I previously wrote about what cross-grinding is and why it’s not always bad. Here is a photo of one of my skates showing the distinctive marks left by cross-grinding.
Cross-grinding leaves many small lines perpendicular to the length of the blade.
If the cross-grinding wheel is too coarse (like the one I used with my Ferodowill skate holder), these can keep the blades from gliding nicely or worse, catch the ice and cause a fall. I discovered this when I took my Ferodowill-sharpened Jones skates out on the ice. As long as you smooth them out (e.g., by stoning the blade), they’re nothing to worry about.
On January 23, 1917, Joseph Henry Ferodowill of St. Paul, MN, was granted a patent for his skate holder. It’s basically two C clamps on a metal base, with some screws that make it adjustable.
The advertisement says it’s good for “Lengthwise and Cross” grinding. The picture in the advertisement above looks like the wheel is set up for cross grinding.
I got one of these skate holders and used it to sharpen my Robert Jones skates. Once I’ve skated on them, I’ll post the results. I also sharpened a new pair of blades I’ve been working on. Here is a video of how I did it:
Sharpening skates with a Ferodowill skate holder
First, I used witness marks and adjusted the holder to align the blade.
Second, I used long, steady strokes to sharpen the blade.
This bench grinder has a 6″ wheel, which means I put a 3″ radius of hollow on the blades. Do not use this hollow for regular skating, it will not be satisfactory. But I’m interested in seeing whether it performs better than the totally-flat sharpening Robert Jones recommends.
This little handheld sharpening device was patented in 1920 by George H. Berghman of Chicago, IL. You squeeze the handles together at the top to open it. When you release the pressure, it clamps onto the sides of the blade. Then you slide it back and forth and the grinding stone inside does its work. The stone’s diameter is one inch, which means it puts a 1/2″ radius of hollow on your blades.
Side view showing the grinding stone.
There are loads of these available on eBay and other internet sites for pretty low prices (though not as low as the original—$2.50 according to the price tag on mine, but only $1.25 according to advertisements in Boys’ Life. I guess girls are not supposed to use it.
Boys’ Life vol. 10, no. 12 (December, 1920), p. 67.
The device seems a bit unwieldy. When I squeeze mine, it feels pretty wobbly—You have to be careful to keep the blade opening even along its entire length. And in mine, the stone is stuck to one side. I think this is a defect in my particular one rather than part of the design because the back of the box says to rotate the stone frequently by “turning the stone with thumb and forefinger.” Mine won’t budge.
The stuckness of my stone means that only one side of the holder opens with respect to it, so the stone will never be centered on the blade. This would cause uneven edges and really mess up my skating if I relied on it! But if it weren’t stuck, I suspect alignment would be rather difficult because there would be one more moving part.
To conclude, here’s an advertisement directed at hardware stores that promises the sharpeners “do a good sharpening job… and give you a good profit.”
It also features a sharpening machine: a bench grinder with an 8″ wheel and a skate-holding jig. The 8″ wheel implies a 4″ radius of hollow since it is set up to cross-grind.
Back in the days when all serious skaters did both figures and freestyle, everyone had two pairs of skates, one for figures (called “patch skates”) and one for freestyle. But having two pairs wasn’t a requirement to begin skating. Everyone started out with only one pair. A second pair wasn’t considered necessary until second test or thereabouts. Today, experienced freestylists getting started with figures may find them very difficult. For one thing, they leave too many flats to pass any test. Why did it work back then? I think a big part of the answer is the way skates were sharpened. Back then, skaters with only one pair of skates used combination grind, which seems to have been forgotten.
Flats occur when both edges of the blade touch the ice. When you get the light to hit the ice at the correct angle, the tracings left look like two lines separated by the width of the blade. This happens even if you are skating on a curve! In contrast, when you’re on an edge, your blade leaves only a single line. Whether your skate leaves a single line or a double line depends on how far to the side you lean as you glide: you have to lean far enough to get the other edge off the ice. How far you have to lean is determined by the centripetal force as you go along a curve, which is a function of your velocity. Having a flatter hollow on your blade means you don’t have to lean as far to get your other edge off the ice, enabling you to go slower on a single edge. Sid Broadbent has a good discussion of this in Skateology.
Today’s freestyle skates are typically sharpened to a fairly deep radius of hollow. 1/2″ is quite common, and some skaters go as deep as 3/8″. For figures, you want a much flatter hollow. 1″ is the usual starting point; they went up from there. A shallow hollow digs into the ice less, helping you avoid flats and glide for longer from a single push. It also makes turns easier. But it means you have to skate correctly: if you’re not right on the edge, a patch sharpening will skid when a freestyle hollow would feel secure.
