CBN Wheel for Tormek

[wootz]

This thread continues the discussion started here http://forum.tormek.com/index.php?topic=2831.45 where grepper gave excellent summary on CBN wheels.

My wheel came from http://woodturnerswonders.com/collections/tormek-cbn-wheels/products/tormek-cbn-wheel-600-grit-10-x-2-inch-12mm-arbor

The original stone of the Tormek T7 has a diameter of 250 mm, the CBN wheel has a diameter of 254 mm. At first I thought it is just a little too big for the water trough, but it fits fine, though almost flash, and runs without brushing the trough.

With the width of 50.8 mm, the shaft protrudes just enough to tighten, as seen on the next photo.


The CBN wheel bore matches the Tormek's shaft, mounts square and runs perfectly round, and no lateral wobbling whatsoever.
Weighs 1920 g, i.e. less than half of the stone, runs effortlessly.

The grit is coarser than the stated 600, feels and grinds like ANSI/JIS #300.
They say the boron nitride crystals don't crash as easily as diamonds with use, so I wouldn't expect the grit to settle down much.

The CBN wheel looks fascinating on the Tormek, like a tamed milky way, and gives a clear bell ring when struck with a finger nail, reminiscent of Buddha temples.

Unfortunately, the CBN wheel of this make has grinding surface somewhat saddle-like, concaving from sides to the middle; not much, yet you can see it with a naked eye.
And this is really disappointing, as otherwise the wheel is so good.



On the few knives I have tried so far, the wheel middle part don't even reach the blade; as a result the heel and tip sections of the blade risk overgrinding.
Because of that you cannot really run it dry; you need a water flow to show points of contact with the wheel, and adjust sharpening routine to compensate for that.
Since I read that the boron nitride particles can cause pneumoconiosis when inhaled, I will not run it dry anyway.

As to the CBN grinding ability, I liked how fast it ground the ceramic and Bohler Vanadis-10 (the hardest blades I got at hand).
Better than anything else we use with Tormek.

[grepper]

Wootz – Thanks for the follow up!

"Unfortunately, the CBN wheel of this make has grinding surface that is somewhat saddle-like, concaving from sides to the middle; not much, yet you can see it with a naked eye.
And this is really disappointing, as otherwise the wheel is so good."

I would be very disappointed too!  Especially considering that it will always be that way and there is nothing you can do about it.  I would consider it to be a problem, contact the dealer, inquire if that is normal, and consider returning it.  I would ask the dealer to put a flat edge on other wheels they have in stock and see if they have a flat one.  Sharpening only on the edges of the wheel just can't pan out all that well.

From all the reviews I read, you will have that wheel for a really long time, if not indefinitely.  Considering that, even though returns are a pain, you might as well start out with a flat one!  I'm saddened and actually surprised to see that.  I would think that since those are metal wheels they would be nearly perfectly manufactured. 

"They say the boron nitride crystals don't crash as easily as diamonds with use, so I wouldn't expect the grit to settle down much."

Again, only from reviews I read, many said they do settle down after a month or two of use.  It will be interesting to hear your periodic observations over time.

How do you like the lack of wheel goop in the trough an around the machine?  I would think that would be a big plus.

Thanks again for the follow up, and keep us informed!

[Elden]

   I guess you get what you pay for?!

[wootz]

This saddle-backed shape was completely unexpected, moreover that the wheel is machined precisely otherwise.
The WoodTurners Wonders are responsive, but it makes little sense to return this particular wheel, as all their 10" wheels seem to be the same.
They suppose this might be due to electroplating done wrong, and that they "have contacted the factory to ask them about this and I will get back to you."

I really like how mess-free this CBN wheel is compared to the stone.
And effective. I didn't see much difference between the CBN and SG on a mainstream kitchen knife, but did appreciate it as started sharpening the harder steels.

Am now in quest for a truly straight and finer CBN wheel.

[grepper]

After seeing your surprising review, I did some searching around and found only 1 or two old reports of wheel surface concavity.  I would think that if this was a common problem it would be all over the web.  Others reviews stating their wheels are "dead flat", etc. It also was not clear if the problem wheels were the older bonded surface or the more stable electroplated variety.

Good to hear that your dealer is responsive.  IMHO, an electroplated CBN wheel with an anything but flat surface is not acceptable, even if they have others that are the same.  It could just be a bad batch, specially imported from the Orient.

