Pro-Filer Users: What's the diameter of your cylinder?

[tstop4me]

This post is addressed to readers who use the Pro-Filer manual skate sharpener by Edge Specialties, Inc.  There's been conflicting info on this forum and elsewhere concerning the 7/16" ROH kit:  whether it is in fact a distinct kit or a relabelled 1/2" ROH or 3/8" ROH kit.   I'd like to settle this once and for all.  Please supply the following info:

Approximate date of purchase:

Stated ROH of kit:

Diameter (in inches) of sharpening cylinder:


Here's my info:

Approximate date of purchase:  July 2015

Stated ROH of kit:  7/16"

Diameter (in inches) of sharpening cylinder:  3/4".


Note that a 3/4" diam cylinder would theoretically correspond to a 3/8" ROH.  I called the company to check whether they had shipped the wrong kit.  Brad Anderson told me it was the correct kit.  He told me that a smaller diam cylinder was needed to yield a ROH equivalent to that produced by a power sharpener with the wheel dressed to 7/16".  [I asked him what was the diam of the 3/8" ROH kit.  If I recall correctly (not entirely sure now), it was 5/8".]  Makes sense since the actual blade ROH will likely be larger than the cylinder radius due to various factors such as wobble and variations in pressure.  I will defer for later discussion the actual ROH produced by a stated kit.  This post is concerned only with the kit itself.  Thanks.

[Bill_S]

In my Pro-Filer review page, I have this footnote...

Footnote 4:  New 7/16" ROH is said to be available (but see note below). The Pro-Filer is advertised to be available in a new 7/16" radius of hollow (ROH). Halfway between 1/2" and 3/8" ROH, this is a very common sharpening radius among figure skaters.

NOTE: When I ordered the 7/16" kit, I got a call from Brad Anderson telling me that it's essentially the same as the 3/8" kit. He said that there's only a tiny 0.001" difference between the hollow made by the 3/8" and the 7/16" on most skate blades. I didn't check his math, but decided that I'd just make do with what I had. I really didn't need another 3/8" kit.

(Added 5/2014, note added 12/2014)

-------------------

I just measured my kits, and here are the numbers (diameter of opening in the aluminum holder was measured to approximate stone diameter):

Orange anodized - 0.998 in. (1/2" ROH) (purchased 2014)
Purple anodized #1 - 0.755 in. (3/8" ROH) (purchased 2014)
Purple anodized #2 - 0.752 in. (3/8" ROH) (purchased ~2011)
Purple anodized #3 - 0.751 in. (3/8" ROH)  (purchased 2002)
Clear anodized  -  0.999 in.  (1/2" ROH) (purchased ~2004?)



Like you, I find this to be a mildly deceptive practice but Brad DID call me about the order. Regardless, I like how well the sharpeners work for me.

[Matsumoto]

I think I brought my Pro-Filer around September 2014 - it was the 7/16" ROH kit.  I just measured the diameter of the rough sharpener and I get 0.755", which works out to be just a bit above a 3/8" ROH.

Interesting findings - I never thought to measure before.

[Bill_S]

Out of curiosity, what color are your Pro-Filers?

[tstop4me]

Out of curiosity, what color are your Pro-Filers?

Mine are purple.

[Bill_S]

That's what I expected. No difference, but sold under two different ROHs.

Even though the difference is a quoted 0.001" at the blade, I'd expect better from them.

[AgnesNitt]

from here:
https://mdmetric.com/tech/cvtchtfdm.htm

7/16 in is     0.4375 inches in decimal or  11.1125 mm

3/8  in is    0.3750 in diameter or 9.5250 mm


Unless I'm completely off track,to me it looks about 0.0625 inch is a lot more than .0001.

That's almost a tenth of an inch, which is visible to the naked eye.

[tstop4me]

from here:
https://mdmetric.com/tech/cvtchtfdm.htm

7/16 in is     0.4375 inches in decimal or  11.1125 mm

3/8  in is    0.3750 in diameter or 9.5250 mm


Unless I'm completely off track,to me it looks about 0.0625 inch is a lot more than .0001.

That's almost a tenth of an inch, which is visible to the naked eye.

No, the ~.001" difference that Bill is referring to refers to the difference in the depth of hollow (DOH) measured at the blade between a 7/16" ROH and a 3/8" ROH.  The DOH is the difference in height between the edges and the bottom of the hollow (assuming a properly centered hollow with even edges).  Freestyle skating blades typically have a width ranging from .150" to .170".

