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46 Posts
Discussion Starter #1
Hi, Matt Behning here with another $200 high quality mod.

Anyone can go out and start making carbon fiber parts with all the "kits" out there, spending $400+ getting the expensive: peel ply, vacuum bagging film, bagging tube fitments, one way valves, double sided bagging tape, special breather cloth, mold release, and other components. This is a how to on how to make the exact same high quality CF part with alternative tools for about $200 (start to finish); all the while using the highest quality Carbon Fiber and Resin. I'll show you what works and what doesn't. It's not as easy as the youtube videos and other write ups make it look.

Here I'm going to make a carbon fiber cowl as practice before making a new subframe. This is for my 2000 Honda CBR 929. But you can make anything for your car, boat, house, etc. Using these instructions you can learn to make a DIY carbon fiber hood, instrument panel, brace, a boat, cover, tail gate, bike frame, seat pan, etc.

Highest quality CF-$17 a yard (you'd need only a half a yard tops for a small part 3 layers)
24oz high quality epoxy resin-$25
small electric vacuum pump-$60
digital scale:$7
4 mil poly plastic film sheet for bagging- $10
Duct tape- $6
Painters tape-$5
water based clay-$10
carnauba Wax-$5
Fiber glass cloth for mold-$10
fiber glass poly resen-$15 (or you can use the epoxy resin that is about twice the price ounce for ounce)
80grit and 220grit sand paper-$6
clear vinyl tubing 1/8" and 1/2"-$4
foam brushes-$5
rubber gloves-$5
two 1/4 x 1-1/2" bolts-$2

Things you need that you probably already own:
-plastic cups
-cling wrap
-measuring tape
-puddy knives
-a drill
-a wood drill bit (any size around 1/2")
-an old sweat shirt or fleece fabric
-wax paper
-wire brush or wheel
-old spray bottle (use an empty windex or something)
-old piece of 2'x'1'x1/2" piece of wood
-old juice or milk bottle
-piece of card board (cereal box works)
Vacuum bagging is the gold standard in getting the best/strongest end product, as opposed to "free lay up." Which is saturating the carbon fiber cloth the best and most even you can, without adding too much weight in excess resin; avoiding trapped air bubbles; getting the wetted out cloth to conform to the mold with gravity; on and on problems exist when you attempt to save time and effort by not using vacuum bagging.

The I made were made using the professional industry standard of vacuum bagging, (but in my budget method:)

First thing to understand is there is some basic Carbon Fiber terminology to know before you buy. (my un-official understanding)
1.) Never buy anything except the PAN manufacturing process (pitch process is less quality)
2.) Never buy CF that doesn't come on a roll... usually they come on rolls 50 inches wide and can be purchased by the yard... average price is $20-25 a yard that is 50 inches wide. Folded or remnant fabric left over from other people's projects is just a gamble.
3.) Pre-preg carbon fiber- is great. However it needs to be stored in a freezer because the resin pre-infused CF cloth will cure at room temperature eventually. (can be shipped to you at room temperature fine). ALSO, you need an oven big enough to bake your part in on a mold that can tolerate up to 500 degrees... take away: leave pre-preg CF for the pros that make lots of parts from expensive molds in big ovens.
4.) Weave- that is the orientation the groups of tiny strands of carbon fiber are arranged in when the manufacturer produces the "cloth" sheet of carbon fiber. Not all weaves are created equal (read my HOW TO: Start DIY Carbon Fiber. Layers, weaves, resin, etc thread).

For example there is:
Twill: the classic "carbon fiber look"ie: 2x2 twill ... that means two bands of CF are patterned next to each other in the weave
Plain: that is the classic checker board looking weave...

