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Posted by: Vacca Rabite Jan 29 2007, 06:56 PM

I like my big black bumpers, but I don't like how heavy they are.

I was thinking that I could make a fiberglass mold out of the steel insert, and then fill that with some high density foam, like modern bumpers. Put it back in the rubber insert, and call it a day.

Problem is, I don't know the first thing about laying up fiberglass.

Help?

Zach

Posted by: okieflyr Jan 29 2007, 07:26 PM

Another, maybe simpler approach would be to make a high density foam log, and carve it to fit it the same space as the steel beam. The higher the density, the more weight. The foam can be worked like a light wood with saws,sanders, and sureforms..

QUOTE(Vacca Rabite @ Jan 29 2007, 07:56 PM)

Posted by: Vacca Rabite Jan 29 2007, 09:53 PM

Are there any good websites for fiberglass layup?

I think using the fiberglass as a mold will be easier then carving a big log of foam.

Zach

Posted by: Aaron Cox Jan 30 2007, 12:09 AM

brando had the same idea!

do it maybe expanding foam to make a mold?

Posted by: Brian_Boss Jan 30 2007, 08:55 AM

In my opinion fiberglass is like a lot of things in that it is very easy if 1) you're not in a hurry and 2) it is not a particularly challenging project. I wouldn't recommend making a 906 cooling shroud in one weekend as your first effort. Where it gets tricky is when you want to make a part as thin and light as possible or you want it to look beutiful unpainted.

I bet that if you do 30 minutes of research on the web then go to a good body supply or boat supply where they can help you select materials, you will do fine.

You could also try a little practice piece to get the feel of the materials.

You don't have to lay up the whole piece at once so, if you screw up, just let it set, grind it back and keep going.

The only area of your project I can see issues with are the points where the bumper shocks attach.

Hope some of this helps.

Posted by: toon1 Jan 30 2007, 09:42 AM

Is it possible to use the steel insert as a mold? If you use foam as a mold you can't use polyester resin, it will eat it. You can use epoxie resin. I like the epoxie resin, there is no bad smell.

laying up FG is easy, once you get the mold the way you want it and you are ready to glass, mix the resin and paint some on the part. Take your FG cloth and lay it on the resin and paint more resin over the cloth.

work small areas at a time or things can turn into a mess quick. If a section dries and you have to go back over it, most resins will still chemically bond even after 72 hours.

I don't know what the insert looks like but what if you cut it all out just making a skeliton, leaving the mounting points, carve a peice of foam to fit behind it and put the top back on?

Posted by: Brian_Boss Jan 30 2007, 09:54 AM

Another thought, how about making a light weight steel support that bolts to the shocks. Maybe just a slightly curved piece of 1/8 x 2" flat with some round tube welded on to mate with the shocks. Put this in the plastic bumper (heavy original steel piece removed) and fill with high density foam.

Thinking is that the rubber skin filled with foam would be stiff enough not to need the fiberglass.

Just an idea.

Posted by: Vacca Rabite Jan 30 2007, 10:01 AM

QUOTE(Brian_Boss @ Jan 30 2007, 10:54 AM)

Posted by: hcdmueller Jan 30 2007, 10:02 AM

I have been thinking about doing the same type of thing with my bumpers. I don't want to permanently modify my car but I want to drop the weight off the ends. Those bumpers weigh a ton. I have a lot of time on my hands at the moment. I was thinking about using metal brackets to attach to the shock absorber thingies and working out a fibreglass shell inside the rubber bumper.

I can't wait to see what you come up with.

Posted by: Aaron Cox Jan 30 2007, 10:41 AM

surfboards - foam core, fiberglass/resin on the outside....

Posted by: sww914 Jan 30 2007, 11:12 AM

You can buy sheet urethane foam from airplane building suppliers. you can glue it together with bondo or polyester glazing putty and shape it with a surform file (cheesegrater) and then finish it with sand screen and sandpaper. Urethane foam works with polyester resin, styrofoam works with epoxy resin. You can't shape styrofoam (polystyrene) with sandpaper, you must cut it with a hotwire. Look at aircraft spruce's website, composites, and then foam.
Epoxy will melt urethane, polyester will melt styrene.
So you can form your foam and then glass right over it just like a surfboard.
Sand the fiberglass to shape, put a gloss coat of resin over the top, sand and paint.

Posted by: WRX914 Jan 30 2007, 11:21 AM

The down and dirty way is to use the green 3m tape found at autobody paint shops and tape the entire bumper to be replicated. Next, you will need to apply a mold release agent to the tape on the bumper (usually rattle can type will work). Next, you will need to buy fiberglass chop-mat, not the woven type... Cut the mat into long strips about 2" wide and 3-4' long. Get a buch of these strips prep'd before you introduce the resin. Mix up your fiberglass resin and begin "painting" the resin to the taped bumper. Once the bumper is coated with resin, begin laying the strips of chop-mat on the bumper. After the bumper is coated with the strips of chop-mat, repeat the process all over again. Do this 5-7 times, let it cure and you will have your mold to make your bumpers...

just that easy.

Posted by: highways Jan 30 2007, 02:56 PM

Having worked as a composite technician in aerospace as well as doing boat repair and composite model sailplane building... I just have to say that
:fiberglass : + :can of worms: + + :tar and feathered: + = :project failure accompanied by record levels of self loathing:


Actually- there are easy ways and hard ways to do things. And there are lots of decent ideas being thrown out here. Just need some pictures, a plan, and some material test experiments to know what you're getting into.


I personally would probably start going about it as okieflyr suggested below. Carve a blank (I like hot wires), sort of 'cut and paste' to shape, add filler to shape even better, then glue into bumper. I would only worry about the density of the foam as far as 'ease of shaping' goes. But when it comes to finished rigidity you can always wrap it in some 4 ounce clothe. Real bumper foam is EPP or Polystyrene- and is very soft. This could be a 4 hour project as opposed to a 3 week mold making project.

QUOTE(okieflyr @ Jan 29 2007, 05:26 PM)

Posted by: okieflyr Jan 30 2007, 07:20 PM

You can use extruded foams from HD/Lowes and it is easy to carve, but will require more epoxy/fiberglass reinforcement because of it's low density.
www.fibreglast.com can provide materials as well as West Marine boat supply.

My reccomendation is to use a 2 part urathane foam, as you can purchase it to make a higher density log. It can be cut in the required curves on a bandsaw, sureformed, drilled, screwed, glued. This will provide better suport on the hot summer days with a hot and heavy rubber bumper on top.

Posted by: highways Jan 30 2007, 07:33 PM

I'd recommend going with Blue foam made by Dow. It's used as insulation and comes in different thicknesses. It's roughly the same density as urethane foam, it's extremely strong in compression- and you don't have to mix it up and make it which is a messy process. You can hotwire cut blue foam or white polystyrene but you can't use heat on urethane- burning urethane produces cyanide gas. I would also recommend high quality epoxies from West Systems (Boating glass supplies) because epoxy is compatable with all foams. Polyester Laminating resin eats most foams, but is compatable with urethane.