Introduction: Easy Carbon Fiber Mold

About: We're born, we make, and we die. So start making!

For the 3D printed student design challenge: I am a UC Berkeley Junior studying Mechanical Engineering. I used Fusion 360 to design the mold, and 3D printed the mold out of PVA filament. Wondering why I should get your vote? Read to the end to find out!

I started Bike Builders at Berkeley with one main goal in mind: build a full suspension carbon fiber mountain bike. Hoping to complete it before I graduate, I thought it best to start doing research. I found that molding carbon fiber is a difficult, expensive, and labor intensive process involving multiple part molds of high surface finish, pressurized balloons, etc.

However, one night at the precipice of sleep, I had an idea for making intricate carbon fiber parts easily and on a budget. I couldn't stop thinking about it in the morning, or for weeks after. This instructables goes through the steps of testing my idea.

The idea is simple and only a few steps:

  1. Design your part in CAD
  2. 3D print the part out of water soluble filament
  3. Wrap the part in Carbon Fiber
  4. Dissolve the plastic in a bath of water
  5. Do a flood coat on the Carbon
  6. Sand and polish the flood coat of resin



  • Carbon Fiber Kit: fiber weave, resin, brush, etc.
  • PVA filament


Step 1: CAD Design

***Descriptions in pictures help explain the text below

The first picture is a simplified CAD design that would not work as a final mold for a real bike. However, it provides a lot of hands on experience and is cheaper and quicker than skipping to the final design.

One issue with the first picture is that 3D printed PVA will never be high enough quality to mold surfaces intended for bearings. Another issue is that this mold creates a very hollow head tube, which would likely be too weak for a bike

I have made another CAD model to serve as a comparison. In the second picture we can see what a final design would look like using my mold making process which begins with making cylindrical layup aluminum end caps to give us high tolerance bearing cups and then we would combine it with the rest of the frame.

Another option is outlined in the third picture, where we make the entire front part out of aluminum and then wrap it in carbon fiber.

Step 2: 3D Print the Mold

There is nothing too special about printing the mold; if you're already proficient it should be easy. I recommend storing the mold in a bag with desiccants if you don't plan on using it right away to prevent water in the air softening your mold.

The only issues I ran into are as follows:

  1. My PVA filament softened immensely. This is because I tested it as soon as I received it, but then left it open for a long time before going to print my mold. In-between new and so soft it clogs the print, your filament will come out with the occasional popping** sound. These both happen when the filament has absorbed too much water from the air. The solution: dry the filament out in your oven. This probably isn't safe to do in an oven used for food. I dried mine at the lowest possible temperature my oven would go to for about 2 hours.
  2. PLA support failed. I think my bed temperature was too low, which caused the PLA to warp and not support the PVA. I'm not sure though, and because this is just a test project I didn't worry about the quality of the print.

Step 3: Carbon Fiber Layup

To be honest, this was kind of a mess. I had never done Carbon Fiber work before. My method, after a little bit of research, was to wrap the mold in fabric and then apply the epoxy onto it. Then I did the same thing with another layer of fabric. I did have to cut the fabric in a few places to get it into the corners, this was difficult wearing gloves. Luckily my amazing girlfriend stepped in to help.

In terms of actually working with Carbon Fiber, I would watch a bunch of videos. I am not an expert by any means.

Step 4: Dissolve and Cut the Mold

I chose to cut the mold while I was dissolving it. The benefit to this is that it will be easier to do the flood coat when trimmed.

The pictures are in order. Long story short I submerged it in my sink and flushed out the water every time I noticed it getting slimy. At a certain point I got impatient and trimmed up the ends with a Park Tool Carbon Fiber hacksaw blade. It would be easier to do with a Dremel and cutoff disk, but I didn't have one on hand. Either way, keeping 100% of the dust out of your lungs is very important. I did this by cutting it wet, which seemed to keep everything from becoming airborne.

Step 5: Flood Coat

There was not enough resin on the outside to sand and polish, so I mixed up another batch and layered it on as thick as possible. This one took a long time to cure, which could be the nature of flood coats; more likely I messed up the ratio or didn't mix enough. It eventually hardened all the way though.

The first photo is without the flood coat and the last two are with it. It hasn't been sanded yet so it isn't super smooth, but now there is an actual layer of resin over the carbon fabric.

Step 6: Finishing Touches

I didn't actually end up sanding and polishing mine, as all of my tools are at home. However, I believe it is possible to lightly sand and polish the resin. If I try over winter break, I will update the instructables. When I make a full bike, I will certainly be sanding, polishing, and painting the entire frame.

Keep in mind, most resins/epoxy's are not UV resistant and therefore will still need a UV resistant coating to protect them from the sun.

Step 7: Show It Off!!!

I am quite proud of this experiment. It started with an idea and ended with an actual process that we will continue looking into. There are many more things that need to be tested and validated before using this method to make a bike, but we are well on our way.

I hope you enjoyed, and I hope you will share your thoughts in the comments below. Also, this instructables is entered in the 3D Printed Student Design Challenge. Any winnings will go to my club to continue our research, so please vote for this project!

3D Printed Student Design Challenge

Runner Up in the
3D Printed Student Design Challenge