You can get different thread weave designs and thicknesses of Carbon Fiber if you want; but you don't have to.
If you need help deciding what weave, how many layers of CF you may need see my thread on the strength testing I did:

5.) Tow- that is talked about in "k" or thousands of units. I test 3k tow (2x2twill weave) CF that means there are 3,000 filament strands of CF in each thread group of CF that is being weaved. I also test in this experiment 12k tow (Plain weave) that means there are 12,000 filament strands of CF.... naturally the higher the tow, the thicker the fabric will be... but as you will find out in the testing... that doesn't mean it'll be stronger. See the picture of the ebay seller I bought from and the two fabrics I purchased from them:

6.) weight or GSM- it goes up with the higher the tow and better weave you buy. My 3k tow 2x2twill weave has a weight of 5.7oz per yard squared If I wanted to pay 30% more I could get an even tighter plain weave from Hexcel with the same 3k tow strands weaved in a product that is 5.8oz per yard squared. these two 3k products can be converted to a weight of about 200 Grams per Sq meter. The 12k product I was using is 300 GSM.
7.) Resin- is the liquid product you mix with the supplied hardener that cures (without the need for air, because it doesn't dry). Usually a 2:1 formula. Google it if you want to know more. The main thing you need to know is that you should buy epoxy resin
as opposed to cheaper polyester resin that is available at the hardware stores. Epoxy has superior strength, UV light protection, and clarity. You get what you pay for with resin so do your research. I used "Max Clear 1618 epoxy resin" I've also used "Max Clear High Performance epoxy resin"... but the 1618 is slightly more fluid and better for vacuum bagging since it soaks into the CF better.

Click on the link and they have TONS of good info on the product link (second from top)
Welcome to Polymer Composites Inc. Product Categories

More terms can be found on the two main manufactures of CF for the commercial DIY: - Glossary of Carbon Fiber and Composite Terminology
Toray Carbon Fibers America - Carbon Fibers and Composites Terminology

46 Posts
Discussion Starter #2
I come to you with this budget how to after completing basic experiments like this:

That Vaseline is NOT a good mold release:

Strength testing and weight comparisons with different weaves and layers of Carbon Fiber:

And making these couple two piece parts:

Plus lots of messing around with free lay up etc wasting CF and epoxy to self teach myself:

or "a single piece of duct tape will seal a home made vacuum bag fine" That's false, along with 13 other designs I tried. Everything from medical tape, truck bed liner sealer, hot glue, heat gun sealed, plastic, ziplocks, and different types of plastic.

You can also save a lot of time here learning the skills no one else really posts about, like how to make a clay mold.
1.) Clay was too moist when molding the clay so it dried incorrectly and cracked (turns out you don't have to let the clay dry)
2.) tried to salvage job 1 and found clay was too inconsistent to proceed to casting
3, 4, 5) was a week long pain staking attempts to use foam and it turned out to be FAR more time consuming than working with clay
6.) Complete restart, made this up in short three hours... now to casting
7.) LOL, spraying some "great stuff" foam into a mold was a disaster

46 Posts
Discussion Starter #3
Getting Started, Making a mold. All great Carbon Fiber parts come out of molds. So to make a permanent custom mold I can re-use in the future I decided to make a negative mold out of fiberglass. This fiberglass mold can be used again and again to make positive pieces (more on that later). To make the negative mold you have to create a positive mold out of clay. To start you need a solid base... I decided on wood.

here's my bike's tail with the seat removed and some bolts for adjustable reference to determine how high the front of the cowl needs to be to get a stream line flat profile... the piece of wood can't be thicker than this.

The bolts I used

Another way to look at it

Using a piece of cardboard I created a template to cut a piece of wood from to create a sturdy base to build my clay mold up from... make sure the edges are far enough within that you won't have wood showing through the clay and causing an inconsistency to show through... but don't make the piece too small where the clay can sag into a gap and deform

had to chisel a relief so the wood wouldn't raise higher than the tail fairing

You'll want to secure the piece of wood to have a steady base... you can determine where to drill by placing a small piece of double sided foam tape with a sticky side facing up and the other side without the backing removed and lay one on each of the holes to be drilled, then place the wood carefully where the piece will be bolted and push down well enough to indent the foam tape... it will stick to the wood.

Using an elastic cord to keep the other end of the base down tight.

46 Posts
Discussion Starter #4
So now we get into building the clay positive mold (to create the negative mold out of fiberglass that will then become the final negative mold to make Carbon fiber cowls out of).

You can buy a 10 pound block of water based clay at any craft store and it's a nice malleable medium to work with.

