Flat bottomed sharpening?

[Query]

You folks have been discussing the Blackstone FPV. But the original poster asked about the Blademaster flat bottom sharpening, not Blackstone. Blademaster provides a form dressing system for ordinary sharpening wheels (presumably for multiple brand sharpening machines, including their own) so those wheels will create a FPV.

See page 10 of https://blademaster.com/web/img/cms/2018%20BMCatalogue%20Email.pdf

This includes Blademaster's estimates of equivalent ROH for various flat bottom specifications. The confusing thing is that they do not adjust that estimate for blade width - which makes no sense.

However, note that Blademaster here, as on page 17 of their catalog, has somewhat unusual recommendations for ROH for figure skaters.

In particular, my understanding is that, while there is a fair range of personal choice, the most common ROH among figure skaters is 7/16" (but many ice dancers choose 3/8" on MK Dance blades, because MK Dance is ground "thinline" - i.e., it is narrower at the working surface). But Blademaster seems to be implying that figure skaters usually choose larger ROH.

Blademaster does imply that some figure skaters want flat bottom sharpenings. (Blademaster seems happy to provide whatever anyone might ask for,  - for a price. If you bought everything in their catalog, you would spend a lot of money. )

[Kaitsu]

You folks have been discussing the Blackstone FPV. But the original poster asked about the Blademaster flat bottom sharpening, not Blackstone.

Could you kindly tell us more clearly how this was explaining why Blackstone claims 2 degrees FBV bite angle to be equivalent with 12 degree bite angle in ROH?

[tstop4me]

You folks have been discussing the Blackstone FPV. But the original poster asked about the Blademaster flat bottom sharpening, not Blackstone. Blademaster provides a form dressing system for ordinary sharpening wheels (presumably for multiple brand sharpening machines, including their own) so those wheels will create a FPV.

See page 10 of https://blademaster.com/web/img/cms/2018%20BMCatalogue%20Email.pdf

This includes Blademaster's estimates of equivalent ROH for various flat bottom specifications. The confusing thing is that they do not adjust that estimate for blade width - which makes no sense.

However, note that Blademaster here, as on page 17 of their catalog, has somewhat unusual recommendations for ROH for figure skaters.

In particular, my understanding is that, while there is a fair range of personal choice, the most common ROH among figure skaters is 7/16" (but many ice dancers choose 3/8" on MK Dance blades, because MK Dance is ground "thinline" - i.e., it is narrower at the working surface). But Blademaster seems to be implying that figure skaters usually choose larger ROH.

Blademaster does imply that some figure skaters want flat bottom sharpenings. (Blademaster seems happy to provide whatever anyone might ask for,  - for a price. If you bought everything in their catalog, you would spend a lot of money. )

Blackstone discloses technical details of their flat-bottom V; hence, there is a basis for rational discussion.  If you look through the Blademaster documentation you cited, you will note that they disclose no technical details of their flat-bottom architecture (what is X5 through X9, and what is GX6 through GX8?); hence, there is no basis for rational discussion.  I did a quick (by no means thorough) search for Blademaster details outside the documentation you cited, and came up empty.  If you've found relevant technical details, please provide them.

If you're merely arguing that the original thread launched in 2014 asked about Blademaster and should be limited to Blademaster, and that Kaitsu should have launched a separate thread on Blackstone, that's a mere formality our moderator can readily address by splitting the thread if they deem appropriate.

[Query]

I'm simply saying that Blademaster's system (BFD=Blademaster Flat Bottom) may be significantly different than Blackstone.

As a first cut, you could take a common hockey blade thickness, and estimate the angle from Blademaster's table of equivalents.

I suppose one could call Blademaster and ask for details.

Other websites have tried to address Blademaster's shapes:

At https://sharpskates.files.wordpress.com/2012/10/bfd-flyer.png and https://sharpskates.files.wordpress.com/2012/07/bfdflatbottom1.pdf Blademaster implies that their flat bottom shape actually retains a bit of an arched radius, to improve strength - but is not specific. But as you have pointed out, Blackstone isn't specific either - or rather, the dimensions they give are contradictory.

