Honda CBR 929rr/954rr: peel ply

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Friday, August 4, 2017

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.

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 now we move to the step of cutting out some Carbon fiber cloth for your project. The easiest way to measure how much you need is to use an old shirt or piece of fleece. Using a large enough piece of material, press it into the the details and crevasses of the mold. When you make a part mold make sure to be mindful of the limitations of vacuum bagging to make highly complex parts. To narrow or deep contours for the vacuum and material to conform to will result in a flawed part. This part will be a two piece part for that reason.

After the cloth is adequately representing what a piece of carbon fiber will contour to in the mold cut the excess off this substitute fabric as you are going to be using it as a template to cut out your Carbon fiber... obviously leave some excess for good measure.

The reason you want to use a substitute material for measuring is because the more you handle dry carbon fiber cloth the more the weave will distort. The strands pull apart and bunch up and cause what's called "crimp." Crimp not only translates to a flawed pattern, it's also not as structurally as strong.

If you are using two different weaves or types of Carbon fiber than obviously the first layer you cut out should be the pattern you want showing if you have a negative mold like this. Also take note of the orientation or "grain" of the fabric weave (like wood grain) as you cut the carbon fiber piece to place in the mold. Do you want the pattern to be horizontal, vertical, or diagonal?

after cutting out the piece you want you can tape the edge of the CF on the roll to prevent distortion while the roll is stored... not everyone does that, so it's up to you.

So I used one layer of 3k 2x2 twill and two layers of 12k plain weave. Please don't be a poser and use just one layer of CF for the outside layer and then use fiberglass for the subsequent layers... if you're that cheap of a person then safe yourself the time and just buy some "carbon like" vinyl sticker and cover the part you're trying to make. For a part like this you'd save maybe $5 by doing that.

After you get it cut out you need to weigh it in order to later calculate how much resin to mix up. This is a cosmetic part that I'm not worried about structural integrity or minor weave flaws in so I obviously didn't care that folding CF isn't a good idea if you want perfection. To avoid folding for large pieces of CF you want to weigh than you'll need a large enough piece of clear acrylic or equivalent to place on the scale first. (don't forget to zero it out)... then place your CF on the clear plastic... you can view the read out through the clear plastic. A 2"x2" sheet can be bought at most hardware stores for $5-$10. Or if you're budget savy you can borrow the glass shelf out of your fridge or the 3"x3" grate out of your oven for free

When you cut out the layers of carbon fiber most fabricators pay attention to detail and cut out the layers as such the weaves alternate in different directions every other layer. I figured: "why not?"

After you cut out all the layers of CF you need to make your alternate "peel ply" that'll serve as a porous barrier between the CF and the breather cloth that'll be soaking up the excess resin. Without a "peel ply" type layer the breather cloth would permanently cure to the CF.

To emulate what is peel ply I simply took cooking wax paper (not parchment paper, tin foil, etc) and used a wire wheel or even a wire grill brush and poked into the wax paper. Being careful to only create the thousands of pin holes, not tears through which the CF could bond to the breather cloth through.

Before you mix up your resin you'll want your mold to have the mold release on it. "Mold Release" is very expensive... so are releasable coatings that you can put on your parts. I learned from youtube that Carnuaba Car Wax is a perfectly acceptable alternative... problem was the guy in the how to video didn't explain how to apply it right. So the correct way is to use the sponge that comes with it and apply a layer to the mold. Let it air dry completely... don't slop on the layer or feel the need to rub it in etc. Just nice even smooth layer like you would if you were to be applying it to wax your car... after the layer dries then apply about 2 more layers in the same way each making sure not to distort or smear the thin layer below it. And do not remove it (like waxing a car).

(left) before (middle and right) after one layer

HOW TO: Make a Carbon Fiber Part (Part 7: two part piece and final steps)

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 after a total of 12 hours the part seemed hard enough to turn off the vacuum and peel away the clay... you can re-use and re-use the clay... I just put it into gallon zip-lock bags and add about two cups of water in to re hydrate the clay again. (This obviously cured at room temperature in my garage.)

Got the part out of the bag and the breather cloth is still on the peel ply etc.

The perforated wax paper worked as a great alternative to peel ply

The little scraps of wax paper peel off no problem

Just for reference the part isn't fully cured yet and to show this I was able to cut some of the loose threads... the part is about as stiff as cardboard so don't take the risk of deforming your part to cut all the excess off or anything.

