Experiments: Effects of balancing Wissota grinding wheels

[Bill_S]

There have been some questions about balancing grinding wheels and the resultant surface finish on blades. My Wissota skate sharpener vibrates very little and I get a very smooth finish on blades.

I am going to perform some experiments to see how static balancing of the wheel improves finish. I have an old pair of Gold Seal blades that will be the subject of this experiment. I plan to sharpen one blade with the current Wissota setup that I purchased a couple years ago, then make some changes and repeat on the other blade.

Wissota claims that their sharpening wheels are balanced. The question is to what degree are they balanced to pass their tests. Another question is how much production deviation exists among all their wheels. The superior blade finish now achieved by my current machine could be the result of luck. Perhaps the rigid machine geometry and mass of this machine absorb slight imbalances.

I purchased a Oneway Wolverine grinding wheel balancing system for $69, but the price went to $81 just days after I placed my order. I purchased one for a 1/2" arbor so that it would work with the Wissota's 1/2" arbor.

https://www.highlandwoodworking.com/onewaywolverinebalancingsystem.aspx

These are designed for bench grinders that have two grinding wheels, so the kit came with a ball-bearing balancing stand, two adjustable balance spools (a right-hand thread version, plus a left hand thread version), and a bag of balancing nuts and screws, washers, a pair of machined 1/2" thrust washers, and a wrench.

My first test was to determine how balanced my spare Wissota figure skate sharpening wheel was. I expected a little bit of imbalance in the static balance stand, and I was not disappointed.

The video of the wheel on the ball-bearing stand is nearly 5mb, so click at your own risk - https://www.afterness.com/skating/images/wissota/balance/wissota_wheel_balance.m4v

It's not surprising that it has a heavy spot, but from the slow movement seeking equilibrium, it isn't bad. This is my spare wheel, not the unit in my sharpener, and it has not been dressed. Dressing will likely affect balance.

In addition to the balancing stand in the kit, the OneWay Wolverine system provides a means to balance wheels. Although made for larger bench grinder wheels, I believe that I can make this work for my Wissota wheels.



Continued next post...

[Bill_S]

Here are some of the kit components that I intend to use. There are more kit parts not shown in this photo.



The genius of this system is the balancing wheel clamp. For larger bench grinder wheels for which it was designed, this clamps onto the wheel. There's both a left-hand and a right-hand spool included, but I'll use just the right-hand side. BTW, spare clamping spools are said to be available for $36, but I could not find a retailer selling just those.



I don't have space on the arbor to use both halves of the balancer spool. I will use just the balance adjusting piece in place of the existing Wissota clamping washer.





The balancing nuts and tightening screws ride in a machined raceway inside the spool, and can be repositioned to achieve a balance. Note the new position of the screws and nuts in the following photo. Washers are provided if more weight is needed to balance a particular wheel.



I plan to replace the stock clamping washer of the Wissota grinding wheel with this unit. They are the same height and roughly the same clamping diameter. I will use  double-stick tape to hold it in position on the wheel's blotter so that a static balanced assembly (wheel + balancer) doesn't shift.

[Bill_S]

Plans from here: I hate to tear into a working tool for experiments like this, so the experiments will come slowly over time. Also note that cell phones have built-in accelerometers and apps are available to quantify vibration. I've already done some informal tests of vibration using two different apps.

I've also ordered some inexpensive analog accelerometers from overseas that I may mount onto the machine in the future. This may permit dynamic balancing of the whole system, not merely static balancing the grinding wheels. This would be quite the undertaking, especially if I design a strobe to interface with the accelerometers to indicate the position of rotating imbalance. If it works, it could balance the whole system, motor and wheels, in the running state.

Of course the overriding question is what difference will I see in a sharpened blade? How much will it improve things? Can an average skater tell the difference if a sharpening machine is not causing severe blade roughness?

[Query]

You are going all out on this!

Do you do this type of balancing on your shop tools? On your car engine?

[Bill_S]

I had to balance an older, inexpensive band saw that I once owned. It shook so much that I couldn't see the scribed cut line on the wood that I was cutting.

It took a different method, one using a dial indicator for testing dynamic balance. When I was finished, I could stand a nickel coin on edge placed on the table while it was running.

EDIT: I found the old bandsaw video. It's an ancient file, so quality isn't great but you can see the coin standing on edge with the saw running. https://www.afterness.com/skating/images/wissota/balance/bandsaw-nickel-standing-1.m4v

EDIT 2: My new bandsaw, a Laguna 14|12, runs smooth as silk. It's cast iron and steel instead of aluminum, so it won't ever require as much fussing.

