HOW TO: Make a Carbon Fiber Part (Part 3: making a fiberglass mold)

HOW TO: Vacuum formed Carbon Fiber Part for $200 (Part 1)
HOW TO: Make a Carbon Fiber Part (Part 2: making a clay mold)
HOW TO: Make a Carbon Fiber Part (Part 3: making a fiberglass mold)
HOW TO: Make a Carbon Fiber Part (Part 4: making the budget vacuum bag)
HOW TO: Make a Carbon Fiber Part (Part 5: mold prep and cutting CF)

HOW TO: Make a Carbon Fiber Part (Part 6: vacuum bagging CF in mold)
HOW TO: Make a Carbon Fiber Part (Part 7: two part piece and final steps)

It took tons of time getting the clay angles equal as I could... come to find out I should have spent even more time getting them exact down to the millimeter because what's not so noticeable on the clay mold is VERY noticeable on a final product. More on that later.

Also, if you need a break until the next day or anything all you have to do is place a layer of damp paper towel over the clay and then put plastic (like a trash bag or cling wrap) over the wet paper towel to prevent it from drying out... Every 24 hours simply lift up the plastic and spritz water onto the paper towel... you can postpone your project as long as you want doing that everyday... assuming you're not working outside in the sun in which case you'd need to bring it inside.

Once you have your final shape you like you can lay out your sheet of twill fiberglass cloth on the mold to cut the excess off the cloth before you get out the resin... Also make sure you cut relief cuts for the sharp angles (see red dotted line in picture)

After you cut out the shape you like you can put whatever type of mold release you want on the clay mold that you like... or none at all, but the clay might stick to the fiberglass making a mess to clean out your fiberglass mold.

Here I used dawn dish soap (hence the green color in later picks) However now I use simple cling wrap you can buy at the grocery store to create a barrier between the piece I'm copying and the mold I'm creating. It's clean separation and there is no mess to wash out. Or you can use carnauba wax in the method I show later to form a wax barrier that functions as a great mold release when several built up layers dry (more later).

Really make sure your dry cloth is conformed to every contour of the mold after you put down your mold release (cling wrap, carnauba wax or whatever you choose).

You can use the cheap poly resin... I usually use about double the amount of liquid hardener they recommend for a small piece like this just so I don't have to wait 12+ hours for the mold to cure. You still have about 5 minutes before the resin starts to congeal and harden... If you're not comfortable with that than follow the box. It's not essential to follow the recommendations because it's only a mold, not a functioning part that will be used. (I do follow the CF resin instructions)

I mixed up 5 ounces of resin to wet out just the one layer of fiber glass here plus a second layer in spots with scrap cloth...

My dawn dish soap mold release was working but it turned out to be a mess... stick with carnuba wax (more later)

I waited an hour for my twill cloth to harden before moving on to strengthen the mold with the thick fiberglass cloth. But you don't have to wait until the first layer cures, but you should only mix up enough resin at a time to do small sections or one layer in this case with this small part. But that's me using double the amount of hardener so I don't have to sit around.

Both the twill cloth and the thick fiberglass matte are the same price per package; however the thick cloth is nice to quickly bulk up a piece like this.

I used two layers of the thick matte and I used about 18 ounces of resin to wet out this... I mix up 9 ounces with double the recommended amount of hardener at a time just because it sets up so fast... but that's just how I do it... you can discover your own preferences. When it comes to the resin for the Carbon Fiber, I follow the directions strictly. 

You'll also notice I put a plastic bag over the wetted out fiberglass and that's because it's easier and cleaner to work out the air bubbles AND it's a clean way to completely eliminate the annoying cured strands of glass that can form when you don't put plastic over. And Don't worry, resin does not need air in order to cure. 

poly and exopy resin does not stick to any plastic

I waited a day before popping the mold off the clay, but I could have done it in just a couple hours.

Had to wash the gunky soap and clay out of mold... that's why I switched to just cling wrap, but you can use carnuba car wax (more later).

I cut the excess off with tin snips but you can use a cut off wheel if you have one... Make sure to leave extra on the sides that way you have a cutting reference when your carbon fiber part comes out of the mold.

Sanded with 80 grit sand paper on the flip side for any extra slivers of glass.

Sanded the inside of the mold too in prep for spot filler. You can use whatever type of filler you like if you didn't make your clay model precise enough (like I did). Learn from me, Clay is MUCH easier to perfect a good shape out of than fixing your fiberglass mold after the fact. I won't bore you with how to use body filler... see google if you need instructions on that

Needless to say it was time consuming and you can again, learn from my mistake. Here's a pic by pic of each step in the process. 

You may notice towards the end of the steps the mold is painted with a black layer... That was also a massive waste of time. 

The plan worked in theory. That is, resin doesn't stick to plastic and it releases from it. True. However, the method of dissolving the ABS plastic in acetone and painting it on without it causing defects in the layer below was nearly impossible. 

Lol, I even went the extra mile and polished the plastic layer I eventually got laid down.... Again, don't waste your time doing this step.

It's FAR easier to avoid all these mistakes by:

1.) making your clay positive (or negative) mold perfect as you want your final part to be so then you don't have to do body work to fix it.

2.) Simply use carnauba wax on whatever surface you want to mold release from (more on that later). 