So take a hand full or two and put it on a cookie sheet or something smooth and waterproof that has water sprayed onto it (otherwise it'll hopelessly stick to the sheet) Then take something like a can of chain wax and get it wet and roll out the clay.

Don't forget to not make the same mistake I did and trust painter's tape to keep the wet clay from ruining your paint. Hind sight I'd take a large sheet of cling wrap and wrap one layer on the tail... you can get a nice 24" wide stuff at moving supply places like U-haul or maybe even hardware stores.

Then you can cut out strips to take up the extra space.

Rinsing the can or whatever you use will help it not stick

Also a fine mist of water on the clay: however, don't get the clay too wet because then it gets to soft or soupy and won't hold it's shape.

46 Posts
Discussion Starter #5
So you put that extra piece down, spray it lightly with water, and then you can draw the can or whatever towards you to meld the pieces together

Clean the can off once and awhile. You can spray it down and wipe off the clay that way... then give it a spray to keep it moist before going back to work on it.


46 Posts
Discussion Starter #6
In hind sight this clay is getting too moist and it's susceptible to damage like this easily... it'd be best to start over... but for the interest of explaining more techniques with working with clay I found I'll post the rest of the pictures.

Again, you can see that the clay is far too malleable and has sunk into the space between the wood base and the fairing... but at the time I was interested in learning about the best way to level the clay and you might also benefit from practice like this.


46 Posts
Discussion Starter #7
With the excess scrapped off the straight edge you can put it on your knuckle like this in case you need some clay

Some more tips

put some tape on a puddy knife and you can keep a quick reference to maintain a level height


46 Posts
Discussion Starter #9
So after you work all the sides and the top smooth to the way you like you can proceed to personalize the piece by cutting out angles or prefabbing clay shapes if you want to add them for raised effects. The possibilities are endless.

Place the cut out on the wet cookie sheet to cut up any graphics you might want in the body piece you are making out of carbon fiber.

I put a cut into the top where the exact middle is. This will help you get things even.

Make sure the cut out for where you place your pieces is even.

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.

46 Posts
Discussion Starter #10
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).

46 Posts
Discussion Starter #11

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

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.


46 Posts
Discussion Starter #12
Had to wash the gunky soap and clay out of mold... that's why I switched to just cling wrap.

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 venture.

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.

46 Posts
Discussion Starter #13
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).

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 flexability 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 refernce. Make the bag large enough to account for the contours of the part

Duct tape (or any tape I could find) 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 in the ICU

When you put the tubing in the bag you may want to place it not on the part it's self 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

46 Posts
Discussion Starter #14
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 dry water based clay needs to be revived.

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.

46 Posts
Discussion Starter #15
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. And if you're reading this and planning on doing this for a mas production product your making to sell than you're no different than the posers who remove the "600" on their bike and slap on "1000rr" for show.

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.

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

46 Posts
Discussion Starter #16
Next is set up. The $60 shipped vacuum pump I use has decent reviews and is the most mass produced pump you can find. It's one weaknes is that it probably isn't meant to run 12+ hours so even though it has a little fan, it gets burning hot after an hour or so... just like your sport bike would if you let it just idle. I didn't realize this at first so the clear air compressor oil that comes with it ended up burnt and I had to change it out... luckily the little pump didn't burn up. So now when I run the pump I run it outside and have a floor fan pointed at it just a few inches away turned up on high while it runs. Now over heating is not an issue and it runs for 12+ hours straight no prob... I have it run outside the garage door also because the pump is annoying to listen to.

It draws 3cubic feet per minute (CFM) but "they" say 1 or 2 cfm is adequate. However, the lower cfm you go, the better you have to fully make sure your system is perfectly air tight. So far, despite all the clay etc, I have never got a vacuum bag to be 100% leak proof. thankfully the maximum negative pressure anything can be on earth is -29 in.hg... which is actually zero in reality because it's impossible to be less than zero pressure... all -29 means is you're overcoming the +29 pressure that exists on earth at sea level.

