LocostUSA.com

So I am finally getting around to doing a write up on my carbon fiber and kevlar floor. I am not going to go into how to stir your epoxy, correct laminate layups or anything like that. That would be a ton to cover! This a simple write up on how to do a carbon floor for your car however if you have any questions, simple or hard to answer... ask away!

Thanks to Tim Huff and John Wanberg for their help!

1st Read the whole tread before getting started. Often people post questions and comments are are very useful.
2nd Make a small panel first for practice. Carbon work is all about practice... "Just doing it" is number two
3rd Buy and/or read these books! They will teach you a ton! http://www.amazon.com/s?ie=UTF8&field-a ... %20Wanberg

Floor Make Up

The floor is made up of three main parts.
1) Kevlar. This goes on the underside of the floor is for wear and penetration resistance.
2) Carbon Fiber. Kevlar on its own is not very rigid so that's where the carbon fiber comes into play. You will want to go with plain weave because it is cheaper than twill and is way easier to handle. However if you need something that lays well and is pretty, twill is the way to go. If you want Formula 1 stuff go with this http://compositeenvisions.com/textreme- ... -1112.html
3) Balsa. This is used as the "core material" (coremat, foams, etc can also be used but they generally will not give the same impact protection). The reason why a core needs to be used is that as the cross sectional area is increased, the part becomes more rigid. Two layers of carbon on kevlar is nowhere as rigid as a sandwich panel. Lets say it like this... with just four clamps on my chassis to hold the floor up, two guys can stand on the inside of the floor and it barley budges. The best part is the floor trimmed is 14lbs total.

So lets get started. Your qtys will change based on your floor size.

Layup
.250thick endgrain Balsa
http://www.fibreglast.com/product/end-g ... dwich_Core
2 layers 5.7oz Plain Carbon Fiber
http://cjcompositestechnology.com/carbo ... -fabric-50
2layers
http://cjcompositestechnology.com/kevla ... 7-oz-50-in

Materials
gloves! (long sleeves too)
Masking tape (Frog tape is good)
Packing Tape (resin wont stick to it)
2 sheets (48x96) MDF
Vacuum pump. I use this one for all my layups. You can use mineral oil in it. http://www.harborfreight.com/25-cfm-vac ... yhQfvldWt0
Vaccum bag http://compositeenvisions.com/airtech-k ... 0-917.html
Vacuum bag tape (grey sticky stuff) http://compositeenvisions.com/tacky-tap ... l-503.html
Mylar (two pieces to cover both MDF sheets)
Breather material http://compositeenvisions.com/vacuum-br ... 0-501.html
Peel ply (optional, i will discuss this more down the post)
Vacuum Bag Fitting (optional) http://compositeenvisions.com/vacuum-ba ... m-504.html
Mixing/Measuring tub http://compositeenvisions.com/mixing-co ... t-403.html
Scale (if you want to be precise)
UV Safe Epoxy (you can use polyester resin but that stuff stinks bad and you will need a mask for sure, check to make sure your resin is kevlar compatible) http://compositeenvisions.com/epoxy-and ... resins-65/
Epoxy filler (optional)
Squeegees
Scissors that cut Kevlar... your home ones will not work. Harbor freight has a few that will though.
Roller http://www.jamestowndistributors.com/us ... o?pid=2109
at least one other buddy you can buy beer and pizza for, 2 is better though.

Steps
1) First get everything out. Prep is a big key here since it is a large layup



2) You will need to lay the mylar on the MDF and tape the edges down using the packing tape. You can use packing tape in place of the mylar
but it is time consuming and you will probably get lines in your part where the tape overlaps. Once that is done put them aside.

Note: If you don't want a gloss finish, you can use peel ply on top of the mylar to get a satin or rough surface depending on what you buy. You still need the mylar so that you don't get resin on the mdf. After this whole process using the mylar... the mdf will still look new so you can use on other projects.