BTW, Blackstone's number do identify the flat width and edge height - if https://salemskates.com/flat_bottom_form_dressing.html is correct. Unfortunately, without a specific blade width, there is still no way to identify the angle those two dimensions create. That guy also claims that Blackstone offers a dressing system for other brand sharpening machines too. But he also implies flat bottom shapes give the inexpert skate tech more potential to mess up.

At least with conventional ROH systems, the hollow shape is fairly clear. But, as this discussion points out, neither Blackstone nor Blademaster give enough details to determine the exact cross section shape.

In fact Blackstone's image https://blackstonesport.com/technology makes it clear that they are assuming a (hockey) blade width of .070 - .100 inches - and they aren't specific as to which the equivalents were determined.

I don't understand Blackstone's argument - why does putting the top of the hollow closer to the ice make it better and faster? I guess you could say that, since the physics of ice skating remains under debate (e.g., does the boundary layer behave as a 3 dimensional liquid, or as something much more complex, as some recent studies have suggested), they determined that empirically - and that would be fine if everyone agreed it was true. (Which they don't. Many hockey players have stated online that they notice no difference between standard arched constant radius hollow, and flat bottom sharpenings. I haven't found anywhere where figure skaters have made similar comparisons. It might be amusing if a good figure skater here would - but there are costs to doing so.)

[Kaitsu]

First FBV sharpening test to Coronation Ace blade is now completed by using Blackstone 100/75 spinner. Unfortunately I did forget to take my precision square with me, so we used Blackstone Z-02 BAT gauge to check edges evenness. As you can see from the picture, we didn't succeed so well at first trial. There is 0.25mm error in skate carriage height adjustment, which caused 0.035mm height difference to the edges height. I used H.D.I gauge to measure edges height difference.

As we failed to get hollow into the middle of the blade, I cannot measure all features what I am interested. Or I can measure, but they are not giving us the correct information. I need to make new attempt to grind hollow in to the middle of the blade.

I could conclude already from the existing measurement that width of the hollow is not 100 THOU (2,54mm) like stated on the spinner. Measured width seems to more close to 75 THOU (1.91mm) than 100 THOU. We can also conclude that if the bottom of the hollow is kept as a datum, there is 1 degree bite angle difference between the outer and inner edge. This should not change even we adjust skate carriage height. Even the bottom of the hollow is a bit wrong datum when we try to evaluate bite angle, in my opinion it is indicating exactly those problems what explained in earlier post. Before making any final conclusions, I need to make new test.

I can confirm that it is possible to make FBV sharpening also to figure skate blades. Will I ever start to make FBV sharpening's to figure skates, most likely not.

ps. actual measurement data cloud points are visible under the red lines. 

[tstop4me]

Interesting results.  What was the depth of the channel (hollow)?  Obviously considerably more than the target range of 0.0005" to 0.001" (0.0127 mm to 0.0254 mm) stated by Blackstone.  I can see how a spinner controls the width of the channel (hollow) and the edge angles.  But I don't understand how the depth of the channel (hollow) is controlled to the extreme accuracy stated by Blackstone.

[Kaitsu]

The thickness of the grinding wheel is 8mm. Hollow in the spinner has to be wider than wheel, otherways you cannot dress the wheel. So in theory wheel thickness defines the maximum blade thickness on both sharpening methods (ROH & FBV).

Depth of the hollow what you get is blade thickness specific. Also this is valid to both sharpening methods (ROH & FBV). Wider the blade is, deeper the hollow you get. Deeper the hollow is, more bite you will get. This is something people dont usually realize when they ask same ROH than in previous skates. I can do the same ROH as in previous skates, but bite angle can be then different. Such can happen easily example if you change from Coronation Ace to Ace Lite. If we would like to be accurate, we should talk about bite angles instead of hollow radius. Then you would get always same kind of sharpening even blade thickness varies...at least in theory.

Why I say in theory? (sorry...a bit out of topic). How many of us has wondered what happens when blade thickness is someting than 4mm and why hockey player can manage so shallow hollows compared to figure skaters even the balde is so narrow? It is for sure that blade thickness has some impacts for the skating, but what is totally missing from the hockeys? It is the chrome removal grinding. It is not just ROH which defines the angles of the edges you use for skating. Each edge you use for skating has also two edges. One of those you can define by choosing certain ROH, but the other side of the edge comes from the factory. If they roll that another side of your skating edge, like Wilson usually do, angle of the edge changes. This is why I hate so much blades where chrome is removed. Each blade is unique, even left and right foot.