With such a big discrepancy, it’s no wonder freestyle skates don’t work well for figures. I think people have forgotten about combination grind. Skaters who did figures and freestyle with a single pair of skates typically used an in-between hollow, something like 3/4″ or 5/8″. This worked adequately for the lower levels of both disciplines. But once they became more skilled, these skaters needed a deeper hollow for control in freestyle and a shallower hollow for good figures. Hence the two pairs of skates.
The outcome is: If you are trying to do figures and find that you have way too many flats, try asking for a flatter hollow next time you get your skates sharpened. It should help you get rid of flats, but will feel very strange and possibly mess up your non-figure skating.
The two other main differences between patch and freestyle skates are:
Soft boots allow the ankle mobility necessary for fine edge control. Back when everyone did figures, boots were much less stiff. Skaters didn’t need super-stiff boots because they weren’t doing all the big jumps seen in competition today. Even beginner boots are awfully stiff for figures today.
Skaters often shaved off the bottom of the toe pick on their patch skates to avoid extraneous marks on turns. Blades designed for figures came with this modification out of the box. At the lowest levels, this isn’t necessary.
Cross-grinding refers to sharpening skates with a grinding stone whose axis of rotation is parallel to the skate blade. This means that if you hold the skate sideways (blade parallel to the floor), the grinding wheel rotates down. This is how the ordinary bench grinders from the hardware store are set up.
A bench grinder. It’s better not to sharpen your skates on one of these. Image courtesy of Wikimedia Commons.
In contrast, most skate sharpening machines have the grinding wheel oriented parallel to the blade. Its axis of rotation is up and down, 90 degrees from the axis on this bench grinder.
The usual skate sharpening machine setup. Image courtesy of Wikimedia Commons.
Such machines generally have a cross-grinding wheel as well as the main sharpening wheel. The people who do the sharpening may use the cross-grinding wheel to remove excessive rust or try to even the edges on new or poorly sharpened blades.
Sid Broadbent, who makes skate sharpening machines, has this to say about cross grinding:
We realize in the case of tabletop machines, their cross grinding capability is certainly advantageous for badly damaged hockey skates, but much of the time it is used whether needed or not. Excessive material is removed, a perfectly accurate groove is destroyed which then has to be reestablished. This excessive metal removal does not affect the overall geometry of a hockey blade since it is removed uniformly over the entire length of the skating surface—or should be. When this approach is used on figure skates, their effective life is reduced to about six sharpenings! An enormous and unnecessary waste of an expensive skate.
Broadbent, Skateology, VII:7
It seems to me that the problem here is more misuse of cross-grinding than use of it at all. I think what Broadbent is hinting at is that some skate sharpeners have this as their standard procedure:
Cross-grind to make the blades “flat.”
Put the right hollow on with the parallel stone.
I put “flat” in quotes in #1 because I want to bring up a point about cross-grinding that seems to have been forgotten: When you cross-grind a skate blade, the hollow does not become flat. It takes the radius of the grinding wheel. So, on the bench grinder pictured above, you may end up with a 3–4″ radius of hollow. Of course, this will change as the wheel wears down. But if you want, say, a 1/2″ hollow, and you happen to have a grinding wheel with a 1/2″ radius, you can get what you want by cross-grinding. Plus, you’ll be able to sharpen all the way up to the toe pick! A parallel sharpener can’t reach a small area just behind the toe pick because the diameter of the wheel is too large.
If you follow the procedure above, you’ll end up with uneven edges unless you’re careful to hold the blade perpendicular to the radius of the cross-grinding wheel. It’s tempting for sharpeners to think of the result of cross-grinding as “flat” and go from there when they put the final hollow on. But because the hollow is not actually flat, a new hollow that looks centered will actually be slightly off-center. That’s because sharpeners use witness marks to align the blade in the holder for sharpening described by Broadbent (VII:1–VII:5). These are marks made on the groove of the blade by lightly touching it to the grinding wheel. When they’re centered, you have the blade aligned…as long as the original groove was centered! If it wasn’t, you need to make a correction.
Determination of the amount of height correction to remedy a specific out-of-squareness error is a matter of experience and experimentation. In any case the effect of any correction would be assessed at intervals throughout the sharpening process by removing the carriage and checking edge squareness with the precision square … then making any further necessary height adjustments.
