Many times when upgrading an audio system, the need arises to blend custom fabrications with factory panels. One option is to add a “pod” on top of an existing panel, but no matter how well the pod fits and how skillfully the work is executed, this technique tends to look added on. Another possibility is to screw and glue the fabrication to the OEM panel and then use fillers to blend the two parts together. This method allows for a seamless look, but requires the refinishing or recovering of the entire factory panel and lessens the factory integrated look. Many panels cannot be covered in one piece and require expensive upholstery work, and if painted, the original texture and factory appearance of the panel will be lost.
Recently, I was tasked with upgrading the front stage of Metra Electronics 2009 CES demo vehicle, a 2007 Cadillac Escalade. The goal was to install a 5” midrange and 8” midwoofer in the place of the factory 6” driver. We wanted a clean, integrated look, and durability was a consideration as the vehicle is scheduled to be well used as a demo vehicle for Metra’s new high end line of Vibe speakers.
The first step in this upgrade was to do some careful measuring to determine how much clearance was available inside the door for the two drivers. It was determined that there would be to be spacer rings made to give clearance for the power window motor and window glass. These were created using ¾” MDF and a perfect circle router jig. While the router was out, I also fabricated trim rings from 1/2” clear acrylic. The acrylic rings will allow the woofer and mid to sit flush and will also allow for some cool lighting effects later on. In this case, to fully reveal the new product, the plexi rings were designed to fit outside the grille of the speakers, but in many cases, they would be designed to expose only the cone and surround of the speaker, hiding the mounting hardware from view.
In this installation, the wooden rings will bolt to the metal of the doors, and the acrylic rings will become part of the door panel. The speakers will screw into the wooden rings and remain behind when the panels are removed. In this case, I mounted the woofer parallel to the metal of the door with no angle, but wanted to tilt the midrange for better sound quality. To accomplish the angle mounting, I fixed three long stainless bolts to each 5” ring and used nuts and washers aim the speakers.
Once the speaker mounting was taken care of, I moved to the panel fabrication. The first step was to protect the panel. This process requires a lot of bench work and it would be easy to stain or scratch a nice OEM part, so it’s a good idea to protect the entire part with a layer of masking tape. In our case, the panel had been painted with a vinyl dye without proper surface preparation, causing the dye to peel and flake. We were able to be a little less cautious because we knew we would be refinishing it in the end. I layed 2” masking tape as smoothly as possible, avoiding wrinkling in the area I was working in. The picture shows the second panel in progress and a tape template created using three layers of tape applied over the first door’s mold allowing both doors to be identical.
Next, heavy duty aluminum foil was applied over the taped area using 3M77 spray adhesive, again, taking care to apply the material as flat and smooth as possible. A good trick here is to use a fresh Bondo spreader to help smooth out the wrinkles. You can see the outline of the tape template through the foil. This will help guide where to apply materials and where to trim in later steps. Next, a coat of mold release or carnauba auto wax will help fiberglass to separate later on. Note that this process is done on the car to ensure the panel is in its installed shape and the careful use of masking paper to protect the vehicle.
Using polyester resin and full pieces of 1.5oz. fiberglass matt cut slightly larger than the work area, five layers were applied to the door panel. It is important to catalyze the resin towards the slow end of the mixing scale to give extended cure time. This extended cure time allows all the layers to be applied in one batch which eliminates lumps and air bubbles. Also, too much MEKP can cause heat to build up warping the part or even damaging the factory panel. Each layer was thoroughly wetted with resin and rolled out with a fiberglass roller to avoid bubbles.
The fiberglass was allowed to cure overnight. Even though it was hard in a few hours, it is less likely to warp if left on the panel until fully cured.
After it was fully cured, this part which now carries the exact shape of the outside of the panel was removed and its’ inside surface (the side that was in contact with the OEM panel was taped, foiled and waxed in preparation for another fiberglass layup. In some cases, this first piece could be used for our fabrication, but because we want our piece to be an exact copy of the door panel, the thickness of the fiberglass makes this piece about ¼” too large in contour. Another piece molded to the inside of this one is preferable because it will be an exact copy of the door panel on its outside surface. Five more layers of 1.5oz. matt were cut and applied to this mold, rolling thoroughly to ensure a smooth solid part.
