Grinding Wheel Speed (SFM)
Affiliate link — we may earn a commissionGrinding wheel speed is how fast the edge of the disc moves, measured in surface feet per minute (SFM) or meters per second. It's a function of both RPM and wheel diameter. A 4-1/2-inch wheel at 11,000 RPM produces about 13,000 SFM. Every grinding wheel has a maximum rated speed printed on the label. Running a wheel faster than its rating can cause it to shatter. Larger wheels spin at lower RPM to keep the surface speed safe. That's why a 9-inch grinder runs at 6,000 RPM while a 4-1/2-inch grinder runs at 11,000.
Why It Matters
Exceeding a wheel's rated speed can break it apart while it's spinning. Always match the wheel's max RPM to your grinder's speed. A wheel rated for 10,000 RPM on an 11,000 RPM grinder isn't safe. Check the number on the label every time you mount a new wheel.