[Query]

At least one coach sold an expensive tool to help skaters learning to spin to center their spin. I seem to remember it was somehow tone coded, so a skater could figure out how to adjust their body based on what they hear.

Maybe you can use the accelerometers to create a comparable tool for skaters too.


I wonder if static balance is the main issue on grinding wheel vibration. E.G., if the shaft axis is not a principle axis, it would wobble while rotating even if balanced statically. Maybe there is even an imbalance in the motor.

Would it be better to spin balance the wheel while it is mounted horizontally on the machine, not while it is vertically mounted on your balancing stand?  In other words, maybe you don't want to spin balance just the wheel itself, but must include everything it connects to, including the motor, and be in the proper orientation, to do it perfectly. Could that be a significant issue?

I guess to do it optimally (i.e., not just to detect the vibration, but to determine the appropriate correction), you need to sync accelerometer measurements to the rotation of the wheel. If you use the accelerometers in your smartphone, it would be nice if there were a very lightweight marking on the wheel, that your smartphone camera could pick up to do the sync. You would also have to right a fairly complicated app. Maybe more complicated than it is worth. But I wonder if such apps already exist.

I guess you can't simply attach a heavy flywheel in place of the relatively lightweight one in your machine, so a little wheel imbalance doesn't matter, because that might burn out the motor, or bend the shaft.

[Bill_S]

At least one coach sold an expensive tool to help skaters learning to spin to center their spin. I seem to remember it was somehow tone coded, so a skater could figure out how to adjust their body based on what they hear.

Maybe you can use the accelerometers to create a comparable tool for skaters too.

Sounds like a solution in search of a problem.

I wonder if static balance is the main issue on grinding wheel vibration. E.G., if the shaft axis is not a principle axis, it would wobble while rotating even if balanced statically. Maybe there is even an imbalance in the motor.

Would it be better to spin balance the wheel while it is mounted horizontally on the machine, not while it is vertically mounted on your balancing stand?  In other words, maybe you don't want to spin balance just the wheel itself, but must include everything it connects to, including the motor, and be in the proper orientation, to do it perfectly. Could that be a significant issue?

??
I don't intend to use a balancing stand for dynamic balancing. It will be done in the regular horizontal operating position, running, with the accelerometer mounted to the machine indicating the degree of vibration. I could probably get balance close through trial and error placement of the balancing weights while recording vibration levels for each run. Of course, I'd start with the grinding wheel statically balanced to get close.

I guess to do it optimally (i.e., not just to detect the vibration, but to determine the appropriate correction), you need to sync accelerometer measurements to the rotation of the wheel. If you use the accelerometers in your smartphone, it would be nice if there were a very lightweight marking on the wheel, that your smartphone camera could pick up to do the sync. You would also have to right a fairly complicated app. Maybe more complicated than it is worth. But I wonder if such apps already exist.

To speed dynamic balancing (at the cost of tooling design time), I'd integrate a strobe. LEDs are suitable for the strobing illumination for this task, and are the simplest/cheapest to make. If I don't see an improvement in blade finish after static balancing, then there's no point going further with dynamic balancing.

BTW, there are cell phone apps that use the phone's camera and phone's LED light working together to determine RPM of a rotating object. I've used one called Video Tachometer to determine the actual RPM of my sharpener motor (3580 RPM). I just put a small Sharpie dot on one spot of the wheel and adjusted the app so that the dot stood still. (You can see the dot on the photo above showing the wheel mounted in the sharpener.) The app then tells you the RPM.

I've experimented with two cell phone vibration measurement apps already. One can interface with an accelerometer like the one that I've ordered. For my iPhone, the apps are Vibro Lite and Vibration Analysis. I believe that the basic versions of these apps are free, and you can pay more for more functionality.

I guess you can't simply attach a heavy flywheel in place of the relatively lightweight one in your machine, so a little wheel imbalance doesn't matter, because that might burn out the motor, or bend the shaft.

??
There is no separate flywheel on my machine. The grinding wheel clamps directly to the motor shaft and is driven directly by it. In a sense, the grinding wheel is its own flywheel.

[tstop4me]

??
There is no separate flywheel on my machine. The grinding wheel clamps directly to the motor shaft and is driven directly by it. In a sense, the grinding wheel is its own flywheel.

Also, simply tacking on a separate heavy flywheel to an existing system would likely exceed the torque and power rating of the motor.

[supersharp]

Bill—thanks for mentioning the rpm app, I’m going to set that up and keep track of my wheel rom as the wheel diameter changes.

[Kaitsu]

I’m going to set that up and keep track of my wheel rom as the wheel diameter changes.

