This is the anchor for a series of posts about skate sharpening.
When you get your skates sharpened, the skate technician passes your blade across a grinding wheel in a sharpening machine. In most machines, the grinding wheel is parallel to the skate blade, like it is in this video:
The video mentions dressing the wheel. This means that, before the skate is sharpened, the edge of the wheel is shaped to a portion of a circle with the desired radius. This is called the radius of hollow. About half an inch is common for both freestyle and hockey. Figure (i.e., patch) hollows start at an inch and go up from there. A larger radius of hollow produces a shallower groove on bottom of the blade that feels less sharp. A smaller radius of hollow produces a deeper groove that feels sharper.
Patch skates, which have a shallow hollow, feel very dull and tend to skid, but glide very well and produce few flats (double lines, which occur when both edges touch the ice). This is desirable behavior for figures. Freestyle skaters prefer a deeper radius of hollow, which lets them grip the ice better, making it easier to land jumps and do other tricks.
The optimal radius of hollow depends on the skater’s size (a larger skater should use a shallower hollow) and the ice conditions (a deeper hollow is better for harder ice). The width of the blade also makes a difference. Ice dancers with dance blades generally prefer a smaller radius of hollow (typically 3/8″) because dance blades are narrower than freestyle and patch blades. The narrowness of the blade means a deeper hollow is necessary to get the same bite angle, which is what you feel when you skate. It’s the angle at which the edge hits the ice.
A seemingly small difference of 1/16″ in the radius of hollow can make a big difference in how the blade feels. When you can’t stop after getting your skates sharpened, it may be because the radius of hollow is just a little smaller than what you’re used to. If your blades still feel dull, it’s possible the radius of hollow is a little larger. Or your edges could be uneven.
As the person in the video notes, it’s important for the sharpener to align the blade so that the hollow is centered. If it’s not, the edges will be uneven and have different bite angles. When this happens, your skates may feel ok at first, but soon you’ll be skidding off one edge while the other grips the ice very hard. You can check the levelness of your edges by holding the skate upside down and putting a quarter or other flat object across the blade. If it’s perpendicular to the blade, your edges are level. If it tilts, you need to get your blade fixed. There are also special tools, like this one, for measuring edge levelness.
Next time you get your skates sharpened, ask what radius of hollow your sharpener uses. Then, you can keep asking for that number to make sure you get the same thing every time. Or, you can try changing it to see what works best for you. If you want to really get into the details, read Sid Broadbent’s Skateology: A Technical Manual for Skaters Regarding Skates, Skating Fundamentals, Skate Sharpening. It’s available on his website.
Skate sharpening has changed over time, and future posts will focus on different aspects of sharpening. The radius of hollow needed its own post because it’s so important.