Experiment: Metal Removal Rate of Wissota Sharpener

[Bill_S]

I was curious about how quickly the Wissota, in my hands, removed metal from a skate blade. I performed a quick experiment to measure it.

I used an old but still serviceable Coronation Ace blade (10-1/2" length) for the experiment. I gave the blade a fresh sharpening before I started to make sure that ROH (Radius Of Hollow) differences would not affect the readings. The grinding wheel was dressed again before starting the experiment without changing the ROH.

I marked a position about halfway along the blade that was 6.5" from the root of the toe pick. I used a Sharpie and a small adjustable square to scribe a reference line where I would position a Starrett micrometer for measurements.



I took four measurements before the sharpening began and averaged them. Then I began to sharpen, counting passes through the machine.





EDIT: I added this 2.5MB video showing my sharpening technique....

https://www.afterness.com/skating/images/wissota/metal_removal/wissota_sharpening_pass-1.m4v

After sharpening 20 passes using my typical speed of about 1 inch/second and light pressure, I measured again five times and averaged the readings.



Before sharpening - 0.77703 inch (19.74mm) (average of four readings)

After sharpening - 0.77514 inch (19.69mm) (average of five readings)

Difference - 0.0019 inch (0.05mm) after 20 sharpening passes.

A human hair is about 0.002 to 0.004 inch thick according to one source. Making twenty passes removed less metal than a human hair is thick. That surprised me, but then again, I have to make a lot of passes when changing someone's ROH. That should have been a clue.

Variables that affect metal removal rate with any given grinding wheel would include speed of the blade traveling against the grinding wheel and applied force. I found that 1"/second gives a nice surface finish, so I standardized on that. Force is another variable, and I use a light touch. With heavy pressure, more material would be removed, but mistakes could accrue faster.

FWIW, I measured the metal removal rate for a Pro Filer hand sharpener in time, not passes. I used one for many years before getting the Wissota powered sharpener. Because the Pro Filer is a hand tool, it is very slow. I measured 0.003 inch from the edges to 0.004" from the hollow on one blade after two hours of sharpening. It would normally not take nearly this much time to sharpen a pair of blades with it, but I had to be able to measure the results.

If anyone wants to measure the metal removal rate on their own machines, just append to this thread. However, please stay on topic.

[Kaitsu]

Bill,
Thank you for your experiment. It's always nice to read your experiments. At the same time I am feel ashamed as I have almost every time some comments which can be interpreted to be negative feedback. Also this time I would like to comment few things.

You mentioned pass-tough speed and grinding pressure as a variable. They are truly variable in your experiment, but if we start to compare machines or different operators, we have plenty of other variables too.

Based on the pictures you use Wissota´s 100 grit wheel. https://wissota.com/product/blue-wheel/
Wheel type and coarseness is one major variable, which would be good to list in your experiment parameter. Another assumption is that you're living in the location where electrical network frequency is 60Hz, when someone else may live in country which uses 50Hz electricity. This means that your electrical motor might have 20% higher rpm than someone else. Electrical motors are same, but they may have different type plates to meet local MEPS requirements (minimum energy performance standard).

In Wissota wheel is mounted directly to the electrical motor shaft when in some other machines there is belt drive which has some pulley ratio. In such a case it might be difficult to know exacts rpm´s of the wheel, even you would know electrical motor speed. Wheels are also available in different diameters. 3", 6", 7" and 8" wheels are I guess most common used sizes, but they also wear when they are used. Someone may have wheel which is brand new and someone other uses wheel which is end of its lifetime. To get one step more close to apple to apple comparison, I would propose that you use following calculator to calculate what the actual cutting speed was in your experiment.
https://www.nortonabrasives.com/en-us/norton-wheel-speed-calculator

Just for example, let's imagine that you use your Wissota @ 60Hz (nominal rpm 3450 rpm) and wheel size is 7". Your cutting speed would be 32.12 m/s. If I would use exactly identical machine at 50Hz (nominal rpm 2875 rpm) and my wheel would be 5.12", cutting speed would be 19.58 m/s. If we would manage to keep the same pass-thought speed / pressure and I would use exactly same wheel type as you are, in theory your machine should remove 39% more metal than mine. If we forget the impact of frequency and focus just to the wheel size, 5.12" wheel @ 60Hz would mean 23.49 m/s cutting speed. That also remarkable variable.

Just to compare, my incredible edger wheel is spinning ~5000rmp @ 50Hz (measured speed). If I use new 3" wheel, my cutting speed is 19.95 m/s. I can use it until wheel diameter is 2" and in that wheel size cutting speed is just 13.30 m/s. I can see 3" vs 2" diameter difference very clearly already from the spark spray while sharpening. I need to make also more pass-thought with the wheel which size has reduced. I will try to records some picture or video clip in some day. You had already nice picture from your spark spray pattern.