Broadbent, Skateology, VII:4
That makes sharpening much more complex. And you don’t realize that the the blade is out of square (or the edges are uneven) because you think the cross-grinder made them flat, they’ll never become even. For a figure skater, having uneven edges feels like one side is too sharp and the other side is too dull.
Don’t cross-grind unless you’re careful about not taking off too much blade and making sure the edges are even. But when done properly, cross-grinding can actually work out well.
Early skating authors had a lot of bad things to say about deep hollows on ice skates.
I have said nothing of those skates whose surfaces are grooved, and are commonly called fluted skates, because I think their construction is so bad, that they are not fit to be used; in fact, they are so generally disapproved of, that I shall dispense with explaining their defects.
…
Ladies’ Skates should be fluted.
Jones [1772], 37, 95
Fluted skates, if at all useful, are only fit for boys, and should not be used by moderately weighty persons, or those who are heavier than boys of thirteen usually are, as the sharp edges cutting too easily into the ice, prevent the possibility of figurings; indeed these skates are even dangerous, for the ice cuttings, collecting, and hardening in the grooves, raise the skater from the edge of his skates, and thereby endanger his balance.
Williams 1843, 113
The feeling of “sharp edges cutting too easily into the ice” is familiar to everyone who has ever had the skates’ radius of hollow suddenly decreased, intentionally or not.
I do not recommend fluted skates, or those with a groove or channel along the bottom of the steel. They certainly take an easier hold of the ice than the ordinary kind, but they can only be worn by light weights, and, in any case, are treacherous servants. The tiny shavings of ice which are cut up by the edge are sure to collect in the groove, where they become impacted into a solid mass which can hardly be cut with a knife. By degrees the groove is filled up, and, lastly, the compressed ice projects beyond the steel, and causes inevitable falls. Many a person has fallen repeatedly without any apparent cause, and has only regained the use of his skates when the groove has been cleared with a strong knife. This habit of the skate is termed ‘balling.’
“On the Ice” 1863, 17
Walsh (1877) gives a good description of how skates were sharpened using a grinding wheel. The grinding wheel does not produce a flat cross-section; instead, the blade’s curvature from edge to edge matches the radius of the grinding wheel:
The Skate-Blade was formerly fluted to prevent supposed lateral slipping, but this fluting is quite unnecessary and is now obsolete, the concavity given to the skate-blade by grinding it on the lap at right angles to the length of the blade being more than sufficient to ensure the cutting edge holding the ice without slipping laterally. The blade of the skate should be no deeper than will ensure a curve being made without the edge of the boot, to which the skate is attached, touching the ice.
Walsh 1877, 726
Today, figure skaters use much deeper hollows. It’s even reasonable to say that all today’s figure skates are fluted, but skaters don’t seem to have problems with ice balling up in their blades. What happened?
References
Robert Jones. 2017 (1772). A Treatise on Skating. Edited by B. A. Thurber. Evanston, IL: Skating History Press.
In 1852, George Anderson, a member of the Glasgow Skating Club, published the following advice on skate sharpening under the pseudonym Cyclos:
The edges should … be kept sharp by occasional grinding, perhaps once in a season, or even less; and in doing it, the iron should be held across the face of the grindstone, which, by giving an almost imperceptible concavity, ensures a sharp edge.
Cyclos 1852, 34
A grindstone, or grinding wheel in today’s metal shops, is the abrasive stone that forms the core of a bench grinder. The stone spins fast, grinding down the surface of whatever it comes in contact with (keep your fingers away!). This produces lots of hot sparks when grinding metal (including skate blades).
To sharpen a skate on this grindstone, you’d hold it sideways, with the toe pick pointing to the left and the heel of the blade pointing to the right, perpendicular to the stone. Then, you’d turn the crank (or have an assistant turn it) so that the wheel rotates counterclockwise. As the wheel spins, you’d slowly push the blade across the stone from left to right, starting with the toe and ending with the heel, then lift it up and repeat. After a number of strokes, the blade would match the curvature of the stone.
The radius of hollow this produces depends on the size of the stone. The one in the photo has a radius of about five inches. Five inches sounds like a really shallow hollow—too shallow even for figures, by today’s standards—but keep in mind that blades were wider then. Cyclos writes,
The lower surface of the iron should be a quarter of an inch broad or thereby.
Cyclos 1852, 34
The width of the blade makes a difference. (This is why ice dancers use deeper hollows than freestyle skaters—dance blades are narrower.) According to Sidney Broadbent, what you feel when your blade hits the ice is the bite angle, not the radius of hollow (ROH). This is the angle created at the corner of the blade by sharpening. Make it too small, and you skid. Too large, and you can’t stop. Broadbent gives an equation relating the ROH (R), blade thickness (T), and bite angle ($latex \theta$).
