Skate Sharpening for Figure Skaters
Frequently Asked Questions
Your blade can be your best friend or your worst enemy. Whenever you skate, you trust your personal safety to it. It is the origin of every force that drives every movement that you make. If you intend to be a good skater, you need to know it like an extension of your body; how it feels and how to use it. You need for it to work the same all the time, so you may find it useful to know something about how it works.
I feel that there is generally too much mystery surrounding skate sharpening. What constitutes a good sharpening job is not mysterious at all. I hope that these questions and answers will clear up some of the mystery.
In the following, I have tried to base my discussion on sound scientific and engineering principles, and whenever something is my opinion, I will state it as such.
Q - Why does the blade slide on the ice?
Water has the uncommon property of expanding when it freezes. This is one reason that you need antifreeze in your car. It is also the reason that ice cubes and icebergs float (and why the Titanic sank). If you apply pressure to ice, it melts. So, when the blade presses against the ice, it creates a thin film of water which acts as lubricant, and allows you to slide. When you are skating, you actually are sliding on a thin film of liquid water. At least this is the commonly accepted theory (some recent research has disputed this.)!
Q - Why does the blade turn when I lean?
Next time you skate, glide straight ahead on a flat. Using your ankle and nothing else, tilt the skate to the right or left, and feel how it turns you in that direction. Look at the shape of the blade. Viewed from the side, it curves up at the front and back (it has "rocker"). Pressed into the ice, a short length of it is actually in contact with the ice. As it is tilted onto an edge, you can probably envision that this length of contact is slightly curved. As the blade moves along the ice, it will follow this curve.
The curve will be deeper if you lean your ankle more. It will also be deeper if your blade is more strongly rockered, as most blades are toward the front. As you glide on an edge, press slightly forward on it, and feel how it tries to curve more.
Q - What is the hollow?
A - You probably know that your blade has two edges, inside and outside, and that there is a "hollow" between the edges. You may also know that the hollow can be "deep" or "shallow", and be able to feel the difference by running your finger across the blade.
Refer to the following figure showing a crossection of a blade. The blade is made of a piece of steel of some thickness (a typical freestyle blade is about 0.15" thick). The bottom of the edge is ground out with a circular cross-section (see "how is a blade sharpened", below). The radius of the circle is called the Radius of Hollow (ROH). The shorter the ROH, the "deeper" the hollow. A blade with a deep hollow will hold the ice better, but will also be grabbier and slower.
Q - What is the correct ROH for me?
A - This is a very individual matter. I will state some facts, and then some opinions.
An important thing to note is that ROH does not tell the whole story about how a blade feels. The blade touches the ice only along the edges, so what's really important is the angle between the side of the blade and the bottom of the blade at the edge. Some blades are wider than others. Whereas an MK Phantom is 0.155" wide, an MK Dance is only 0.11" wide. If you have a geometric mind, you can probably see that, given the same ROH on the two blades, the wider blade will have a sharper angle at the edge. So, to give the same strength of edge, narrower blades will need a shorter ROH.
A more acute edge angle (deeper hollow) makes the blade less likely to side sideways, so a deeper hollow gives more secure edges. There is more to it than that, though. It also makes the blade more determined at going where IT wants to go, so it will be harder to control (more likely to grab or "catch an edge"). And, the deeper cut into the ice causes more drag, so the blade will be slower. Given these tradeoffs, one could state that the optimum ROH is one which is just deep enough to give the skater the required edge security, but no deeper.
My personal preference is toward the shallow end. Especially for those learning to skate, I think that learning proper use of the ankle to control edges is important, and that a shallower hollow facilitates this. As the skater becomes more advanced, they are likely to use a deeper hollow to gain security of edge. This may be especially important to advanced freestylers desiring edge confidence on jump takeoffs.
On freestyle skates, I see ROHs varying from 7/16" to 5/8". Personally, I use a 9/16" hollow on my Wilson Dance blade (0.14" wide). I am a Gold level skater.
