A bench grinder is a power tool that spins grinding wheels at high speed. Used mainly for the high-speed removal of metal from surfaces, grinders can also shape, sharpen, polish and hone material. Grinding wheels are made with different composites, including aluminum oxide for hard-surface grinding, fibre and wire for removing rust, and silicon carbide for sharpening tools. No matter the job at hand, you can easily switch from one type of wheel to another.
Turn off the grinder using the on/off switch. Wait until the grinding wheel stops turning. Unplug the machine from the electrical socket to ensure that it does not accidentally start. Wipe down the grinding wheel and the areas around it with a clean rag.
Remove the screws holding the outer wheel cover in place with a Phillips screwdriver. Most outer wheel covers are the parts located farthest from the engine on the extreme left or right side of the grinder if the wheel spins vertically. Remove the outer wheel cover.
Remove the screws holding the spark guard to the inner wheel cover if your bench grinder is so equipped. The spark guard is an adjustable shield used to protect your hands and face as sparks are produced. The guard is located towards the front of the spinning wheel, and it may be removed or swung out of the way depending on the make and model of your grinder.
Locate the hex nut or Allen screw that secures the grinding wheel to the driveshaft of the grinder; it will always be located in the very centre of the grinding wheel. Turn the grinding wheel slowly in a counterclockwise direction using the correct size wrench. Insert an open-end wrench directly behind the grinding wheel as it moves. Attach the adjustable wrench to the driveshaft so that you can hold it and keep it from rotating.
Hold the driveshaft firmly in place while turning the hex nut or Allen screw. Continue to twist in a counterclockwise direction until the nut is removed. Use caution so that when the nut comes free, the grinding wheel does not fall to the floor.
Pull the grinding wheel from the driveshaft. There will also be two concave washers, known as flanges, located on either side of the grinding wheel. Remember the way they are facing relative to the wheel, since they'll need to be put back the same way when you put a different wheel on the grinder.
Position the new grinding wheel in place on the driveshaft. Check to make sure the placement of the two concave flanges is correct relative to the wheel. Slide the wheel on as far as it can go, and seat it properly on the driveshaft. Some driveshafts have a flat spot that should correspond to a flat spot on the grinding wheel's centre hole. Replace the nut or Allen screw.
Hold the driveshaft still using an open-end wrench, then tighten the nut or Allen screw by turning it clockwise. Be sure it has been tightened securely, then replace the spark guard and outer wheel cover using Phillips screws. Plug in the grinder and turn it on to make sure that it's operating properly.