I believe you did mean rpm and not rom.
I would like to remind rpm comes from the electrical motor nominal speed and pulley ration (if such exist). They do not change even the wheel diameter would change. What changes is Surface Feet Per Minute (SFPM) or Meters per second if you use metric units. It changes because circumferential length of wheel changes. Here is easy calculator for that use. https://www.nortonabrasives.com/en-us/norton-wheel-speed-calculator

It is quite interesting to see how much the cutting speed reduces when wheel gets smaller. Reducing wheel size typically impacts also to the wheel balancing. From here you can find some information why wheels typically requires balancing
https://www.haimer.biz/products/grinding-wheel-adapters/knowledge/why-balance-grinding-wheels.html?gclid=Cj0KCQiA8vSOBhCkARIsAGdp6RQSG4mklJkROSSW_Eg7qnWYARPD4o1hSUCjVrDiC5y3rEqKNtZVbY0aAiGFEALw_wcB

[supersharp]

Correct, I meant RPM and of course the RPM is consistent, what was I thinking???  I need to measure the speed at the edge of the wheel, which I can at least calculate with rpm and wheel diameter. 

[Bill_S]

Houston, we have a problem

The screw heads on the Oneway balancing clamp interfere with a cast reinforcing rib on the sharpener's top cover. I have a plan of action that I hope resolves the issue. I will replace the provided button head screws with setscrews to hold the balancing nuts in place.

Here is a side view of the Oneway balancing unit that shows how the screw heads protrude from it. This is just enough to make contact with a cast-in rib inside the top cover. The offending rib is shown in the background of this photo.



Work to this point

I sharpened one blade using sharpening wax and careful technique to establish a baseline for wheel balancing effects. I set it aside.

I started the sharpener and placed my iPhone on the table of the sharpener while running. With the VIBRO Lite app running, I measured vibration peaks in the x, y, and z axis. A face-up phone defines these to be: X - left/right, Z - long phone axis, and Y - up/down out of the phone's plane. The photo below shows the app recording peaks in vibration. The phone was placed on the center of the table with the phone's bottom aligned with the edge of the table casting. I did have to increase the sensitivity scale in the app to get the graphics to display.

Click to enlarge to read the peak numbers.



Balancing steps:

I pulled off the grinding wheel in order to install half of a Oneway balancing unit as a replacement clamp for the grinding wheel. After loosening the clamping nut, I did an experiment to determine the clearance between the motor shaft and the hole in the grinding wheel.

With the nut removed and the grinding wheel loose on the shaft, I mounted a dial indicator to measure the forward/backward movement of the wheel on the shaft as I nudged it.



It was a tight fit, with about 0.003" total displacement. That's awfully good, and makes other tasks more efficient.

[continued in next post]

[Bill_S]

[continued]

I used thin double-stick tape on the Oneway balancer to ensure that it didn't shift between static balancing and installation.



In a series of steps that I won't relate here, I used the sharpener as a fixture to center the balancer and its washer on the grinding wheel before tacking things together. Once centered and stuck together, I took the assembly to the static balancing stand.



The stand has ball bearings to reduce friction so that the wheel can freely rotate. After a bit of adjusting the position of the locking screws and captive nuts, I was able to get things statically balanced fairly well. See the video linked below for the results of the static balance, and compare it to the video of an unbalanced wheel in the first post.

https://www.afterness.com/skating/images/wissota/balance/wissota_wheel_balance_after.m4v

Good so far. I took it to the machine and mounted the wheel/balancer assembly to the Wissota sharpening machine.



When I attempted to mount the sharpener's top cover, that's when I realized that there was some interference between the Oneway balancing unit and a cast rib in the cover. I believe that it's only the screw heads that are interfering. If that's the case, I'll remove the existing screws and get some short set screws to lodge the nuts in their proper locations. The 1/4-20 x 3/16" flat point set screws should arrive within a day or two.




In the meantime, I ran the vibration app again after static balancing, but without the top cover in place.



The vibration amplitudes were reduced by about 1/3 in all axes. This is promising, but the real test will be sharpening the second blade and comparing the finish with the baseline blade.

[supersharp]

That wheel looks great after the balancing!  I am looking forward to hearing how the sharpening looks after you get your set screws.

I did the same kind of side-by-side comparison with pairs of old blades while working through all of the different things on my machine and found it really interesting.  Sometimes you only get a small change, but after 5 small changes, things can really look better.  I find that you can get a good assessment of smoothness by comparing how it feels to rub a microfiber cloth along the edges and hollow and also by running a fingernail down the hollow.  Sometimes it is really difficult to get a photo that shows the difference, even when you feel that the two blades are clearly different.

