help with fiberglass (or CF) foam composite layup

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#1

I’m interested in building a simple structure out of a fiberglass over a structural urethane foam core. For those who are familiar with guitar amp construction I basically want to build a combo amp cabinet carcass. For those who aren’t familiar this is basically a rectangular “box” shape with four sides (front and back are open).

I would like to use carbon fiber or this “black fiberglass” I’ve seen but will not be making any molds since this will likely be a one-off part.

So, is there a good way to achieve a durable clear coat on top of a layer of woven fabric without molds and vacuum bagging? Anything I can brush or roll on? Are automotive clear coats sufficient?

As for the structural construction my plan is to miter the edges of my foam sheets and join them together with hot glue. Next I’ll cut notches to insert wooden strips to use as “hard points” that I can screw into to install the front baffle and back panels as well as some wooden dowels for other small mounting points (handles, chassis, etc…)

Once the foam is fully loaded with its wooden hard points I plan to glass all the corners with tape and the follow up with two layers of regular 4oz cloth all cut tight to the inside dimensions. Then the outside face will be covered with one layer of 4oz glass and an outer layer of either carbon fiber cloth or black fiberglass for the “look”. This top layer will be cut a bit larger and wrapped around the edges to overlap with the inside glass and dress up the sides of foam. Obviously I’ll be using epoxy resin due to the urethane foam.

So, any major problems with this approach? My goal isn’t absolute lightness… I just want something lighter than the standard plywood carcass and at least strong enough to let someone sit down on it without cracking in half :slight_smile:

Sorry for the long post…
I appreciate any advice the group can give on this project.
-Matt

#2

Welcome!

With PU foam you can use PER or epoxy resins. PS foam and PER and you will get melt down…

I use to have my HS skater students to do CF Pre-preg wrap a PU foam skate boards, vacuum bag and oven cook them…they could not break them at all! And they tried hard! :cool:

You might will want to make a small scale test for see that you will need to have raduis corner to be able to wrap the corners.

If only 1 layer of CF / Blk. FG then consider painting the foam black so you can’t see thru the cloth to the foam…

#3

Yeah, somehow I got my wires crossed and forgot that the ability to use cheaper polyester resin was the reason I bought the urethane foam in the first place :slight_smile:

Do you feel that vacuum bagging is necessary? I don’t have the equipment for it unfortunately.

How about producing a smooth, durable clear finish? I’ve seen some people suggest rolling on an extra layer of resin with a wire roller. What I’m after is as close as I can get to a clear gel coat finish that shows off the weave of the carbon fiber or black fiberglass. I know the easiest way to do this is a good quality mold with a super smooth finish and good release agent. But I’m looking for a shortcut :slight_smile:

Thanks for the reply!
-Matt

#4

black fiberglass is very rigid and i would suggest using it only for flat panels. even if the part has only a small amount of curves, the only way to go is by using vacuum. in the end it will never pass off as carbon to the trained eye. its missing that golden glow that carbon has.

#5

I have seen a black fibreglass (200g per m) that was no stiffer than regular.black texalium is a lot stiffer.As aga says it never looks as good as real carbon.