[Kaitsu]

Depth what balckstone gives for their FBV is valid to the certain blade thickness what they do not tell. This is what I tried to explain earlier. I am not sure if they try to a bit fool people in their sketch by comparing Hockey player FBV sharpening (3mm) to goalie ROH sharpening (4mm). This would at least give maximum hollow depth difference. Even at the ROH sharpening 3mm blade thickness would give shallower hollow than 4mm blade, even ROH would be same in both blades.

I didnt give the depth for the hollow and "real bite angles" for two reasons...
1. Edges were not even, which means that one edge was 0.035mm higher that the other. However the calculated depth of the hollow was following (0.035/2)+0.150= 0.1675mm. This I measured with H.D.I gauge from the one location.
2. Edges height values what I did get by another method didnt match with my H.D.I gauge measurements. As the edges were not even I didnt start to investigate why two different measuring methods didnt give same results.

We will get more detailed data when I manage to do better gringing for the blade. That I try to do in next week.

When "real bite angles" are measured, I should use the edges (line between the highest points) as a datum. Now I used bottom of the hollow as I didnt have any other realiable datums. In my opinion bottom is the hollow or channel does not need to be parallel to the edges. Most important it that edges are in square to the side surfaces of the blade. That I will try to improve on next grinding attemtp. I hope you can understand what I mean.

[tstop4me]

Thanks for the response.  I'll wait for your further measurements.  Blackstone's presentation is very confusing to me still.

ETA:  I've gone over the Blackstone material again, and I've identified the major source of my confusion.  In standard radius of hollow (ROH) sharpening, we are explicitly concerned only with the edge angles.  For a given blade thickness, the edge angles are controlled by controlling the ROH. The depth of hollow (DOH) per se is not explicitly a parameter of concern:  the DOH results incidentally from the blade thickness and the ROH.

But in FBV sharpening, as presented by Blackstone, we are explicitly concerned with both the edge angles and the depth of the channel (hollow).  And according to Blackstone, the depth should be much shallower than is found in standard ROH sharpening and much more accurately controlled.  E.g., Blackstone offers three different depths, with the difference in depths between adjacent values being only 0.00025" (0.00635 mm = ~6 microns!).  To avoid significant overlap between adjacent values, that would mean that each depth would have to be maintained to a tolerance of ~ +/- 0.00005" (0.00127 mm = ~1 micron!).  I worked with such tight tolerances in semiconductor wafer polishing.  I don't see how that can be attained with spinners, grinding wheels, and skate sharpeners.

[Query]

I think good hockey players get by with longer ROH - i.e., wider edge angles, even though they have narrow blades and often skate on cold, hard ice, because Hockey players are told to skate very "aggressively". They push very hard against the ice. They helps them do the sudden stops and direction reversals that help them confuse their opponents by being less predictable. It may not create the aesthetically beautiful skating that is expected in figure skating, but that doesn't matter.

Hockey skaters have a huge advantage. I was told by a hockey coach that a typical hockey skater only stays on the ice for about 45 seconds at a time. That means they indeed can push very, very hard, during those short times, giving deeper penetration into the ice.

I'm not exactly sure how the difference in rocker radius affects the differences. Hockey blades have a longer rocker radius (more flat) in the center than figure skates. As best I understand it, they spend a lot of their time gliding on that. (But they have shorter rocker radius at the ends, for fast turns.)

I think hockey skaters typically push and stop off the center of the blade too. The longer central rocker radius gives them more length to push off of, or stop on. And that lets them accelerate very fast. Of course they need to push very hard against the ice to take advantage of that - but, as mentioned above, they do.

Another aesthetic factor is that figure skaters are not supposed to have much (if any) side slip. That requires sharp edges, which are achieved in part by shorter ROH. There is of course no such aesthetic standard in hockey.