Little vacuum pumps like this can pull maybe -28 maximum. So whether you have a little pump like this or 700 horse power v8 vacuum pump make no real difference if both were used on the same vacuum bag set up. The only difference would be if you had horrible leaks the big pump could hold more of a negative pressure than a 3cfm pump. That's the basic understanding I have of these pumps, but all I'm saying is don't waste your money getting a fancy air pump. However no mater what project you are doing a good rule of thumb is "your pump may be too weak if you can not draw down to full vacuum within 5-8 minutes of turning on the pump"

Now on to the ever popular topic of how much epoxy resin to use for a given amount of Carbon fiber. I'll be the first to say I'm not an expert. I'm going off my thorough testing and instructions I received with the Max Clear resin I bought. There are only debates about the exact ratio of carbon fiber to resin ratio's that you should use and how to infuse them. Some people set up their vacuum bag dry and draw the resin through one end, through the CF, and turn off the resin infusion once it reaches the other side... Other's like myself understand that requires infusion mesh and extra steps to achieve the same end product. So I'll talk only about the breather cloth method.

Then there is the debate about do you calculate your resin based on "fiber weight fraction" (wf) vs "fiber volume fraction" (vf)...
Resin fabric ration - Composites Central

The instructions you get with the Max Clear resin (which I am VERY happy with) say to use 65% carbon fiber to 35% resin by weight (equals 100%). I measure in ounces just because that's what most people do. However, I found the instructions UNDER estimate the amount of resin you need for a given vacuum bag job. This may be due to the fact they assume your set up will use exactly the ideal amount of resin to result in the perfect ratio of Carbon Fiber to Resin that is achieved in a correctly done vacuum bag set up like this.

That is: Whether you calculate the perfect amount of resin or slop on an entire jug of mixed up resin on to your Carbon fiber before putting it in the vacuum bag... you're going to end up with the same CF to resin ratio of about (65%/35% in the end product (assuming you have everything set up right as described here). (some claim 60% is the max)

The problem with the manufacturer's instructions pouring out just enough resin (65/35) because that's how much resin ends up staying in the part is neglecting to account unintentional loss... that is, some resin is going to stay in the bottom of the cups you mix it up in, some resin is going to saturate into the bleeder cloth, etc. I'm surprised at this, but I'm sure it's so they can't be accused of recommending customers to use too much resin.

The evidence of their under calculated resin is evident in the example on the left of the picture where I weighed out 65% worth of carbon fiber to a measly measured amount of 35% resin that barely filled the bottom of the cup.

Through this how to project I learned the correct ratio by purposefully using a little too much resin: 39% fabric to 61% resin which I calculated to be 2.23 ounces by subtracting the dry weight of my bleeder cloth before the vacuum bagging to the weight of the bleeder cloth after the job which had cured resin in it.

The ideal ratio I now use is 57% Carbon fiber fabric to 43% resin.

This ratio is only applicable to Max Clear 1618 epoxy resin because I tried it with the thicker viscosity of Max Clear HP "high performance" and you need more resin than 57/43 and even then the resin is too thick to use in vacuum bagging easily because it didn't migrate evenly as 1618 does. Meaning the HP didn't distribute under the mechanical pressure that is created under full vacuum... the part wasn't ruined. But the HP is best used for hobbyists that do free lay up projects with epoxy resin such as encasing bottle caps or other knick knacks in a layer of clear resin on a table top.

So as I said before I intentionally error'd on the side of using too much resin knowing it would result in telling me the correct ratio.
So with all resins you have two liquids to mix together in certain ammounts (this is 2:1) to activate the resin to start curing or hardening. Air is not required because it's curing not drying (like paint). This mix takes over an hour before it even starts curing to the point it could be considered less fluid like... that's why it's great for vacuum forming.

