A Dremel rotary tool is an adventure in a box. There are literally thousands of uses for the original, high speed rotary tool and they are happy to tell you about each and every one of them. Rotary tool novices should start with something more basic, such as cutting and sanding. Trimming a countertop is a precision job that is perfect for the Dremel and its novice user. Cut a straight line and sand the edges. Sounds easy, but remember--let the tool do the work for you. A Dremel is hazardous when pushed too far.
Hold your Dremel rotary tool firmly in one hand. Depress the clutch button with your thumb. Grasp the retaining nut on the tip of the tool and twist it counterclockwise with your free hand.
Slide the shaft of your cutting bit into the retaining nut on the tip of the Dremel rotary tool. Twist the nut clockwise while still holding the clutch button to lock the bit in place. Snug the nut with the wrench end of your combination tool.
Loosen the retaining screw in the end of the cutting bit shaft using the screwdriver end of your combination tool. Twist the screw loose and hold it by its head. Slide the point of the screw through a hole in the center of a cutting wheel and twist it back into the bit. Be careful when snugging the screw with your combination tool. Over tightening will cause the disk to crack and under tightening will allow it to fly off during operation.
Plug up the Dremel rotary tool, turn it on and adjust the speed to its highest setting. Hold the tool so that the spinning, cutting disk is at a 90-degree angle to the surface of the countertop. Gently touch the cutting wheel to the counter top to cut into the surface. Trim a little at a time off of the countertop with the Dremel. Make your cut as deep as it will go from the top of the counter, then from underneath.
Turn off your rotary tool and unplug it from the power supply. Depress the clutch button and loosen the retaining nut with your combination tool. Slide the shaft of the sanding bit in place and lock it down with the retaining nut. Snug the nut with the wrench end of your combination tool.
Loosen the screw in the end of the drum section of the sanding bit. Push a sanding belt onto the drum section of the bit. Tighten the tension screw on the sanding bit with the screwdriver end of your combination tool.
Plug in your Dremel rotary tool, turn it on and adjust the speed to its highest setting. Touch the spinning, sanding belt to the rough cut edge of the countertop. Sand along the length of the top and bottom edges as well as along the center where the cut will be the roughest. Continue sanding and shaping until the new edge of the countertop is uniform with the rest of the unit.