Stiffening Rib Core?

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#1

Hi guys,

I’m thinking about adding some stiffening ribs to one of my large parts. I’d like the cross-section of the stiffeners to be trapezoid shaped and run the length of the part, which has a gentle curve. Typically I would just cut some hard foam to make stiffener cores but the gentle curve of the part makes this more complicated so I’m thinking some soft foam that I could hot wire would be ideal. In this case the foam will not add any stiffness just give me the rib shape I want while being able to conform it to the curve.

Does anyone know of a soft foam that is polyester and hot wire compatible? Currently I’m thinking soft polyurethane foam, but any other ideas would be appreciated.

#2

I sometimes used pipe insulation. Costs about nothing, can be bought anywhere, is conformable, and when cut in half has the right shape.

And it is styrene resistant.

#3

i use the pink insulation from home depot. comes in 4x8 sheets you might have to glue layers together to get the thickness but it works well and can be sanded to get the shape right… i normally use it for rapid tooling or just farting around… i have thought of trying it as a core but… usually the stuff i make at home is not structural. btw it can be easily glued and seems to be pretty chemical resistant.

#4

Thanks for the suggestions guys.

Dallas - is the pink stuff styrene resistant? I didn’t think it was.

#5

If you part is getting vacuumed you can use almost any kind of core. Personally I would never use any foam I could buy locally in my parts.

#6

Yeah me either. But this is just a form to give me the rib shape I want, its not really intended as a structural part of the laminate.

#7

pink/blue insulation foam is not styrene resistant…
But if you do find a core, your idea is a good one for stiffening. You can lay the foam rib into the stack, or add a sleeve around it, and put it mid-stack or on top, depending on your part usage.

#8

Has anyone tried to use minicell foam before? Its non porous closed cell foam that’s really common for outfitting small boats. I have a ton of that lying around and its pretty light and cheap.

#9

Any foam will work, as long as it is closed cell. The foam type won’t add much to the strength anyway, until you get into the higher density stuff.

#10

Your minicell comment got me curious. I have a call into one of the suppliers to see if its styrene resistant. The descriptions I’ve found say that you can also cut with band saw or hot wire.

How stiff is this stuff? Does it try to stay flat or does it retain its shape after bent?

#11

Its very stiff depending on thickness. We use 3" thick blocks in kayaks as pillars to keep the boats from flexing.

It can be hot wired, cut with a saw or knife, or shaped with dragon skin or a belt sander. It shapes and holds it shape really well.

When cut thin minicell flexes really well, and conforms to curves. In the paddling industry its been used to line helmets. However, if you go too thin (less than 1/4") it will be less resistant to being crushed.