Front Clip Mold Those of us that have lightened our cars for racing learn quickly how much easier it is to get weight out of the back of the 928 as opposed to the front. Our front clip project last year taught us that the hood, two front fenders, and front bumper cover weighs 58 pounds. That s without the chin spoiler! So I decided to make a mold of a complete front clip so we could make our own carbon fiber or lightweight composite front end. I think we are on the right track when we finished yesterday, the MOLD for the part (without the wooden struts) weighed only 30 pounds, and it is a lot heavier than the part will be. We anticipate a 20 pound-or-less front clip, a savings of 38 pounds off the nose of the car. We will also gain a certain cost advantage as anybody who has rumpled a front fender or hood can attest. Now, if/when we rumple a fender we can make another! It s a good thing that a man s memory is poor and selective. Part-way through this process I remembered that I hate bodywork. I came to that conclusion making the plugs and molds for our fender flares, and again on the rocker panels. If memory was not poor there would be no 2 nd child born by any woman, nor 2 nd fiberglass projects. Still, the benefits out-weigh the temporary insanity of it all, and we pressed on.
Before I continue let me introduce Myles Lowery from our staff to those of you who do not know him. Myles has an Industrial Technology degree from the U of WI, and is the fella right behind me assembling kits and making parts. Had he not been here to assist me with this project, I probably wouldn t have even attempted it. His knowledge and enthusiasm was invaluable. The car we selected for the mold was a late-model 928 with 400,000 miles and a blown engine. The body was straight, and that s what was important. The late model car starts with a lower coefficient of drag than the early cars, so that s why we went with it. The finished part will have the headlamp stickers applied to it, so it still looks like a 928, and we can mold a front clip with or without fog lights. We started by removing the windshield wiper assemblies, sprayers, headlights, fog lights and parking lights. Then we fitted and leveled the hood as best as we possibly could. Then we filled all the seams between the bumper and fenders, bumper and hood, the cowling, and headlamp holes. Plugs were shaped to the headlamp holes to close them off before the filler was added.
Days and days of filling, sanding and leveling followed. We even found flaws in the OEM panels and fixed them to make them more aerodynamic and smoother. Before we got too much further, we thought we better pull the molds from the fog lamp areas. These extra small castings would allow us to make front clips in the future with or without the fog lamps molded in, depending on what we wanted.
Having pulled the fog lamp molds, we then stuffed them with structural foam also, and filled them in. Again more sanding, shaping, and filling. The fill areas went from being to just an inch or two on either side of the seams to almost 10 on each side of the seams. After each finished block sanding, the dust was cleaned and the car was marked with a clean hand and a Sharpee. A L meant a low spot that needed to be filled. An H was a high spot that needed more sanding. An X meant that section was perfect DO NOT TOUCH! Between our other work, this took literally weeks slowly changing everything to X s. We were VERY fussy.
Finally it was time to put the car into primer. We used a sandable filling primer to hide and fill any small scratches.
...and that wasn t the end of the sanding but instead the start of the next generation of sanding. Now we wet-sanded the primer exposing high and low spots that we couldn t even feel before When we felt we had it right, it d get another coat of paint in a contrasting color and then wet-sanded with blocks to ensure we had it right.
When the front clip could not be improved anymore, it got another coat of filler primer, and then a final wet sanding with 600 grit, 800 grit, and 1200 grit.
Now its time to wax. And wax. And wax. Four coats of industrial-strength mold release wax are applied. This is a very hard wax that will fill imperfections and more importantly assist with the mold releasing from the plug. Each coat of wax is applied, let to set up a bit, and then buffed with power buffer to a high gloss shine. Then you ruin your new shine by doing it again apply the wax, let it haze up, buff to a shine. Repeat 4X. Yikes! This is the final photo of the plug just before we start casting the mold around it. The finish on the plug will be exactly the finish on the actual part that comes out of the mold.
Then a coat of PVA is sprayed on and let to dry. The PVA is another mold release agent that puts a thin saran-wrap-like film over the entire piece. When the PVA is dry (12 hours) the white gel coat was sprayed on. This was let to dry 24 hours. The Gel coat is the first coat of resin, and is designed to impart a smooth glossy finish onto the surface. In these pictures, we have started trimming omni-directional short strand matt and test-fitting it over the gel coat just prior to hitting it with resin for the first time.
Time for the first coat of fiberglass resin. Mixing small batches, we wet the fiberglass matte down with brushes. The brushes dab the resin down through the matte to remove the air bubbles and confirm penetration. Cardboard is added in the wheel wells to hold the wet matte up and around the lips that we wanted.
A day later, another layer of heavy chopped omni-directional matte is applied in the other directions and also wetted down and allowed to harden. Then a 10-ounce woven fiberglass cloth is laid down over the top of the mats, and it is soaked in resin too which bonds it to the other layers. Molds have to be heavier and thicker than the parts you pull from them, so at this point weight, reinforcement and layers is not a bad thing, it s a good thing.
Time for cribbing. Wooden reinforcements or cribbing need to be added to the outside of the mold to hold the fenders and panels exactly in the same position they are in now when the mold is off the car. And, the mold needs to be strong enough to push and shove on when we are laying up the finished part. We started by leveling a board on stanchions across the front of the car, then measuring our distances down to the car, taking measurements every inch. This pattern was transferred to plywood, and enabled us to cut a rib to exactly the outer shape of the mold at the point we wanted. Five of these ribs were created and added to the crib. The cribbing is carried all the way to the nose of the mold, and then attached to each other with 2X4 s. The finished crib is flat and level on top so that, when we flip it upside down, it will sit flat on the floor when we make the new part.
Imagine what would happen if the mold did not sit flat upon the floor, or if it was allowed to flex in any direction. The mold would have a twist in it, and the part would have that twist as well, and ultimately, it would not fit on the car!
Pulling the mold! Truly the most exciting day in this project. The cribbing is done, the fiberglass is all set up, and all we have to do is get the mold stretched and off the car. You ll note that we set the cribbing aside and did not affix it to the mold just yet. Because of the shape of the 928, and the fender and cowling lips we had, we knew that we would have to stretch the mold out and up and over all those lips in order to get it to release. If the wooden cribbing was on, we figured there would be no way to do that! Believe me, it was hard enough as it was. It took 3 of us (Ryan, Myles, and I) about 3 hours to work with wedges around all the edges and pop the mold. The look on Myles face pretty much says it all.
The mold was laid into the waiting cribbing, and fixed to the ribs with fiberglass resin and woven cloth to give it the final strength it needed to hold its shape. No 928 s were harmed in the making of this film Here is the car immediately after pulling the mold, and the guys removing the headlamp and fog lamp plugs to return the car to normal. A little sanding and paintwork and this 928 can return to the streets where it belongs.
The finished mold is strong and ready to produce perfect, lightweight front clips for anybody s race car.