Friday, 30 November 2007 09:00

Fabricating Parts Requires Plugs, Molds and Limitless Imagination

Written by Rich Evans

In last month’s article, I talked about our race against the clock to complete the customizing of the Ford Mustang GT in time for SEMA. Now that the dust has cleared, I’ll explain in more detail the mock-up procedure for our new parts, including how our plugs were made.

A plug is a prototype part used to make a mold of the final part and subsequently to produce the part over and over again. We used the same process that has been used in the fiberglass parts industry for decades, which was actually adapted from the old process of wax molding. Wax molding goes back several centuries and used wax molds and  liquid metal to make the metal parts. In our case, we used polyurethane foam, liquid foam, and fiberglass.

Once the project was approved, my concept drawing determined that I needed to fabricate about sixteen custom parts. This was going to require some help. I called my friend Benjamin Esquivel, a master with twenty years of experience at fiberglass tooling and prototype design.


He started in the camper shell business, then moved on to making custom fiberglass parts for the motorcycle racing circuit. His talents also include architectural design and making carbon fiber bodies for funny car dragsters. With his help, we made all sixteen fiberglass parts and also have the molds to continue production.

We used 3 oz. fiberglass matting, resin, and catalyst for our splashing, which I will explain in a little bit. We used 4 lb. polyurethane foam to shape and make prototype plugs of the hood scoops, side skirts, lower parts of the bumpers, and the rear wing.


For the most part, the front and rear bumpers were made using molds made from cardboard around the car and liquid foam. For larger areas, the 4 lb. polyurethane foam is impractical. We need to mock up a quick and dirty cardboard mold to pour the liquid foam into.

Mocking Up Parts    
Start out by drawing with a grease pencil where the scoops will go.

    Rich tip:  Before proceeding, it is important to stress wearing proper gloves. It can really mess you up if you get these toxic materials on your hands and then rub your eyes or other sensitive areas. I always use MicroFlex diamond grip gloves which, in my opinion, are the best quality gloves in the business.


In a little work area we created for the purpose, the hood was splashed by laying down a sheet of 3 oz. matting and coating it with resin, mixed with 2% catalyst. Make sure the resin completely saturates the matting. Now add a second piece of matting on top, giving six total ounces of fiberglass matting.
Rich tip: The fenders were taped over with masking tape for the eventual over hang from the splashing.

We continued to saturate, flipping the piece over to saturate through the other side. Next we laid this matting on top of the hood and formed it with our hands

    Rich tip: 
Squeeze all the air bubbles out of the matting. The easiest way is by using a fiberglass roller.


After splashing the hood, we mocked up foam pieces previously cut roughly to size and drew contour lines to follow the shape of the hood. Next the pieces were attached to the hood with bondo. We continued by drawing more contour lines and reference markings for shaping.

The concept drawing was always nearby to keep us on track sticking to our original design. To shape the foam faster, a cheese grater was used for the rougher cuts, then sanding blocks with 36 grit sand paper were used for fine tuning.


Now seal up the foam plug with 3 oz. fiberglass matting. It should look like a mummy. From here, we used bondo and did our usual body finishing techniques (see Custom Corner at www.autobodynews.com). The only difference is that going by our reference markings on the foam, we used different colored hardeners with the bondo; that way it was evident when to stop sanding when we sanded through one layer of bondo and got to the next color. This facilitated keeping the finish looking even while we mirrored our other sides. Finally, we finished off our plugs with sealer, primer, and then polished them up with 600 wet sandpaper.


Plugs for bumpers

Due to the mass of the bumpers, a slightly different procedure was called for to accommodate larger areas. First a mold was formed around the car where the bumper would be. Plain cardboard was sufficient since it wasn’t really necessary to make a specific shape, just leave enough excess foam to carve away when shaping.

When the cardboard mold was mocked up, we poured in a mixture of liquid foam mixed 50/50 with catalyst. As this foam dries, it expands through the open area and leaves us with a large foam shape similar to the 4 lb. polyurethane foam that was used for the scoops.

The rest of the process is pretty much the same.

    Rich tip:  Carve away on only one half of the car. Use this half to make reference templates to mirror the other side. It took seven templates made out of cardboard and bondo for the front bumper alone..

Once each plug has a smooth, polished finish, it is time to make the molds. This is a whole different process that requires more detail and a lot of steps. So we’ll end here for now. Next month’s new article will teach how to make your own molds from your new plugs.


With these procedures, the sky’s the limit on how many different custom parts can be made from fiberglass -- including your own custom body kit. With these molds you will have the tools to create your own production line. Until then, try making your own plugs and I’ll see you next month to finish everything off.
Rich Evans, owner of Huntington Beach Bodyworks in Southern California, is an award winning painter and fabricator. Currently he is offering workshops at his facility so he can share his special techniques to other industry professionals. For more information about Evans, visit www.huntingtonbeachbodyworks.com.