Dremel rotary cutters are versatile tools often used for cutting straight lines or for shaping and grinding. They may not be the first tools you think of when you need to cut a circle in rigid material. However, because a Dremel is small and handheld, with the right cutting attachment and a piece of string you can use it to cut a perfect circle of any size. You can use a Dremel whether your project requires a round solid piece or a perfectly round hole.
Fit the Dremel with a small-pointed cutting attachment. This can be any cutter designed for the material you're working with and shaped so that the point is a straight stick, rather than a wheel cutting attachment (which won't work with this technique). A pointed carving tool or high-speed cutter with an end shaped like the tip of a drill are both good options.
Work out the radius of the circle you want to cut. The radius is the measurement from the centre of the circle to its outside.
Tie a length of string to the centre of a piece of craft wire. Measure the length of your circle's radius along the string from the point where it's tied to the wire and tie a knot. Cut off the string on the other side of the knot.
Create a ring for a string compass using wire. Wrap the wire around the head of the Dremel behind the flanged plastic at the tip, just before where the bits are attached. Form a ring with the wire that's large enough to spin freely on the Dremel's neck, but not large enough to fit over the flange. If your Dremel is a newer model without a flange, position the wire past the large buttons on the neck. Twist the wire securely in place.
Cut the circle. Position the loose end of the string at the point on your material where you want the circle's centre to be. Secure the end of the string with a thumbtack through the knot. Stretch out the Dremel until the string is taut. Turn on the Dremel and cut a circle by moving the cutting tip through the material all the way around the centre point, keeping the string pulled tight.