by Skammers » Thu Sep 13, 2007 1:49 am
Fenders 101
Note: I am not a fiberglass guy, I have never built fenders before. I was able to examine what other builders have done and built accordingly. As an aircraft mechanic I have some experience with fiberglass but not much. No drawings were made or needed. All cutting was made with a hand held jig saw. A fiberglass guy could probably give you much more information and make it more professional, but then that would take all the fun out of it.
A. Draw a profile of the fender shape you want on the side wall or on a peace of heavy paper. Cut it out and tape it to the side of the trailer above the wheel and stand back and see if it’s acceptable, if not, adjust drawing and repeat step A.
B. Trace the outline onto 3/4 plywood and trim as needed. Using cardboard, draw a full size template /profile of the widest part of the fender keeping in mind the width needed. Determine how wide the fender needs to be and adjust the template accordingly, be sure to leave one inch clearance between the inner fender and the wheel/tire. In the area around the wheel opening be sure to add some extra length of wood for trimming the wheel opening.
Note: I used a small grinder with an adapter for sanding disks, use as heavy a grit disk as you can find, use for shaping the wood frame.
C. Transfer the shape of the template to plywood and start cutting the cross section pieces needed to complete the mold, use the same template for all the cross sections, only shorten them up accordingly as you go from end to end. As the cross sections become shorter be sure to keep using the master template to maintain the correct contour. Use the grinder to ajust conture as needed. Attach the cross section pieces using screws or other sutable means.
Note: Be sure to attach two straight 2x4’s to the back side of the mold to ensure it remains flat.
D. Repeat step C for the other side keeping in mind the need for a left and a right fender. You don’t want to make two fenders for the same side.
E. Remove the 2x4’s holding the molds straight, and screw both fender molds together back to back. Fabricate some kind of holding fixture so both sides can sit on a table for sanding. Due to the methods and tools available for assembling the mold some differences will be apparent. Using a sander with heavy grit paper sand both sides of the form to achieve asemerty as much as passable. Mark and trim the wheel well opening as needed. When satisfied its close enough reattach 2x4’s to keep the mold straight.
F. Applying foam filler to the mold. Using tape or other suitable means tape up the inside/bottem of the wheel well area to limit the amount of foam as it is applied to the top side of the mold. Purchase some polyurethane two pack foam from your local insulation supplier usually under thirty bucks. Don’t even think of using the stuff from the local building supply house. Fill the areas between the plywood sections that contour the fender as needed. When the foam has expanded and is hard, it’s vary lumpy, use the grinder to remove the high spots then sand it down to match the contour of the mold. Use caution as you start getting close to the finish grade.
G. Apply a layer of fiberglass mat, don’t use cloth as it is thinner and harder to sand. After the glass hardens, sand off any lumps or high spots. A power sander is recommended. This is where you have to decide weather or not the fender will be a one off or a mold that you can make more fenders from.
(1) If the fender will be a one time thing, continue to apply several layers of glass, at least three to give it adequate strength. With the final layer you should have a fender close to the desired shape. At this point its time to remove all of the material from the inside of the mold. When removed you will have a fender ready for final paint and finishing.
Note: Be sure to apply glass to several inches on the back side of the mold to facilitate mounting of the fender from inside of the fender well area.
(2) If you want a mold to make more fenders, continue to finish and sand to the desired quality and finish. The more time spent sanding and filling will result in a higher quality product.
H. Ok its time to use the mold/fender you have created to make a negative from which the actual fender will be pulled from. (Ref. see Fenders 201)