Then,

blade width    ROH     DOH

.150"            3/8"     .0076"
.150"           7/16"    .0065"
.150"            1/2"     .0057"

.160"            3/8"     .0086"
.160"           7/16"    .0074"
.160"            1/2"     .0064"

.170"            3/8"     .0098"
.170"           7/16"    .0083"
.170"            1/2"     .0073"

That's why measuring the actual ROH at the blade requires proper instrumentation and measurement technique.  That will be the subject of a future post.  There is also the issue of bite angle and the effect of such small tolerances on actual skate control.  For readers not familiar with machine shop work, a difference of .001" (25.4 microns) is damn small. 

Note that the difference in DOH between 7/16" ROH and 1/2" ROH is actually less than the difference in DOH between 7/16" ROH and 3/8" ROH.  By this criteria, a 1/2" ROH would be a closer approximation to a 7/16" ROH.

[tstop4me]

That's what I expected. No difference, but sold under two different ROHs.

Even though the difference is a quoted 0.001" at the blade, I'd expect better from them.

Well, let's see what happens with my latest order.  I recently ordered a 3/8" ROH kit, expecting a different kit from the 7/16" ROH kit, based on my conversation with Brad a year ago.  I won't be happy if they're the same, and will have to return it.  Anyone out there have the 5/16" ROH kit?  If so, please report the requested info.  Thanks.

[Bill_S]

Agnes,

I've got two graphics already online that may help explain why a large difference in ROH means a small difference in the difference between the height of the edge vs. the hollow.



...and this one is to scale, but magnified...



It's because the blade is very narrow. In math classes in an ancient era (think slide rules), I always liked to take concepts to the limits, usually zero or infinity, to explore the behavior of an equation. If you think of a zero width blade, there would be no difference in the edge vs. hollow. It's zero like the center-line in the illustration above. The two measurements are the same because they go to the same point along the same line.

Extending this to the real world, the thinner the blade, the less difference there is between edge and hollow for any given ROH. A blade is thin compared to the diameter of the sharpening stone.

[Query]

I apologize for mis-remembering that the 7/16" were really 1/2", when in fact they are about 3/8", according to what you folks have measured. I have only bought the 3/8" model (twice) (the 7/16" model wasn't available, and at the time I liked my blades very sharp), and they are a bit worn now, so any measurement I took would be pointless.

.001" sounds insignificant (and on the phone, Brad insisted it was), but I would claim it isn't. In your diagram, there is a perceptable difference in edge angle.

I hve tried skating on blades with 3/8" vs 7/16" ROH. It was easy to tell the difference. A lot of figure and hockey skaters will tell you they have experimented with small ROH differences, and have developed strong preferences. It could all be psychological, but I don't think so.

Even if it all is psychological, Honesty is good for business. It's a good company, delivering a quality product. Why play games with something as easy to verify as the radius of the stone? You don't even need precision machine shop tools to tell the difference.

[Bill_S]

I agree with you. It's eye-opening to feel small differences in blades/edge.

That's why I wish Edge Specialties would make an actual 7/16" Pro Filer instead of sending a 3/8" kit and claiming it doesn't matter.

[AgnesNitt]

I've had 3/8 one week and the next week 1/2...I.can.tell.the.difference...

I have the 1/2 " pro-filer, but my sharpener told me I was killing my inside edges with it....well,tht could be me...not the pro-filer....so I sve it for times I can't reach a sharpener and need to stretch a sharpening,

[Query]

Actually, can any of you tell me why small differences matter? The edge angles are only slightly different from 90 degrees - why should a tiny difference from that matter so much?

Part of my problem is that I don't have a detailed physical model of what the interaction is between the blade and the ice. If the main point of an edge is to increase lateral resistance (i.e., sideways skid-resistance), what is so different between a flat blade (infinite ROH) and a hollow ground blade?

It's easy to understand why an over-burr would matter - that's like having a deeper keel on a boat. But people notice a difference between ROH's even when skate techs make a point of de-burring the edges.

[riley876]

I was under the impression that it was the depth of the hollow that mattered rather than the angles.

i.e. the depth is somewhat in the same ballpark as the ice's water interface layer, maybe the blade effectively aquaplanes on the hollow, and the edge itself is the keel.  If the keel touches all the way through the water layer to actual solid ice it's good.  If not, then less good.
Maybe BS, but my best guess.

[AgnesNitt]

I agree with you. It's eye-opening to feel small differences in blades/edge.

That's why I wish Edge Specialties would make an actual 7/16" Pro Filer instead of sending a 3/8" kit and claiming it doesn't matter.

