03/31/2025
Ever wonder why your sharpening process produces larger burrs? Perhaps a few folks will find this post interesting. To get efficient grinding of heat treated steel and to develop "manageable grinding burrs", the surface feet of the wheel must be at a level that is proper for grinding heat treated steel. That surface feet grinding speed number is between 4,000 to 6,500 SFM. That is for both vitrified and plated CBN (Cubic Boron Nitride) grinding wheels.
What does that mean? It means that the RPM of the grinding wheel needs to be delivering a speed (RPM) that allows the wheel to run at the prescribed SFM to get proper grinding.
Example: a grinding wheel that is 2" in diameter, has a circumference of (2" x 3.1416 or) 6.28" (.523 feet) around the OD of the wheel. To get to the 4,000 SFM minimum for grinding HT steel, the 2" wheel needs to be spinning at 7,600 RPM. (4,000 SFM/.523 ft).
What happens if you don't reach the minimum recommended grinding SFM? Running a grinding wheel using too low of surface feet on heat treated steel will develop higher levels of heat and wheel pressure. This will create larger, thicker grinding burrs, burrs that are very difficult to remove, perhaps even impossible by normal stoning processes.
Most skate sharpening machines do not have true grinding spindles that are capable of high RPM output. Instead, the the grinding wheels are attached to electric motors, so basically the RPM range wil fall into the 1800 to 3600 RPM band.
In some of the new CBN wheel machines as well as the older sharpening machines running vitrified wheels, the wheel diameter is between 6 and 7", so, a grinding wheel that is 6" in diameter, has a circumference of 6" x 3.1416 or 18.828" around the wheel or 1.57 feet. To get to 4,000 SFM minimum with a 6" wheel, the wheel needs to be spinning at 2,500 RPM. (4,000 SFM/1.57'). If the wheel is attached to a 3,600 RPM electric motor, the SFM for a 6" wheel is 5,700. (3,600 x 1.57'), putting the process in the mid range for efficient grinding for heat treated steel.
The result is the machines running the larger diameter wheels (CBN or Vitrified) will grind more efficently, produce less wheel pressure and heat, give a better finish, while developing much smaller burrs on the skate blade.
FYI- The burrs developed in sharpening are the root cause for high on-ice friction on skate blades as well as the root cause for the severe lacerations.
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