I would be also interested to know all measured values and not just their average. Some people are more skilled to use micrometer than the others and I believe measuring uncertainly can vary a lot from user to another. From the numbers we can perhaps conclude if you were flattening the edges in every measurement (theoretically possible scenario). This is not easy measurement when you don't have flat surfaces which would be parallel to each other's. So I can easily expect that there was 0.01mm variation between the measurements which would be already 20% measuring uncertainly.

This experiment is very interesting, but in my opinion theoretical cutting speed values are already telling that if everything else would be 100% identical, bigger wheel removes faster metal than smaller wheel. Higher cutting speed should be in theory very easy to compensate. You just make less passes than small wheel machine operator and we should end up removing same amount of metal. However, frontal area of the blade causes often unexpected problems.

For the skater's information that we removed 0.01 - 0.05mm metal from their blade does not tell so much. This is nice to know information for skate techs and sounds impressive, but for the skater it is just number which sounds very very small. Just about half of human hair thickness, as Bill said. However at least I cannot convert this number in to format that I would understand what it means for the skater. For this reasons I have never made similar experiment or even traced the original profile to every skater. I am focusing to measurements which are easier to explain how they affect to the skating and how the profile develops over the times. This does not mean that my way would be the only right way. Every measurement and experiment what has done develops us in way or another.

I think this kind of experiment could be even more useful if it would be changed a bit. I would measure amount of removed metal from the two or even three different locations. It would be more informative to understand how much you removed metal from the location where you start your grinding compared to other locations of the blade. Starting position behind of the toe picks is where 80% of critical and irreversible sharpening mistakes are done with the power grinders. Target is I remove same amount metal from all over the blade, but that is actually not so easy. From that I have so many example pictures.

If someone decides to repeat this experiment, it is important to use similar blade than what Bill used. Using Tapered, Parabolic or stainless blade might cause own variables. Also ROH I would keep same than what Bill used.

Bill, if you feel that this post is too far from the original topic, you can request administrator to remove it.

[Bill_S]

Valid points there.

My grinding wheel spins at 3580 RPM unloaded (measured). The grinding wheel diameter is currently down to 6.80 inches in diameter.



It is Wissota's soft 100 grit wheel, available from them. Be careful when just comparing grit numbers alone because not all abrasive materials are the same. See this video from YouTube about surface grinding, grits, and finish - https://www.youtube.com/watch?v=gjz0Zt76GJ4

I completely agree about using the same, or a similar blade for this sort of experiment. I began the experiment with Gold Seal blades, and they have a complex geometry for clamping. I carefully adjusted the skate holder to give even edges, removed the blade to make the initial measurements with the micrometer, re-clamped and then made 20 passes.

I found that the measurement did NOT change after 20 grinding passes, and suspected that merely re-clamping this blade caused uneven edges. I obviously removed material from only one edge, and that wasn't reflected in the micrometer measurements. The micrometer still read the unchanged high edge. Here's a photo of how uneven the edges of this blade became after 20 passes when I didn't re-adjust the skate holder after reclamping...



When I obtained the sharpener and edge tools, I created a table for the edge level indicator for various thickness blades. It calculated the difference between left and right edge height based on the lines showing on the edge tool. From my table, the photo above indicates that the difference in edges was between 0.003 and 0.004 inches. The fact that the blade was clamped, centered, unclamped for measurement, then reclamped adversely affected edge level even with no skate holder adjustments.

To reduce setup steps between clampings, I switched to simpler, flat-sided blades, and chose the Coronation Aces. Without having the complex side machining of the Gold Seal, it could lend itself to reclamping with fewer issues. A measurement after the test showed that these blades retained level edges. (This reiterates that there is no easy way to accurately center all blades on a sharpening machine - yet. That's a big reason why setup time takes so long when carefully sharpening blades.)

And of course different steels used in different blades will affect measurements.

You asked about the individual measurements included in the average before and after. I removed the micrometer completely between measurements, then re-positioned and remeasured. Here are the measurements (four before, five after). They show very little deviation.

Before            After
0.7770           0.7753
0.7770           0.7751
0.7771           0.7753
0.7770           0.7750
---                 0.7750

I did attempt to measure another spot on the blade near the spin rocker (1-1/2 inches back from the toe pick's root), but because the blade is so highly curved there, my measurements had too much scatter to include. Without a measuring fixture to eliminate errors, I opted to omit them from the results I gave above.

