The Good Ol’ 80/20 Rule

More time on planning and prepping goes a long way.

In this article, we’ll be exploring ways of manipulating and working with complex fiberglass objects with angles and curves. This will give the enclosure that we’re building perceptional depth while adding structure to its form. I’ve always been a firm believer in the idea that if you spend more time on planning and prep work (80 percent) than on manual labor (20 percent), you can get more accomplished.

First and foremost, let’s talk about shop safety. As always, remember to use safety glasses at all times, and be sure that you read all power tool manuals to ensure that you understand the tool, inside and out — this way, you can make sure that you don’t loose your ten best friends.

Before you start building anything, it’s a good idea to have a design of the enclosure in your mind or down on paper...thus, a building material list can be made. Having a list of all your tools, including any glues, fiberglass, fleece, and hardware, is the best way to be prepared for the task at hand.

For the enclosure in Rob Hephner’s Ford Focus, I needed to go back to the table saw and cut out several parts:

1) An outside trim ring to hold the sub rings.

2) Two sub rings.

3) Internal braces for the box.

4) Stands for setup of glassing.

Now that the parts have been ruff cut out (Photo 1), finishing becomes the next logical step. I made a 3/8-inch rabbit cut on the sub rings and the trim ring so the fleece could be stretched and stapled in place. The depth of the rabbit cut is the same thickness of the fleece. Now, when spray bondo is applied and sanding is done, there’ll be no major transition between the two materials (Photo 2). This is best accomplished on a table router. If you don’t have access to a table router, a hand router can used on a nonskid surface — this will let you do the delicate work. In Photo 2, you’ll notice that I only go half way around with the rabbit — this must also be done on the opposite of the ring, 180-degrees away. I rounded over the opposite side of the “rabbited” edge with a 1/2-inch round over bit for a smooth finish. With this, the fleece will not look as if it were going around a right angle corner when pulled over the wood rings. The same is done on the outside trim ring, but only on the ends (Photo 3).

Bolting the components together becomes the next task. When the separate components were being fashioned, center lines were drawn on each piece. This will help to establish the center of each segment after cutting them into circles. This will also divulge where to drill, so that the bolts can used to pin the rings and hold them to the outer trim panel, thus creating a form (Photo 4). Figuring out the angles of the rings to the trim panel is done by first knowing what you want the sub tub to look like. Do you want the sub to be normal or reversed mounted? It’s solely up to the builder. In this case, I wanted both to happen. After finding the appropriate angle, glue was used to set the part and it was left to dry.

Looking at Photo 5, you can see the “rabbited” parts and their orientation to the entire component. I added the fleece next, but this turned out to be harder than I thought. The idea was to cover the whole thing at one time; well, that turned out to be near impossible. That breaks one of my own rules: Matt’s Rule #10, “always design it so that it can be covered in vinyl.” Luckily, I found a way out of this. Instead of covering the whole piece at once, I covered it in three separate sections. The fleece is stapled and trimmed to the area where the rabbits where made for a clean smooth finish (Photo 6). After a bit of work, you can see what the sub tub now looks like (Photo 7). This part will now be soaked with tooling resin on both sides. I like to use tooling resin because it’ll shrink less than normal polyester resin. On a complex piece that’s an element of a larger component, it’s important to keep all your sizes as close as possible, because if the parts were to contract too much, they wouldn’t be able to fit together. In the large middle section, I’ll add a small section of fiberglass mat to the back of the sub tub. This will not need a large amount of glass mat due to the curved shape of the piece (Photo 8).

With all the components completed, the box can now be built. First, the floor must be mated to the side wall. This is accomplished using a 1/4 chopped strand made into a paste that will be placed in the gap between the floor plate and the side wall. The internal brace must then be placed — this will give the box a strength in its mid section so that an excessive amount of fiberglass mat will not be needed (this is always a good idea to do if weight is a big deal). Moreover, this will not allow the box to flex in its midsection (Photo 9). In Photo 10, you can see the brace in the background, “glassed” in place. I used a used 1/2-inch Baltic for the supplemental struts to the outer and inner walls.

Next time, we’ll wrap up the enclosure and start sanding, sanding, sanding. I’ll also share a neat trick that I used to cut holes in PVC pipes for the capacitor windows in the processor rack.