Anyone using fiberglass for body construction?

[jgmick]

I'm thinking of taking a run at making a fiberglass shell for part of an excavator, maybe part of the crew cab or top. Do any of you folks do that and/or can you give some advise?

I looked at some stuff in the local hobby shop and did some on line searching. Seems like a lot of stuff out there and I'm not sure where to start. My experience on this stuff is limited to some minor boat repairs. I can make a mold and/or make a master pattern out of wood and use RTV to cast a mold.

What's the best way to dive into this?

[JAMMER]

What I do just get some fiber glass screen and get some fiber glass at your local part store . A piece of glass would help but not necessary a piece of metal will work. then lay the fiberglass screen out over the glass and spread the fiber glass you got at the parts store over it. When it hardens break it loose from the glass or metal you will have a starting point to make what you want. If you spread the fiberglass thin enough over the screen you will be able to bend it. This should get you on your way. Ed

[jgmick]

I'm heading toward more of a 3-D shape. (Like a shoe box cover) Edges curved and corners rounded. I have banged out most of the details for a mold, now I have to figure out the materials.
Among other things I'm trying to decide on a gel coat layer or not. I'm not sure that gets me anything. I assume I will have to wet sand and fill the finished surface and fair it into the sheet metal side walls with body putty. The gel coat doesn't really get me much.
I like your idea of using a piece of glass and making a really thin layer that would be bendable. That's slick. May have a use for that.

[frizzen]

I've never done a glass layup for something in this size, but you're going to have issues trying to get any of the corners of the mold to come out right.

I would try to make up a female mold, so you'll have much less finish work. Use fiberglass mat (not cloth, it won't be as flexible). Youre going to want to spend time breaking up the mat enough to get it down into corners. I wouldn't mess with gel coat until you know if you can get a reasonable pull from the mold that won't take finish work.

I might even try to go with a can of the 'fiberglass reinforced bondo' instead of doing a layup. It's harder and stronger than pink bondo, and shouldn't put up as much of a fight to get the corners to take, or the inside smoother.

[ramjetexpress]

have you thought about a heavy Lexan ? There are lots of how to make a vacuum mold on google and what not . Your wife may not like the use of the oven

[jgmick]

[QUOTE=frizzen;I might even try to go with a can of the 'fiberglass reinforced bondo' instead of doing a layup. It's harder and stronger than pink bondo, and shouldn't put up as much of a fight to get the corners to take, or the inside smoother.[/QUOTE]

I have looked at the Bondo line and thought that the filled stuff would be good to use as part of the layup. Have you used the reinforced stuff? Could it do the job all alone in corners/edges without any mat?

I have done some molding with other materials and the mold will be able to be taken apart in sections, so I'm not to concerned with getting it to release the part.

[frizzen]

I'd feel pretty comfortable with trying a pull with the 'glass reinforced bondo. The green one with chopped fibers.

It's a little harder to work than bondo because it's stringy, and it'll probably be a thicker wall than you could pull with straight 'glass, but should hold better detail. Try to get it perfect before it cures, sanding sucks.

[jgmick]

I'm kind of committed to the sanding op after molding. There is going to be a lot of stuff that will need to be added/filled in addition to the material finish. (I agree, it sucks.) but I need to fill/prep it for paint. Thicker wall doesn't hurt. There is space available for quite a bit of material. I was planning on adding some ribs on the inside for stiffness anyway.

As far as pulling it out of the mold, all of the internal corners are filleted in the mold and the edges/corners of the mold can be removed individually so I think I'll be OK with that.
(No such thing as too much wax on the mold.)

How well can you add additional material to a cured part? I assume scuffing it up with coarse paper to break the sheen will work. Any surprises there?

I think I'll get some and just try it out on some scrap stuff and learn to work with it.