Making molds for fiberglass parts

[LethalEthan]

Any of you guys done it? Or made custom parts from fiberglass at all? Thinking of making some custom air ducts for a winter project

[300D50]

Never done it, but have a YouTube vid or three saved on doing CF ducting/airbox stuff.







The cast tape method is brilliant.

[300D50]

HMMOG, youtube links now auto-embed???!!!!

[4g63mightymax]

#Forum Winning!

I used to work with fiberglass in high school all the time for stereo systems. We used to buy fleece at the fabric store and stretch it around things, and then soak it in fiberglass resin. In fact, that's how I made the entire tail of my motorcycle. It was 100% fleece, and came out beautiful. The finish was rough, but with a little bondo it was mint. We also covered trunks in ton foil, trash bags, and saran wrap and made molds of trunks for speaker boxes.

Once thing I never did was using actual release agents. That would be all new to me.

[LethalEthan]

I like the fact that he's using a Male mold for his tubes. I was thinking split mine and make female molds. Using Male molds seems like much less work, but the issue with that is the outer dimension of the new piece is bigger than the original. That may be a problem for me since I need my tubes to fit into the factory airbox.

The issue I'm having with making female molds is my pipes will need to be two pieces, and will need to be connected somehow after they're done.

I have a general idea now of how I want to do it, just need to find the right materials.

[300D50]

Hmm... Maybe use a flanged female mold that bolts together, and a piece of intertube to inflate and press through the bag on the inside?

[LethalEthan]

That's kinda what I was thinking. I was planning to skip vacuum bagging and just lay carbon fiber by hand since they're not perfectly round tubes, but I think I should look into vacuum bagging a little more.

I have two intake tubes, that are 2 pieces each. I'm thinking right now I'll stick them together and make them 1 piece each, then cut each tube down the middle with a scroll saw. So I'll have 4 pieces total. Mount the pieces to a board and mold them with a small flange around the edge. Once I have 4 molds I'll make the tube halves, trim the flange when they're done and combine the halves with a little resin.

It would be nice to be able to mold them as one solid tube though....

[LethalEthan]

Gonna be a slow project but I think things will come out really nice. I've looked a lot more into vacuum bagging and even resin infusion, and I'm thinking now that's going to be the way to go. It's more work in the beginning, but less in the end. Hopefully I'll be able to pull perfectly clean, finished parts from the bag that will only require a bit of trimming.

So here's where we're at so far. The front halves are pretty much ready to mold, just waiting on a friend to spray them with clear, paint, whatever we can just to get a nice smooth finish.

Here I've trimmed the lips off that hold the tubes into the stock airbox. I was worried about the small channel locking them into the molds, plus once they're made of carbon the lips won't be able to be pushed into the airbox anyway. The edge will still fit inside, and I'll use some silicone or window weld to attach them to the box.

Untrimmed on left, trimmed on right



Split down the middle but a little offset so the seams won't be on the very top. The split on the end of one is a little concerning. I missed my mark a little bit and the end of the tube curves back around on itself just the smallest bit. It won't be a problem in the molding process because these front halves are actually rubber and pretty flexible. It may bite me in the ass when I go to remove hard carbon parts from the molds though. Worst case scenario in the end, I'll have to break the mold to remove the part.

[LethalEthan]

The front halves require a good bit more work before molding. The stock air intakes have resonators on them that I wanted to remove. Which meant cutting a huge hole in the bottom of them. I'm filling it with plastic weld which I can sand smooth before spraying with whatever we decide.













Top hole is covered and just needs to be sanded down. The bottom I have about half covered before I ran out of plastic weld.

[4g63mightymax]

One thing I learned long ago when doing fiberglass stuff for my motorcycle was that it wants to change it's shape as it cures, kind of like when you heat up a piece of metal. I wonder if you will need some reinforcements on those pieces where they meet up so that when they are cured they still fit together. Either way, this looks like a fun process. I'm excited to watch it play out.

[LethalEthan]

I've read a little bit about deformation of parts due to different resins curing at different temps and speeds. From what I've read so far, I need to make my molds out of carbon if I plan to make the parts out of carbon to combat this a bit. Its definitely something I need to read up on a little more though. I think since I'll be vacuum bagging things, it SHOULD help to keep things pretty straight.

The front halves are going to take a bit of effort since they're rubber. I'm worried the vacuum will pull them flat instead of keeping their shape. Plan right now is to mount those pieces to a board with a bit of spray foam to help them keep their shape.

[300D50]

Spray foam for sure, and get the "low expansion" stuff.

I'd say use pink/blue foam to get things close, then glob the sprayfoam down over it to fill the gaps.
Less chance of the inside not curing fully and the vacuum squishing it out when you go to make a part.