With a deeper hollow, you may be able to go longer between sharpenings.
The following graph shows bite angle versus ROH for various blade widths (The MK Dance is 0.11" wide, Wilson Dance is 0.14" wide, most skates are 0.15" wide, Phantoms are 0.155" wide at their widest part). Given a desired bite angle and the width of your blade, you can look up the radius of hollow required to give that bite angle. A 10 degree bite angle is pretty deep, and a 7 degree is fairly shallow.
Note that on side-honed blades, the side of the blade where it meets the ice is cut at an angle to the plane of the blade, so the bite angle is effectively increased by this amount. On side-honed blades that I have examined, this angle appears to be between 2 and 3 degrees. An exception is the Phantom Special, on which the side is cut at an angle of about 9 degrees! Note that the geometry is slightly different for this case, so the blade will behave differently than one that simply has a very deep hollow.
Q - What is the rocker?
A - If you look at the blade from the side, you will see that it curves up front and back. This is rocker. Blade companies generally specify the "rocker radius" for their different blades. If you draw a circle of this radius (typically 7 or 8 feet), approximately the back 2/3 of the blade will have a fairly circular contour. The radius of curvature decreases toward the front (there is more curve), giving the blade a complex shape.
The increased curve toward the front of the blade has an interesting effect. If you move your weight forward on the blade while on an edge, it will want to turn on a deeper edge. You may know that you spin on this part of the blade. You probably have also felt how the blade can grab if you rock back on it while spinning.
A long radius of curvature gives a faster, more stable blade. This is why speed skates have very little rocker. It is also gives less maneuverability, which is a reason why figure skates curve more at the front.
In my experience the rocker radius that is published by the blade manufacturers must be taken with a grain of salt. MK blades are mostly specified to have a 7 foot radius, John Wilson blades, 8. A recent check of many new blades from our rink's pro shop indicated that the MK blades were pretty close to their specified 7 foot radius, while Wilson blades were closer to 6.
Of more concern is the considerable deviation that is seen, in the form of local "humps" in the rockers at various points on the blade, of both brands. Their specified radius is not precisely controlled. I even had a serious skateability problem with Wilson Dance99 blades as a result of a hump right in the middle of the rocker.
Of course, it is also quite possible that careless sharpening can introduce such problem as well.
Q - What is a Dance Blade?
A - If you examine dance blades, you might notice a few differences. First, they are short. Dancers tend to do lots of tight footwork, and the short heel gives less to get tangled up (step on, lock with your partner's blades or your own, etc.). Secondly, they don't tend to curve up as quickly on the front, so they are not particularly good for jumps and spins. Also, they do not have the pronounced toepick that is seen on freestyle blades, since they are not expected to be used for jumping.
Dance blades are less forgiving than freestyle blades. Many dancers have experienced getting their weight too far back and falling over backwards!
Dance blades are often narrower than freestyle blades. So far, I am unable to deduce a reason for this design feature, and have not heard it explained satisfactorily. They are definitely harder to sharpen accurately because of this.
Q - What does the toepick do?
A - There are two parts of the toepick, the part that hangs down (the drag pick), and the part that sticks out in front (the master pick). The drag pick is the last thing to leave the ice on an axle, the first thing to touch on a jump landing, and just touches the ice on most spins.
If you rock forward on the blade, you can only go so far before hitting the toepick.This forwardmost point is called the "Forward Balance Point". When you spin, you are skating on this point, with the toepick just touching the ice.
Because of the toepick, note that you cannot skate on the length of blade forward of the forward balance point..
Q - How is a skate sharpened?
A - The skate is sharpened with a rotating grinding wheel. Prior to sharpening, the wheel is "dressed" (using a special diamond-tipped tool) in such a way that it has a circular cross-section (whose radius is the Radius of Hollow). The skate blade is clamped into a holder, which holds its bottom surface perpendicular to the grinding wheel. Your friendly skate sharpener moves the clamped blade along the rotating grinding wheel to refresh the hollow in the bottom of the skate. The sharpening machine has a special guide to keep the blade perfectly aligned with the grinding wheel.
