second project

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#1

Hello,

I am making an unpainted cf air intake for my motorcycle. It is cosmetic so I am not bothered by extra weight. I made a male mold from styrofoam and covered it with bondo to smooth it out. I want to overlay cf and then pour acetone inside to eat out the foam.

I would make this part in 2 pieces but the hole (air intake) in front is too small to be able to get inside to bond the pieces together. I will try a 2 piece part in the future.

My questions are:
How many layers of cf do I need?
Should I use any chopped mat and/or fiberglass first?

If I use 2 layers of cf, do I need to paint it black first so that the bondo does not show?

Any suggestions on how to cut the pieces of fabric to lay it up? I was thinking of 1 piece on the bottom and hopefully overlap that with one large piece on the 2 sides.

ANY other suggestions are welcome. I already screwed one up!

Thanks,

Chris

#2

-Next time use epoxy and woven glass over the styrofoam.

-Use blue HD foam sold at lowes

-If you need filler use epoxy, and microbaloons, NOT BONDO - cant stress that enough.

-Laquer Thinner will desolve stryofoam to a liquid. While Acetone will turn it to a fibery goo, but still desolves it well.

  • 2 layers of 8 ounce carbon will be plenty strong.

Thats all Ive got.

Edit: Heres my latest styrofoam project. I think the blue foam carves nice. I use those cheese graters in the dry wall section at Lowes. The work really well.

#3

F4i or RC51? :smiley: I can’t help it i’m a bike nut!

#4

Get your carbon fiber “stack” up to a total of 18oz. you could do that with three layers of 6oz c/f or a layer of 12oz followed by one layer of 6oz.

It’s all subjectional i guess… i’m sure two layers of 9oz would be fine, but remember if you plan on adding mounting tabs you need to make the part thick enough to hold up under use and vibration from the tab/mounting area.

I use bondo for plugs, but i toss them in the trash after. I’m guessing he says do not use bondo because it does shrink after it cures and it continues to slowly shrink after. If you use an epoxy filler buy, talc, glass microbaloons and mix those together with the pre-mixed epoxy to achieve the desired consistancy. Do not use cabosil as a sandable filler … that filler/addative doesn’t sand too well. I would say to do a project the size you are doing ( 2 ram air intakes) you will need a quart of each filler. Epoxy… just use an inexpensive epoxy like West Systems. These epoxy based fillers will take around 24 hours to cure to a sandable solid.

Keep at it man… looks like you are on the right track :cool:

#5

Thanks for the help guys.

JRL,
What do you use to glue the foam together?

Fastrr,
This is actually for a custom Harley but it does have some sportbike type parts. I included a picture taken during construction.

#6

That bike is insane! Im jealous!

I use 3M 77 to glue the foam. Ill admit though. It sucks for this app. It will pull apart if the foam is slightly warped.

The 95 would probably work better. Im just not willing to spend more money on spray glue when I still have 77 left.

#7

Try using Gorilla glue as it is a PUR foam…

#8

Bondo is mostly PER and it will melt PS (polystyrene) foam but not PUR foam.

Maybe (more than 1 way to skin an air intake…) try like what you did with PS foam, bondo and then wax it up really well.

Cut some added resets for added bulk where fasteners will be located.

Spray paint black over the wax surface (many light coats as it will be inside the finish part) and let it full dry. This will hide thin layers.

Maybe also make a fitted plug to fit into the opening to hold the CF cloth while drying?

Then lay up the added areas for fasteners first.

Then the 2x or so layers of CF cloth, insert the plug (with added wax or PE coating) and let it fully cure.

Wash the PS foam out and with a pick or scribe, reach in the hole and chip out the bondo as best as you can…?

#9

What type of wax would I use, just release wax? If I could paint over wax that would easily solve the painting problem. I ruined my first mold by painting it. I forgot to test whether or not the paint affected the small exposed areas of foam. It did.

I assume the wax would allow the bondo to not adhere to the finished part, which would also solve any issues of bondo breaking off later.

The resin/filler suggestion sounds like the correct way to have done it.

Thanks,
Chris

#10

Thats the main reason why I dont use it. Plus it has a horrible work time. Which leads to sloppy filling. Which leads to more prep, and finishing work. Thus wasting time. Plus, it doesnt like to stick to anything.

Actually, Ive gotten really good (and effecient) at working with it, but initially everything above was true. I still hate it though.

As far as epoxy goes. You know when its going to kick. You can control the amount of “sandablity”…i.e…more or less micro balloons, and you can control the work time. The best part is the peace of mind that when you come back in the morning, misterious dents/lines/creases/etc… will not randomly show up in your finished piece overnight. Just like anything, it will take some practice to figure out what works for you.

#11

Hello,

I finally finished something other than a flat plate! It is certainly not perfect but I am very pleased. I had this motorcycle air scoop designed in my brain for some time and was always hesitant to actually start it. I kept asking people for advice and everybody said “just try it.” They were correct. The only way is to learn is to just do it. This forum is a great help.

I used West System epoxy and it has a yellow look. I did clear coat it for UV protection. There are some bubbles but not too bad. Is it the brand of epoxy that gives it the yellow tint? There are three coats of epoxy over the male mold.

#12

All epoxy resin will be amber or yellowist, it is for bonding the fibers and PUR clear coat is for the clear, deep look.

#13

What is PUR?

#14

I read that epoxy resins are the strongest and are more compatible with carbon fiber. If this is true, does that mean any “real” carbon fiber layup such as race car parts have a yellow tint? I have not noticed a yellow tint on any parts that I would assume are made with epoxy resin.

#15

PUR Polyurethane clear coat (sprayed)

Maybe those race car parts were made with pre-preg CF?

#16

Are we talking about the resin that is used to bond the carbon fiber? The resin that is placed in the mold, or over the mold in my case? Or are we talking about a clear coat that is sprayed over the epoxy resin? If it is sprayed over the epoxy, will it eliminate the yellow tint?

#17

yes West epoxy turns yellow/green so much so that it is visible in the finished part. I hate that resin. Try using Huntsman resins or do a search here on the forum for other good resin types/brands. My suggestion would be, use the West Systems on non-cosmetic parts.

Any slight bridging will leave a resin rich area where you will see the tint/color of the resin. But i have seen West Systems turn a carbon fiber part yellow where there was no bridging. IMHO it’s junk for cosmetic parts.

PUR is polyurethane clear coat 2K. 2K is a spray on, two part system that uses a resin clear coat and a catalyst. If you would like a decent inexpensive 2K try UPOL brand or Xtreme. You will need an air compressor, inline air filter, hose, and hvlp or lvlp paint spray gun too. 2K clear coats have isocyanites that are deadly - always wear an osha approved respirator. There is no better clear coat than a good 2K.

#18

I’ve heard of sealing foam plugs using one-part rattlecan polyurethane clearcoat. Haven’t gotten a chance to try it yet, though.