The Staff of Motorsport Marketing
The Staff of Motorsport Marketing Writer
1/24/18 2:55 p.m.

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story by matt smith

For true gearheads, a car is never just a car—it’s a four-wheeled heap of possibilities. Whether you’ve got an old Triumph Spitfire or the latest …

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frenchyd Dork
1/24/18 3:56 p.m.

I’ve made many parts with carbon fiber and only rarely vacuum bagged them. The difference in weight between a vacuum bagged piece and a squeegeed piece is trivial.  

Formula one and other professional racing groups can vacuum bag and justify using prepeg in an autoclave to save those few ounces or gain that last iota of strength but at the grassroots level it’s a barrier to most.

On my  Jaguar XKE V12 race car the stock steel hood weighed 280 pounds. The splash mold I made weighed 105 pounds. So I assume a part made with fiberglass matt would have weighed the same.  Maybe 10 pounds less if made with cloth. 

The carbon fiber hood weighed 78 pounds and if I’d bought prepeg,  vacuum bagged it, and used an autoclave it would have weighed 65 pounds.  

There are other ways to get carbon fiber down in weight. For example use foam. Foam adds depth or dimension which will give bodywork more stiffness with less weight.  Supply houses that sell fiberglass, carbon fiber, etc also sell the light plyable  foam required. 

te72 New Reader
1/24/18 9:39 p.m.

Good info. I'm fairly partial to working with aluminum myself, so far. One of these days when the budget allows for a TIG welder, things could get interesting...

frenchyd Dork
1/25/18 2:36 p.m.

In reply to The Staff of Motorsport Marketing :

I voted your article up because in one neat area you put all of the good and bad of each together.  

I might disagree with some points. But the article was well organized and a fast read.  

rennkafer New Reader
1/27/18 3:31 p.m.

6061 machines just fine.  I've made thousands of parts from it when I worked at a race shop.

Also, you left off 5052 as one of the more common sheet aluminum used by fabricators.  

frenchyd Dork
1/29/18 1:01 p.m.

In reply to The Staff of Motorsport Marketing :

I’ll argue that fiberglass work is messy.  Maybe you haven’t approached  it properly?   

The method I  use is


get all materials ready with a little extra should something happen. 

Wash/clean the pattern part. Use scotch tape to cover any holes etc. Wax the pattern part with 4 good coats of wax.  I use furniture wax high in carnuba. Wax buff repeat 3 more times. Make sure you get edges of things.  

cut fiberglass/ carbon fiber ( use a new pinking shear on carbon fiber) Oh by the way, you use fiberglass Matt or a chopper gun making molds even for carbon fiber parts. Lay your pieces in a manner you can pull one coat at a time even with sticky gloves on. Matt it doesn’t matter about how you lay it out. Cloth put each layer about 45 degrees to the devious.  I use big cardboard boxes as a temporary bench and set it so it’s handy once I am ready to go 

get your equipment  ready and a way to clean the equipment after. Put on your protective gear, make sure the hose is ready the compressor is drained, filled and cooled back down


mix the catalyst with your gelcoat then spray your gelcoat. If I’m using Matt then I use the same spray gun ( after cleaning) to spray resin onto the Matt then use the rollers to roll the Matt into the resin and get the air out.  You can use the same spray gun to spray resin for cloth( either fiberglass or carbon fiber) but use a squeegee to remove excess resin.  I just use bondo spreaders as my squeegee.  


once you have all your layers down then you need to keep checking for the point where the material starts to get leathery.  That’s when you take you sharp utility knife with a fresh blade in it and cut off the overlapped edges. Doing it now will keep you from having to grind the edges. ( and keep all that mess and itch out of the air) if you start too soon it will be like trying to cut wet paper with a dull scissors. If you wait too long the blade won’t cut.  

kb58 SuperDork
1/29/18 1:30 p.m.

Another "best" thread posed as a question no less.

Since I'm free to decide what "best" is, the answer is boron fiber.

Nah, I take that back. Composites are so messy, smelly, and unhealthy, stick with aluminum.

What's the next thing you need answers to?

edmagoo New Reader
10/8/19 4:37 p.m.

Interesting video on the differences between carpet fiber, kevlar, and fiberglass.

Carbon Fiber vs Kevlar vs Fiberglass - Which one is right for YOU?


alfadriver MegaDork
10/8/19 5:03 p.m.

In reply to edmagoo :

seems kinda canoe like 

350z247 New Reader
1/22/21 11:18 a.m.

I'm not sure a agree with these rating scales. In what world do ABS plastic and carbon fiber cost and weight the same to make an identical part?

matthewmcl (Forum Supporter)
matthewmcl (Forum Supporter) HalfDork
1/22/21 12:40 p.m.

I know this is a zombie thread, but just to throw a tidbit on from the instruction I have had in the past...

Carbon fiber is very strong, but only when the fibers are properly aligned, prestressed, etc. For the methods most hobbyists will use (hand layup, etc.) the carbon fiber will not be any stronger than good S-glass (structural fiberglass). Carbon fiber is awesome in and of itself, but if you are designing something to not break, and doing hand layups, the carbon part won't really be any stronger than an S-glass part made with the same hand layup techniques.

It is a little like welding. If you want to use exotic steels to get ultimate performance, you will need a lot more know-how and equipment than just being able to run a good bead.

Ranger50 UltimaDork
1/22/21 12:49 p.m.

In reply to matthewmcl (Forum Supporter) :

I see that with the "professionals" making carbon parts for drag racing and pricing accordingly. Most of what I see needs some turns in the middle. Yes, it's light but when it's going 150.... it's pushed in like a bulldog nose or flapping around like a bed sheet on the clothesline in a wind storm...

matthewmcl (Forum Supporter)
matthewmcl (Forum Supporter) HalfDork
1/22/21 12:57 p.m.

In reply to Ranger50 :

That is not actually a strength thing, because it did not break.  That is a stiffness thing, which as frenchy pointed out long ago, is actually best increased with some appropriate foam skinned with  composite on both sides.  But yes, considering how much "carbon fiber look" can drive the price of something up, it can all get a little silly.  Personally I like kevlar (or at least a blend) since it can allow for a reasonable approximation of ductile failure in composite parts.  I assume I will screw up somehow, somewhere, and a part that stays together a little bit seems better than a part that breaks apart.

DjGreggieP HalfDork
1/22/21 1:33 p.m.

I used aluminum to create a mount and fill the space left from the OEM mirrors on the Intrepid, then had the local vinyl guy wrap them in a Carbon Fibre vinyl that closely matched the APR mirrors I was wanting to install. I can not remember what the alloy numbering to it was. 

Olemiss540 Reader
1/22/21 2:00 p.m.

License plates and self tapping screws. Next question.

jerel77494 New Reader
11/1/21 2:52 p.m.

Only problem with T6 is, once you weld it, the heat treatment is gone; you have to heat treat it again.

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