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-calculatorJust 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.