Skate Sharpening: what, when, where

What is sharpening all about?? Why can't I just use a knife sharpener?? What's all this hollow and radius stuff about anyway??

If you have never examined the blade of an ice skate, then you might expect it to be sharp like the edge of a knife. However, this is not the case. The blade of a hockey skate is 0.120 inch (about an eighth of an inch) thick and the bottom is cupped inward. This inward cup is called a hollow. The hollow actually creates two edges on the ice skate blade - an inside edge and an outside edge. The inside edge is the side of the blade which is nearest your big toe. The outside edge is on the side of the blade which is nearest your pinky toe.

Hollow - The bottom of your skate blade is not flat. It looks thus (from the front or back):

The "hollow" is described in terms of the radius of the circle (or semi-circle) that is cut into the blade. Having a hollow allows the blade to "grip" the ice. A typical hollow for hockey skates might fall in the range of 1/4" to 3/4". The smaller the number (a deeper hollow), the "sharper" the blade. A "sharper" blade allows the skater to better make turns and hold edges, but may make the skater slower because the blade is digging deeper into the ice and it also makes it more difficult to stop. A lighter skater should have a deeper (smaller number) hollow, while a heavier skater should have a shallower hollow because his or her weight will dig the blade deeper into the ice. A good skater, even though he may be heavier, can also have a deeper hollow, because his skill and leg strength allow him to control the edge. Goalies should have a shallower hollow to allow them full lateral mobility. Speedskaters hone their blades until they are flat. The chart below shows suggested hollow depth for hockey skates for different weights, assuming good skating ability. Expert skaters may want a deeper hollow and less experienced skaters may want a shallower hollow than the chart shows. In addition, defensive players may want a shallower hollow and forward players may want a deeper hollow. It may take some trial and error to find a hollow best suited for your taste.

So, how deep is the hollow?

The number that is used for the hollow grind is the radius that is placed on the grinding wheel as mentioned earlier. The depth of the hollow is dependent on this. The smaller the radius, the deeper the hollow. The mathematical relationship is

See the math involved. As an example, let's look at the 1/4 inch hollow. This is used for a good skater weighing 55 pounds. The depth of the groove down the middle of the blade (the hollow) will be 0.0073 inches. In plain English, one would call this about seven thousandths of an inch. Not very deep, but that's all that is needed.
     
Weight (Lbs) Hollow (inches) Depth (inches)
55 1/4 0.0073
85 3/8 0.0048
125 1/2 0.0036
150 5/8 0.0029
165 3/4 0.0024
185 7/8 0.0021
Goalies should add 3/8" to the hollow listed above.

Radius and rocker - The bottom of a hockey skate blade, as seen from the side, is curved at the front and back, and the center is mostly flat:

   \______/
Hockey skaters have found it desirable to put a radius on the bottom of the blade to improve maneuverability. The radius is specified in feet and it is usually selected based on the skater's height. The process of putting a radius on a skate blade is called profiling. With profiled blades only part of the blade touches the ice at any one time. The smaller the radius, the less blade touches the ice, and the easier it is to turn. However, with less blade touching the ice, you will lose speed and stability. That is why speedskates are long and flat, with much blade on the ice. Imagine your hockey blade is part of the circumference of a very large circle. The radius of this large circle is the number quoted to describe the profile of the blade. Below is a chart of suggested profiles vs. a player's height.
   
Height Radius
4' 3" 6'
4' 7" 7'
4' 11" 8'
5' 3" 9'
5' 7" 10'
5' 11" 11'
6' 3" 12'
6' 7" 13'

In addition to the radius another important aspect of profiling is where the tangent line intersects the blade. This is called the rocker and will define the high point of the blade. For general skating this should be in the center of the blade; this is called a neutral rocker. If you play defense where you will be skating backward most of the time, the rocker should be forward of the center of the blade, in the direction of your toes; this is called a defensive rocker. If you are a forward the rocker should be behind of the center of the blade, in the direction of your heel; this is called a forward or attack rocker.

How often is a matter of taste - Some people get their skates sharpened after every four skating sessions. Others wait 40 sessions before sharpening, which is a bit extreme. Remember, if you get your skates sharpened often the blades will need replacement sooner than if you didn't, but it might be worth the luxury of freshly sharpened blades every skate. If your skates feel like they are sliding sideways, it's probably time to get them sharpened. Also, if you just bought a new pair of skates they will need to be sharpened because they are not sharpened at the factory.

Serious players will sharpen their skates based on the ice conditions before the game. Soft ice has the effect of making the hollow seem deeper because the blade will sink deeper into the ice for a given weight. As such, the player will have the skates sharpened with a shallower hollow for that game. Conversely, hard ice will make the hollow feel shallower and a deeper hollow will be used for that game.

So how is it done? We like the Dupliskate system so we will discuss that here, although there may be other comparable systems out there that are equally good.

