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.