3) Cut all of your materials to the right size but hold off on the vacuum bag. Here are two tricks of the trade. Run tape along the edges once you make your cut. It will make the carbon and Kevlar be easier to handle and will keep them from coming apart. Trick two is below. Once you know where you need to cut, snip the end of the edge thread and pull on strand of carbon fiber out. This will give you a clean cutting line to go off of.



4) Put one MDF panel on the floor and lay all of your materials in backwards order of how they will be laid up so you can just pick up and place as you go.



Note: Now you can do this laypu on the floor by putting a piece of mylar between the bag and first layer (floor, vacuum bag, mylar, layers, mylar, bag) but by using the mdf you know that it will be flat and you wont have debris all over it.

5) Now you need to prep your bag... put the vacuum tape on but leave the peel away layer on the top side as shown on so that resin doesn't ruin the tape. The bag needs to extend well past the layup so i did 60" wide bag to 50" wide carbon. Do not snag the bag or do anything that will put a hole in it. Searching for leaks will be bad enough.



6) add a layer of breather material. I did not do this and had a few air bubbles. By doing so you can apply more even pressure to the panel and get everything bubble free.

7) add you MDF with the mylar side up.



ok lets mix some resin. Read the instructions! Most epoxy resins are a 2:1 ratio but look at what you have first before going further. Also follow temperature instructions. You will want to measure them separately or use the lines on your tub to get a 2:1 mix of resin and hardener. Mix only enough to get one layer done at a time.



9) Evenly spread the resin on the mylar. Look for air bubbles that you can pop manually or with a heat gun/ hair dryer on the slow setting to tin out the resin. You may wan to wait until the first resin layer has become tacky (you glove sticks but nothing comes off) before adding the first layer of kevlar but i didn't.

10) Each time you add a layer... add resin. Squeegee the excess resin off and relocate it to dry areas or discard in a different container.

11) Now... once you get to the Balsa layer, it is advised that you mix your epoxy with a filler. Why? It keeps the balsa from sucking all of the resign out of the fabrics. This is not as important on the bottom layers since gravity will help but the top may have issues. I didn't use a filler i laid down a layer of resin, waited for it to tack then added one more layer of resin to that one before adding the next layer. I had small issues at the end but i am not sure if this was due to not enough resin or inadequate pressure since i didn't add the extra layer of breather cloth.

12) Once all the layers are added you can add the last piece of MFD with the mylar side down. Add two more layers of breather cloth and seal the bag all the way around.

13) hook up your vacuum pump using a hose or vacuum bag fitting. If using a hose, make sure the end of the hose is covered in breather cloth, as shown, so that you don't plug the system with the bagging material. Also make sure you have a good seal around the tube. This is the biggest reason to get the vacuum fitting if you can. Make sure you are pulling full vacuum... in Colorado that is hard to do. Listen for air leaks and fix them if you have low vacuum. Again, don't do like I did, add a few layers of breather material to the whole top side. Be careful not to fluctuate the vacuum, releasing it and applying it. This may cause air bubbles that you don't want. You probably wont be able to turn the pump off and keep full vacuum so do what i did and leave it on over night or until the resin has cured. How do you know the resin has cured?Well those cups you have probably have resin in them still so you will be able to tell when it is cured based on that. But i would say to leave it overnight, make sure you have oil in it, and check it frequently to ensure you don't start a fire or something.

_________________
My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

cont.

It should look like this once trimmed ..





Finishing....



see the bare balsa edge in the pic? Don't leave it that way it may delaminate over time or get messed up. There are a few things you can do to finish the edge after trimming.

1) Fill with epoxy (this isn't the best option since it may chip)
2) Add carbon tape to the edge, add resin and sand http://compositeenvisions.com/carbon-fi ... 1-892.html
3) What i plan on doing... add a carbon strip (http://www.rcfoam.com/carbon-fiber-shee ... er-strips/)
using a spray adhesive like 3M 77. Then add a top coat of resin. This will process will protect the edge and seal it as well.

