​Foam core material questions?

[Guest]

I don’t know nothing ‘bout no foam core material, stuff like the stiffening diamonds laminated on the bottom of some UL canoes.

But I’m off on a tangent to build a couple of ultra-light blue barrel folding tabletops. Which, since I am far from a light packer, is kinda silly, and probably more proof of concept than anything else. But I can give the UL Mark III and IV experiments away to tripper friends for field testing.

I think I have a line on some corrugated kevlar honeycomb, but would also like to try my hand at DIY laminating some foam core material, covered with S-glass, epoxy and peel ply.

My preferred barrel tabletop shape is this “squared circle”, hinged in the middle, rounded off from two pieces of +/- 10x20 material.



That size works well dimensionally as a 30L solo table, and I know I can save weight on the hinges, and on the lid-sized donut circle stabilizer underneath, which could be economically cut from lightweight minicel exercise foam. I think I can get the “hinge” and underside donut down to a couple ounces at most, so it is mostly the weight of the platform itself.

This sucks for anything but the most minimalist kitchen countertop. Never again.



So, some foam core newbie questions:

What is that foam? Who sells it as a US supplier?

Does epoxy & glass application adhere well to that foam without any fancy footwork vacuum bagging/infusion type tricks? I want a smooth (glass, peel ply, light sanding, varnish topcoat) washable kitchen counter.

Is that foam core available in different thickness? Half inch thick material would be butt-ends-hinged helpful to maintain a no-droop surface. Or maybe two thinner pieces of foam laminated together?

Thoughts on whether that foam core material be stiff enough, laminated with a couple layers of epoxied S-glass layers top and bottom, to maintain a flat surface extending out 10 inches from the barrel lid circumference and not droop on the sides with meal prep weight? The flush center of the tabletop is already sturdily supported on the 10 inch diameter of the 30L barrel lid underneath.

Even with my shade tree skills I want to see if I can get a blue barrel folding tabletop weight under 1lb. And I’d like to try my hand at making a larger one for the 60L barrel.

Tell me about foam core.

 

[wingnut]

http://www.fiberglasssupply.com/Product_Catalog/Core_Materials/core_materials.html
I'm a newbie to foam core and composites myself but have been looking at this supplier for Divinycell foam core. They seem to be reasonably priced, but I have not ordered from them yet to see how the shipping rates and delivery service are. Foam core and composites have got my Interest for making lightweight componants. Just need to do some experimenting.

 

[yellowcanoe]

The more successful foam cores are oven cured so they shape to the bottom. They are not absolutely flat. That said there must be some way of shaping as this person has done
http://www.westcoastpaddler.com/community/viewtopic.php?t=4473

Just an interested groupie here..

 

[stripperguy]

Mike,
I have some recent experience with Divinycell H80, a 5 lb/ft^3 PVC IPN. It requires no special treatment to accept epoxy resin. It is available from various distributors, I bought some from Jamestown (?), and also received sample pieces direct from DIAB (the mfger) when I was still working as a design engineer.
I used some of the 1/8" thick H80, laminated with carbon to stiffen the bottom of my carbon copy Kite, it was overkill.
I have some sample sections on my desk as I type, one of which is 1/8" H80 with 2 layers of 6 oz E-glass on each side, it is incredibly stiff. It weighs 1.25 oz and has 29.9 in^2. This particular sample seems (I can no longer perform instrumented testing) stiffer than a sample section of cedar stripper panel with 3/16" cedar wrapped with single layers of 4 oz E-glass.
For your application, 1/4" and 1 or 2 layers of 6 oz E-glass would likely be more that adequate. S-glass, IMHO, would be a waste of resources and dollars, unless you happen to have some excess laying around.
The table pieces would be the easy part, a lightweight and reliable center hinge would be the biggest challenge.

Hope I helped...

 

[Cruiser]

This is an interesting project, I am wondering if the foam is maybe overkill for the project though. There is no question it is lighter, but your area is very small and I suspect if you compare foam/glass weight versus cedar/glass weight it will be quite small.

I just finished some paddles using 2.3 oz fiberglass and that makes a paddle very stiff, so I suspect 4 or 6 oz cloth is way over kill.

