A bench grinder is a stationary power tool designed for abrasive material removal. It consists of an electric motor that spins two abrasive wheels mounted on opposite ends of a central shaft, often featuring a coarse wheel on one side and a fine wheel on the other. The machine is typically bolted to a workbench or pedestal for stability during high-speed operation. Its function is to quickly alter the shape or surface condition of metal objects by bringing the workpiece into controlled contact with the spinning abrasive surface.
Sharpening and Shaping Metal
The most common application for the bench grinder is using its abrasive wheels to sharpen, shape, or repair metal tools. Aluminum oxide wheels are used for high-tensile strength materials like carbon steel and alloy steel, common in tools such as chisels, screwdrivers, and drill bits. For harder materials like tungsten carbide or non-ferrous metals such as aluminum and brass, silicon carbide wheels are employed due to their sharper grain structure.
The abrasive grains bonded into the wheel chip away material to restore a tool’s edge or modify its profile. For instance, a lawnmower blade or axe head can be ground down to a precise angle using the tool rest for support. Coarser grit wheels (typically 36-to-60 range) are used for rapid stock removal and repairing damage, while finer grit wheels are applied for honing a sharp, smooth finish.
Grinding wheels are also used for removing burrs, which are rough edges left on metal after cutting or machining. This deburring process improves the safety and function of the workpiece by smoothing the edges. Maintaining control requires using the adjustable tool rest to ensure the metal is presented to the wheel at a steady angle.
Cleaning and Polishing Applications
The bench grinder uses non-abrasive attachments, such as wire wheels and buffing wheels, for cleaning and polishing. Wire wheels, made of carbon steel or stainless steel bristles, provide a flexible brushing action ideal for surface preparation. They are effective for removing rust, stripping old paint, and cleaning away weld slag or heavy corrosion from metal parts.
Buffing wheels, often made of cotton or flannel, are used with specialized polishing compounds to achieve a smooth, mirror-like finish. These compounds contain fine abrasive particles transferred to the workpiece by the spinning cloth wheel. This process is used for tasks like polishing jewelry, restoring automotive trim, or bringing a high luster to blades after sharpening.
Essential Safety Practices
Operating a bench grinder requires managing hazards associated with high rotational speeds and flying debris. Mandatory personal protective equipment (PPE) includes safety glasses or goggles worn underneath a full face shield for protection against sparks and particles. The machine must also be securely mounted to a solid surface to prevent movement during use.
A critical safety check involves adjusting the tool rest so the gap between it and the wheel is no wider than 1/8 inch (3 mm). This minimal gap prevents the workpiece from jamming between the rest and the spinning wheel, which could cause the wheel to shatter. Additionally, the abrasive wheel’s surface must be maintained using a wheel dresser to remove dull material, ensuring the wheel remains round and flat and preventing vibration.