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Author Topic: Making fiberglass molds from foam...  (Read 5030 times)

Offline smackhead999

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Making fiberglass molds from foam...
« on: November 17, 2011, 10:06:55 PM »
I have been thinking about trying to make body parts that arent available in the market.  Decided the best way to do this is the design them and then cast molds from fiberglass, in order to recreate the parts in FRP.  I want to design some front fenders that are wide enough to accept the 9 inch wide wheels without massive camber.  These already exist.  I know.  But what I would also like to see is a fender that will accept this width of wheel and tire, but allow the suspension to be lowered more and not suffer fender damage.  Therefor, I envision a high fender lip with some width to it. 

I have been playing with the shape.  Originally thinking I could template the design, transfer it to sheet metal, cut an old fender and use the mounting points from the donor fender, and attach the sheet metal fender design to the mounting flanges.  Then of course mold it, and create a pretty, light FRP product.  This would effectively remove some of the angles that the stock fender shape has.  I also thought, that if I am doing that, I might as well do the front bumper too.  This has proven not easy to do with the same fashion as the sheet metal fender.  So I got thinking about using foam boards the build up and then shape the front, and then cast that with fiberglass mold.

I am after something more modern and aggressive looking.  I spent a lot of time looking at cars from JGTC and their aero designs.  Now I am wondering how do I cast fiberglass over a big ass foam bumper shape?  The foam wont survive the reaction without a barrier will it?

These are just my thoughts.  Maybe it will spark some discussion.
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Re: Making fiberglass molds from foam...
« Reply #1 on: November 17, 2011, 10:24:57 PM »
Reproducing fiberglass parts with consistent quality is a tough job, FWIW.
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Offline smackhead999

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Re: Making fiberglass molds from foam...
« Reply #2 on: November 17, 2011, 10:35:37 PM »
I have done quite a bit of research on vacuum infusion methods for quality parts, but am really just stuck with making the molds around something that has the shape that I want.
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Offline BeatTheTunaUp

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Re: Making fiberglass molds from foam...
« Reply #3 on: November 18, 2011, 07:57:48 AM »
I"m in the planning stages of making a fiberglass engine cover for my motor swap in my boat.   An easy tip I heard, is to just cover your mold with wax paper to protect it from the resin.   There is also a non stick agent you can spray on your mold as well.
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Re: Making fiberglass molds from foam...
« Reply #4 on: November 18, 2011, 08:19:31 AM »
Make it in three pieces (center bumper section, L&R fender extensions), and rivet them together. I saw the (95% complete) widebody from a JSS (JGTC precursor) FB for sale for like $700 IIRC.

Offline gc3

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Re: Making fiberglass molds from foam...
« Reply #5 on: November 18, 2011, 09:53:28 AM »

I am after something more modern and aggressive looking.  I spent a lot of time looking at cars from JGTC and their aero designs.  Now I am wondering how do I cast fiberglass over a big ass foam bumper shape?  The foam wont survive the reaction without a barrier will it?

These are just my thoughts.  Maybe it will spark some discussion.

bondo over the foam will seal it, and easy to smooth out. vacuum bagging process is fairly easy, once you get the hang of it its not too hard to get fairly consistent results. just make sure you wax/mold release the bondo/foam mold really well or you'll destroy the mold easily.


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Re: Making fiberglass molds from foam...
« Reply #6 on: November 18, 2011, 04:46:07 PM »
Buy some books and start small.  A project with a lot less material costs and simpler molds would be a better choice to get into composite work.  The bigger the part the better the o'  :o moment when it doesn't release correctly and you screw up the parts you've just spend days and weeks prepping. 
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Offline smackhead999

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Re: Making fiberglass molds from foam...
« Reply #7 on: November 18, 2011, 05:03:04 PM »
Joel, I intend to do some practice work before going all out.  I am not really sure how the molds with come out with this method, because I am gonna have to shield the foam from the resin with something.  This will definitely not give me a mold quality surface (smooth).  I will probably have to do some work to the molds one its been cast to smooth the surfaces out.  Also, because it would be almost impossible to vacuum bag the mold onto the foam, I am sure there will be some voids regardless if I were to achieve a glassy smooth mold surface from whatever is used to protect the foam.

