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Old 10-17-2008, 10:48 AM
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making small fiberglass parts?

Hello,
I'm doing a custom project and am interested in making some fiberglass bumpers. I currently have them in steel and would like to use the originals for a mold. I want fiberglass due to weight and these will only be supported by fiberglass panels. The part I'm having difficulty with is how to get the fiberglass in the narrow mold once I have a mold made. The bumpers are C2 corvette. Here is a pic.
Thanks,
Scott


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Old 10-17-2008, 04:05 PM
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Once you have the "buck" made , that's the mold name. You take the buck and spray a spray oil ,like Pam........then apply fiberglass cloth to start your mold. Apply enough glass cloth to make it ridgid, the Pam will allow the glass to come out of the mold without sticking to it. Then finish it with putty till you get the smoothness you want, just like doing bodywork.
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Old 10-17-2008, 05:21 PM
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Quote:
Originally Posted by swoodard23
Hello,
I'm doing a custom project and am interested in making some fiberglass bumpers. I currently have them in steel and would like to use the originals for a mold. I want fiberglass due to weight and these will only be supported by fiberglass panels. The part I'm having difficulty with is how to get the fiberglass in the narrow mold once I have a mold made. The bumpers are C2 corvette. Here is a pic.
Thanks,
Scott

Using a lightweight mat (like 0.75oz) will help lay in tight curves or you could use a light cloth. I have no idea how much the bumpers weigh but I wonder how much weight you will save with a small piece like that. Are you sure it will be worth all that extra work?
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Old 10-17-2008, 10:32 PM
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A "buck" is not a mold. I would not use any kind of spray vegetable oil on any part I wanted to paint afterwards. Don't use any kind of silicone spray either

You need to start with a straight part. Get rid of any rust or dents, fill in the bolt holes with water based clay or bondo.


Wax the surface 2 or 3 times with a carnuba based wax such as honey glaze or mirror glaze, giving about 4 to 8 hours between coats. both are available from fiberglass suppliers.

Spray a couple of light coats of PVA, (poly vinyl alcohol),on the bumper, let it cure and now you are ready to gelcoat and begin laying up your mold. PVA is available from your fiberglass supplier.

Spray or brush gelcoat over the surface, make it 15-20 mil thick when wet. Wait 12 hours to make sure it is cured. Then, if you need to, fill in any sharp detail lines with a mix of milled fibers,(1 part) cabosil (3 parts)and tooling resin(1 part) use catalyst. You would do this if there are any detail lines that the glass mat won't tuck into. (you should have some familiarity with how the wetted out glass acts before you try to make a mold, glass won't bend into sharp corners with any less than about 1/4" radius.
For your first lay up use 2 layers of 1 1/2 oz mat, using a isopthalic tooling resin. Roll out ALL the air.

Wait until the laminate gets to a semi cured stage (finger doesn't come away sticky and the really pungent odor is calmed down) and do 4 more layers.

Let this cure for a day or so.



Using bondo, glue a length of 1x6 to the outside of the mold, this will let it sit on the bench without tipping, and keep the mold straight.

Grind off any excess laminate protruding from the edge of the part, then seperate your plug, (original part), from your new mold. Wash off the PVA, then sand the gelcoat surface of the new mold with 600 wet or dry then 1000. polish with 3m heavy duty machine polish and a real wool pad..

The buffing is not absolutely necessary, but it will make a nice finished mold, which will make professional looking parts.

Now that you have a mold, you can wax, pva and repeat all the above steps on the inside of it to build your part.
Do 2 layers of 1 1/2 oz mat , some 3mm coremat and 1 more layer of 1 1/2 mat over the coremat.
That should be stiff enough, and it should weigh less than the original steel part. ( I think 1 1/2 oz mat will lay in those corners ok, but f you have problems with springing back, try the 3/4 oz mat like scrimshaw suggests. Filling the sharp inside corners as described above will help with that as well.

Don't expect it to act like a bumper if you hit anything though.



You can cut you weight alot if you use less resin and glass, or use vinyl ester resin and carbon fiber.

A good, helpful book is called "how to build fiberglass customs and kit cars. " Tex smith publishing. LOTS of real useful stuff in that book.
There is some more involved technique type stuff required to build a mold, but that sums it up.

Here is a thread with a bunch of good links to other places to learn about making molds.

https://www.hotrodders.com/forum/how-...ss-138713.html

You shoud also do a search here and use "mold" as your search terms.

Check out this wiki about making a fiberglass fan shroud, it will give some idea about the actual process of laminating.

http://www.crankshaftcoalition.com/w...***_fan_shroud

NEW INTERIORS has a good pictorial in his project journal about making a mold from a plug he made from scratch.
https://www.hotrodders.com/forum/jour...age=5&reverse=


Hope this helps, mikey
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Last edited by powerrodsmike; 10-17-2008 at 10:52 PM.
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Old 10-18-2008, 12:16 AM
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FYI A buck would be the original part, or The fabricated part, that is usually made out of wood, foam, plaster or other pliable material.

Frank
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Old 10-18-2008, 02:21 AM
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Quote:
Originally Posted by Countilaw
FYI A buck would be the original part, or The fabricated part, that is usually made out of wood, foam, plaster or other pliable material.

Frank

Close.

The part you finally build the mold from is usually called a plug.

A buck is typically a form over which you build a plug or a part, and using that technique is generally called the "buck method".

Lot's of one-off parts are created using the buck method.
The fan shroud in the wiki was made using a foam buck.

I found another good page which goes into a little more detail about making a mold.
http://www.crankshaftcoalition.com/w...***_fan_shroud

Later, mikey
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