Floor Mounting / Attachment

I tried many things to attach the floor to the chassis and have come up with the best two options (those wood inserts and stuff don't work). You can embed the following two options into the carbon during layup but i found it was easier to weld my tabs onto the chassis, clamp the floor and the drill the holes.

1) Weld nuts. http://www.mcmaster.com/#weld-nuts/=r5canb
These can be inserted through a drilled hole from the bottom and secured to a tab with a screw on top. Easy. If you get the weld nust with the holes in the bottom of the flange, you can use a set of ring pliers to hold them while you really sung them down. Some epoxy or 3M 77 will hole them in place as well. Cover up with kevlar to conceal the metal bottom if you like.

2) Perforated base Stud http://www.mcmaster.com/#standard-threaded-rods/=r5cdbu
These are great to use for mounting any carbon parts where you don't want fasteners to show. Just sand the area where you want it to go, put some epoxy down and press this into the epoxy. if you don't want to see the base on top, push a small piece of carbon with a hole over the thread to cover the base. These can be installed from the bottom side too.

Post any questions or comments that you may have for others to review.

_________________
My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

What surprised me is that the balsa wood is basically like floor boards. I thought it had to be sheets like plywood.

_________________
mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

Corvettes have basla core floor which is cool http://articles.sae.org/11722/. The back of the balsa has a thin layer of fiberlass that holds all of the pieces of balsa ends together. This allows it to be flexible as well.

_________________
My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

I will be referring back here when it is time to do the floor and diffuser on my DSR build.
Paul

_________________
Parts left out cost nothing and cause no problems!!

I hope your matrix holds up to abrasion better than this new Ferrari 458 tested on Top Gear, season 20, episode 3.

_________________
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i was wondering, why didn't you infuse the resin, is it because in colorado it is difficult to pull enough vacuum?

what altitude are you in colorado?

why did you use end grane bulsa and not foam, it is porouse?

on lay up of the carbon, did you run the weave in only one direction or did you place the second layer at 45 degrees to the first?

did you need to degas the resin?

_________________
this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

Yeah like most floors of this type it is considered "a wear component" but the kevlar should hold up very well. There is always a trade off. I will need to pay attention to it and place UHMW in spots of concern (mainly the edges).

_________________
My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

i was wondering, why didn't you infuse the resin, is it because in colorado it is difficult to pull enough vacuum?
Yes and no. Yes infusion in Colorado is harder to do but the main deterrent is the added process and cost of infusing. Infusion can go wrong pretty quick. You can easily get too much resin in one area and not enough in another. For simple garage stuff it is easier to to do a wet layup

what altitude are you in colorado?
5280 (Denver)

why did you use end grane bulsa and not foam, it is porouse?
Well... mainly end grain balsa has higher compressive strength (stuff coming up through the floor) than foam of comparable weight. End grain balsa also has a very high strength and stiffness to weight ratio and provides exceptionally high shear, tensile and is good for fire resistance. Yes you can buy foam with some of these properties but at almost twice the cost. Layup is way easier too.

Factors for decision (highest to lowest)
Cost
Road stuff killing my jewels
Stiffness
Weight

Generally on a panel using foam or balsa, the composition is about 50% resin.

http://www.fibreglast.com/product/guide ... -materials
http://www.compositesworld.com/articles ... -laminates

on lay up of the carbon, did you run the weave in only one direction or did you place the second layer at 45 degrees to the first?
Nope. It probably would have made a stiffer panel but i am not sure by how much without running a simulation. Don't hammer me on this.

Here is what my expert buddy said: 90° gives it better directional strength. If you add a 45 to it, the layup will have better torsional stiffness

did you need to degas the resin?
No. I would have if i was concerned about seeing air bubbles. I didnt see any at all though.


FYI here is the cost breakdown for building the floor (minus what i had on hand) and yes I have all the cost breakdowns for building the car.

_________________
My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

I think you should test a couple of samples, maybe you have left overs from the panel you made. I'm still thinking metal floor and more weight.



In my case I was just considering how to choose between an aluminum and a steel floor. I'm thinking aluminum. Any ideas for how to test something like this? Maybe something like a weighted pendulum swinging against a 1 square foot target.