I would be tempted to make up a cedar panel with leftover B&C strips, cover it with 2.3 oz cloth, cut in half as required and use something like these barbed hinges (bedded with epoxy) to make your table.

https://www.amazon.com/16-Barbed-Hinge-Pair/dp/B003Z0NT78

I suspect this would pretty much meet your strength and weight goals and still keep it economical.


Brian

 

[Jim Dodd]

I would just add , put the hinges on the bottom side, or flip it over !

 

[Guest]

I have some sample sections on my desk as I type, one of which is 1/8" H80 with 2 layers of 6 oz E-glass on each side, it is incredibly stiff. It weighs 1.25 oz and has 29.9 in^2. This particular sample seems (I can no longer perform instrumented testing) stiffer than a sample section of cedar stripper panel with 3/16" cedar wrapped with single layers of 4 oz E-glass.


For your application, 1/4" and 1 or 2 layers of 6 oz E-glass would likely be more that adequate. S-glass, IMHO, would be a waste of resources and dollars, unless you happen to have some excess laying around.
The table pieces would be the easy part, a lightweight and reliable center hinge would be the biggest challenge.

I like the sound of that H80 foam, even if I had to laminate a couple pieces together for a thicker butt end stiffening fold out. Having thicker hinged ends, probably more like 3/8 to ½ inch, butted flush together when folded out helps keep the tabletop undroopy level.

(BTW, shade tree tinkerer here, what the hell does “29.9 in^2” mean?)

I have plenty of 4oz and 6oz S-glass and epoxy to play with (no E-glass except tapes). I’ll investigate and see about the availability of foam pieces cut 10x20”; it is light enough that US shipping should be cheap at that flat package size.

This is an interesting project, I am wondering if the foam is maybe overkill for the project though. There is no question it is lighter, but your area is very small and I suspect if you compare foam/glass weight versus cedar/glass weight it will be quite small.


I would be tempted to make up a cedar panel with leftover B&C strips, cover it with 2.3 oz cloth, cut in half as required and use something like these barbed hinges (bedded with epoxy) to make your table.

https://www.amazon.com/16-Barbed-Hinge-Pair/dp/B003Z0NT78

I suspect this would pretty much meet your strength and weight goals and still keep it economical.

I like that idea too. If I ever had leftover cedar or cedar strips I would try that in a heartbeat, but I’m not a wood strip guy, at least in terms of leftovers laying around the shop to experiment with. I may have to think about glass laminating two thinner pieces of lighter wood.

The ideal material would be some inexpensive and readymade stiff plastic, requiring only cutting to shape and hinging, perhaps even without any glass and epoxy coating work, but I haven’t found a product or material of that ilk, and wasn’t happy with the rigidity of corrugated plastic (Coroplast).

A lighter weight hinge might be as simple as a strip of Nashau 357 duct tape along the top, easily replaced or overlapped as needed. Or a thin aluminum piano hinge.

I would just add , put the hinges on the bottom side, or flip it over !

To fold out undroopy stiff together I think I need the hinges on the top, so the butt ends of the two halves meet || flush and level and can’t bend downwards.

In that top hinged guise the folding sides are held firm onto the barrel lid via two Velcro straps attached around the barrel handles, and the tabletop halves are near ½ inch thick butt-end-together droop resistant.



I know I can do better and lighter than my initial effort of a shop scrap plywood base & lauan top, epoxy, varnish and brass hinges. The “donut” circle underneath doesn’t need to be full sized to support weight with a stiff enough top, and that bottom piece could be cut from something similarly weightless, as simple as a narrow hold-the-top-in-place “ring” that surrounds and captures the barrel lid.

I’ll try to amass some different materials and diddle with designs this summer.

 

[Jim Dodd]

My reasoning was to eliminate the hinge hump, was to make a level serving table. I can see me spilling my fresh cup of Hot chocolate, as I slide it off the table, and bump the hinge.

Maybe at least, recess the hinge.

Jim

 

[stripperguy]

Mike,
That's 29 square inches...I gave the surface area so you could extrapolate to find the weight of your barrel top.
If I had 29 sq in weighing 1.25 oz, you would have -----(fill in the blank) sq in weighing ????
I like the look of those barbed hinges, easily buried inside the laminate.

 

[Guest]

Maybe at least, recess the hinge.

I like that idea, but you over estimate my rudimentary shop skills.