If you attempt this experiment, you will find that places to make reliable measurements are limited. I chose to use a point where the blade's edge, and the inside were mostly parallel to reduce errors due to micrometer positioning.

BTW, I did make a video of a sharpening pass on my machine, but didn't get it processed for yesterday's post. It shows the blade positioned near to the wheel, the machine turning on, the movement of the blade through the sharpener with sparks, and finally turning the sharpener off. It's 2.5MB.

https://www.afterness.com/skating/images/wissota/metal_removal/wissota_sharpening_pass-1.m4v

[Query]

Ummm.

Not to be picky, but you re-dressed the wheel.

If we assume that your initial dressing was somewhat flattened, because the initial sharpening (or any prior sharpenings with that dressing) slightly ground off the central portion of the wheel more, then your subsequent sharpening may have removed more steel down the center line of the blade than on the edges.

And AFAICT, your measurements were taken at the edges. So maybe the first few sharpenings removed little or nothing there??

In other words, perhaps you shouldn't have re-dressed, to give an optimal test.

Also, could you use reference points that would let you apply your micrometer without unclamping the blade?

And - is it possible that the micrometer applies enough pressure to bend or flatten the edge a bit? That might mess your measurements up. I don't know of a fix to that, but it is worth considering.

I may be completely off base here. Maybe none of these effects are significant. But I notice that you engineering types love to push measuring things to insane limits. So I'm giving you an option to do it a little more.

BTW, is it normal for mechanical vernier micrometers that read to .0001 inches, to show a measurement noise of several ten thousandths of an inch, as your apparently did? I recently went out of my way to supplement my (used) vernier micrometer, which had similar noise, with a new digital one, that was consistent to below .0001 inch, though it is theoretically one of lower quality, because I thought that noise excessive.

[Query]

Also - no one would bring blades back to you immediately after a fresh sharpening, unless they were unhappy with the sharpening - which obviously won't occur for you.

So, the question is, what is the amount of metal you remove sufficient to re-sharpen blades that have had normal use - say, 20-40 hours on the ice, to reasonable standards of sharpness? And if my assumption is correct, that hand sharpening speeds are slow enough that hand sharpening reshapes the metal more than it removes metal, what would be the amount you would need to remove that way, to resharpen them?

If the amount of metal you removed in your tests IS accurate, and none of my silly ideas is significant, maybe we can ignore the cost of replacing blades, if people sharpen blades your way - because it would take many, many sharpenings to remove enough metal - say, at a rough estimate, .1 inch - before the blade starts behaving much different on the ice. I had based my claims that the cost is significant, and frequently far exceeds the cost of the sharpening itself, on what several very good skate techs told me - that they seek to remove .003 inches from figure skating blades in each sharpening. But you are removing less.

[Bill_S]

A lot of questions, but here goes with some of them. I also had heard that a typical machine sharpening removed 0.003 to 0.005 inch each time. In fact, that's one of the reasons that I wanted to try this experiment.

As far as a typical sharpening, I remove only enough to bring sharp back edges according to feel. Once that's done, I stop. If there are deep nicks, I'll explain to them that they could either remove them at the cost of the blade life, or ignore them. As long as I address any high spots, they won't feel much difference. That's especially true in the tail of the blade where skaters usually collect the most nicks but spend little time skating there.

The dullest pair of blades that I've sharpened were a pair of brand new MK Pros. Even though there was a factory sharpening, the edges were rounded over. It took around 15 passes to get them sharp.

I know that redressing the wheel is one possible variable, but I wanted to sharpen a blade like I usually do - dress immediately prior to sharpening. To not do so would introduce the other variable and invite criticism that I didn't dress the wheel before I sharpened. See the dilemma? I took the chance that dressing was fairly repeatable. I'm making an assumption that subsequent sharpening passes take down the edges equal to the hollow if the sharpening geometry remains identical between the "before" sharpening and subsequent sharpenings.

If you look at the side of Gold Seals, they present all sorts of complications for re-clamping identically. I could have made a fixture to do that, but it was easier to move on to a simpler blade construction like an Ace. If you think about it, you wouldn't be able to hand sharpen a Gold Seal with a Pro Filer for very similar reasons. Each Gold Seal blade must be centered to the wheel each time it is clamped. That usually involves making a mark in the hollow, give the wheel a partial turn by hand, and reading the ink scuffed from the mark. It takes time, and gets you close, but only your first pass or two will verify proper centering for truly level edges. With a general purpose skate holder, there is no easy shortcut.

The Wissota 3D holder has a fairly wide clamp that prevents me from taking measurements while the blade is in it. That's the first thing that I checked. It would remove some of the experiment's complexity and improved accuracy.

