Last reviewed by the Product Safety Team in February of 2025.
For grinding, smoothing, and shaping metals, granite, marble and other hard surfaces, portable cup wheels remain a popular abrasive choice. Diamond cup wheels work best on the hardest materials, like concrete or stone, while aluminum oxide or silicon carbide wheels are the better choice for metals and softer stones.
In the 1950s, metal backs were added to the aluminum oxide and silicon carbide portable snagging cup wheel design to improve structural integrity, reduce heat transfer, and reduce vibration in demanding grinding applications. A metal back provides many benefits, which have not changed over the years:
- Mounts easily on a portable tool using a threaded bushing
- ~10% lighter in weight than a cup wheel manufactured without a metal back -- an important factor in reducing operator fatigue and increasing precision
- Adds rigidity and strength to the wheel
Wheel and Back Design
Norton portable cup wheels employ a variety of metal backs. Each back has been designed and tested in accordance with ANSI B7.1 to ensure compliance with safety standards. The back is then intentionally paired with a specific cup wheel design. On larger wheels, the metal back is visible. On smaller wheels, the metal back is concealed under the blotter, offering the rigidity needed from its hidden position. While the appearance may be different, each metal back is performing its designed function.
By providing optimum structural integrity, metal backs are an important safety feature of portable cup wheels. Proper usage is also important for operator safety. To achieve maximum safety and productivity benefits, remember these key safety tips:
- Always use a cup wheel guard. Guards designed for other wheel types do not provide adequate protection should a wheel fail.
- Never exceed the maximum operating speed marked on the wheel.
- Ensure the backup flange is at least 1/3 the wheel’s diameter. Smaller flange diameters do not provide adequate support.
This is by no means a complete list of portable cup safety guidelines. Please refer to the “Do's and Don'ts of Portable Abrasive Cup Wheels” and “Safety Requirements for Using Abrasive Cup Wheels” articles for additional information.
For additional information on this topic or if you need any other abrasive safety information, please review the Norton Product Safety page, ANSI, OSHA, and all literature provided by the abrasive wheel and machine manufacturer. You may contact the Saint-Gobain Product Safety Department at (508) 795-2317, or contact your Saint-Gobain Abrasives representative with any safety related questions.
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