The goal of the sharpening job is to remove just enough metal from the bottom of the blade to renew the edges. A steady hand is required, so that no part of the blade is ground more than another.
Q - Is the toepick ever ground?
A - Yes. You can see that after a blade has been sharpened many times, the profile of the edge will be the same, but closer to the boot. If the drag pick has been left untouched, the drag pick will be at a different relative position than when the blade was new, and the skater's technique will change to accommodate this. It is therefore desirable to occasionally remove tiny amounts of material from the pick, so that the profile is retained. This is a tricky operation, easy to overdo.
Q -My blades aren't flat on the sides - what's the deal?
A - Generally, less expensive blades are of constant thickness, with flat sides. As you get into the more expensive blades, you may see two features: they may be tapered from front to back (wider at front, narrower toward back), and they may be "side honed" (material ground from the sides so that instead of being flat, they are concave).
Depending on the blade design, side honing may create a sharper bite angle at the edge. It definitely makes a blade harder to sharpen with level edgees.
A blade design variation worth noting is the "Coplanar". These blades have the high quality steel and stronger construction of high-end blades, but are of constant thickness throughout, thus easy to sharpen well. In addition, they have a unique mounting geometry with certain claimed advantages (because of their flat, coplanar mounting plates, they can be repositioned on the boot without changing the blade angle.).
Q - How often should I have my skates sharpened?
A - "When they need it". It depends on how much you skate and how hard you skate. If your edges are damaged or no longer feel secure, then it's certainly time. I try to remember that nice feel of freshly sharpened skates, and when they don't feel that way, it's time.
If you examine the bottom of the blade right after sharpening, the bottom of the blade will have a uniformly satin sheen. With more skating, the blade bottom near the edge will begin to appear dull. As these dull bands get wider, you might want to think about resharpening your blade.
When I sharpen, I use the fact that a sharp edge does not reflect light. If you view the edge under a strong light, the degree that it reflects is a gauge of its dullness.
Q - Are new blades ready to skate on?
A - Figure skate blades generally come from the factory already sharpened. My observation is that this sharpening job is generally of low quality, usually having a very coarse grind and rather unlevel edges. I have also observed considerable variation in toepick height between two blades of a pair (this leads one to wonder about the quality control in the curve of the blade!). Also, the factory ROH may or may not be appropriate for the particular skater.
I always sharpen new blades before skating on them.
Q - How can I tell if the edges are level?
A - Ideally, the centerline of the hollow is halfway between the two sides of the blade. If it is not, one edge will be higher than the other, and will have a sharper bite angle. If too far off, the effect will be assymetrical edge strength (for example, inside edge grabby, outside weak), and flats that want to turn.
Your skate sharpener should always check that your edges are level after sharpening. Although perfection is neither possible nor necessary, large errors are unacceptable. A common way to check this is to balance a coin (or other straightedge) on the bottom of the blade, and "eyeball" it. I think that this method is really too imprecise to detect any but really gross errors. I use a miniature, precision machinist's square to check that edges are square with the side of the blade. Other devices for checking this are also made. Note that side-honed blades are much more difficult to check, because side of the blade is not flat.
Q - Do nicks have to be completely removed by a sharpening job?
A - Not really. It is extremely important that any deformation of the metal on the side or bottom of the blade next to the nick be ground away. I observe that a slight "hole" in the edge is generally not noticeable, and in the interest of prolonging blade life, I generally do not completely remove large nicks.
Q - Can I sharpen my own skates?
A - A handheld stone can be used to lightly hone the side of an edge, slightly refreshing it, or especially to remove a nick. It is rather risky to attempt honing within the hollow by hand.
One can purchase products that contain a cylindrical hone mounted in a guide that holds the hone centered over the hollow. There is no reason that these cannot work, but bear in mind that the width of the groove in the guide needs to match the width of your blade (beware of tapered blades!), and the radius of the hone needs to match your ROH.