I thought about how the edge might become deformed under the pressure of the micrometer, but guessed that with sufficient number of passes, this potential error would become less significant. At least edge deformation would be similar between the initial and final measurements.

My micrometer is calibrated in 0.001 inch gradations, and I merely interpolated to the next digit when the index was between two marks. It is not going to be perfectly accurate to the fourth decimal place, but at least I was able to characterize when it was between two readings. Measuring inches precisely out to 4 decimals places is hugely problematic, and even involves temperature control.

In my case, it was an experiment, done with reasonable care, among internet friends. It's not going to be National Bureau of Standards accurate. I did it because I haven't seen anyone else attempt it, and I wanted to get a handle on metal removal with my current setup. I'm satisfied that the results are ball-park accurate for my machine.

[Query]

I take it that you feel people don't skid much from minor nicks, so what you usually do is good enough.

I wanted to sharpen a blade like I usually do - dress immediately prior to sharpening.

But do you usually also deburr after every sharpening? That removes some steel too, though it would be difficult to control that precisely.

How many passes do you typically take on a sharpening, if the person hasn't gone longer than usual between sharpenings?

For this test, did you balance the wheel each time you dressed it?

Did you use a lubricant or polishing fluid?

I wonder if the effort you put into this makes your results completely atypical. I.E., maybe people only need to remove .003 inches if they don't put that much time and effort into it?

Anyway, what you did shows that if you do everything carefully, the Wissota can remove very thin layers of metal. Do you believe one can do as well with it as one could using the most expensive skate sharpening machines?

[Bill_S]

A small nick in the edge of a blade won't hurt a thing IF YOU TAKE OFF THE HIGH SPOTS. That includes dressing down any protrusions along the side of the blade. When I'm stoning the side of a blade, my goal is only to remove any burrs that stick up.

I aim to take 6 or fewer passes when sharpening, but there are exceptions. I've done my own blades in as few as 3 passes and sufficiently restored the edge.

For this test, did you balance the wheel each time you dressed it?

I cannot static balance a wheel after dressing as you describe. You'd have to remove the wheel to balance it, and any remounted wheel would require redressing for perfect concentricity. In your supposition, you're immediately in an endless loop.

I did not use a lube, wax, or polishing fluid for this test.

[Query]

So, you removed about .0019 inches in 20 passes, or about .000095 inches / pass.

3 passes would then be about .000285 inches. And 6 would be .00057 inches, over 5 times smaller than the .003 inch standard that many people claim. Pretty good.

Assume you use $650/pair Gold Seal blades, and that you discard the blades after .1 inch is removed (a very rough estimate, assuming you don't bother to trim the toepick), and that deburring doesn't remove significant metal, you will get about 175 (6 pass) sharpenings lifetime out of the blades, not counting the first one that installs the initial hollow. 

Which costs you $3.705 / sharpening.

Not counting the lifetime of the wheel and the diamond dresser, or the sharpening machine, or electricity.

Since you are a small time skate tech who isn't making a living at this, shall we assume you will do 200 - 500  sharpenings, spending $2500 - $3500 on all your fancy equipment? I guess initial equipment costs would be around another $5 - $17.50/sharpening, which is more than the value of the blades lost in a sharpening. Does that sound about right?

For an individual skater, it would take a lot of years to justify the cost of all that fancy equipment.

That said, I figure a lot of people spend far more money driving to a first class skate tech's shop and back, than the other costs, so maybe it is worth it.

But perhaps this is really just another hobby for you. It doesn't have to make economic sense.

[Query]

>I said:
>For an individual skater, it would take a lot of years to justify the cost of all that fancy equipment.

Let me clarify. I started sharpening for myself because I was unsatisfied with the job done by the skate techs I took my skates too. Either they did a bad job, or they were inconsistent in terms of what they produced. (If I had started with a skate tech who produced good, consistent results, I would never have bothered.) Eventually it became a skill to more or less master, that I could be proud of.

But then when I tried to convince other people it was worthwhile, I justified it in terms of cost. With maybe $125-$150 in hand tools, it should have been easy - a lot of people around me were driving 2 or 3 hours round trip time to very good skate techs. The cost of driving alone justified buying the tools within a few months. But in fact, I had trouble convincing people they could do it, or that it was worth it. (In all fairness, they often carpooled - and sometimes one coach or skater would bring all the skates for many skaters to and from the first class skate tech. I saw the same happen among hockey players, and I knew a couple speed skating sharpener who sharpened for a large group of beginners, then taught the dedicated ones to do it for themselves.)