So the fear here is that you made a very good floor, but not a great impact protection. Fiberglass or aluminum might be better. Aluminum will deform to the size and shape of a rock that hits it. Fiberglass will break strands at the point of impact, but will also bend a great deal. I tried to break a fiberglass sample with a sledgehammer once, it wasn't a great idea. The sledgehammer came back at me at an equal speed. Before YouTube fortunately.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
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Great comment and I knew someone would ask that but its always great to discuss for safety so I will shoot away. That same question has come up may times. There are way too many scenarios to test and where do you draw the line? How much road debris do you plan on running over? Look at this for example... nothing would stop that.

http://www.youtube.com/watch?v=nJUWXRWK4xs&sns=em

Yes I have done simple test like putting a sharp punch on it and hitting it with a hammer... barely went through. I if you hit it with a hammer straight on... the floor will win and your arm will not. I feel much better with a kevlar floor than aluminum one so I think it just comes down to the individual. You can do like a lot of guys do with aluminum floors and put a piece of steel under them for protection.

I think the chances of hitting road debris, having it come up through the floor and hit you are far lower than a suburbia SUV not seeing you and hitting you directly.

Also... the car has no windshield or side panels! In your regular car...how many times have you run over road debris vs a rock hitting your windshield?

_________________
My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

I think this would provide more protection than a steel or aluminum floor, especially for the weight! They don't make bullet proof vests out of Kevlar for no reason!

Thanks for posting this, one more material to consider for my floors! What are your thoughts on breaking the floor panel into smaller pieces for each "bay" that is formed by the chassis tubes, and making the floor panels flush with these tubes?

i also considered when the floor panel was made, did you not think that the floor could be routered out where the tubes are, giving a little more ground clearence but still retaining the smooth underbelly?

or do you think that would compromise the integrity of the panel?

instead of welding on tabs, if the tube spaces were routered out then the panell could be riveted to the tubes.

there's nothing like the feel of a smooth underbelly!

and there's nothing like improving on someones design to make it worse instead of better!

as far as strength compared to aluminum,i would think this floor is as strong as an aluminum/honeycomb sandwich, its just the amount of fixing points compared to the amount of edge exposed, if it were as i described, routered out to allow it to go up inside the tubes and then riveted to them, in a crash situation it would be less likely to break away from the chassis, also the sections of the floor up inside the chassis tube structure would stiffen the chassis considerably.

infact, the strongest way for this type of floor construction would be to fit the floor into the chassis, routering out the spaces for the tubes and then afixing another skin over the chassis tubes on the inside thus making the floor and chassis one unit, using this method, most of the cross braces and diagonal tubes could be ommited from the chassis but leaving the outline frame rails to mount the suspension, steering, roll cage and pedals etc.

on final fitment, i would suggest an adheasive between the panel and the chassis tubes.

_________________
this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

Sure you could do that. Make one big panel and cut it up but you will need to seal each edge prior to installing.

_________________
My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

When it was desinged the floor thickness was added in. If it needs to go lower... that's what the coilovers are for

sure you could route the panel but you need to seal the edges (balsa and water don't mix) and kevlar does not play nice with anything. Once you cut it... if you can... it freys.

Whatever fastening system you use needs to have a large head or washer to distribute the load. I didn't use rivets because i need to remove the floor.

I also want the floor to take the impacts, etc... not the tubes (unless you are using UHMW in those areas). Compromising structural tubes is never a good idea.

If you sandwich your floor with the tubes you have a whole different set of issues. You cant just skin the top. You need a special adhesive to bond the carbon to the steel and use resin everywhere else. Then the floor might de-lam because your tubes will want to flex and do things on their own like move differently at temperature or CTE. You would also need to mark or pre-drill your set mounting tubes. I prefer my seat mounted to steel tubes since the track guy can see that and not freak out. It also makes me feel safe that me and the car will stay together in a crash regardless of what the floor does.

_________________
My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.