So don't give up on Woodturners and get a correctly manufactured wheel.  Those things are not exactly inexpensive and ones with a flat surface are available.

Please keep us informed!

[wootz]

Thank you

[Waterstone]

Maybe you know Derek Cohen, an Australian furniture maker and tool maniac. He had similar issues with CBN wheels. He's running them on a dry grinder but the point is the same.

http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp.html

Klaus

[grepper]

I don't know, but I suspect that the wheel in that article is a bonded CBN wheel as opposed to an electroplated wheel.

I'm like totally not an expert at all in CBN wheels so it would be cool if somebody who is would post. I mean, there is every chance that I don't know at all what I'm talking about. 

It is my understanding that bonded CBN wheels have a coating of CBN impregnated resin bonded to the surface of the wheel.  This bonded layer can be somewhere between 1.5mm and 6.5mm thick.  Bonded wheels are actually friable, and can be dressed.  A bonded substrate could continue to be abrasive even if it became dished because the bonding layer is fully impregnated with CBN.

Electroplated CBN wheels have a mono layer of CBN crystals fused to the surface of the wheel in a layer of nickel electroplate, the thickness of which is determined by the size of the abrasive.

http://www.breu-diatools.com/en/production-process/

Nickel is not all that hard, somewhere between 48 and 58 HRC depending on treatment, but CBN is bested only by diamond as far as stuff we can use hardness goes...  Pretty tough stuff. 

From my totally uninformed perspective, I can understand how a bonded wheel could become dished as the resin substrate is abraded away, but it would seem that the only way an electroplated wheel could become significantly dished would be if the CBN layer was compromised exposing the relatively soft nickel electroplate and wheel material, or if the wheel was badly manufactured with a concave surface to begin with.

Anyway, that's why I suspect the wheel in the article is bonded rather than electroplated.  Just a guess.

[Ken S]

Wootz, great trailblazing work!

Grepper, excellent informed commentary!

The saddle shape seems an unnecessary frustration for an otherwise outstanding product. I found a well done article on dry grinding which advocates dressing a slight crown on the grinding wheel instead of leaving it flat. The purpose of the crown is to limit the actual grinding to a smalller point of contact, thus limiting the heat production. I don't know that this crown technique would work with all tools. It should work with flat edges like chisels and planes. And knives. I would rather have a crown than a saddle.

I am surprised that the saddle effect is not eliminated during production. Surely a factory inspector would have access to basic tools like a straight edge.

A test request for the microscope brigade: Using either identical tools or different sections of the same edge, would you please make photos showing the difference in the surface roughness when the final pass or two is made using avery light touch? Depending on how much difference is shown, varying the touch could potentially add to the usable range of a "single grit" grinding wheel.

My family is awakening. .Must dash.

Ken

[Ken S]

These links seems informative.

https://www.youtube.com/watch?v=WDFGa9pxCgQ

https://www.youtube.com/watch?v=-nQxfT5kumE

Be sure to pay attention to what Ernie says about CBN and mild steel. These are not wheels for every use.

This video offered some good thoughts for choosing dry grinders to use with CBN wheels.

https://www.youtube.com/watch?v=CDNNEDjFcag

Ken

[grepper]

I did a bunch of searching around trying to find the thickness of the abrasive/bond layer of electroplated CBN wheels.  As far as I can tell the thickness of the layer is primarily determined by the size of the CBN crystals due to the fact that the abrasive layer is comprised of only a single layer of abrasive crystals bonded in nickel electroplate.  I only found two references, one being 0.07 mm (0.0028"), and the other 0.05 mm (.002").



From: http://blog.cdtusa.net/cbn


Can you see 0.05 mm with the naked eye?  Yes, but it is very minimal, especially in comparison to the irregular surface of grinding wheel.  Use a caliper or feeler gauge and check it out.

Moreover, assuming the wheel was flat to begin with, having even a 0.05 mm concavity would require the entire abrasive and metal bond layer to be completely removed.  If just the abrasive itself became slightly worn down, the deviation from flatness would be only a portion of the total layer thickness and would start to border on being imperceptible.  For general tool edge grinding it would be more or less irrelevant.