With your more expensive tools, it is even harder to justify, unless you become a pro. I doubt many people in this forum will be convinced to buy their own Wissota or other brand powered skate sharpener. And

When they look at the extraordinarily expensive equipment the fancy shops use, or when you say it takes you 45 minutes - despite your prior machine shop experience - that just makes them less likely to attempt it. I get that you are taking a very dedicated approach, trying to take the skate sharpening art to its limits. But if you told them that you could do a better job in 5 - 10 minutes than most skate techs probably do, that would be more convincing. And if they could do it cheaper to boot, that would help too.

Many people on this forum spend huge amounts of time trying to do as good a job at figure skating as they can. Most will never reach the levels of their coaches, let alone the finest performances they see on TV. But they don't need to, to enjoy it, and feel a sense of pride. Likewise, most of them could at least match the quality their current tech probably delivers. Unless they happen to have one of the best skate techs in the world, which, for obvious reasons, isn't true.

[Bill_S]

With your more expensive tools, it is even harder to justify, unless you become a pro.

With all the expenses involved, skating itself is hard to justify. Some of us do it for the love of the sport, despite the cost.

[Query]

With all the expenses involved, skating itself is hard to justify. Some of us do it for the love of the sport, despite the cost.

Good point.

And I get that you are trying to take the perfection of sharpening as far as you can.

I just hope people understand they can do a pretty good job without going to such extremes. Probably better than the average skate tech, if they care at all to try to get it right.

[Kaitsu]

If anyone wants to measure the metal removal rate on their own machines, just append to this thread. However, please stay on topic.

I tried to follow the process as accurate as I could, but surely there are some small differences. Quite many things you realize when it's already too late to redo something. Example the location where I took the readings should been selected and marked more carefully to the blade. I had only one marker line which I tried to keep measuring position and I used same 6.5" measurement position as you did. Better would make two lines and ensure that micrometer jaws are always between these lines. Also measuring position should be selected blade specifically and not trying to repeat someone else process too detail level. Blades are not anyhow 100% identical.

In second measurement where I measured material removal rate after 20 sharpening passes, I noted that I don't need to move micrometer so much  to another location when you easily get  0,01mm different readings. Also from measurement results you can see that my second measurement was less repeatable.

I do not know if your blade was suffering similar heavy unevenness from stanchion side as mine test blade had. As I was a bit worried how wobbling micrometer affects to reliability of my measurements, I tried to get stanchion side to be also in square before actual test. In practice I made it by grinding ½" hollow also to stanchion side. I tried to ensure that both sides from the measurement locations are very accurately in square when I used same side surface as a reference. That was much easier in first grinding where you can make as many sharpening passes as you want to get edges 100% even. When making those 20 passes, amount trials are limited. I didn't succeed in second grinding with accuracy what was the original target.

Measurement results were something what I didn't expect, but they helped me to understand that I may need to take back some words what I have said. Smaller wheel does not automatically mean lower material removal rate. I expect that my pass-through speed is lower than yours. This compensates partly the material removal rate between small and large wheel machines. Still I have problems to understand why it looks like I removed so much more metal than what you did. Even the measuring results looks quite repeatable, still I would say that we can have easily 0,02mm measuring uncertainly. Can the differences explained with measuring uncertainly, that I cannot know surely.

I was considering building measurement jig which would use two dial gauges which would make measurement more reliable from the same location, but I do have only magnet stand for dial gauge. That is not enough for my needs and I didn't want to use too much money money for this study. Another reason was that I kept this one time study. It someone else duty witness if me or Bill has missed something in our studies.

For skaters the information how much we remove in one sharpening is quite useless, but for skate techs who uses power grinders, this study is very interesting. At least we have now two measuring results which gives some evidence to things what we have probably read or heard from someone. Study took totally almost 2 days and even the results were witnessing that I was wrong, I want to thank Bill about this challenge. Most likely my brains continue processing this all couple weeks. How can it be so that I removed more material? That might remain mystery, but as said we have now some numerical facts and much more information how we have end up to say that 20 passes removes 0.05...0.07mm metal.

Here you can see more details about my study...https://youtu.be/KIDnw7AQPd0

[Bill_S]

That's very, very interesting. Thank you for taking the time to do this! The experiment does take time, and you made thoughtful preparations

While the experiments show small measured metal removal rate differences, an uncontrolled variable is the operator (as you know). It is interesting to me that the results were so similar given two different machines, in two different countries, operated by two people who have never met each other.

I am planning to re-run my test, but with the original pink, 80-grit ruby wheel instead. I want to see how much the grinding wheel type affects metal removal. I wanted to static balance the ruby wheel before I begin my second metal removal-rate test, but I misplaced one of the three thin nuts that serve as counterweights on my second balancing unit. I intend to resolve that issue in the future and test the ruby wheel to have a third data point.

