Tech Today: Mobsteel Suicide Slab Gets Audio Makeover

WORDS BY JOEY KNAPP

It’s been a while since we’ve shared a build log, so I thought I would show off a collaboration through Pinnacle Autosound and Simplicity in Sound. The car belongs to a Simplicity in Sound client we’ve worked with in the past. This one is a ’64 Lincoln that had a bit of a resto-mod done by the Mobsteel guys. The tired, original motor came out, and a hot Coyote motor was installed along with a modern fuel injection system.

The stance was reliably lowered (no airbags on this one) and the interior was modified, with the highlight being a smooth center console that runs the length of the interior. When our client purchased the car, it had a full Rockford Fosgate system that had seen better days. The rebuilt doors each had a 5 ¼-inch component set powered by a 4-channel Rockford amplifier. The trunk housed the 4-channel amp, and another Power series mono amplifier that powered a pair of Rockford 12-inch subwoofers. In our initial talks with the client, the plan was to get a modest refresh of the existing system, and add in a few cosmetic upgrades. As things sometimes go, modest got thrown out the window, and the plan jumped up to a full Focal Utopia M build, with a pile of Mosconi Pro series amplifiers to power the system.

The preliminary meeting with the client came shortly after I had gotten my CNC up and running. After looking at the car and seeing the materials and finishes used in the interior, I came up with an initial plan for the doors. There were a number of polished aluminum accents in the interior, so my plan was to machine some aluminum accent pieces for the door grilles.

The door panels were made in two parts, with the center lifting off and being easily secured with a single screw. After talking with Bing about the plan, we decided the center of the doors would be shipped to my shop in Florida and I would fabricate and install the grilles there. My draft sketches kept with the feel of the existing work in the car. A thin exposed aluminum ring would be bordered by a black painted outer ring.

To add a little more detail to the grilles, I planned on incorporating the Lincoln name as well as the Continental Star logo. A final layer of detail would be flooding the engraved areas of the star and grille with black epoxy before polishing.

Creating the Door Grille Design

I would be modifying the inner part of the door panels, and leaving outer part as it was. By designing my grilles to fit within the confines of the existing speaker cutouts, I would be able to keep the material and stitching a perfect match. My plan was to design a single grille shapethat would work on both the front and rear doors. The existing speaker cutouts in each door were a little different, in addition to the front and rear doors being slightly different, too.

To determine what the shape would be, I taped up the grille areas of one of the front and rear panels. This not only protected the panel,

but also allowed me to draw on the door to determine a shape. It took quite a bit of time to come up with a shape that would fit the existing speaker cutouts as well as the differences in the front and rear panels. When I had a general idea of the shape, I opened up a photo of the door panel in Adobe Illustrator and worked on the design of the piece. I tried a number of possible options for the star logo, the Lincoln type and the aluminum and acrylic painted piece layering. By creating the shapes in Illustrator on the photo of the door it gave me relatively accurate scaling for the pieces I would cut out on my CNC. With just a few measurements on the door panel, I would be able to properly scale the parts I had designed.

I went through a couple iterations of how I would attach the grilles to the doors. What I decided on was an acrylic pocket with a 1/16-inch thick by 1/8- inch wide lip at the top. I would cut the panels to the size of the pocket and then the lip would hold the pocket in place. The lip would also give me a clean line to blend to with body filler.

Before I cut any parts out of aluminum or acrylic, I first cut the proposed shapes from ¼-inch MDF. I typically will cut samples from MDF to make sure they are just how I want them. MDF cuts very quickly on the CNC, so I find it’s better to check parts I am unsure of with an inexpensive and cheap medium first.

I was glad I checked first. I ended up cutting a number of MDF pieces before getting the correct shape. Sometimes the digital version of designs does not always translate well to the actual piece, and this was the case with the grilles. After cutting the layers out of MDF, I found some of the corners and the top angle had to be adjusted. I had to make sure I would have enough material to cover the profile of the grille, and with the size of the tweeter hole cut in the door panel, it was very close. Cutting out the samples allowed me to fine-tune the shape so it would work on all the doors.

Making the Door Grille Pockets

With the shapes set, it was time to start cutting the pieces that would form the grilles. Each grille would be composed of three different acrylic pieces and two aluminum pieces. The pocket for recessing the grille was made from two pieces of acrylic. The top layer was the previously mentioned piece with the thin lip. The bottom piece would have magnets embedded in it to help hold the grille securely.

After many years of drilling magnet holes by hand, it was nice to have a machine do it for me! Once I glued in all the magnets, it was time to bond the two acrylic layers together. The top layer of acrylic was very thin, and had to be glued to the bottom layer. To keep the shape from distorting while being glued, I used the MDF insert sample to hold the shape.

Once all the pockets were glued together and had time to dry, I moved on to integrating them with the doors. First I had to carefully peel back the upholstery from the fiberglass panel. Luckily, the material was mainly just glued along the edges. With enough of the raw panel exposed to fit the pocket, I traced the perimeter of each pocket carefully on the door. I opted to cut the shape with an airsaw instead of a router because the panel still had the material attached at the top.

