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View Full Version : Foam I-beams-- any thoughts?



Techno
06-02-2002, 03:08 PM
I decided to scap the wood, mostly because of the 3 coats of epoxy. I remembered I still have Divinylcell foam and will use it instead. The planned use for them was cosmetic and can wait.

I'm planning on epoxing 2 layers of 6 oz. glass on both sides of the 2'x4' sheets. Then I'll cut these into strips and epoxy, fillet and glass them into I-beams. These are thinner sheets but should be fine for this. Once the beams are done I'll bond and glass them in. First I'll try standing on them just to see how strong they are.
The flange to be bonded will be tapered to eliminate a hard spot.
Thinking of a 3" hieght with 3" flanges.


These are stiffeners for the deck and pad.

The wood ones would need a 2"x6"x8' board and half would be waste, this still would weigh a bit. The foam ones should only weigh a couple pounds for all of them. I've been trying to reduce weight where I can. The foam floor came out half the weight of the plywood one. Same for the seats. I'm carrying 2 batteries so the more I save the more I come out even.

Sound like a good plan or what? Any other ideas? I don't like the half circle or triangle re-inforcement systems, they aren't as effective a structure.

Also have to change my dash board. Anything besides marine ply? My only concern is steering wheel strength, thought of using foam but??? The thing is I only need a small piece, might be able to buy a small section but haven't checked yet.

Wile E. Coyote
06-03-2002, 11:44 AM
Sounds like a good idea. If I understand what you're trying to do, check out www.preforms.com. This may be of interest, and possibly save you some time and effort.

SHADOW
06-07-2002, 02:48 PM
Techno-

I did my deck with with one inch dyvinicyl and 2 layers of 5 oz kevlar, vacuum bagged. I used a 3 inch X 1 inch piece at 90 degrees (three inches placed vertically) under the deck every four feet. Its plenty solid and we're talking about a large section. For the dash I used one inch dyvinycil with 1/16" aluminum on each side (to hold against the torque of nuts on the various screws/bolts coming through the dash), covered with kevlar. It was overkill. 1/2 or 5/8 should be plenty.

If you can afford it, vacuum bagged kevlar/divinycil is the way to go. Kevlar is expensive, but if you look at its strength, stiffness, toughness and impact resistance, its worth it. Vacuum bagging will reduce weight by up to a third and increase strength by insuring a tight glass to foam bond. Its a lot lot of hassel/cost though.

You glass plan should still work and is easier to wet out if you don't vacuum bag, but getting the glass wet out tight to the foam is the key to strength. Do the dash in foam with the alumimun on either side for strength/weight reduction.

www.aircraftspruce.com has some interesting reading on composites.

SHADOW
06-07-2002, 03:06 PM
Just checked aircraft spruce site, they no longer have the general information on composites, but its in their free catalog.

Techno
06-07-2002, 08:32 PM
I've decided to just laminate some top hat sections. The foam would have taken a lot of glass and forming glass into a half an I-beam is twice the work of a top hat shape. I was going to make 2 'C ' shapes but making one is the top hat.

Making a mold and clamp now for this.

The dash idea seems good. I wouldn't have thought you could use foam but since your already using it...

My stiffeners for the hull will be-not in order, 1 layer of 24 oz. roving and 3 layers of 6oz. cloth with some graphite I already have, more than strong enough. These are only 3' long. 2"x2"
The 13' long stiffeners for over the sponsons on the deck won't use the graphite.

The mold/ clamp is a an upside down T shaped length of wood with radius where needed. Covered with 6 mil plastic. The top clamps the radius partly down the sides. The sides clamp both the sides and the flange at the bottom.
I plan on wetting out the fabric in layers on a sheet of plastic then flop the pack onto the mold and clamp up. I have no relief in the mold, its straight sided.

My attempt at vacuum bagging was sloppy and didn't work. I might try this though for the pad area though.

The preforms seemed to be for commercial buyers and they didn't have prices, I hate sites without prices!

SHADOW
06-07-2002, 08:55 PM
Techno

If I'm correctly visualizing what you're saying, it should work nicely.


For your next vacuum bagging attempt you might try this: use some cheap caulk (about a dollar a tube at Home Depot) to seal the plastic. Just run a bead and push the plastic into it, and put some in any creases you have in the plastic. It holds vacuum great and beats the double-sided tape when working with odd shaped objects.

Good luck!