In the meantime, thanks again for taking the time to compare results. They are very interesting.

[Query]

For skaters the information how much we remove in one sharpening is quite useless, but for skate techs who uses power grinders, this study is very interesting.

Most blades do not break. They become unusable after too much metal is removed, so the relationship of the rocker profile to the toe pick is no longer desirable.

So the amount of metal removed / sharpening is inverse to blade lifetime, and to the amount you spend replacing blades.

Both of you managed to remove astonishingly small amounts of metal / pass. And Kaitsu, the marks that are counted on the main scale of your micrometer are 1 mm apart, right? If so, you manage to get astonishingly consistent measurements out of your micrometer. Either your technique is much better than mine, or my equipment is in bad shape, because I'm no where near that consistent.

But If you take skates to an average local skate tech, who removes a LOT more metal than you two (one dubiously competent skate tech told me he was taught to remove 1/32 inch / sharpening), blade replacement, rather than the sharpening itself,  or replacing boots, is often the principle equipment cost, comparable or greater than the cost of paying for your skating sessions, maybe even more than some people spend on private skating lessons.

So I claim the amount of metal removed is very important.

That is what I tell people to try to convince them it is worth learning.

Of course, people who drive long distances to go to a first class skate tech spend even more money driving. No one has ever claimed that figure skating is an especially cheap sport.

Then again, if people had to pay either of you what your time is worth, as experienced engineers (I assume that's what you both are), to spend an hour or two sharpening a pair of skates, and they had to pay a fair share of your equipment costs, that would be remarkably expensive too!

[Bill_S]

Wissota 80-grit pink-wheel metal removal rates

Executive summary - the coarser 80-grit wheel removed even less material that the 100-grit blue wheel did after 20 sharpening passes. This is a surprising and completely unexpected result. Blade surface finish was not as good however.

I ran the 20-pass test a total of two times with the pink wheel. I removed 0.0008 inches (0.020 mm) on the first 20-pass test run, and 0.0014 inch (0.036mm) on the second run. I purposely slowed down the grinding passes on the second run to see if that made a difference. It appeared to be a contributing factor in the difference between these two runs.

---
The Test

I wanted to compare the 80-grit pink grinding wheel that ships standard with the Wissota 911 sharpener to the optional 100-grit blue wheel that is designed for figure skates. I used the figure skating blue wheel for all of my sharpening, and the previous test results were for that grinding wheel. I balanced the 80-grit wheel so that it matches what I've done with the blue 100-grit wheel. The Oneway Wolverine balancing kit that I purchased had two balancers, so the second was fitted to the 80-grit wheel and static balanced on the included balancing stand. I now have two different grinding wheels, and both are balanced in the same manner to reduce vibration.



There's another thread here http://skatingforums.com/index.php?topic=8710.0 that shows the balancing steps if someone is curious.

I prepared the test blade as I did before by sharpening it and ensuring level edges. I used a 10-1/2 inch Coronation Ace blade as I did before with the other wheel. To ensure that I could re-clamp the blade in the holder as close to identically as the first time for the initial sharpening, I drew Sharpie marks on the blade at the mounting corners of the skate holder clamp. It's not very visible in the photo below, but the registration marks were made at both the front and the rear corners of the blade clamp.



After the initial sharpening to ensure level edges, I re-dressed the wheel once more. I did not re-dress between the 20 sharpening passes. The wheel showed a slight discoloration from swarf when the test was completed, but it wasn't loaded up.



For the second test run (another 20 passes), the wheel was dressed again twice, once before the test run to achieve the "before" measurement condition, and then again before the next run of 20 passes..

After the initial sharpening and verifying level edges, I measured the runner height at a location 6.5 inches behind the root of the toe pick, just as before. I made a dozen measurements, removing the micrometer completely from the blade each time. After measurements were complete, I discarded the highest and the lowest reading, and averaged the rest.

The spreadsheet with data appears below:



In the summary, I mentioned that the blade finish wasn't as smooth as I got with the blue wheel. It felt rougher along the edge too. Here's a photo showing the finish achieved with the pink wheel...



There are repeating artifacts showing that are easily photographed. It's not as bad as some blades that I have received for sharpening, but not ideal.

The movement of the skate holder wasn't as smooth with this 80-grit wheel during the grinding passes compared to the blue wheel.

For figure skates, I prefer the feel and resulting finish of the 100-grit blue wheel from Wissota. However I was completely surprised by how little metal was removed after 20 passes with this wheel. Between the two runs, it is obvious that the speed of the grinding pass is a factor.