[Bill_S]

The delivery of the set screws won't happen today. It's been rescheduled for tomorrow.

In the meantime, I set about to quantify the precision of the motor/grinding wheel interface. In short, it's spectacularly good.

The grinding wheel mounting flange indicates zero movement in the axial direction when the motor shaft and flange are turned. Proof?... here's a video.

https://www.afterness.com/skating/images/wissota/balance/wissota_motor_flange_runout.m4v

In a separate measurement, the shaft itself has about 0.0003" total runout. Runout is compensated for in use as the grinding wheel is dressed with the diamond. Regardless, only 0.0003" total shaft runout is fabulous.

[Bill_S]

Even after receiving an email stating that my package was rescheduled for delivery tomorrow, it actually arrived today.

I replaced the protruding button-head screws with the new set screws to lock the balancing nuts into place. They do not stick up above the unit like the button-head screws did.



These worked very well. The only drawback is that you cannot have a nut over the hole in the device in which they are loaded. That would be somewhat unlikely, but that configuration could be overcome with some strategic rearrangement of the other balancing nuts. I didn't have any issues to deal with, and the set screws worked perfectly. They are flat tip set screws so that they don't chew up the aluminum balancer.

I spent about 15 minutes getting the grinding wheel balanced on the stand through iterative repositioning of the nuts in the track. Once balanced to satisfaction,  I mounted the wheel with balancer attached onto the sharpener. A gently snugging of the shaft's retainer nut is all it takes. Too much force will crush a wheel.



I affirmed that the balancer didn't contact the top cover of the sharpener by turning the grinding wheel gently while lowering the cover, then tightened it into position. I took a dressing pass on the wheel to remove any eccentricity commonly encountered in a fresh wheel install.



I then used the iPhone app once again to check on vibration levels. This is a screen shot of the app on the phone after it recorded the peak accererations encountered. It's a tiny bit better than before. The extra mass of the top cover and the wheel dressing to make the wheel perfectly round are the probably causes. This is about as good as I can make it with static balancing alone.



After all that, I sharpened the second blade to compare with the initial blade sharpened before the experiments. I'll try to get some photos tomorrow.

I do think that a purpose-made balancer similar to this would be a great accessory for Wissota to offer to customers. Because I don't have experience using other sharpeners, I don't know how well the concept could be applied to them. Using a balancer like this is very straightforward. It should not be too expensive for just the balancing stand and the component that I used from the Oneway kit to clamp the grinding wheel.

[Bill_S]

Here are photographs to qualitatively assess the effects of balancing the wheel. Executive summary - on my Wissota with the current grinding wheels I use, the blade finishes are very, very close.

Here is a blade sharpened before balancing steps were undertaken. It's the control in this experiment.

[click to enlarge]



Here is a blade sharpened after balancing steps were undertaken.



More to come later.

[supersharp]

Can you feel a difference in the smoothness?  Sometimes I can feel the difference more than I can see it.

The Incredible Edger has a 3" wheel.  I will look at how much vertical clearance there is--not much, really.  I have been hot-gluing used washers to my wheels as balancing weights, and there is maybe 5mm of clearance before you would be hitting the cover.

[marc]

demain je dois recevoir ma blademaster 850 d'occasion à 1350€.
j'avais hésité avec une wissota à 700€ (par contre problème pour trouver les meules).
Quand je vois ce que vous avez fait, je suis presque jaloux et je me dis que la wissota était presqu'aussi bien que la bladdemaster.
Je cherche partout en france  pour trouver une équilibreuse pas chère, et c'est très dur.
Et j'ai un copain qui peu me donner un coup de main.
Je pensais que l'affutage des patins  était compliqué mais pas à ce point....
centrer la meule... mouvement régulier.... et en plus de tout çà l'équilibrage des meules...
mais apparemment tu ne vois pas trop de différence?
C'est assez compliqué d'équilibrer les meules.
Avant de commencer à affuter je tiens à penser encore que de finir avec un cylindre abrasif serait assez bon. (peut être sans équilibre la meule?)

[marc]

exuse me!!

tomorrow I have to receive my used 850 blademaster at 1350 €.
I hesitated with a wissota at 700 € (on the other hand, there was a problem finding the wheels).
When I see what you've done, I'm almost jealous and tell myself that the wissota was almost as good as the bladdemaster.
I am looking everywhere in France to find a cheap balancer, and it is very hard.
And I have a friend who can give me a hand.
I thought the sharpening of the skates was complicated but not that much ....
center the grinding wheel ... regular movement .... and in addition to all that the balancing of the grinding wheels ...
but apparently you don't see too much difference?
It's quite complicated to balance the grindstones.
Before starting to sharpen I still want to think that ending with an abrasive cylinder would be good enough. (can the grinding wheel be unbalanced?)

