We left you last month after constructing the subwoofer enclosures, and previously I talked about how Chris and I built the mechanism to convert our 2002 Civic demo car to center-drive. This time, you'll see how we built the custom center seat that became the control center for our machine. Our original idea was to simply use an aftermarket seat for this purpose, but eventually we decided that nothing was available that would really fit the style that we were planning for the car. As a result, we built our seat from scratch using our fiberglass techniques. This is the first article in which we've discussed these techniques, and you'll see them being used extensively from here on as we construct the custom interior for our Civic.
The seat is a fairly high-stress part in any car when you consider some of the forces that are exerted on it. To make our seat very strong, we first built a 1" square tube steel frame that would eventually support the fiberglass seat. This frame was welded together and bolted into the car using some of the factory parts. The front of the frame attached to the inside factory seat bolts on both sides, while the back was supported by a factory steel brace that ran along the front edge of the stock rear seat. This frame was also gusseted with another tube section that was cut at a 45-degree angle on each side and welded to the corners of the frame.
With the frame complete, the next step was to make the seat. We used MDF to make frames for each of our panels first, then fiberglass to create a solid surface over the frames. This is a technique that you'll see us using quite frequently, since it is fast and effective. We came up with a style for our seat that we liked, then cut the shapes out of cardboard. Those shapes were then cut out of MDF with a router to make the pieces for our frame. These were built with a 3/4" MDF solid base, with another ring around the outside edge that was also cut out of 3/4" MDF. The rings were then glued and nailed to the solid bottom pieces, forming an inset area that would eventually contain the seat cushions. Finally, the edges of each piece were rabbeted on the router, creating an edge to later attach the fiberglass to.
The bottom of the seat frame was built the same way, although dual rings were used to make the bottom cushion area 1.5" thick for added comfort. The back and bottom sections were attached together with more MDF, and the sides were placed at slight angles to promote comfortable seating. The rear view shows some of the bracing that holds the frame together, attached to the main seat sections with super glue. A close-up of the rear view also demonstrates how the steel sub frame attaches to the seat, with 1/8" steel "wings" welded to the sides of the main frame. The seat bolted to this frame from the front, with the seat cushions concealing the bolt heads for a stealthy effect.
One other unique feature we wanted to incorporate into our seat was the ports for the 15" subwoofers. This really gives the listener an interactive experience with the bass, making it very intense. With our completed frame removed from the car, the rings for the ports (the open areas on each side of the seat frame) were attached with super glue to begin the framing process.
The frame was then re-installed into the car for the fiberglassing procedures. We always like to have the panels installed in the car whenever possible, as it greatly lessens the chance of warpage. The sides and back part of the seat frame have also been added, which create the seams where the seat will eventually mate up with the other trim panels in the car. We also covered the area under the seat with plastic sheet before fiberglassing to keep the fiberglass off the floor of the car in addition to protecting our emergency brake mechanism. It's also important to tape off any areas of the frame that fiberglass will harm, such as the inserts sections for the seat cushions. Any fiberglass that gets in will only cost us time later, when we have to grind or sand it out.
With the frame completed and bolted down, it's time to start the fiberglass process. The first step is to stretch material over the frame, forming its three-dimensional shape. We like to use thin material, like stretchy polyester grille cloth or cotton, which is available at any fabric store. The thin stuff is very easy to stretch, and it is much less likely to warp than thicker materials like fleece. It is stretched tightly over the frame, and stapled into place (super glue can also be used to attach it in areas where staples won't work). Fiberglass resin can then be brushed onto the cloth, which will form a solid surface when it dries. We use a basic, general-purpose, polyester-based resin for all of our projects, since it's easy to work with, cheap, and readily available.
While the hardened resin will form a solid surface after curing, the cloth is fairly thin and brittle, so additional layers of fiberglass must be added. We used thin fiberglass mat, which is actually long strands of fiberglass that are held together in a sheet by a binder. The binder breaks down when resin touches it, making the mat very flexible and easy to form over curves. This mat is rated by weight, with heavier weights denoting thicker mat. We used thin, 1/2-ounce mat exclusively, building more layers when we needed additional thickness. The mat was cut into 2"- or 3"-wide strips, then torn into square pieces that made it very easy to lay over complex shapes such as our seat. After applying six layers of the mat, the seat was very strong and durable.
The mat tended to make the surface somewhat uneven, so we applied a layer of DuraGlas, a reinforced body filler, over the curing fiberglass. It's very important to do this with the piece still in the car, as it can cause warpage. It's also important to let it cure for at least 12 hours before removing it. DuraGlas is very difficult to sand by hand, so we used angle die-grinders with 2" sanding wheels (available at major home improvement stores) to grind down the surface of the panel. This made the surface fairly even, but it still required a layer of Rage Gold body filler and some hand-sanding to make it perfect. We'll cover this procedure in more detail next month, so check it out. With the seat shape complete, we checked the fit from the rear, and also the fit of the port opening to the subwoofer enclosure. With the seat complete, it was ready for primer and paint, but we'll save that for another day.
Check out SteveBrownUniversity.com for information on some unique opportunities to learn these techniques hands-on, and keep those questions coming to sbrown@alpine-usa.com.
01: The seat construction started by first building the structure out of steel. One-inch-square tube stock was welded to the car for the basic frame. | 
02: The seat itself began with the laying out of individual sections using MDF. These pieces were created using a router. | 
03: The seat sections were super glued together in the desired shape inside the car. |
04: This shot shows the bracing behind the seat sections, along with the temporary blocks used to hold the seat on the frame. | 
05: Metal brackets were welded to the basic seat frame, then drilled and tapped so that the seat could be bolted to the brackets from the front side | 
06: The seat frame was pulled out of the car, and the frames for the subwoofer ports were built using MDF. |
07: The seat frame was placed back in the car, and the sides and back for the seat frame were created using MDF. Notice that the grille cloth for the ports is already in place | 
08: The seat frame was then stretched with grille cloth and covered with fiberglass resin. | 
09: The grille cloth was strengthened with six layers of fiberglass mat to form the seat's structural surface. |
10: DuraGlas was applied to the surface while the seat was still in the car. | 
11: Once the DuraGlas was cured and sanded with the grinder, Rage Gold body filler was used to smooth out the rough edges and complete the shape | 
12: This rear shot shows the shape of the seat back, along with the arc-shaped mounting surface for the bottom panel. |
13: The port is now mated with the seat, and shaped to prevent port noise. | 
14: Here's the completed seat, ready for polyester primer and paint. | |