, or what the spacing between it is. Theoretically there doesn't need to be any.



 
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Jeff Roltgen

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Joined: 2008-06-04
Location: Rapid City, SD

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Subject : RE: Torsion Box telegraph issue
Posted : 2009-06-12 7:54 AM
Post #35496 - In reply to #35492
Brian - regarding materials and spacing, my past project involved a 5 layer sandwich: 1/4" MDF ply, 3/4" Honeycomb, 1/4" MDF center core, 3/4" HC and 1/4" MDF Ply which yeilded a 2 1/4" thick panel. Poplar hardwood was used at a thickness of 1 3/4" to match the 3 center core pieces as exactly as possible. Outer skins lay over to add up to 2 1/4" . No spacing to speak of from hardwood to honeycomb - I was careful to get the material to nest snug within the hardwood frame.


 
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Brad

Posts: 87

Joined: 2008-04-22

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Subject : RE: Torsion Box telegraph issue
Posted : 2009-06-15 1:42 PM
Post #35511 - In reply to #35496
Does anyone have technical specs for the honeycomb material? I know for example that Rigid SM (pink version) compresses 10% at its rated capacity of 20psi. I bet the honeycomb manuf has tech specs too. If not, one could setup a fairly simple testing appartatus to figure out how much it compresses at various vacuum levels.

Brad
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