The acrylic pocket I fabricated had the lip at the top, so there was a little bit of wiggle room for any cut areas that weren’t perfectly straight. Next, I glued the pocket into the new opening. I test fit each pocket as I cut the doors, and noticed the pockets didn’t sit completely flat. I was concerned that when I molded them in, they might warp.

The pocket was only ¼-inch deep, so any slight amount of deflection would be very visible with the grille inserted. To keep them completely flat, I decided to make the aluminum inserts. That way I could secure the aluminum pieces in the pocket to help keep them from warping.

Door Grille Aluminum Bits

I’d only cut a few small keychains out of aluminum on my CNC. I did some research and found that a single flute bit was supposed to be superior for cutting aluminum. In making these rings, I would use the single flute bit, and also a 90-degree V-bit for the etched details. While laying the piece out in VCarvePro, I realized how much empty space there was in the middle of the grille opening. To keep from wasting that space, I inserted the four Continental Star logos in one of the grilles. I didn’t know what the design of the trunk would be yet, but I knew I wanted to incorporate the star logo there, too, so in another one of the grille centers I inserted three large star logos. This would give me the ability to have matching accent pieces in the trunk.

Once all the aluminum pieces were cut, it was time to add the epoxy to the engraved areas. I shared a few photos of this process in my CNC article a few months ago. One important thing I learned about epoxy is to let it sit a few days before sanding it. Otherwise, it won’t adhere as well to the aluminum. Not giving it enough time to cure increases the likelihood that it will gum up the sandpaper. Another trick I have learned is to mask off the surrounding areas before applying epoxy. Protecting the non-epoxied areas helps reduce sanding and cleanup time.

I mixed the two-part epoxy and added the black dye. It takes just a very small amount of dye to color the epoxy. Depending on the piece and how precise I need to be with the epoxy application, I apply it with either a syringe with a large 16-gauge tip, or just a popsicle stick. While the epoxy self-levels, I will typically smooth it out with a filler spreader.

Since I haven’t had to polish any larger pieces before, I worked on a single grille first, so I would know what to expect. As I have in the past, I waited for the epoxy to cure and then started working on sanding the excess down with 180-grit sandpaper. I moved to finer grades of paper and then attempted to polish the surface. The assortment of polishing gear at my shop was not producing the results I wanted, so I contacted my aluminum guru buddy, Shon Besharah. Shon suggested polishing wheels and supplies by Zephyr. I ordered a kit from them and gave it a shot.

I had a very hard time polishing the open center grille frame on the polishing wheels. After a few close calls with the grille getting wrapped up in the polishing machine, I decided to phone a friend again. This time I called on the help of a local friend of mine, Charlie Thornton, who is an excellent auto body technician. With Charlie’s help, all of the grilles and star logos were polished to an almost mirror shine.

Now that the tedious part of the aluminum work was done. I could focus my attention back on the door panels. I taped up the aluminum inserts so I could place them in the acrylic pockets to help hold their shape while bonding. To protect the upholstery, I pulled it up over the top of the panel, and taped up any exposed parts. The bonding agent I chose was duraglass mixed with a bit of polyester resin. I have found this mixture works well for adhering and filling. When I placed each grille on the panels, I made sure they touched at the same points, so each one would have the same angle.

Door Panel Upholstery

When the filler had hardened and all the rings were bonded, I knocked down the highpoints and edges of filler with some 60 grit sandpaper. I applied and sanded two coats of USC White Gold filler, taking care to blend smoothly into the panel. Now it was finally time to apply the upholstery back on the panel.

The tolerances I left for the grille layers did not include upholstery under the grille. Because I wouldn’t have any material on the contact surface of the acrylic pocket and grille, I taped up that area of the panel. This would allow me to remove the tape after I sprayed the contact adhesive on the door. Not having glue on that area would make it easy to trim and remove the upholstery.

I knew some areas would be very close to not having enough upholstery to cover the pocket. To make covering the panel easier, and to make sure I could position the material more precisely, I started by only gluing the area directly around the ring. Once the glue dried, I removed the tape from the contact point of the pocket, so no upholstery would stick there. When all the pockets were covered, I sprayed the back halves of the panels and upholstery and covered those parts.

The final project for the doors was to make the pressed grilles go into the grille trim rings. In the past, making the parts for pressing the grilles would have required me to under- and over-size pieces using flush-trim and rabbet router bits and different sized bearings. Since I had designed the grilles in the digital domain, it was only a matter of clicks to make the files for cutting the larger and smaller pieces on my CNC router.

The grilles would have a center spot for the star logo to sit in. That piece was also easy to add, because I had a digital file for it as well. I chose to make the plug for the star logo in acrylic instead of MDF. I was afraid the thin points of the star might deform or break when pressing if they were MDF. With the help of the CNC router, making pressed grilles has never been so easy!

At this step in the project, I had completed what I needed to at Pinnacle Autosound, in Lake City, Fla. To protect the grille pieces, I put each one with the different layers in the acrylic recess pockets in each door and taped them in place. I didn’t want to fully assemble them until I got to Simplicity in Sound, in Milpitas, Calif. I bubble-wrapped the panels a number of times, and sent them off to meet me in a week.