| Electric Motor | Converts electrical energy into rotary motion. | Copper windings, laminated steel core, insulated housing, and a rotating armature in brushed designs. | Electrical current creates a magnetic field that turns the rotor and transfers power to the gearing system. | Loss of power, overheating, burning odor, excessive sparking, or inconsistent speed. | Keep ventilation openings clear. Replace worn internal components only with compatible parts; disconnect power before inspection. | Essential |
| Carbon Brushes | Deliver electrical current to the rotating armature in brushed motors. | Conductive carbon compound with a spring and flexible lead. | The brush remains in contact with the rotating commutator while the spring maintains contact pressure. | Intermittent operation, visible arcing, reduced output, or brushes worn near their service limit. | Inspect as recommended by the tool manufacturer. Replace brushes as a matched set when applicable. | High |
| Armature and Commutator | Transfers motor torque to the spindle through the gear train. | Copper commutator segments, steel shaft, laminated iron core, and copper windings. | The armature rotates inside the magnetic field; the commutator switches current through the windings to maintain rotation. | Heavy sparking, burnt marks, rough rotation, unusual vibration, or a shorted winding. | Do not use abrasive cleaning methods that damage the commutator. Replace the assembly if windings or the shaft are damaged. | Essential |
| Gears and Gearbox | Changes motor speed and transfers torque to the spindle, usually through bevel gears. | Hardened steel gears, bearings, seals, and a metal or reinforced housing. | The pinion gear drives a larger bevel gear, reducing speed while increasing usable torque at the disc. | Grinding noise, gear chatter, excessive play, leaks, or abnormal vibration. | Use the specified gear lubricant and avoid overloading the tool. Replace damaged gears or bearings rather than continuing to operate the grinder. | Essential |
| Spindle | Supports the abrasive accessory and transfers rotational force. | Heat-treated steel shaft with a threaded end and retaining shoulder. | The spindle rotates with the output gear while the flange and nut clamp the wheel or accessory in place. | Visible wobble, damaged threads, difficult accessory installation, or excessive radial play. | Clean the threads and shoulder before fitting an accessory. Replace a bent or damaged spindle; never compensate with loose washers. | Essential |
| Flanges and Lock Nut | Center and secure the wheel or accessory on the spindle. | Machined steel or hardened metal, commonly with a backing flange and threaded lock nut. | The flanges distribute clamping pressure across the accessory while the nut prevents movement during rotation. | Damaged faces, cross-threading, slipping accessories, or an accessory that does not seat flat. | Use the correct flange orientation for the accessory. Tighten securely without excessive force or impact-tool use. | Essential |
| Wheel Guard | Helps contain fragments and deflects sparks away from the operator. | Stamped or cast steel, sometimes with a corrosion-resistant finish. | The guard forms a protective barrier around part of the rotating wheel while leaving the working area accessible. | Cracks, distortion, missing fasteners, poor adjustment, or movement during operation. | Install the guard required for the specific accessory and operation. Do not operate the grinder with a damaged or missing guard. | Safety-critical |
| Side Handle | Improves control and reduces the chance of losing grip during high-torque work. | Threaded metal mounting insert with a molded polymer or rubberized grip. | The handle attaches to one of the available mounting positions so the user can control the tool with two hands. | Loose threads, cracked grip, damaged mount, or excessive handle movement. | Install it in the position that provides the best control. Tighten by hand and inspect the mounting threads regularly. | High |
| Power Switch and Lock Mechanism | Controls electrical power and, on some tools, maintains operation without continuous finger pressure. | Insulated polymer body, conductive contacts, spring, and mechanical actuator. | Moving the actuator closes or opens the circuit; a lock mechanism holds the switch in the operating position when designed for that function. | Sticking, failure to latch, unexpected shutdown, or failure to stop when released. | Keep dust away from the switch area. Replace a faulty switch immediately; do not bypass safety mechanisms. | Safety-critical |
| Power Cord or Battery Pack | Supplies electrical energy to the motor. | Flexible insulated cable for corded models, or a rechargeable cell pack with protective electronics for cordless models. | The cord delivers mains power, while a battery pack provides controlled direct current through its protection and control circuitry. | Frayed insulation, loose connections, reduced runtime, overheating, or failure to start. | Do not use damaged cords or swollen battery packs. Store batteries in suitable conditions and use the correct charger. | Safety-critical |
| Cooling Fan and Air Vents | Moves air through the tool to remove heat from the motor and internal components. | Plastic or metal fan connected to the motor shaft, with molded or machined ventilation openings. | Fan rotation draws ambient air through the housing and expels heated air during operation. | Overheating, reduced airflow, blocked vents, or a rattling fan. | Clean vents with dry air or a soft brush. Avoid covering the openings and allow the tool to cool during heavy work. | High |
| Bearings | Support rotating shafts and reduce friction. | Sealed ball bearings with hardened steel races and balls. | The balls roll between the inner and outer races, allowing the armature, gears, and spindle to rotate smoothly. | Grinding or humming noise, rough rotation, heat, shaft play, or vibration. | Bearings are generally replaced rather than lubricated in place. Inspect them whenever the gearbox or motor is serviced. | High |
| Abrasive Disc or Accessory | Performs the cutting, grinding, sanding, polishing, or wire-brushing task. | Aluminum oxide, zirconia, diamond, silicon carbide, abrasive fiber, or steel wire depending on the application. | The rotating abrasive surface removes material through cutting edges, abrasive grains, or wire contact. | Cracks, chips, glazing, excessive vibration, reduced cutting speed, or an expired or damaged disc. | Match the accessory type, diameter, bore, and maximum rated speed to the grinder. Inspect before every use and replace damaged accessories. | Safety-critical |