People can tell. We have a Silver dancer at my rink who sharpens his own blades to 13/16. He got there through working until he found something he liked (he got rave reviews from the retired Nationals coach so he does a good job)

[tstop4me]

I was under the impression that it was the depth of the hollow that mattered rather than the angles.

i.e. the depth is somewhat in the same ballpark as the ice's water interface layer, maybe the blade effectively aquaplanes on the hollow, and the edge itself is the keel.  If the keel touches all the way through the water layer to actual solid ice it's good.  If not, then less good.
Maybe BS, but my best guess.

No, the angles are what really matter.  I wanted to defer this discussion to a separate post, and limit this thread to the Pro-Filer kit.  I'll post a diagram later.  But here's a brief preview.  More than one angle is involved.  But one is easy to understand.  Each edge is similar to a knife edge.  For a knife, an important angle is the included angle:  the smaller the included angle, the sharper the edge.

Several complications to consider before we do a deep dive into this topic:

(1) The physics and chemistry of ice skating is really not well understood.  Ice by itself is really not well understood.  For most materials, the density of the solid state is greater than the density of the liquid state.  Water is a peculiar material in that the density of the solid state (ice) is less than the density of the liquid state (water); that's why ice floats on water.  For many years (as often described in high school physics texts), many people thought that the pressure and friction exerted by the blade on ice caused the surface of the ice to melt, and the blade glided over the resulting film of water.   Later studies showed this was not true.  A surface chemist found that ice inherently has a quasi-fluid surface layer.  A non-technical summary can be found here:  https://www.exploratorium.edu/hockey/ice2.html.

(2) The actual ROH at the blade created either by a standard grinding wheel or by the Pro-Filer doesn't necessarily match the radius of the wheel or stone.  Vibration, wobble, pressure variations, and other factors will likely cause the actual ROH at the blade to exceed the radius of the tool.  Because of the narrow width (or thickness) of the blade, and the small differences involved, measuring the ROH at the blade is difficult.  The only convenient tool that I'm aware of is the HDI (hollow depth indicator) gauge made by Edge Specialties (http://www.pro-filer.com/hdi/), which makes the Pro-Filer.  The HDI gauge doesn't measure the ROH directly; it measures the depth of hollow (DOH), which I discussed above.  If you measure the blade width (or thickness) separately with an instrument such as a micrometer or vernier calipers or thickness gauge, you can calculate the ROH from the DOH and the width (or thickness), assuming that the hollow is cylindrical.  I bought an HDI gauge to check what I was really getting, either from my skate tech or from the Pro-Filer.  For the 7/16" Pro-Filer kit (which has a 3/8" radius stone), the blade ROH I'm getting varies from 7/16" to 1/2" (this will depend on various factors, including the skill of the sharpener).

(3) Remember, discussions of blade geometry usually rely on idealized mathematical models.  Real blade edges will deviate.  For example, most skate techs hand finish the outside of the edges with a flat whetstone.  Some skate techs also hand finish the hollow with a curved whetstone.  Such hand finishing will mess up the idealized geometry for sure.

But, yes, given the small deviations involved, I can feel the difference between 3/8", 7/16", and 1/2" ROH (most noticeably when entering a one-foot spin).  I switched skate techs because my previous one was originally delivering close to my requested 7/16", but in recent sharpenings, more like 9/16".

[tstop4me]

It's easy to understand why an over-burr would matter - that's like having a deeper keel on a boat. But people notice a difference between ROH's even when skate techs make a point of de-burring the edges.

Query, in several instances, you have mentioned straightening the burr.  Do you know of any skate techs that actually do that?  I do, when I sharpen my blades with a Pro-Filer.  I do not remove the burr with a flat whetstone; I straighten the burr with a honing steel.  But I've yet to come across a skate tech who uses a honing steel; they've all used a flat whetstone to remove the burr.

[riley876]

Wouldn't a side grind with a handheld stone give a more consistent edge, vs a honing steel.   Since the honing steel method is completely dependent on what burr you had to begin with.   And I can't see how that could be controllable.

[tstop4me]

Wouldn't a side grind with a handheld stone give a more consistent edge, vs a honing steel.   Since the honing steel method is completely dependent on what burr you had to begin with.   And I can't see how that could be controllable.

Any hand finish operation is subject to the skill of the operator and subject to inconsistency (and so are most power sharpening operations).  All I can say is that a honing steel gives me a wickedly sharp edge (which I prefer, but others don't); sharper than any I get with a whetstone; and sharper than any that a skate tech has ever delivered to me.  I sharpen knives, and always finish with a honing steel.  So one day, I thought I'd try it on my skate blades, and wow was I surprised. 

[riley876]

OK, must try it next time.