HOW TO: Make a Carbon Fiber Part (Part 4: making the budget vacuum bag)

HOW TO: Vacuum formed Carbon Fiber Part for $200 (Part 1)
HOW TO: Make a Carbon Fiber Part (Part 2: making a clay mold)
HOW TO: Make a Carbon Fiber Part (Part 3: making a fiberglass mold)
HOW TO: Make a Carbon Fiber Part (Part 4: making the budget vacuum bag)
HOW TO: Make a Carbon Fiber Part (Part 5: mold prep and cutting CF)

HOW TO: Make a Carbon Fiber Part (Part 6: vacuum bagging CF in mold)
HOW TO: Make a Carbon Fiber Part (Part 7: two part piece and final steps)

So FINALLY Back to the Carbon Fiber! But don't down play the importance of making a good mold... like any body shop car painter can tell you: a high quality paint job (or CF part) isn't in the matter of minutes it takes to put down the paint... it's in the hours and hours of prep work.

So assuming you know how the principle of vacuum bag forming a carbon fiber part works I'll get to the explanation on how I made the core important pieces of any vacuum bag set up. That is:

1.) A mold to place your carbon fiber on that is wetted out with resin to cure on in the shape of the part you want.

2.) An air tight enough bag to hold the negative pressure of the vacuum and thus the part to the mold.

3.) A large enough and thin enough bag to have the flexibility to hold the carbon fiber tight to the mold while it cures

4.) "breather cloth" or in our case: some old felt cloth or sweat shirt to soak up the excess resin pressed out in vacuum bagging. The excess resin can add weight and weak points in the final carbon fiber piece. Another benefit to breather cloth is to not have excess resin run down your tubing and into your vacuum pump

5.) "Peel ply" or in our case: cooking wax paper with tiny holes punched through to serve as a breathable, yet non-stick surface between the "breather cloth" and the part to allow excess resin and all air to flow through it. 

6.) "Mold release" or in our case carnauba wax so your part doesn't become bonded to the mold, yet provides thin enough barrier to copy the mold well.

7.) A vacuum pump and tubing to provide constant negative air draw during the entire time it takes for the part to cure.

8.) Resin (talked about it earlier).

If you need to know more, google it

The first step is to make a vacuum bag. I use this 4 mil clear plastic poly film. Get the highest clarity because it contains the fewest impurities (recycled materials) that add stiffness and weakness to the film. 

Lay out a large enough section not only for the part, but also for it to fold over on top of it's self

You can put your mold on the film to use as a reference. Make the bag large enough to account for the contours of the part

Duct tape (or any tape I could find that’s affordable) can not completely seal a vacuum bag, but it does good enough to hold the bag in place until we get to the clay step. So you put the film on half the tape and once you match the bottom of the bag on top you can tape it.

To create the proper vacuum bag you need the top of the bag to have more material than the bottom. That way the part can lay on the bottom of the bag and the bottom of the bag can accept the ends of the larger top that has extra material to conform to the contours of the part.

Then tape it

Take a couple foot section of your clear tubing and cut halfway into it about every 1/2 inch going down six inches to ten inches of it. This is to simulate the expensive valve vacuum bagging pros use that draws air out of the bag without getting clogged with resin or sucking down to the bag and losing negative pressure in the bag. The multiple tiny cuts in the tubing allow the air to be drawn out down the length of the tubing in the bag evenly. This also prevents it from sucking down on the side of the bag and thus losing suction in the bag. 

I got the idea from the chest tubes that we use at the hospital

When you put the tubing in the bag you may want to place it not on the part itself and instead make sure it's resting in the bag as such... then extend the breather cloth in the bag to touch the notched tubing

A third technique to create enough top of the bag material is to create "tents" in the side of the top layer of the bag that'll meet with the flat bottom part of the bag that has to be resting on the flat surface underneath so your clay that you are adding to the taped edges doesn't pull the bag away from the mold. And obviously you'll want to stop after you made these three sides of the bag because you'll seal the last section once you put your mold with the carbon fiber in it etc in the bag. Make sure the opening is large enough to put it all in.

Next is making the clay sheets that can make the air tight seal that is impossible to replicate with hardware store affordable alternatives to the SUPER expensive "double sided vacuum bagging tape" Believe me I've tried it all:

So first you take a big long piece of poly film (as long as your bag is) and then get it wet with some sprays of water to prevent the clay from sticking to the bag.

Then put about this much clay on the bag and spray it with water too.

Then you can roll it out when you fold the other side of the plastic over it containing the sticky mess.

I wear some rubber gloves when handling the clay not so much to prevent getting dirty, but it's way faster than trying to make it to the sink and wash off.

Roll it out as flat as you dare... I made it about a half inch thick or so... that way you can spread out from the core to any leaks. 

Then you can bring it over to your bag set up, peel off the top plastic layer, and cut a piece wide enough to cover the taped seam completely... this includes the "tented areas" If you are doing the clay cutting process in a different place than you will be running the set up under vacuum you should either move there now... or do this step on a piece of ply wood or heavy card board so you can transport the project without the heavy clay pulling away or even compromising the bag

You can make one wide strip to fold over itself of cut two skinnier ones and place them down to achieve the same sealing effect.

Just make sure on corners that clay is touching clay and that plastic is surrounding the clay when done because if it dries too much it can leak... but sprays of water is all water based clay needs to be revived. I’ve been using the same clay for 3 years now.

Make sure your part still has room to get in and out of the bag you're creating.... Don't forget to have extra clay strips pre-made to close the opening. As well as some extra to clay to seal any leaks you discover when vacuum is applied.