I see no reason why the mechanically inclined skater who can afford it should not purchase their own sharpening machine and do their own skates.
Q - What does a sharpened edge look like?
A - If you examine a sharp edge in a strong light, you should see no reflection from the edge, even looking with a strong magnifier.
Q - How should I deal with my skate sharpener?
A - I suggest that, once you find a skate sharpener that you like, stick with them. The reason for this is simple. Every skate sharpening machine has slight differences. A blade can be resharpened on the same machine with minimal metal removal, protecting your blade investment.
You should be prepared to interact a little with the person who sharpens your skates. Hopefully, they will be willing to discuss any problems that you perceive. The most important piece of information that you will need to supply is the radius of hollow that you want:
Q - How long should it take to "break in" freshly sharpened skates?
A - Most skaters are conditioned to expect a bit of an adjustment period after having their skates sharpened. The common symptom is that skates feel "grabby": edges catch, and stopping is difficult. Skaters with newly sharpened skates are often seen doing things like dragging their skates sideways on the ice, running blocks of wood along their blades, etc., to dull them into skateability.
The correct expectation is that properly sharpened blade should have little or no adjustment period. It should never feel grabby. It should simply feel more secure. (exceptions are the cases of changes made to a blade, such as correcting previous sharpening errors or changing the depth of hollow, or sharpening an exceptionally dull blade).
The edge of a well sharpened blade should feel very smooth as a finger is run along the edge: proper edge finishing will have removed the metal burrs that can cause grabbiness, and give the edge a smooth, not draggy feel. Be careful: a sharp blade can cut (though a well-finished blade is less likely to).
Q - How can I monitor the quality of my sharpenings?
A - First, you should be alert to any differences in the feel of the blade after sharpening. Are your jumps or spins different? Do the edges grab, especially one more than another?
When you buy a new blade, take a few minutes to trace its contour on a piece of paper. Occasionally, after sharpening, compare the blade to this contour and note any visible changes to the rocker. In particular, if the same person has been sharpening your skates, visible changes are something they should want to know about.
Q - How long should blades last?
A - If I have previously sharpened a blade, I find that each sharpening removes only about 0.001" of metal (a typical piece of paper is about 0.004" thick) on a resharpening. If there is 0.1" of sharpenable depth on the blade when new, this means that you might get as many as 100 sharpenings out of a blade. With monthly sharpenings, this would give a blade life of up to 8 years. Sharpenings to restore edge level will take off much more metal. So will sharpenings to change radius of hollow. I believe that skaters typically get much shorter blade life, for various reasons. Still, a careful sharpener can do much to prolong blade life, and protect the skater's investment.
Larry Commerford wrote saying that he believes that my 0.001" is optimistic, and that 0.004" or 0.005" is more realistic, in his experience. He says that he sharpens mainly skates from precision team members, and that they are typically pretty chewed up. I would have to agree that my 0.001" is a "best case" number, coming from an ice dancer who babies his skates.
I have seen some skate sharpeners "flat grind" a blade before sharpening it. This practice will obviously do much to much to shorten blade life.
Q - What are common sharpening flaws?
A - While the goals for good sharpening are quite easy to quantify, skate sharpening is a manual operation, and as such is very much a "craft". The most often seen flaw is unlevel edges. If the centerline of the grinder is not aligned with the centerline of the blade, one edge will be higher (and sharper/grabbier) than the other. The effect of this is that one edge will grab while the other seems weak. If really bad, a flat will pull to the right or left.
To achieve an even grind, the sharpener must move the blade along the rotating wheel with constant force and speed. With time and repeated sharpenings, it is inevitable that errors will accumulate, and show up as uneven rocker. The degree to which this happens is a measure of the skill of the sharpener. Sometimes a particularly heavy hand in sharpening can alter this curve in one sharpening.
Q - Where can I read more about blades?
A - An excellent reference is the publication "Skateology", written by
Sidney Broadbent, and available from
Return to Chuck Wright's home page http://www.chuck-wright.com