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Originally Posted by CAM2  Fiberglass resin doesnt eat up the stock plastics but it doesnt adhere or bond to it too well either without through holes drilled in it or grinding it......Peace |
So roughing up the plastic with 80 grit wouldn't be enough for a decent bond? I was concerned about that, since some plastics just don't want to stick to fiberglass resin. I guess that leaves fiberglass more as an option for making fairing parts from scratch, rather than making repairs.
To make a custom fiberglass fairing part, either a mold or a one time use form will be needed. A mold can produce a better finish on the part, but it consumes a lot of time and materials for something you only intend to use once. Molds are better suited for jobs where you need to make more than one part and they need to be identical. This leaves a single use form as the better option for a part you only need to make once.
Start by locating some styrofoam (expanded polystyrene). It's usually white, but sometimes blue. Polypropylene (spelling?) foam is very similar to styrofoam, and it seems to be becoming more common for shipping packing, but it's kinda rubbery, so it's not good for a form. Another common foam is urethane foam (usually brown), but this is another foam to stay away from since it produces toxic fumes when heated above a certain temperature. If you have any doubts about whether a piece of foam is urethane foam or styrofoam, put a few drops of gasoline on it. Urethane foam isn't bothered by gasoline, but styrofoam melts in gasoline.
Fiberglass cloth comes in varying weights. Boat supply and aircraft supply companies that sell fiberglass normally stock 10 ounce and 8 ounce cloth. I've also seen 6 ounce listed in a catalog, but I've never worked with it. If my memory isn't off, all of the cloth I've seen sold at autoparts stores (and the automotive section at Walmart) is 8 ounce. Cloth sold at hobby shops is 2 ounce and lighter. 10 ounce cloth is stiff and can be difficult to fit into some curves. It's best left for high strength applications that you won't need for a bike fairing. 8 ounce cloth is a better general use cloth, is more flexible, and has makes parts with a good strength. 2 ounce can be worked into some really tight bends, but will require a lot more layers to make a part with a decent strength. The hobby shops sell it for uses such as making R/C planes or bodies for R/C cars. If you need to make a small complex part like a scoop with compound curves, 2 ounce might be the better choice, but remember that extra layers of cloth will be needed for strength.
Back to the foam...
If you need to build up the needed shape from more than one piece of styrofoam, it can be glued with plain old Elmers white glue. A hot glue gun (the low temp ones are better for this) is another option, but the styrofoam insulates the glue and it will take longer for the glue to cool off and set. Spray adhesives usually contain solvents which can eat styrofoam, so it's best to stay away from them.
The fiberglassing can be done on the bike, but this will get messy and you'll need to cover the bike somehow to keep the dripping resin off the bike. The better option is to make your styrofoam form so that it can be removed from the bike and do the fiberglassing off the bike.
If you are sanding or sawing (a hacksaw blade, without the hacksaw, is good for quick cuts) the styrofoam, wear at least a dust mask. You don't want to get the stuff in your lungs. The styrofoam can also be carved with a sharp hobby knife or a razor blade. For dishing out a concave area, you can bend an old hacksaw blade to the approximate shape, heat it with a propane torch, then use it to melt/carve out the concave. Keep in mind that the styrofoam will melt away from the hot metal, so don't try to cut out too much on the first pass. For cutting a round hole, find a piece of metal tubing a little smaller than the desired hole, heat it with the torch, then stick it into the styrofoam where you want the hole. Keep in mind what parts of the bike are behind the styrofoam, when using hot metal to cut/melt the styrofoam.
Once you have the styrofoam shaped the way you want it, remove it from the bike and apply the fiberglass (using epoxy resin) as described in my earlier post. After the layers of cloth and resin are applied, set the parts aside to cure overnight. Now we come to the one time use part of the form... Dig the styrofoam out of the fiberglass part. Get as much out as you can, then use a gasoline soaked rag (wear gloves) to melt out the remaining pieces. A dremel can be used to trim the edges of the fiberglass to the finished shape (again, use a dust mask or a respirator when cutting or sanding the fiberglass).
