Radius Explained

 

The Skate Truck would like to help players understand the technical side of sharpening to better determine what is the right fit for them.

The radius may be the most important thing regarding skate sharpening, yet also the most misunderstood. Most skaters don't know about setting up for a custom radius to suite your specific skating style. However, even minor changes in the radius will make the skate react and feel very differently. Therefore, I thought I would take a short bit of time to explain this to people if they are interested.

What is the Radius?

The radius is sometimes referred to as the hollow or groove. I'm willing to bet that you were never asked by a local shop what radius you would like ground onto your skates!! That's partially because a lot of the people working there don't understand it properly. Also, the skate shops don't want to take time to readjust and re-dress their wheels to a new radius. this results in using up the wheel much more quickly, again cutting into their profit margins! So, most skate shops simply leave their diamond dresser set up at a "mid-point" around 1/2" radius.
 
A SMALLER RADIUS results in a "deeper hollow", more pronounced tips, a "sharper" feel (we'll address sharpness next), and more edges (surface area). With more surface area in contact with the ice, the skater feels more grip, but also results in more drag (slightly slower).

A LARGER RADIUS results in the opposite: a more "shallow hollow", less pronounced tips, a "no so sharp feel", and less surface area in contact with the ice. This gives the feeling of less grip, but also gives much less drag (faster).
 

What is Sharp?

If someone makes a comment after a new sharpening that their skates aren't "sharp", what they really mean to say is that "This skate does not have enough edge to suit my skating style". Olympic speed skaters actually have their skates honed with no radius (just flat). They are looking for maximum glide. Obviously they have to be extremely careful in corners without the benefit of even a small radius to help in grabbing the ice (that is why when they fall it is almost always during a cross over in a corner). But, don't ever think these skates aren't sharp!
 

What Size Radius is Right for Me?

So, the all important question becomes: "What radius should I have on my skates?" The local shops don't even ask you what you want. Instead, they just stick with one size and sharpen all their skates to that size. When it comes to radii, one size does NOT fit all! There are many different things to take into account in determining the proper radius. Even after settling on one, you may want to make small adjustments on subsequent sharpenings to "fine tune" to your personal taste.

The factors that go into determining your radius include weight, skating style (skater assignment), and ice temperature, and skill level. We will look at these in more detail here.

WEIGHT-an extremely light skater can tolerate very small radii (deep hollow). Because of their lighter weight, they do not cause the skate to "dig" into the ice as much. A heavy skater trying to skate on a small radius will bite into the ice so hard they will have trouble stopping without chatter or going over the top of their skates. They will also lose glide to excess friction and be working harder. Of course, they will hold a very tight turn! Based upon weight, a general starting point would be as follows: very light (3/8"); average (5/8"); heavy (3/4"); hockey goalie (7/8" - 1 1/4").

SKATER ASSIGNMENT-HOCKEY-1/2" is a common radius for kids through high school. Forwards will generally prefer smaller radii than defensemen of the same weight. Goalies continue to have very large radii to "kick out" the puck without catching an edge.

SKATER ASSIGNMENT-FIGURE-kides under 60lbs usually skate on 1/2" radii. A 5/8" radius will take care of most recreational skaters. When in a professional program, it is best to discuss proper radii with the instructor, based upon the type of programs they will be performing.

ICE TEMPERATURE-Optimum ice temperature for a rink is usually around 25 degrees Fahrenheit. Temperatures from 17-23 is considered "hard hockey ice". 25-26 degrees is considered good figure skating ice. Usually on colder/harder ice, people prefer a slightly smaller radius (and vice versa)

SKILL LEVEL-As people get advanced and along the professional ranking, they tend to use smaller radii, as they have the combination of leg/ankle strength and talent to "get away with it".

 


What Radius of Hollow (ROH) Is Right for Me?

The selection of a Radius of Hollow for your skate blades is an individual decision, but we can give you the facts and recommendations to help make your decision easier.

The Radius of Hollow determines the bite angle of each blade edge. The selection of ROH and bite angle determines the performance characteristics of the blade. The correct application of any ROH results in a blade with sharp edges. A smaller radius of hollow 1/4" ROH means that a blade will have edges with higher bite angles than a blade with a larger radius of hollow 1" ROH. The higher bite angles result in edges which penetrate the ice deeper increasing drag and requiring more energy to accelerate.

 

What ROH do the NHL players choose?

The most common choice of radius of hollow for hockey players is 1/2". According to a recent study of all NHL players 47% choose to skate on a 1/2" ROH. The next most common ROH in the NHL is 5/8" ROH.

Begginers and recreational skaters should try an ROH of 5/8" or 3/4".

Better Glide - Skaters select higher ROH's (1" or higher) when they are looking for increased glide.

More Friction - Skaters choose lower ROH's (3/8" or lower) when they are looking for more friction and control.

 

Inconsistent ROH (Radius of Hollow)

Due to a combination of sharpening equipment tolerance variations, lack of operator training, and poorly marked settings, ROH can vary from machine to machine, operator to operator, and shop to shop. Even though a skate can be perfectly sharpened, changes in ROH will give a different feel due to change in bite angle. This may give the impression of an improper sharpening. The Skate Truck offers a trained professional operator( Frank Tocco, 6 years experience) along with the most advanced equipment available. One of the latest equipment upgrades is the height comparator guage, allowing precision height adjustments to within 1000 of an inch.

 

 

All About Hollow Radius?

