The brushes in a DeWalt mitre saw are part of the tool's electric motor. The brushes conduct electricity from the stationary part of the motor to the spinning part. Over time the brushes wear down and you may experience problems with your mitre saw. Replacing the brushes is a simple process and requires no special tools.
All electrical motors use brushes to transfer electrical power to moving parts. The brushes are on the stationary part of the motor. The spinning part of the motor contains "commutators" that make contact with the brushes as they spin by. As the brushes and commutators make contact, electrical current is passed to the spinning part of the motor. This electrical current supplies the power to spin the blade on a DeWalt mitre saw.
The two carbon brushes in DeWalt mitre saws are not really brushes in terms of having fibres. Modern motor brushes are made from hardened graphite powder. The term brush stems from the time when they were made from braided copper wire, and from the fact they still "brush" against the commutators on the spinning part of the motor. The carbon brushes are attached to springs, which allow them to maintain the correct position as they wear down from friction.
As the brushes in an electric mitre saw wear down from extended use, they can become too short to make proper electrical contact with the commutators. This can result in the saw losing power, making odd noises, or running at a lower speed. Bad brushes also can cause the saw's electric brake to stop working. This wear is normal, and the brushes can be easily replaced with just a screwdriver.
The brushes on a DeWalt mitre saw are located beneath the two round screw caps at the back end of the motor casing. Unscrew the caps and pull out the springs underneath. The brushes are attached to the springs. If the brushes are less the 1/8 inch long, they need replacing. Also replace the brushes if they're pitted or have a rough edge. Match the curvature of the new brushes to the curvature of the contact point inside the hole during installation. Run your saw for several minutes without cutting anything to properly seat the brushes.