Why grinders need respect
An angle grinder is a compact tool that spins an abrasive wheel at very high speed. It cuts, grinds, cleans and sharpens, which makes it one of the most versatile tools in a metalworking shop and one of the more dangerous. Common grinders typically spin their discs at thousands of revolutions per minute. That energy can shatter a damaged wheel, throw debris, or pull the tool out of your hands if the wheel catches.
Most grinder injuries come from a few causes: missing guards, wrong or damaged wheels, poor grip or stance, and inadequate protective gear. All of them are preventable.
Know your tool and read the manual
Grinders differ in disc size, speed, motor power and features such as paddle switches, side handles and electronic soft start. The manual lists the compatible wheel sizes and the maximum speed. Read it before first use and keep it with the tool. The general habit of checking tool manuals and warning labels applies here more than almost anywhere.
Cordless models are convenient and have no cord to snag, although they spin down slowly after you release the switch. For battery models, remove the battery before changing a wheel. Corded ones should be unplugged. This also applies to the heavier cordless angle grinders.
The guard
The guard is a curved cover over part of the wheel. It deflects sparks and debris and offers protection if a wheel breaks. Keep it installed, adjust it so the closed side faces you, and never remove it to fit a larger wheel or reach into a tight spot. A grinder without a guard is much more dangerous.
Wheels and ratings
Wheels, also called discs, come in several kinds:
- Cutting (cutoff) wheels are thin and meant for cutting only.
- Grinding wheels are thicker and meant for removing material and shaping, usually with the face or edge of the wheel as the maker specifies.
- Flap discs, wire wheels and cups are used for finishing, cleaning rust and blending welds.
Safety rules to follow:
- Match the rated speed. Every wheel is marked with a maximum speed. It must be equal to or higher than the grinder’s no-load speed. Never mount a wheel that is rated lower.
- Match the size. The wheel diameter and arbor hole must fit the grinder, and the wheel should not exceed what the guard is designed for.
- Use the wheel for its purpose. Cutting wheels are not designed for side loading, and grinding with the side of a thin cutoff wheel can break it.
- Inspect before use. Look for chips, cracks and wear. Discard a damaged wheel and do not use one that has been dropped. Some bonded wheels carry a date or other markings, so follow the manufacturer’s guidance on shelf life and storage.
- Mount correctly. Use the supplied flanges and tighten the nut with the proper wrench. Avoid using the wrong nut or leaving out parts.
- Run a new wheel first. After mounting, let the grinder run at full speed for a short time with the guard between you and the wheel and everyone else out of line with it.
Store wheels flat and dry, away from moisture and heavy objects.
Sparks and fire
A grinder throws a stream of hot sparks that can travel several feet. Before you start:
- Clear flammable liquids, rags, paper, sawdust and similar materials from the area.
- Check what is behind and beneath the work.
- Keep a fire extinguisher nearby.
- Direct the sparks away from you, bystanders, vehicles, windows and fuel containers.
Grinding certain metals, such as magnesium, can start metal fires that are hard to extinguish, so check before working on unusual alloys. Grinding aluminum can also clog ordinary wheels, so use products made for it.
Protective gear
- Safety glasses plus a full face shield. Wheels throw particles at high speed, and glasses alone leave the face exposed.
- Hearing protection, since grinders are loud. Hearing and dust protection should go on before the tool does.
- A dust mask or respirator suited to the material, particularly for grinding paint, rust or coatings.
- Gloves that fit snugly and are made for the task, with no loose cuffs.
- Close-fitting clothing, sturdy footwear and tied-back hair, with no dangling jewelry or drawstrings.
- Long sleeves and natural-fiber or flame-resistant material, since synthetic fabrics can melt when hit by sparks.
Handling the tool
- Secure the workpiece. Clamp it down. Never hold small pieces in one hand while grinding with the other.
- Use both hands. Fit the side handle and hold the grinder firmly.
- Let the wheel reach full speed before touching the work.
- Stand to the side, out of the line of the wheel, and let the guard sit between the wheel and your body.
- Keep the cord or cable clear of the wheel and your path.
- Use light, steady pressure. Forcing the wheel overheats it and risks binding.
- Do not set it down while it is spinning. Wait for the wheel to stop completely.
Kickback
Kickback happens when the wheel pinches or catches in the work, and the tool is thrown back or sideways. It is more likely when cutting in a bind, when a wheel is at the wrong angle, or when the work shifts. Avoid it by supporting the work on both sides of a cut, not twisting or bending the wheel in the cut, and keeping a firm grip.
After the job
Switch off, wait for the wheel to stop, unplug or remove the battery, and let the work cool before handling it. Brush off dust and check the wheel and the guard. Regular tool inspection catches problems before they hurt someone.
This article is general information. Always follow the manual that came with your grinder and wheels.