I like ultra sharp edges too.   I do have my own unique method to sharpen my skates:

http://skatingforums.com/index.php?topic=6386.0

Which, after changing to a 320 grit belt, has been getting me lovely sharp edges that last incredibly well (50+ hours so far, and still razor sharp),  but I have been side grinding with a handheld stone.   I get BIG burrs off this sharpening technique, but they're out sideways, so completely useless to leave on.

I always thought the traditional longitudinal grinding of ice skates isn't optimal for making a consistent edge.   After all, you don't sharpen a knife by dragging it lengthwise down a stone, do you?

[tstop4me]

OK, must try it next time.

I like ultra sharp edges too.   I do have my own unique method to sharpen my skates:

http://skatingforums.com/index.php?topic=6386.0

Which, after changing to a 320 grit belt, has been getting me lovely sharp edges that last incredibly well (50+ hours so far, and still razor sharp),  but I have been side grinding with a handheld stone.   I get BIG burrs off this sharpening technique, but they're out sideways, so completely useless to leave on.

I always thought the traditional longitudinal grinding of ice skates isn't optimal for making a consistent edge.   After all, you don't sharpen a knife by dragging it lengthwise down a stone, do you?

Well, if you get big ragged burrs with your home machine, you may be better off removing them with a whetstone (Pro-Filer leaves fine burrs).  But even when I have a skate tech power sharpen my blades and hand finish with a whetstone, I find that 2 or 3 swipes with a honing steel will still produce a noticeably sharper edge (a whetstone will still leave a fine burr).  Also good for touch-ups since little or no metal is removed.  I've found that a smooth honing steel works best; otherwise, use one with fine grooves.  Many grooved steels have a smooth tip, which works well for skate blades.  With the right diameter honing steel, you can hone the edges along the inside of the hollow as well as on the outside. 

[beginner skater]

I always thought the traditional longitudinal grinding of ice skates isn't optimal for making a consistent edge.   After all, you don't sharpen a knife by dragging it lengthwise down a stone, do you?

Am I missing something? I thought that's how it was done, thinking about carving knives, and those long steels

[riley876]

https://www.youtube.com/watch?v=rTKV5-ZSWcE
https://www.youtube.com/watch?v=t39rhQs6Hqc

Yes, it's drawn down the length of the stone, but the knife edge itself isn't aligned exactly with the motion.  i.e. it's on an angle to the motion.  Admittedly if you tried the handle would hit the stone, but still...

[Query]

Query, in several instances, you have mentioned straightening the burr.  Do you know of any skate techs that actually do that?  I do, when I sharpen my blades with a Pro-Filer.  I do not remove the burr with a flat whetstone; I straighten the burr with a honing steel.  But I've yet to come across a skate tech who uses a honing steel; they've all used a flat whetstone to remove the burr.

I haven't heard of anyone else using a honing steel. Usually a flat stone, and/or a hard rubber "stone". I also haven't seen anyone else use a belt sander. But whatever works for someone, is good.

I was shown how to use my first Pro-Filer by the pro shop manager, Don Giese, who sold it to me. He usually did leave the re-pointed burr, even on machine sharpenings, which is one of the reasons his results felt sharper than most of the others. Don coached, speed, hockey and figure skating, and I think he used to be a top ranked U.S. ice and inline speed skater. But he did a lot of custom work, and sometimes shortened or removed the burr for skaters who didn't take good enough care of their edges to deal with the burr, which is quite fragile. He is now largely retired.

The person who used to manage the pro shop at Bowie Ice Arena also left a long repointed burr, creating very sharp edges.

(Edge Specialties' instructions for Pro-Filer used to describe sharpening using a reopinted burr, but I rhink they have now removed most of the details.)

But most skate techs produce less sharp edges. E.g., Mike Cunningham, a respected sharpener at Skater's Paradise, with many high profile clients, mostly deburrs, by default. (He and I looked together at blades he sharpened under a microscope.) His theory is that the skater should not notice a significant difference in the way a blade feels after sharpening, as long as he/she sharpens reasonably offten. But, like any good skate tech, he too does custom work, and will do what the customer asks for.

Many skate techs who think they deburr, actually leave some repointed burr, that you can feel, or see under a microscope.

Blackstone Flat-Bottom V sharpening equipment grinds an edge that resembles a repointed burr, but I think the "V" is a little thicker than a repointed burr. I don't know any figure skaters who say they've tried it. Anyway, the entire shape is built into the way they dress the wheel, so is produced differently.

BTW, I think I got "over-burr" from the knife sharpening community, not the skate sharpening community. And I should note that I have yet to see a sharpening burr that is a clean, well-ordered sheet. Edges and burrs are usually quite uneven, under a 50-100x microscope.