$latex \sin\theta = \frac{T}{2R} &s=4$
Broadbent 1997, I:2
T is the thickness of the blade, and R is the ROH. Today’s freestyle blades are about 0.15″ wide, so with a pretty normal 0.5″ ROH, the bite angle is about 8.6 degrees. For a patch blade with the same width and an ROH of 1″, the bite angle is about 4.3 degrees. Dance blades are narrower, about 0.11″ wide, so a 0.5″ ROH on a dance blade produces a bite angle of 6.3 degrees. This is why ice dancers prefer a deeper hollow.
Cyclos recommends blades that are much wider—0.25″. A five-inch ROH on a quarter-inch blade yields a bite angle of about 1.4 degrees, which is very shallow. It corresponds to a three-inch ROH on a modern patch blade, which is what Robert Ogilvie recommends for high-test skaters (1985, 111).
Conclusion: Cyclos’s recommendations are in line with late twentieth-century thinking on patch sharpening when differences in equipment are accounted for. I’ve neglected differences in ice, though, which do play a role.
To end, Cyclos warns readers of the dangers of learning on grooved skates, like those used for freestyle, dance, and recreational skating today:
it ought not to be grooved, as is sometimes done,—much to the detriment of the beginner, who, after learning on grooved skates, will feel himself like a cat on walnut shells when he puts on plain ones.
Cyclos 1852, 34
Skaters using patch skates for the first time may identify with this remark.
The radius of hollow is very important to skaters because it determines how the blades feel on the ice. It’s set during sharpening. When you get your skates sharpened, you can request a particular radius of hollow. What if you don’t know what hollow your blades have? Or if you want to check that the hollow on your blades is what you want it to be?
To answer these questions, use a blade gauge. Blade gauges aren’t readily available commercially, though experienced skate technicians generally have one (or a set, depending on the design). I made my own out of aluminum using the CNC router at CIADC.
Blade gauges for freestyle and figures. The numbers represent the radius of hollow in inches.
To use them, try to fit the arm of the gauge into the hollow on the bottom of the skate blade. Here’s an example.
See how the gauge doesn’t fit all the way into the hollow? One inch is too big for this blade. It’s a freestyle blade.This one fits into the hollow with room to spare. 3/8″ is too small.9/16″ is just about right.
9/16″ is what I asked for last time I got these skates sharpened. The person who sharpened them did a great job!
I recently ran across an explanation of how to sharpen skates from March, 1919—just over 100 years ago.
Don’t try to draw file at first, … Cut right across the runner first, filing in the usual manner and watching closely the file marks, see that they do not cut down over the corner of the runner. In this manner work down the entire length of [the] runner until all the rounded corner has removed; then take the file in both hands and draw file all the cross marks off. This will enable you to see exactly what you doing to the skate runner; show where to file and where not to.
Perhaps it may be well to file and then draw file two or three times in succession before the skate has been sharpened to suit. By working alternately thus the skate runner can be brought down to a straight or slightly curved bottom, with square, sharp corners, so much desired in skates to enable the skate to `bite’ the ice. The skate may be grooved with a round file if desirable, but skates so grooved, while good for beginners, are not capable of making as much as when worked off flat on the bottom.
Hobart 1919, 12.
I think it’s interesting that hollow grinding, which is so important to skaters today, was considered only suitable for beginners. This goes all the way back to Robert Jones, who says “fluted skates” are “so bad, that they are not fit to be used” (37). Today, only speed skaters have their skates sharpened flat across the bottom.
Hobart continues with a little more advice:
…when you can sharpen skates with a file you may regard them as not being first class skates The runners of really good skates are so hard a file will not touch them and the sharpening must be done with a grinding wheel of emery, carborundum or something similar. But you can use the same method of alternate cross and lengthwise grinding so as to ‘see what you are doing’ to the runner, and not to grind off too much at one place and little at another.
Ibid.
Using a grinding wheel is the modern technique, but cross grinding (grinding with the wheel perpendicular to the blade instead of parallel to it) is generally frowned upon because most cross-grinding wheels are of a very large diameter. Cross-grinding makes the blade’s radius of hollow equal to the radius of the grinding wheel—something like 5 inches—which is generally not what modern skaters want. The parallel grinding wheel then puts the right radius of hollow on the blade. This process takes off a lot of metal, which shortens the life of the blade. But if the grinding wheel has the radius of hollow you want (and back then, people wanted large ones), it’s less of a problem.
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.
