Creating Symmetrical Shapes

For many car audio fabricators, creating cool and unique shapes and integrating them into a system is very rewarding. Rather than using the status quo method of cutting with a jigsaw to make a shape, this technique employs templates and an inverted router table to create more professional and repeatable shapes.

Start by cutting a piece of chipboard (available at most upholstery shops) that's the appropriate size for the shape that you'll need. Before you start sketching out your shape, you should create "crosshairs" by drawing center lines for both the vertical and horizontal dimensions.	Sketch a full-scale version of the desired shape on the chipboard. Try to keep the shape centered on the crosshairs.	"Clean up" your lines by using templates such as circle and oval guides for best results.
Smart Templates by Mobile Solutions (www.mobilesolutions-usa.com) are an indispensable part of my tool collection because they allow me to quickly draw and create unique shapes with ease. By combining sections of different templates, you can create an unlimited number of shapes. With proper use of templates, the finished shape can be comparable to CNC-cut pieces.	This shape was "cleaned up" using arc templates for the top, bottom and sides, and oval templates for the corners.	Once you've created a shape that you are pleased with, carefully cut out the "better half" of your chipboard template. If your shape is symmetrical in both the vertical and horizontal directions, you can cut out the "best quarter" of your shape.
Place the chipboard template on a piece of 11/44" MDF with the straight edge of the template flush with the straight edge of the MDF and transfer the shape. While it is possible to simply cut the shape with a jigsaw and sand it to your desired shape, more professional results can be achieved when the arcs and corners are shaped using routers and templates.	Rough cut the shape to within 11/416" to 11/48" of the line (the closer the better, as long as you don't cut into the line) to reduce the amount of material that the router bit will need to remove.	Using double-sided template tape, attach a template to the first section of the shape.
Use an inverted router table with a flush trim bit to copy the shape. When making complex shapes, make sure not to cut beyond the intended area.	The 0.25" spiral flush trim bit available from Mobile Solutions is my favorite. The main advantage of this bit is that the bearing and cutting edge are extremely close and allow duplication from templates as thin as 11/416". The small diameter also allows duplication of more intricate shapes. One drawback to this bit is that the spiral design makes the bit put more lateral stress on the template compared to a standard flush trim bit, so liberal use of template tape is always recommended, especially on small and thin pieces.	Attach the next template, making sure that the point where the first section ends and the second section starts are perfectly flush, and then use the inverted router and flush trim bit to cut the second section.
Repeat this step until your shape is complete, then inspect your "half-template" and block sand any imperfections with 80-grit sandpaper.	Make a duplicate of your "half-template" on another piece of 11/44" MDF by tracing it with a pencil, rough cutting with a jigsaw and routing with a flush trim bit. If you have a "quarter template," make three copies of your shape.	Attach both "half-templates" with double-sided template tape on another piece of MDF (11/44" or 11/42"), making sure that the edges are aligned perfectly, then use the flush trim bit once again to create your final shape. If you have "quarter templates," attach all four pieces to create the final shape.
Using this technique creates perfectly symmetrical shapes that look much more professional than asymmetrical jigsaw-cut shapes.