Aluminum trim pieces and grilles have become more and more common in custom installs these days. Many installers, however, still shy away from aluminum in favor of acrylic, believing that it's harder to work with and requires special tools. In fact, with some practice you'll find aluminum is no harder to work with than acrylic and can easily be routered into any shape needed.
When I originally began replacing my acrylic grilles with aluminum versions, my first thought was to go with one-piece aluminum billet. However, unless you own or have access to a CNC machine that can cut large grilles like the ones for my 13-inch subs, you'll find the cost of setup, machining, and material can get very expensive.
My next idea was to use a flow jet machine that employs water to cut aluminum sheet into any shape needed. But again, programming costs and setup can also get expensive, and you'd still need to assemble the grilles, unlike one-piece billet. Casting would be another option but requires foundry skills and equipment followed with machining. So I did what most installers do: Use what's available in the shop, in this case a jigsaw and a router table.
Before you begin routing, here are some important tips:
1) Always wear eye protection!
2) On a router table the bit turns counterclockwise, so rotate your work clockwise to cut against the blades. If you cut with the blades they'll catch and launch your work across the shop!
3) Use small amounts of WD40 on the blades to cool them and prevent galling. This will give you smooth, clean cuts.
4) Keep fingers away from the bit! Mobile Solutions also sells some great router accessories that can save you a hospital visit. Check them out.
5) Straight cut bits work best with aluminum (I like the three-bladed laminate flush-cut bits). However, when working with 1/8-inch or thinner aluminum I've found the spiral bits do just fine.
In this case I used the grille rings that came with the speakers, screwed them to MDF, and using a flush-cut bit, copied the shape. Another option is to use circle templates available from Mobile Solutions (mobilesolutions-usa.com) or make your own as I did.
Once the templates are ready, outline the shapes onto an aluminum plate. I prefer 6061 aluminum.
Next, using a jigsaw with a metal cutting blade, such as a Bosch T118, cut close to the lines in order to minimize the amount of material to be routed. To reduce scratching the aluminum, cover the foot of the jigsaw with masking tape. Next, using double-sided adhesive tape, attach the templates to the aluminum pieces.
Repeat the tracing, cutting, and routing until all the parts needed for the grilles are finished.