Thoughts on Fiberglass Rear-Skirt Design

[stevey_frac]

Originally Posted by MetroMPG

That'll be the polyester resin. You want epoxy - it'll say so explicitly on the packaging.

Yes, i caught that. You and I both wrote our posts at the same time, and I wrote mine without knowledge of the contents of your post. :P

That's why i'm going after this Rayplex company. I think they're less expensive (especially in larger volumes) and i also think they have higher quality materials.

[MetroMPG]

If it helps at all, a brand name I know of for marine epoxy fiberglass repair is "West System".

[stevey_frac]

Originally Posted by MetroMPG

If it helps at all, a brand name I know of for marine epoxy fiberglass repair is "West System".

Are you certain that epoxy resin is stronger, and that it's not the fault of a crappy crappy tire product? It just seems to me like polyester plastic is fairly resilient...

EDIT: Nevermind. I looked it up. Epoxy resin >>>> Polyester resin.

[evolutionmovement]

West Systems make good products. Used them to repair boat damage caused by the maniac owner of the marina while transporting them from storage to water and back and really beats the Bondo stuff I had used on cars in the past. For any kind of auto body, I recommend marine products as they are designed to withstand a more harsh environment, though the cost often reflects that so it depends on how permanent you want the job to be.

[stevey_frac]

I think my project for this week (read: this saturday) is going to be putting in the synthetic tranny fluid, and fabricating and installing a grill block. That leaves next Saturday wide open for trying to make a mold. I want to think about it a bit more. The way I wanted to do it, i wouldn't be able to get the part out of the mold. Which means i think I have to make the other side of the mold. The female counterpart to the male piece i wanted to make. And that's gonna require more thought.

[Bicycle Bob]

I've done a lot of fiberglass, and taken a course at Abaris, and I'd say that if you are having trouble with polyester being weak on a simple panel, you are not handling it right. In composite work, we count on the strength of the fibers; the resin is just there to keep them lined up. The advantages of polyester are that it is compatible with Bondo, and MUCH EASIER TO SAND AND POLISH. The more variable cure times are a great convenience. You can get better properties from isophthalic types, or the strength and toughness of average epoxy from vinylester resin, but it has a short shelf life, so you have to find a shop that uses it to buy a gallon. The advantages of epoxy are low shrinkage and a true water seal, even over rust. It also has less odour and a more manageable health hazard. There is one epoxy, SB-112 from System Three that is compatible under bondo and polyester, but you can usually put epoxy over the esters.

[Bicycle Bob]

Originally Posted by stevey_frac

Keep in mind i'm a computer geek. I have the fine motor control of a spastic 2 year old.
EDIT: Wait.. i re-read that, and i know what your going for. It'd be fairly sexy, and not nearly as much art as i thought it was. :P

<grin> Chet Kyle remarked that some of the early entries at the IHPVA looked like they were build by blind men wearing boxing gloves.

Getting from that shape, defined by splines, to a finished product, can be tricky. One way would be to pre-coat one side of thin wooden splines with polyester gel-coat. (It will stick a lot better if you heat the wood first, so the cooling air inside sucks the resin in, while the heat thins it out.) That way, you can build up almost a whole mold surface from splines, and glue them to a backing to hold the shape. Spray foam caulking and plywood might be OK for that, but epoxy putty, blocks, and plywood would be best. Then, you just have to fill the cracks with more gelcoat, sand and polish, and you have a mold. Wax it 3 times before use. Problems over the thickness of the part affecting fit can be sanded out.

[MetroMPG]

Originally Posted by Bicycle Bob

I'd say that if you are having trouble with polyester being weak on a simple panel, you are not handling it right.

Oh, that's a certainty (in my work to date)!

For one, I didn't use enough layers, and for two, the kammback has a cardboard core. Can't foresee any problems there, eh?

[stevey_frac]

Originally Posted by MetroMPG

Oh, that's a certainty (in my work to date)!

For one, I didn't use enough layers, and for two, the kammback has a cardboard core. Can't foresee any problems there, eh?

Fibreglass Questions: Since you guys have worked with it before.

Do i have to wait between applying layers? And how far will one of those kits from Cdn Tire go? Could I make one skirt with one box? or would it take multiple boxes? Do I need to have a core of some sort (i could probably use some thin plywood) or can i just schlep enough fibreglass onto it and it'll work?

Also, i was going to do a kind of raised flat panel, and then i wanted it to have like.. a 1 inch smooth section to rest agains the edge. Can i make the panel large enough to cover the the whole edge, then have a section that angles back to rest against it? It's kinda hard to explain...

XXXXXXXXXX                                                                                                                                                        X
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Where the wheel well is 'up' from that, and those flat edges rest against it. The problem is.. How would i get it out of the mold. Or am i going about this all wrong?

-Steve

[wyatt]

Here is a "simple" method of building fiberglass parts. I think it goes with what bicycle bob had said, but instead of using the wood, you use foam. You can fiberglass over both sides of the foam and have a thick part, or do one side and mechanically (scrape, hack, scratch, sand) remove the foam.