I have seen packing tape and aluminum tape used to do this.  But it will wrinkle and show the edges where lengths are overlapped.
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Re: Making fiberglass molds from foam...
« Reply #8 on: November 18, 2011, 08:03:59 PM »
wait im confused. you want to make a foam mold, then a fiberglass mold, then FRP?

first off, what are you consider FRP? fiberglass is an FRP....?

2nd, whats the 2nd fiberglass mold for?

why not just use the foam (with bondo sealer as i mentioned earlier) mold to make the fiberglass part?

if you have a vacuum pump or a venturi, vacuum bagging shouldnt be difficult for fender sized parts. if you are careful to not ask for too much stretching, regular clear garbage bags will work for your bag as well. (thick ones)

if you can't afford peel ply and breather material, im pretty sure you can find alternatives that are more household.

Offline smackhead999

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Re: Making fiberglass molds from foam...
« Reply #9 on: November 18, 2011, 08:24:07 PM »
Make a model of the parts from foam.  Cast a fiberglass mold around it.  Use the fiberglass mold to reproduce the parts I need from a quality, bagged method.  Sorry if that didnt make sense.

Fiberglass IS frp.  Carbon fiber IS frp.  Fiber Reinforced Plastic.  It doesnt really matter what the fiber is.
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Re: Making fiberglass molds from foam...
« Reply #10 on: November 18, 2011, 08:27:53 PM »
Make a model of the parts from foam.  Cast a fiberglass mold around it.  Use the fiberglass mold to reproduce the parts I need from a quality, bagged method.  Sorry if that didnt make sense.

Fiberglass IS frp.  Carbon fiber IS frp.  Fiber Reinforced Plastic.  It doesnt really matter what the fiber is.
oh ok, i see. you are making a negative mold from your initial positive foam mold/part.
that makes sense.

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Re: Making fiberglass molds from foam...
« Reply #11 on: November 19, 2011, 01:00:17 PM »
The quality of your final part can only be as good as the surface finish your mold is made from.  Get the parts as close to "perfect" as you can before making the molds.  I'd recommend the foam for forming, then a skim coat of bondo followed with smoothing and blocking out to ~100 grit.  Then you want to use a catalyzed primer in order to seal the bondo, or else you run the risk of the mold not releasing the bondo.  Then get that primer smooth down to 1000 grit, compound and wax.  At this point you can make the mold.  Using a film release is the safe way to go, but it does not give you a surface finish that is as nice right out of the mold.  Several layers of wax makes a nicer surface.  Then gel coat, and build the mold.   :yay:
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Offline smackhead999

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Re: Making fiberglass molds from foam...
« Reply #12 on: November 20, 2011, 12:17:10 AM »
Sounds like you have done this before.   :D
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Offline birdman2447

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Re: Making fiberglass molds from foam...
« Reply #13 on: November 20, 2011, 07:40:45 PM »
http://forums.bimmerforums.com/forum/showthread.php?t=1666695&page=2

I dont know his exact process but this could be an option for you?

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Re: Making fiberglass molds from foam...
« Reply #14 on: December 07, 2011, 11:17:56 AM »
You can lay fiberglass directly over urethane foam. It works great. I've done it many times. Once set up you simply clean the foam out from underneath. I use Marglass as a first filler coat (kind of like putting the gelcoat on last) as it has short strands of fiberglass in it and is much harder than bondo. If you are careful about sanding the foam you can make a nice thin fiberglass part without the time needed to molds. I did lots of the parts on my Mazda this way. The faom weighs almost nothing but it is not cheap. I probably would have saved hundreds of dollars if I would have just bought a kit!

 

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