In conclusion, I am still amazed at how little blade metal is removed, and even more baffled by the slower metal removal rate of this coarser wheel. I did not expect that.

[tstop4me]

Wissota 80-grit pink-wheel metal removal rates

Executive summary - it removed even less material that the blue wheel did after 20 sharpening passes. This is a surprising and completely unexpected result. Blade surface finish was not as good however.

---
In conclusion, I am still amazed at how little blade metal is removed, and even more baffled by the slower metal removal rate of this coarser wheel. I did not expect that.

Intriguing result, Bill.  Here's my initial conjecture for a possible cause.  A coarser grit corresponds to a larger grain size; a finer grit corresponds to a smaller grain size.  A coarser grit typically results in a faster removal rate than a finer grit ... if there is sufficient pressure for the larger grains to embed more deeply than the smaller grains.  But you are intentionally using a very light pressure.  Assume the larger grains do not embed more deeply than the smaller grains. Then when you compare the coarser grit to the finer grit, the surface area of abrasive in contact with a unit surface area of the blade could be less for the coarser grit than for the finer grit under some instances (there are, of course, many variables involved here), resulting in a net slower removal rate.

[Bill_S]

Your explanation is very plausible.

I wish there were an easy + inexpensive way to create a testing mechanism that would repeatedly pass the blade by the grinding wheel with a constant speed and force. That would remove the operator variable.

At least I have approximate data on how this operator works with this particular machine. It actually puts my mind at ease knowing that I don't remove enough metal to reduce blade life significantly using my current sharpening technique.

[supersharp]

I have a mixed reaction--yes, that could be beneficial for us as we try to compare things.

But I feel like I get a lot of information that I don't even know I'm noticing by having my hands on the boot while grinding.  A lot of the time when I'm guessing that the edges are now perfect or not, I am correct. Given the size of skaters relative to the tiny differences in speed when a focused, careful person is sharpening, I think we are hitting the point where the differences are negligible.

Always interesting as a thought experiment, though. I thing tstop4me has a good theory about medium vs fine stones.

[Kaitsu]

Many of our test results are fighting against my theories and I have huge challenges to understand if we are talking more about measuring uncertainly or material removal rates. We are talking so small dimensions that at least I have challenges to understand how this all can be possible. I have some challenges to believe even my own measurements.

I think all whom will make this test can agree that we can see sparks and some steel dust on blade after every pass. These are things what we can see easily just by eye. We have also measuring results that in best case we are removing just 0.001mm (0,000039") with one sharpening pass. If we study a bit how small dimension one micrometre (0.001mm) actually is, it looks like it's size of bacteria. Spider web silk thread is said to be 2-3 microns, so it seems we can even split on to half or third. If I remember right, in one training they said that if you cook your hair several times and replace water every time, the grease layer on top of 6th cooking water is about one micron.

https://en.wikipedia.org/wiki/Micrometre#/media/File:How_big_is_1_micrometer?_(10690468113).jpg

We have talked also about using sharpie or marker pen to paint blades before sharpening so that we can see where the wheel contacts. I could find video where they demonstrate that sharpie ink layer thickness would be about 0.003mm (3 microns). Unit conversions are not always so easy, as we can see on this page where sharpie layer thickness was told to be 30 microns. There were also other good comments related to gauge blocks accuracy classes. This is relevant note as they used two different gauge blocks in some stage. But if we forget these details and say that they measured correctly and sharpie creates about 0.003mm thick layer. It sounds quite realistic value at least to me. 

https://hackaday.com/2020/04/20/measuring-sharpie-thickness-the-ink-itself-not-the-pen/

If I paint the blade with marker pen, will I actually remove metal at all or do I just polish ink away from blade? Obviously marker pen in is much softer than hardened steel, so we do not need to do three grinding passes before we start to remove metal. We are removing some amount of metal already at first pass.

I hope this helps to understand why I questionize even my own measuring results. I want to highlight that purpose is not to criticize anyone. I just try explain how my brains are processing when my theories and facts seems to have some mismatch.

To get better understanding to my selves, I repeated 20 pass test with small modifications. What I did do differently compared to previous test?