For a new pair of skates the blades will be profiled first. This is done by placing a profiling template into the machine. The template is manufactured with the desired radius to be transferred to the skate being profiled. There is a template for each different profile: 6', 7', 8', and so on. The template chosen is based on your height as discussed earlier. In addition, the template may be advanced or retarded from the centerline of the blade depending on the desired location of the pivot point (rocker). A wheel on the machine follows the contour of the template, while the opposite side of the machine has the grinding wheel and skate. The operator passes the grinding wheel over the skate blade until the grinder no longer cuts the blade. At this point the profile has been transferred to the skate. It is very similar to the way a locksmith copies a key. See the following pictures for a view of the profile of a hockey skate and using a profiling template.

To sharpen the blade, the grinding wheel needs to be "dressed" first. Dressing the grinding wheel is the process of placing the desired radius on the grinding wheel. A new grinding wheel is flat on the end. If we were to use this to sharpen a skate, we wouldn't get a hollow - just a flat blade. To "dress" the wheel, we need to place a semi-circular shape on the surface of the wheel. For this a diamond wheel dresser is used - this is a metal rod with a diamond tip that is rotated across the surface of the spinning grinding wheel. The rotation follows the path of an arc and the length of the rod determines the radius. (There are markings on the rod that indicate the radius that will be created.) The diamond tip removes material from the grinding wheel and what you are left with is a semi-circular edge on the wheel with the desired hollow radius. This short video clip shows the wheel dressing operation.

The sharpening process is where the Dupliskate machine really excels. The entire process is mechanically controlled so that you get a consistent sharpening every time. In addition, the grinding wheel follows the profile of the blade so you will never lose your rocker.

Sharpening is usually done in two passes. The first pass is a coarse pass where rust and nicks are removed. This is set for a fast speed - about five seconds to traverse the entire blade. On the second and final pass the blade is treated with a lube stick to create a polished finish. The second pass is slower - on the order of 30 seconds. Sharpening is done equally on both blades and that's it.

To finish things up, the craftsperson should pass a deburring stone along the outside of the edges to remove any nicks and burrs. Then the bottom of one skate should be marked with the hollow radius, profile radius, and rocker settings so that the next time you get your skates sharpened you can get the same settings.

A two-pass sharpening removes about 0.005 inch from the blade. Thus 100 sharpenings will remove about 1/2 inch. Newer skates have a line in the blade that marks the point below which the blade should not be sharpened - if you reach this line it is time for new blades.

This video shows a Dupliskate in action.

What can go wrong and how can you figure out where the problem is???

With other systems where an operator drags your skate across a grinding wheel they may speed up or slow down - hold the wheel in one place for too long. You could end up with a blade that is burned, has flat spots, or has completely lost its contour.

Burned blade - A burned blade will be discolored - a metallic blue. If it's not too far gone, another sharpening by a competent craftsman should be able to fix this.

Flat spots - You can spot a blade with flat spots by rocking it on a flat surface - like a formica counter top (one you are not worried about scratching). Rock it from heel to toe - it should rock freely like a rocking chair. If there is a flat spot it will tend to stop on the flat. Another profiling and sharpening should fix this.

Uneven Edges - The thickness of a skate blade varies based on the type of skate. Speedskates have the thinnest blades, figure and goalie skate blades are the thickest, hockey skate blades are in the middle of these. When the skates are sharpened it is important that the operator center the blade on the grinding wheel. This is not trivial since the distance from the edge of the blade to the center of the blade is different for hockey, figure, goalie, and speedskates. As such, the operator needs to adjust the position of the clamp holding the blade so that it is centered on the grinding wheel. If this is not done correctly the center of the hollow will not be in the center of the blade and one edge will be higher than the other (see following picture).

To detect this, place a straight edge on the bottom of the blade. It should be perpendicular to the blade (see following picture).

If it is sloped to one side or the other you need to get it sharpened properly (see following picture).

Bent blade - Place a straight edge along the side of your blade and look for gaps. A bent blade will have uneven edges at the point where the blade is not centered on the grinding wheel. Replace both blades.

While skating - Even our good friend the ice resurfacer can cause problems for our skates. Ice Resurfacer tracks in the ice (see following picture) are caused when the ice resurfacer picks up road grit and deposits it in the ice. This is tantamount to rubbing sandpaper unevenly across your blades - avoid skating through the tracks.

Scenario: The operator takes your skate, locks it in the jig and starts pulling it across the grinding wheel. What's just happened?
You are getting an unknown hollow, if a hollow at all - the grinding wheel should be dressed first to your desired hollow.
You may be getting uneven edges - the blade should be centered on the grinding wheel first.
You may be losing your profile - how can a person follow an 11' radius by eye???

Dupliskate makes skate sharpeners and has some information about sharpening.

Reference source: Dupliskate owner's manual.

Last updated Aug 26, 2007.


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