[Bill_S]

Here are a couple of additional photos showing blade finishes before and after balancing.

[click to enlarge]





Supersharp: I could not feel any difference between the two. I tried running my fingernail down the hollow too, but it just felt smooth. That doesn't mean much though. I don't have the touch sensitivity of a woman. You have an edge there, so to speak.

marc: Don't worry so much. I'm sure that your Blademaster will do a fine job. Don't worry about balancing it while you learn to operate the machine, unless you have noticeable machine shaking. 99% of skate sharpeners in the world don't worry about it. There are a handful of us that are obsessed with finding the limits of what we can do.

[Bill_S]

I used the macro lens to take close photos of the finishes in the blade hollows.

Please note that I didn't address the sides of the blades. The experiment was just about discovering how much difference there is in grinding surface finish between the stock, unbalanced machine and the same machine after balancing.

Before balancing: [click to enlarge]



After balancing:



There's not a lot of difference to be seen on my sharpening machine.

[Bill_S]

What's next?: Probably nothing.

I did receive the 3-axis accelerometer in the mail today. I planned to use it for dynamic balancing of the wheel on the machine while running, but I will likely postpone that extension to this project. I'm seeing very small returns on the effort to improve my current sharpening machine with the current grinding wheel.



I will conclude my findings with this little discovery. Using the iPhone's built-in accelerometer with the Vibro Lite app, I get these readings with the machine turned off. I'm in a quiet home shop with nothing else running, with concrete floor, ceiling, and walls. Perhaps the world itself needs a bit more balance.

[Query]

tomorrow I have to receive my used 850 blademaster at 1350 €.

I don't know if the Blademaster SPB850 comes in a version that works with France's usual power voltage and frequency.

E.g., see https://blademaster.com/web/en/portable-machines/460-spb850.html

You might want to look at the voltage and frequency ratings on the motor - perhaps the motor has been changed. If not, plugging a 110VAC 60Hz motor directly into a 230VAC 50 Hz French power supply could cause a lot of damage. If the motor is rated for 110VAC 60 Hz, I'll leave it to the engineers here to help you figure out what to do.

Also, it is the Blademaster SPB750, not the SPB850, that contains the accessories recommended for figure skate sharpening:

https://blademaster.com/web/img/cms/2018%20BMCatalogue%20Email.pdf

Perhaps you may wish to also buy the accessories that come with the SPB750?

That page says the SPB750

is the same as the SPB850 bench model portable machine, but comes with an 88R grinding wheel and  our SH6500 skate holder specifically designed for figure skates.

But page 17 of
 
https://blademaster.com/web/img/cms/2018%20BMCatalogue%20Email.pdf

says the SPB750 comes with

Multi purpose skate holder, pick protector, finishing wheel and training DVD

and if you look at page 16 - 18 there are some other differences in included and recommended equipment.


Good luck!

Hey, I just noticed that Blademaster, on page 18 of that catalog has somewhat unusual ROH recommendations:

Ladies’ & Mens’ Dance: 1/4”
Childrens Dance: 3/8”
Ladies’ & Mens’ Free Skating: 1/2”
Children’s Free Skate: 5/8”
Combination Figure/Free Skating For all Skaters: 3/4” - 1 1/4”

I suggest you ignore those recommendations.

[marc]

query:
Peut-être souhaiterez-vous également acheter les accessoires fournis avec le SPB750 ?

Le pick protector: je me le suis fabriqué (pas trop compliqué à faire).
J'aurais une meule 8mx ruby et une 88R. j'e vais essayer les 2 et on verra bien.
j'aurais le  pro square aussi et sinon je ferais avec 2 crayon de bois.

par contre j'espère que ça fonctionne au 220v car là je serais vraiment décu.
C'est un détail que j'ai oublié de demander au vendeur (suisse).
Je viens de lui envoyer du coup un mail et il me tarde de connaitre sa réponse

query:
Perhaps you would also like to purchase the accessories supplied with the SPB750?

The protector pick: I made it myself (not too complicated to do).
I would have an 8mx ruby ​​wheel and an 88R. I'm going to try both and we'll see.
I would have the pro square too and otherwise I would do with 2 wooden pencils.

on the other hand I hope that it works at 220v because then I would be really disappointed.
This is a detail that I forgot to ask the (Swiss) seller.
I just sent him an email and I can't wait to hear his response.