How to Make an MDF Ring

A router can cut neat rings from MDF.

Many do-it-yourself projects require a material that is rigid but easily cut to a variety of shapes and sizes. One versatile choice is medium-density fiberboard (MDF). A byproduct of lumber milling, MDF consists of sawdust compressed with wax and resin; it is a stiff, boardlike sheet available in varying thicknesses. MDF can be worked readily with hand-operated tools or simple power tools, such as a jigsaw or router. That feature makes it useful for projects such as subwoofer enclosures that require large rings, which would be difficult to make with conventional boards. The project calls for a partial sheet of MDF that is larger than the future ring's diameter.

Things You'll Need

• Circular saw or jigsaw
• Scrap wood piece
• Double-sided tape
• Workbench
• C-clamps
• Circle-cutting router jig
• Router
• Drill (optional)
• Protective eye-wear
• Dust mask

Instructions

Setting Up

1. Cut a square from the partial sheet of MDF with a circular saw or jigsaw if the sheet is substantially larger than the ring you want to make. Make the square 1 inch larger than the future ring's outer diameter. If, for example, you want the ring to have a 12-inch external diameter, then the square must measure at least 13 inches across.

2. Attach the MDF square or differently shaped MDF piece to scrap wood that is roughly the same size by using double-sided tape. Taping them together prevents a router from damaging your workbench and your workbench from damaging the router's bit.

3. Secure the MDF square to your workbench. If your bench has built-in clamps, then use them to secure the MDF. Otherwise, use C-clamps at the corners of the MDF to secure it to the workbench.

4. Attach a circle-cutting jig to the base plate of a router by following the manufacturer's instructions. Models produced by major brands are pre-drilled with mounting holes to accommodate most routers.

5. Mark the inner and outer diameter of the future ring on the MDF with a pencil. Mark the center of the ring. Drill a pivot hole at the center if your jig requires one.

Cutting the Ring

1. Locate the hole on the circle-cutting jig that marks the outer diameter you intend for the ring, and insert the tool's pivot pin in that hole. Because jigs are calibrated to work with bits of a given size, check the tool's instructions to ensure you have the correct bit size.

2. Position the pivot pin in the pre-drilled hole at the center of the MDF. Put on protective eye-wear and a dust mask, and switch on the router. Give the bit a moment to cut the MDF and settle to its working depth.

3. Guide the router gently in its circular path, applying just enough pressure to keep the bit in contact with the MDF. Cut either clockwise or counterclockwise, whichever feels more natural for you. Let the router work at its own pace, without forcing it through the MDF.

4. Switch off the router after it cuts the circle completely, and lift it out of the cut. Reset the circle-cutting jig to the desired inner diameter for the ring. Position C-clamps at the outer edge of the ring to hold the MDF in place.

5. Replace the pivot pin in the center of the MDF, and repeat the cutting process for the ring's inner circle. Switch off the router, and lift it out of the cut. Loosen the clamps, and lift the work piece and scrap piece of MDF from your bench.

6. Separate your work piece from the scrap piece by pulling them firmly apart. If any of the tape adheres to the back of the ring, pull it off carefully to avoid splintering the edge of your cut.

Tips & Warnings

• Building supply stores often have partial sheets of MDF left over after cutting pieces for customers. Using such an MDF sheet will prevent you from having to store the remainder of a full-sized sheet until your next project.

• MDF sheets are available in various thicknesses. Read the instructions for your project so you know which thickness of MDF to use.

• Most router bits have a cutting depth of 1/2 inch to 3/4 inch. If the MDF you use is thicker than those measurements, then cut one side of the MDF, turn over the MDF and repeat the cuts on that side in order to cut all the way through the material. If a slight ridge results in the middle of the ring where the two cuts meet, use a rasp to smooth the ridge.

References

• Car Audio and Electronics: Subwoofer Enclosure -- Tricks of the Trade
• Car Audio and Electronics: The Basics of Fiberglass Fabrication, Part 3
• Rockler Woodworking and Hardware: Jasper Model 300 Circle Jig
• Car Audio and Electronics: How to Cut Perfect Circles