That's 29 square inches...I gave the surface area so you could extrapolate to find the weight of your barrel top.
If I had 29 sq in weighing 1.25 oz, you would have -----(fill in the blank) sq in weighing ????.

Dammit, I done failed another math quiz

I may look into burying those hinges under the laminate, although there is ample tabletop there to avoid that shallow hinge bump.

I suspect if you compare foam/glass weight versus cedar/glass weight it will be quite small.


I would be tempted to make up a cedar panel I suspect this would pretty much meet your strength and weight goals and still keep it economical.

The more I think about it the more sense that makes in terms of material availability and ease of cutting/shaping. So, a cedar question:

I can special order from a local lumberyard. For a 30L barrel I’d want at least a 9 ½ to 10 inch wide board (and wider if available for a 60L barrel tabletop). A piece at minimum 20 inches long to cut in half/hinge, but I’d really prefer an 8 or 10 foot board length to play with different tabletop variations.

Which cedar would be the best combination of light, stiff and easily laminatable?

Eastern Red, Western Red, Northern White? Hopefully some non-exotic, both available and unpricey.

 

[Alan Gage]

I'm surprised your local yard doesn't stock grade 3 knotty cedar. Pretty commonly used for trim and, at least around here (the middle of nowhere), it seems to be readily available at most yards in widths up to 12". Western Red is all I ever see around here. A 12" wide board would run about $2.60 per foot if I remember right.

For just playing around you might take a look at Poplar too, which should be locally available and cheap. Not that much heavier than cedar and easy to work with.

Let me know if you can't find anything and I'd be happy to send a piece of cedar your way finished down to whatever thickness you want.

Alan

 

[Jim Dodd]

Pink Foam insulation. 1/2", a layer of glass top, bottom, and edge. Easy to shape, no power tools needed ! Gorilla duct tape for the hinge. Done ! As light as a feather
Just don't try and do a table dance on top ! Unless you add carbon fiber
It could also serve as a floating table top, while lounging in the lake, to hold your favorite beverage.

Jim

 

[Guest]

I'm surprised your local yard doesn't stock grade 3 knotty cedar. Pretty commonly used for trim and, at least around here (the middle of nowhere), it seems to be readily available at most yards in widths up to 12". Western Red is all I ever see around here. A 12" wide board would run about $2.60 per foot if I remember right.

For just playing around you might take a look at Poplar too, which should be locally available and cheap. Not that much heavier than cedar and easy to work with.

Let me know if you can't find anything and I'd be happy to send a piece of cedar your way finished down to whatever thickness you want.

Well, ya know, sometimes you have to hammer away at Captain Obvious until he comes to his senses.

Using a wood tabletop platform like cedar or poplar seems an awfully sensible 1[SUP]st[/SUP] experiment to make something lighter and materially easy-peezy to obtain and construct.

My current wood tabletop used heavy shop scrap plywood for a full perimeter stabilizer donut underneath, a circle of lauan top laminated over that, and multiple coats of epoxy and varnish. There is considerable excess weight in those scrap wood materials.

Using something readily available, poplar or cedar, would be easily everyman reproduced

I’m thinking the Mark III and IV tabletop builds will use a lighter weight wood top and a narrow minicel (exercise foam) stabilizer “ring” on the bottom. No fiberglass work, just a coat of epoxy and UV top coat of spar urethane. Maybe run the outer edges cut wood circle though a router for a touch of curvature grace.

I’m not looking to go into production. Well, maybe a little; with some easily shop-cut and finished top, especially without any glass or epoxy work needed, I’d be more likely to do a small production run for friends, including some folding tabletops for 60L barrel tables.

A folding 60L barrel tabletop could be 4 inches in diameter wider and still fit inside the barrel, making a nice companion or small-group work surface.

Off to the lumberyard tomorrow.

 

[Alan Gage]

That sounds like a sensible and promising plan. I was going to chime in here as a couple days ago I cut some cedar boards down to 1/4" thick for seat frame components. I usually use 1/4" foam covered in carbon but this time decided to use wood as it would be less work, time, and expense. The cedar was a breeze to work with, looks great, is probably lighter weight, and was surprisingly stiff and strong. I think at 1/4" thick it would be plenty strong enough for your table. Maybe glue a thicker piece along the mating edges so there is more surface area contact when opened.

Looking forward to seeing what you come up with.

Alan