• Before I was started to make anything else, I tried to find thinnest place from my test blade instead of using 6.5" location. In the thinnest (or lowest) position (of curved shape) micrometer
   anvils are more parallel to the blade where both measuring surfaces are curved. When I did find the best measurement location, I traced micrometer anvil location to the stanchion side with
   sharpie. With this way I could ensure that both measurements are taken more accurately from the same spot.
• I did dress the wheel only twice. Ones before starting and after 10 passes. I can clearly see less sparks than in previous test as the wheel is not cutting so aggressively.
• When I was happy to edges evenness, I used sharpie to mark location where blade was on skate holder. I removed the blade from the skate holder and measured blade thickness to get
   reference point.
• I did put the blade back to skate holder using positioning markings. I made 20 grinding passes without adjusting skate holder height. In the other words I didn't worry the edges evenness. When I checked evenness afterwards, there was slight unevenness. I would anyhow say that the unevenness was quite similar than in my first attempt.

Conclusion was that this time I was able to remove less material. Is it because of less wheel dressings, did I keep this time measuring spot more accurately same or was it because of missing height adjustments? Were the measuring spots less or more parallel this time or in previous time?

One theory could be that if you adjust your skate height several times while sharpening, wheel is contacting in to smaller area. In theory this way you might actually remove more material in one pass if you "jump" from edge to another. Lots of questions are flying inside of my head when we are talking about micron level material removal rates.

Attached the measuring results from the 2nd  20 pass test. Most likely there will be 3rd test in near future.

[Query]

If I paint the blade with marker pen, will I actually remove metal at all or do I just polish ink away from blade? Obviously marker pen in is much softer than hardened steel, so we do not need to do three grinding passes before we start to remove metal. We are removing some amount of metal already at first pass.

I wonder if all magic markers produce layers of the same thickness. Could some ink layers be thinner?

What about light pencil marks? Is there a way to lay down a single layer of graphite? Someone at https://physics.stackexchange.com/questions/12806/roughly-how-many-atoms-thick-is-the-layer-of-graphite-left-by-a-pencil-writing-o estimated a pencil mark as 31.4 nm thick, about the thickness of a single layer of graphite, but I'm not certain that is right or reliably attainable.

Anyway, when sharpening by hand, you push out a sharpening lip or burr off to the sides that you can feel with your finger. (Be careful. Move your finger LIGHTLY across, not along the edge, and to the sides, or you may cut yourself.) I assume there will be no lip or burr from just removing ink.

So, if you feel for such a burr, off to the side, I think you will know you have removed metal. But I'm not sure that is always the optimal way to sharpen a skate, if you intend to deburr.

But there isn't always a burr after powered machine sharpening. After Mike C sharpened a blade using a medium grit wheel (I don't remember the grit - I think it was about 80 by USA standards, https://www.reade.com/reade-resources/particle-measurement/grit-to-mesh-to-microns-to-inches-conversion-chart says that means 165 micron particles), I looked at the edge under a cheap USB microscope. There was no lip or burr.

I have felt a lip or burr after someone else sharpened using a fine grit wheel (e.g., I think about 120 grit, i.e., 102 microns). No doubt there are many other variables, just as in your experiments, including grit size lubrication, wheel speed, wheel and blade composition, pressure, etc.

BTW, on The Science of Sharp website, in an article concerned with sharpening razors (which may be a completely different case), the author wrote that it is not desirable to create a sharpening burr, that you should ideally stop before that happens. He also said that a hardened steel cannot produce a burr to the side that can't be bent straight as I do using hand tools, to create a foil edge - that well hardened steel would break before it could bend nearly that much. Which implies that the working that creates such burrs removes the inclusions that harden the steel. In fact, the softening of sharpening burrs is one the reasons often given for removing them - in applications where you need a very hard steel, the burr, even if it is polished and reformed to be in the right alignment, isn't hard enough.

[Kaitsu]

Today I repeated 20 pass test twice. Wheel is same as in previous test, only size has reduced. Results were logical compared to my earlier tests and this convinced to me that in my hands 20 passes will remove about 0.05 to 0.07 mm from the blades. Today I also witnessed to my selves that more sparks means higher material removal ration, which is quite obvious when nothing else changes than how aggressively wheel cuts. Summary of my tests so far...
1st  0.079 mm
2nd 0.038 mm
3rd 0.069 mm
4th 0.046 mm

There is reason why 1st and 3rd are more close to each others and same in case 2nd and 4th. These ones you should comparable to each others. Removing just 0.02mm with 20 pass would mean that I should almost triple my pass-trough speed, which would lead terrible chatter marks. Slow pass-trough speed might be one negative side of the small wheel machines. In the other hand, very often I need 20 passes to remove nicks from the blades.

Based on the test results what we have, if I would use Wissota and 80 grit / 7" wheel I should make 60 passes for the same blade. To be honest, this is totally opposite than what I could expect. Maybe this comes from the wheel dressing like they explain on the video Bill shared. Coarse wheel is dressed to be so dull that it wont cut so much steel.