[Query]

BTW, I've known figure skaters who use 3/4" - 1" ROH, perhaps because it creates less friction, giving a longer glide. So it isn't universal that figure skaters tend to use shorter ROH.  Especially for School Figures. Possibly for Moves in the Field, though I'm not sure. (Some people advocate even longer ROH for School Figures.) For both of those skating disciplines, glide length is very important, AFAICT, because you are often expected to go fairly long distances off of a single push. (Also, if what I've seen is typical, the speeds over the ice in those disciplines is fairly slow, so maybe they don't need very sharp edges??) If Blackstone is right, and FBV really does create less friction, maybe it would be good for School Figures and Moves in the Field??

Kaitsu - once you fix the uneven FBV edges, hopefully you can find good figure skaters willing to try out your FBV sharpened blades. It would be interesting to know what they think. Ideally, you would want them to at least try to use objective measures - e.g., how long a glide they can create, how fast they can go, how fast they can accelerate, how much unintentionally sideways skid they have, how much they travel when they spin, how stable their jump landings are, etc. If you don't use objective measures, they might be inclined to believe they feel what they expect to feel.

[Kaitsu]

Unfortunately I have difficulties to get good datum's from the chromed side surfaces. This will increase bite angles measuring uncertainly. Form errors are also causing similar issues. Best fitted (red) lines positions will change depending which all measuring points are taken in account. Even H.D.I gauge did give 0.01mm edge height difference when it was rotated 180 degrees. This I did test several times to see that its repeatable issue.

This is the best report what I can provide with reasonable efforts. Please enjoy!
Link to report: https://www.dropbox.com/s/4oga3rl86wi3x6t/FBV%20100_75_reduced%20size.pdf?dl=0

My own conclusions:
* Flat bottom width is not definitely promised 100 thou (2.54mm). Perhaps it is width before diamond grit coating?
* Even there is some measuring uncertainly in the bite angles measurement, it's quite clear to me that there is about 0.5° degrees difference between inner and outer edge
* The edges of the blades have strange gaps. Whether they are caused by a worn spinner or some other reason, I don't know. In any case, various measurement errors were to be expected. Diamond grain coating is not a micrometer precision job with such a grain size
* Measuring results were confirming my thoughts that personally I am not going to jump from ROH sharpening's to FBV´s.
* 1/2" inch ROH would provide 9.4° bite angles. This study didn't help at any level to understand why 100/75 would be comparable with 3/8" ROH.

[Query]

How does the grit size of Blackstone spinners compare to the grit size of coarse and fine grain grinding wheels used in skate sharpeners?

Do you think Blackstone ROH shaped spinners would also give relatively poor results, or did you not test that enough to tell?

Is there anything at all that you like about Blackstone sharpening machines, compared to other machines?

[Kaitsu]

I was using couple years Blackstone ROH spinners in my previous power grinder. In that means I do have much more experience about their ROH spinner than the FBV spinners. Also, on the ROH spinners the actual radius in the blade wasn't same as what they state at spinner. Did the error come from the spinner or perhaps the spinner was not exactly parallel to my wheel? That I didn't ever investigate.

Even there was +0.5mm deviation in the radius, I was able to repeat the radius more accurately than with the original diamond quill system, which was real disaster in that machine. In some reason 1mm adjustment of diamond didn't mean that radius in the blade would change 1mm. With my experience most of the traditional diamond quill machines can have even bigger radius deviations than 0.5mm. People are trusting a bit too blindly to the machine's scales.

During the years I ordered couple new spinners to replace existing ones. Just by judging by eye ball, it seems that Blackstone has made changes to the diamond coating grit size or it is some normal process variation. Check the attached pictures and you can judge by your selves if those two 1/2" spinners do have same grit size. In another picture you can see spinner and Blademaster Ruby wheel side by side.

For the discussions about the Blackstone machines we can perhaps open new thread? 

[Query]

We don't need a new thread. You answered my questions about Blackstone sharpeners sufficiently.

[supersharp]

Excellent study of the FBV, Kaitsu.  I still would like to skate on it to see how it feels, but seeing this confirms my satisfaction with the ROH approach to sharpening. 

I have a pair of old boots that I could use for interesting experiments if I replaced the tongues (current tongue does not protect my ankles enough so all I can really notice is the discomfort).  I can re-profile some used blades and then start looking around for someone with FBV machine... now that I can't get new SkateScience blades, I can't afford to experiment much on them.