Darryl Keil Last Activity 2025-09-09 11:09 AM
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David Thiessen

Posts: 4

Joined: 2014-03-16
Location: Bolivar, Mo USA

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Subject : card board honeycomb compression
Posted : 2014-04-24 8:29 PM
Post #37121
I will be building a hollow core cantilevered table and will use hollow core construction. I would like to use the honeycomb product but have read that it compresses a little bit when it is pressed in the bag. If so does anyone know how much to allow for this? Any advice with the honeycomb would be appreciated for my planning. Thanks


 
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Don Stephan

Posts: 825

Joined: 2003-07-18
Location: Cincinnati, Ohio

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Subject : RE: card board honeycomb compression
Posted : 2014-04-25 5:55 AM
Post #37122 - In reply to #37121
My understanding is that you want to use resin coated honeycomb for its greater stiffness, not uncoated paper honeycomb. When I 've vacuum pressed resin coated honeycomb I used about 15 psi and plastic resin glue. After this was cured, seems like I used 22 psi to veneer the outer skin of the torsion box.


 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: card board honeycomb compression
Posted : 2014-04-25 8:07 AM
Post #37123 - In reply to #37121
The compression is so minimal its really not an issue. With that said, I always press the side that will be the table top, face down on the platen. This way if there is any discrepancy between the honeycomb and the boarder strips it will be on the table bottom where you wouldnt see any deflection of the skin on that side. Not unless you were laying on the floor looking up that is!


 
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Enrico Konig

Posts: 74

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

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Subject : RE: card board honeycomb compression
Posted : 2014-04-25 9:09 AM
Post #37124 - In reply to #37121
I've used the resin-impregnated honeycomb a fair bit and do recommend it. But I always got (and still get) a fair amount of deflection on even the bottom side. Definitely more on the top side but the bottom can never be veneered, in my experience, without flattening. It may be the urea resin glue I use up here (Unibond not available locally) in that it seems to shrink more once cured, and would suck the skins in a bit. So I always assume that with any of my honeycomb projects that I'll have to run it through a flat-bed sander. Normally would lose at least 1/8" of thickness on the sandwich, usually closer to 3/16" if the surface is larger.




 
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David Thiessen

Posts: 4

Joined: 2014-03-16
Location: Bolivar, Mo USA

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Subject : RE: card board honeycomb compression
Posted : 2014-04-27 7:25 PM
Post #37125 - In reply to #37124
Is it necessary to lower the pressure on the pump and does it still provide a good bond at a lower pressure. I do not have access to a wide belt sander so I will have to deal with whatever deflection occurs. That said, should I press the skins onto the core and then press the veneer or veneer the skins and then press them to the core?


 
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Bob s

Posts: 5

Joined: 2014-04-28
Location: Auckland NZ

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Subject : RE: card board honeycomb compression
Posted : 2014-05-04 4:24 AM
Post #37132 - In reply to #37125
I have just used PVA foam I think it was about 15mm with a thin ply on each side totaling about 20mm that's 3/4in and it was light I have vacuumed 6mm that's 1/4in on each side of oak now its getting heavy, these are panels 1040 X 500mm for table leaves that pull out on runners to extend the table, there are other kinds of foams available mostly used for boat building, if I had not found the ply foam ply sandwich I was going to use just foam but put a thin fiberglass on each side before the oak, I would have vacuumed on the fiberglass using a peelply so I got good adhesion when gluing on the oak.
If that is confusing tell me and I will try explain it better.
Good luck what ever you do.


 
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Don Stephan

Posts: 825

Joined: 2003-07-18
Location: Cincinnati, Ohio

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Subject : RE: card board honeycomb compression
Posted : 2014-05-04 7:12 PM
Post #37134 - In reply to #37132
If I understand Bob you first vacuum pressed 3mm (1/8" plywood on each side of 15mm (9/16" foam, and after that cured vacuum pressed 6mm (1/4" solid oak on each side of the plywood, creating a total thickness of about 32mm (1 9/32"? May I ask what adhesive you used between the foam and plywood?


 
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Bob s

Posts: 5

Joined: 2014-04-28
Location: Auckland NZ

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Subject : RE: card board honeycomb compression
Posted : 2014-05-05 2:44 AM
Post #37135 - In reply to #37134
No I didn’t glue my own up this time I bought a 8ft X 4ft sheet of ply foam ply from Gurit a supplier to the boat building industry, if I had to I would use epoxy with a glue powder but a thin mix, I am not familiar with catalyzed PVA but if it cures in a vacuum then I should imagine it would work, I used to use polyurethane foaming glue for edge clashings on foam panels but polyurethane needs air or the moisture in the air to cure so won’t work in a vacuum. When I vac bagged the oak panels on I used epoxy, you can see it on http://perceptionpanels.blogspot.co.nz to give you some idea pictures are better than words.
I hope this helps.



 
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Enrico Konig

Posts: 74

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

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Subject : RE: card board honeycomb compression
Posted : 2014-05-05 8:32 AM
Post #37136 - In reply to #37125
Yes it is necessary to lower the pump pressure when gluing up the honeycomb panel, otherwise the honeycomb will be crushed. I use the Vacupress pump, and I dial it down to 10-12 hg for this first step. Never a problem with the bond. (And I have cut into a few of the first ones to check out the inside, when trying to figure out how to lessen deflection.) Then this sandwich needs to be flattened before the veneer is pressed at full pressure. I've flattened quite a few with just a handheld jointer planer and a straightedge until I discovered a widebelt sander at a nearby shop. The $100 is well worth it, especially when dealing with larger surfaces.

If you use Vacupress's honeycomb panels (and this is the only place in North America where I've found this dense-weave resin-impregnated stuff, at least where you didn't need to purchase a semi-trailer load), I believe it comes with full and clear instructions.
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