The part was allowed to cure overnight and then removed. The tape and foil were cleaned away and the original mold was cut to the desired shape of the insert. In this case it was cut along the line molded into the fiberglass by the tape template. The original shape was obtained by sketching and comparing the shape and location of the speakers to the panel. It is important to make this cut accurate as it will be the template for cutting the insert and the door panel. I like to trim the part with an airsaw just outside the marked line and then sand using a belt sander or angle grinder up to the line, finishing with a hand sanding block for perfect edges.
Once the original mold is trimmed perfectly it becomes a template for cutting the insert and door panel. Mate it up to the part that was pulled from it and using a sharp pick, scratch the outline of the shape onto the insert. Then cut the insert out just inside the scribed line using the airsaw, belt sander and sanding block as accurately as possible.
Next, take the mold and mate it to the door panel and carefully scribe its outline onto the door panel. To avoid slipping while you are marking, a light spray of 3M77 adhesive will make the inside surface of the template tacky. Extreme caution should be used here as any slips will be scratches visible in the final work. If this were the first door being done, you would then apply multiple layers of tape to the inside of this mold, trim it to the exact shape and then peel it out. This tape template would then stick to the other door as a guide to make the two sides match.
Once marked, the panel can be cut using a Dremel tool fitted with a mini saw blade attachment. Be careful to cut inside the line and then sand up to the line perfectly.
Next, carefully tape the cut edge of the hole in the panel. Taping provides a release point for the following steps and gaps the insert so that layers of paint will not prevent a proper fit. I like to use ¾” tape and then cut it flush to the panel with a single edge blade.
After the first layer is applied a second layer applied at right angles will prevent it from sliding off.
Then, the entire exposed surface of the front and back of the panel is taped and trimmed smooth and the insert is slipped into place and taped flush or slightly behind the panel’s front surface. Tape all the way around in preparation for filling the back surface of the insert.
Apply a light coat of wax to the tape on the back side of the panel, avoiding the insert and the seam between the pieces. Prepare 2” wide strips of matt, resin and Duraglass filler. Mix the Duraglass, and working on the back side of the panel, apply a thin film into the line between the insert and the panel. Immediately begin applying the strips of fiberglass over the seam between the two parts. Continue until the matt is built up five layers thick, roll out any trapped air and let the part cure. This step creates a flange on the inside of the door panel that will allow the insert and the panel to be bonded together.
When the fiberglass flange is cured, remove the tape that was holding the insert in place and spread some more duraglass to further fill the gap between the panel and insert. This application should be extremely thin as most all of it will need to be sanded away.
After the duraglass cures, light sanding to expose the fine line between the panel and the insert will allow the insert to be removed. It’s very important not to sand through the tape at any time because the factory finish of the panel would be damaged. At this point you have a perfectly fit fiberglass insert that can be built on to achieve any look you want .
In the next step, I laid the plexi rings I created earlier on top of the insert and marked just outside of their diameter, and cut out the center of the insert.
I taped the outer diameter of the speakers so the acrylic rings would be centered, and slipped them over the speakers. I taped the insert into the door panel and temporarily reinstalled the panel. Once everything was lined up as it would be in the final installation, I used CA glue and accelerator to glue the rings to the fiberglass insert.
The panel was removed along with the fiberglass insert and glued rings, leaving the speakers behind.
The rear of the panel was thoroughly taped to prevent duraglass from leaking through, and the front surface of the panel was duraglassed to permanently bond the rings to the fiberglass insert.
Sanding with 40grit paper while the duraglass was still soft was followed with a coat of body filler contour the shape, and then a couple coats of polyester primer were applied to allow for finish sanding.
At that point I refinished the OEM panel with SEM satin black and matt clear and applied a base coat of black to the insert in preparation for some airbrush work to be done at a later date.
After final finishing is done, the insert will be bonded to the panel using Duramix adhesive on the hidden flange behind the panel.
The best thing about this technique is that it allows a fabricated insert to appear to grow out of a factory panel. The same technique could be used to flush mount a custom grille or amp rack in a rear interior panel or to give a factory appearance to a kick panel speaker installation.
Build and Photos, by Joe Padula Lead Instructor of Installer Institute.
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