It's still in the mold

and a trick to speed up the curing process and possibly make it even stronger than a full "room temperature cure" is by putting it in the oven. HOWEVER, be very careful as your resin or mold may be flammable or if your part is heated too much air bubbles can form in the faster curing set up. So I set my oven to the lowest temp possible of 170 degrees Fahrenheit and kept it cracked open. Turning the set up every couple minutes.

When it reached about 125 degrees Fahrenheit with this candy thermometer resting on it I decided that was warm enough.

When it cooled back down to room temp (after about 15 minutes) It came out of the mold with little effort.

Here it is fresh out of the mold

After it was out for a couple hours it still felt slightly plyable so I decided to put it in the oven for another warming session... I have no idea if this makes it stronger than if I'd just left it alone for a few days to fully cure. I highly doubt it makes it weaker since I heated it up to only 125 ambient temp in the oven (not a core temp from inside the part). After this last heating, it felt fully cured.

Even in the rough state it was looking good

So to make the cowl be a working part that could attach to the existing hinges I first put a layer of plastic in the trunk (to avoid a mess). Then I piled in my clay and leveled it nice making sure it wasn't compressible in any areas.

For the bottom pan I used just two layers of 12K plain weave CF. And I placed a layer of Syrian wrap in between the clay and the carbon fiber pan I was making here.

Having already gone over the whole bagging process I won't bore you with the details. Here I sealed the set up under a plastic sheet cut to fit and sealed with duct tape. Hind sight this was barely adequate, but since it's non-structural or even cosmetic I didn't mind. I was more/less just testing the idea of making the part this way. I taped down some tubing to get the CF to better comply with the details of the mold on the outside of the bag, but under the tape.

Here it is right after about 14 hours of vacuum bagging. Pretty much fully cured.

As you can tell the mechanical compressing of the vacuum was enough to push the vacuum tube under suction into the clay and thus deforming the part. This is valuable info for me not to make a show or structural part on a clay mold.

So now you can measure and cut down your part with a cut off wheel since it's fully cured.

This was just the first rough cut... you can always cut off more. As you can see the flaw that was created from when I was trying to put my wetted out cloth in the mold into the vacuum bag... Again, having some wax paper or plastic over the edges that are tacky and can get pulled away from the mold easily is a good idea. You can also see I completely gave up trying to save my paint job.

Measure, Measure, Measure... here's a second cut down. Just showing you all this in case you can learn at all from my process.

Getting there

Cutting the pan down, using a file for the minor adjustments

Still rough

Almost

Good:

Pan inside cowl, good to go to bond

Since The Max clear 1618 is meant for vacuum bagging it was too thin of viscosity to bond the two parts (think the viscosity of honey or warm ketchup)... it's just going to run down into the crack. This two part epoxy from the hardware store is more like the viscosity of craft clue like "elmer's glue" that has chemicals in it that quickly evaporate within minutes to get progressively thicker until hard.

While bonding I secured it down

After it was bonded it didn't look that much different

After the two were joined together I added more epoxy to the seam

Great fit underneath when I took the back of my bike off.

I taped off and spray painted the graphics I wanted on the part... hindsight this was a HUGE waste of time, effort and resources... it would be far more appropriate to have just got vinyl decals made and clear coat over them.... on the top left you can see how "orange peel" the surface of the part was when I applied a coat of Max Clear 1618 epoxy on the top of the part. Max Clear HP epoxy resin may have provided the "clear coat" effect I was looking for... instead I just used rattle can clear coat that I had been happy with the results to get the final product seen here.

Sanded down the paint job I ruined on my tail

Now to make a Carbon Fiber tail out of a two piece mold... I tried outlining the areas I was to cut out with Elmer's glue to prevent fraying of the fiber matrix after cutting... It seemed to work. I of course let this glue dry overnight so the bead of glue would hold the cut out and the remnant matrix together. Today I don't use the glue technique I simply cut the excess off in manageable squares and stack them up for use in small projects.

You can also see I was repeating the process of using a piece of fleece as a template (the tan fleece)... It's also nice to keep if you ever want to make another part.

The little 3cfm vacuum pump had enough power to do two parts at once

Using carnuaba wax mold release allowed the parts to pop out clean and with a much more smooth finished look.. the chalky appearance is due to the carnuaba wax that isn't wiped off yet.

Before I bonded the two pieces together.

After they're bonded together and before any paint.

Put together on my CBR 929.... now to do the subframe.

(see part one of series to see the picture of the subframe)

"So what's the point?" people ask. Dropping half the weight of your fairings isn't a bad deal is it? (This is a fiberglass cowl I made but never finished... it's a wall hanger just because I ended up getting it signed by Jason Britton and Tony Carbajal

Best of luck on your project!

-Matt Behning