Issues applying duratec to foam plug

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#1

Hello,

I am a student learning how to build plugs, tools, and parts to build our school’s FSAE car bodywork. We decided to use Styrofoam for the plugs because it is cheap and available, and we can mill it for some nice parts. Our plan was to mill the foam, and then use styroshield primer on top of it to create our plug surface. We sprayed the first coat on, and then sanded it. We have done two more coats by crushing it on and using a squeegee to try to keep it pretty flat. We’re having troubles with filling in holes and getting cracking around the edges. Does anyone have any recommendations for this? Would doing a layer of Bondo or maybe switching to regular duratec now solve this? Thank you!

#2

As you’ve found out, styrofoam is not the best surface as far as durability goes. What many tooling companies do is overcut the substrate (cut more than is needed) and then build the surface back up with an epoxy or polyester based putty. The putty can be applied by hand or sprayed. When that is cured, they recut to the correct dimensions. Depending on the part, a layer of glass may be applied to the foam before the putty is applied.

Duratec sanding primer is good for filling inconsistencies in the surface. Builds fast and is easy to sand. Their surfacing primer creates a fine surface that can be polished to a good finish. For a real class A finish, use the topcoat.

#3

Hi roger,
I am doing the similar plug like kilojoule.
My trouble is that i am not allowed use any spraying equipment on cnc machine. I milling it at a cnc machine which is not mine!
If briging plug out, i cannot mill it again? So the dimension will change. How can i do
Thanks

#4

We decided against milling it twice, and instead mill it once with a small offset to account for the thickness of the duratec or whatever surface primer you are using. I think it really depends how accurate you need the mold to be.

#5

Thank you kilojoule,
I will think about it and ask for your help later.