Now we should understand some of the principals - theory of skate sharpening. While it has been described as a groove, a hollow grind, or a ground radius, you could refer to it to your skate sharpener as follows:

  • I normally skate on a 5/8 inch radius hollow
  • sharpen my skates to a 1/2 inch hollow please
  • I would like a 3/4 inch radius ground onto my blades please

By grinding a hollow/radius into your skate blade you are making your edges sharp and depending upon the radius you choose, you are also making your edges more (or less) pronounced in the shape at the tips.
Remembering some school math, you may recall that a 1inch diameter circle will have a 1/2 inch radius.

A sharpening attendant can easily dress (shape) the face of the grinding wheel to the curvature shape of  any radii between 3/8 and 1 or +1 inch.

By dressing the radius of choice onto the grinding wheel, it will be transferred to the skate blade by grinding.

 

What Radius is Best? The Meaning of Sharp

Choosing a radius can be as simple or as complex as you choose to make it. There are many 'experts' who disagree on skate sharpening. There are also some sharpening outfits that have developed sharpening gimmicks, primarily as marketing techniques to attract customers. You should also be able to form opinions on your own. To begin, let's look at what different radii look like on the bottom of a blade. After a skate has been ground it will have sharp edges regardless of how big or small the radius is. Keep in mind that the long speed skating blades are honed flat with no radius (hollow). They are looking for maximum glide.

While they are careful in the turns, don't ever doubt that these blade edges are not sharp!

The real questions to ask yourself are:

  • Is there enough edge or bite into the ice for me ?
  • Is there too much edge or bite for me ?

If immediately upon use you feel the skate is not sharp enough, you may really mean the skate does not have enough edge (bite) to suit my skating.

These are: (1) weight, (2) skating assignment, (3) skill level and (4) ice temperature. The following is general purpose in nature and you must find the right setting for your needs.

In no case should a radius smaller than 3/8 inch be needed, this having too much edge for anyone, and may even create a safety hazard not only for the skater but also for the sharpening attendant while dressing the grinding wheel to such a tight radius.

1 - WEIGHT
An extremely light skater can tolerate a very small radius (deep hollow - lots of edge). They do not have much weight to bear on the ice. Note: beginner level skaters can learn most skills (particularly the hockey stop) easier by having skates with a larger radius (less edge).

As they progress in skill, the radius is decreased back to a normal level. A heavy skater trying to skate on a small radius (too much edge) will bite into the ice so hard that they will have trouble stopping without chatter or going over the top of their skates. They will also loose glide quickly to excess friction. On the other hand, they will be able to hold a very tight turn!

Professionals can skate on smaller radii as they have the combination of leg/ankle strength and skating skills to get away with it. Skating on too small a radius feels like skating on soft ice. While 3/8 inch radius edges are more pronounced than 5/8, they are also more fragile and less durable. A general purpose chart (rule of thumb) for radius by weight for average skating skill is as follows:

VERY LIGHT AVERAGE HEAVY GOALIE
3/8 – 7/16 1/2 – 5/8 5/8 – 3/4 5/8 inch to 1 inch

HOCKEY: 1/2" and 5/8" seems to be a very common radius for players through high school. Forwards generally prefer smaller radius than defensemen of the similar weights. Goalies generally prefer larger radii or flatter cuts so that they can kick out without catching an edge. Although recent trends reveal that a deeper radius is becoming much more common among butterfly style goalies. 

Revelations regarding RADIUS from the Head Trainer of the Edmonton Oilers regarding some specific players when they skated for the Oilers or for Team Canada: Gretsky: 1/2" Coffee: 1" to 2" Messier: 1" Laraque: 1" Pronger: 7/8" Sakic: 5/8" Iginla: 1/2"

FIGURE: Skaters (under 60 lbs.) typically should skate on a 7/16 inch radius. A 1/2 or 5/8 inch radius will take care of most recreational skaters over 60 lbs. When figure skaters get to a level where they are in a serious program, they will be under the guidance of a coach or instructor. The skater should consult these people for advice on the best radius for the program they are performing.

TIP: Individuals can call the shop that did their skates and ask, "What radius are you grinding skates to?"

Note: Institutions that will not divulge the radius setting of their sharpening stone to the skater are:

  • Trying to protect their business, or
  • They just don't know

In either case, institutions like this should be treated with a measure of caution.

SPEED SKATING: Flat - No hollow.

BANDY: Skaters prefer very shallow hollows to permit more glide, due to the increased skating times and larger playing surface.

3 - SKILL LEVEL
As your skating skill level changes, experiment a little with a different radius. Find the one that works best for you.

4 - ICE TEMPERATURE
Most rink managers shoot for an ice temperature of approximately 25 degrees fahrenheit.
A temperature of 17 to 23 degrees is considered 'hard hockey ice', 25 to 26 degrees is considered good figure skate ice.
A slightly smaller radius may be required on colder/ harder ice.
 

Poorly Dressed or Worn Grinding Wheels

The radius of hollow must be applied to the grinding wheel with a diamond stylus. Poor operation techniques and/or out of tolerance stylus can result in miss-sized or out of shape profiles being applied to the grinding wheels. Frequent wheel dressing is required to maintain the proper shape. With use, the grinding wheel profile will wear and change. This can result in incorrect or uneven bite angles. The Skate truck closely monitors the grinding wheel and redresses as needed. Properly dressed stones will greatly impact the quality of sharpening.
 

Proper Skate Sharpening

 

For proper sharpening, the radius of hollow must be centered down the middle of a skate blade. This results in an equal bite angle on both inside and outside edges.

An off-center sharpening will result in one edge being higher than the other and different bite angles from edge to edge. Most sharpening machines require the operator to center the grinding wheel on the skate blade by eye. Therefore, the training, judgement, and conscientiousness of the operator can greatly affect the quality of the sharpening.

 

Optimum Surface Feet Per Minute