46 Posts
Discussion Starter #17
Anyway, in order to calculate how much resin you need:
1.) weigh your Carbon Fiber cloth. Let's Say we have 10 ounces
2.) Use the Carbon fiber to Resin ratio to calculate how much mixed up resin you need. Let's say you also want to use 57% carbon fiber to 43% resin (total always has to equal 100). So take the wt of your cloth and divide it by the percentage of fabric ratio you want .57
3.) So now to calculate how much mixed resin you will need just multiply the number you got in step two that is 17.5 by the percentage of resin your ratio demands .43
17.5x.43=7.5 (you can also get this number by simply subtracting your CF weight from set two's number 17.5-10=7.5)
4.) Now you need to calculate the resin to hardner mix of your resin... this Max Clear 1618 product is a 2:1 ratio of "Part A" to "Part B". We know we need a total of 7.5 ounces of mixed resin. To calculate Part A multiply 7.5 by .66 = 4.95 ounces of Part A. Part B will be 7.5x.33=2.5 ounces (or 7.5-4.95=2.55 ounces)

Don't forget to zero the scale for the weight of your cup.

Make sure you don't put too much Part B in because when you get towards the end of your supply you'll short yourself the required amount of part B to the Part A you have left.

I use a drill with a larger "wood bit" with the sharp spade at the end broke off as a way to mix the resin for about 30 seconds moving about the cup at speed. The instructions say to then pour the contents into a second cup as to avoid using any unmixed resin... however, they may also assume we're not using a power tool to mix either... Some advise against doing this because "it instills air bubbles" however I haven't seen that. Also there's the fact the resin takes hours and hours to cure and under pressure the bubbles are surely resolved.

Now that the resin is mixed and your mold has the 3 layers or so of dried carnuaba wax laid down as a mold release you can apply some resin carefully to your mold with a soft brush. You don't want to be too forceful when spreading it around as to not disturb the hardened wax layer below too much. It's amazing how the palpable ridges of the dried carnuaba wax that feel much like the contours of a stretched piece of leather don't translate on to the final part.
(I did not know about the carnuaba wax mold release in this how too so don't be concerned that you don't see it in the following photos)

I was generous in the loose application of the mixed resin knowing that the excess would be drawn up through the layers of the carbon fiber. It's far better to apply a little too much resin on the bottom of the lay up then the top. However, don't worry to much, the vacuum bag is good at dispersing the resin evenly and extracting the excess.

Then apply the layer of CF that you want to be visualized and make sure the weave is in the direction you like displayed. You can press your CF carefully into the mold... if it's a very sharp corner you could cut the CF to conform to the mold... but I didn't

Apply a layer of resin to the top of each subsequent layer you put down if you have resin left... If you remember from earlier I was purposefully using too much resin in my 39/61 ratio to calculate the appropriate ratio.

second layer that was 12k CF

third layer that was also 12k CF

Then apply the "peel ply" alternative that is perforated wax paper we made earlier. You don't have to put this right in the middle of your part, it just has to be on the edge of it with the breather cloth so it can draw the excess resin into it like if you brought a dry towel to the edge of a puddle of spilled milk it could draw much of the puddle into the cloth eventually by only touching the edge. Put this hypothetical situation into a vacuum bag and you'd nearly all of it.

Then your breather cloth goes on top of the perforated wax paper... I used a piece of fleece that seemed absorbent... you could use a dozen sheets of paper towel or whatever.

When you go to put it in the bag it's very hard to slide it in without pulling the wetted out CF from the mold... this problem created a flaw in my part that I was mostly able to cut out... the solution is to place strips of wax paper or plastic sheeting on the CF before putting it in the bag as to hold down the edge of the CF so it doesn't cling to the inside of the bag as you slide it in.... or you could make the opening to your bag larger.

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Discussion Starter #18
Seal up the bag with the slotted suction tube inside.

Turn on the pump and the fan you may have pointing at your pump... then as the bag is colapsing make sure it has contact fully in the contours of the mold... that is why it was important that the top of your bag has more plastic sheeting than the bottom layer.

This is an example of the air pocket that can occur if you don't push the bagging into the contours as it's sucking down... if you wait until this point under full suction than all you're going to do is tear your bag if you push into it... no worries if this turns up... just clamp the hose or turn off your pump until you can lift up the top layer and re-position it in.

So here's a progression of the excess resin being absorbed into the breather cloth through our alternative peel ply. This is occuring over several hours and you can see the dry white cloth turning more wet and a gray color.

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.)

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Discussion Starter #19

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.

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Discussion Starter #20
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.
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