In Mr. Wootz' wheel, it seems a reasonable conclusion that the surface irregularity is due either to very poor and uneven electroplating, and/or the wheel surface was unevenly manufactured.  I believe Tornado wheels are manufactured in China, so I don't think that sloppy manufacturing and inconsistency in production runs is all that surprising.

[wootz]

Maybe you know Derek Cohen, an Australian furniture maker and tool maniac. He had similar issues with CBN wheels. He's running them on a dry grinder but the point is the same.

http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp.html

Klaus

Appreciate your input, Klaus.
Issues with CBN wheels quality appear to be a broader problem than I thought.
Factories supplying US dealers seem not to bother with QA.
Ordering a CBN wheel without a pre-sale inspection is a throw of a dice in regard to the quality.

To his credit, Ken from WoodTurners Wonders took my case to the manufacturer, and if they can fix their process, will do pre-dispatch inspection for me to assure the wheel is flat-faced.

BTW, neither labels on the wheel and packaging, nor WoodTurners Wonders say anywhere that their CBN wheels are sourced from Eastern Asia.

Thank you guys for your support

[grepper]

Mr. Wootz - Glad to hear that!  It's also good to hear, if I am interpreting you correctly, that Woodturners is standing behind their product and you will end up with a good wheel.  Good for them!  If Tormek produced CBN wheels, (hint, hint) you probably wouldn't have had a problem in the first place.

As always, please post the story as it progresses!

I am 99% sure that Torando wheels are made in China.  I found them on madeinchina.com.

My how times have changed.  It's funny, but when I was a kid, "imported from the Orient" conjured an entirely different impression than it does today.  Today, at least here in the U.S., almost everything is specially imported from the Orient.

In my kitchen cupboard there exists a box of toothpicks with a label on the side; Made in China".  Really?  Toothpicks?  Yes, in the U.S. even toothpicks are specially imported from the Orient.  Anyway, of course, many of the toothpicks are malformed and break easily when used.

A couple of years ago I purchased a plastic toolbox, specially imported from the Orient, about the right size to hold maybe 10 screwdrivers.  It's about 10" x 4" x 1.5".  When the box is opened, even at arms length, one's olfactory senses are assaulted by invidious effluviums that can only be described as a combination of well aged dirty socks, rotting fish and burnt hair.  I would have thought that the putrid stench would have dissipated over a time, but no!  It survives in all of its glory today.  Doh!  I am a victim of the well documented China stink plastic!

I really wish all of you guys could take a whiff so you would understand that I in no way exaggerate!  Seriously, one whiff is all it would take. 

https://www.youtube.com/watch?v=Q8skzjsaJc8

[Ken S]

"Comparing apple's with apples"  is an English idiom for the importance of fairly comparing things fairly on an equal footing. I have not seen this happen when comparing Tormek and dry grinders and CBN wheels.

Using the BMG-100 to adapt Tormek jigs to dry grinders is generally not an apples to apples comparison. I am not an import baster, and using the BGM with an inexpensive grinder will do an adequate job. Let's just not pretend we have found Tormek quality in a hundred dollar dry grinder. Apples with apples would be comparing Tormek with a Baldor grinder or similar.

A CBN wheel with quality materials and machining, individually balanced, will probably cost at least what an SG or SB costs. Like Wootz, I would find a grinding wheel with a saddle unsatisfactory. In fact, an article on www.toolsforworkingwood.com recommends using CBN wheels with a crown shape. (That could easily be a topic by itself.)

I look forward to the ongoing saga of using the Tormek with CBN wheels.

Ken

[grepper]

A test request for the microscope brigade: Using either identical tools or different sections of the same edge, would you please make photos showing the difference in the surface roughness when the final pass or two is made using avery light touch? Depending on how much difference is shown, varying the touch could potentially add to the usable range of a "single grit" grinding wheel.

I'm glad you suggested checking this out Ken.  I do the same thing, even though I had never examined exactly what was actually happening and the results are interesting.  I guess it just intuitively seemed like the thing to do.

I used a very coarse grind and removed enough metal so that no scratching from a previous sharpening remained.  I figured that a coarse grind would best show the effects of light pressure passes over existing heavy passes at the same grit.

If I am interpreting the images correctly, the effect of light passes over heavy passes appears to do about what you would expect:  The depth of the scratches, measured from the newly formed surface, is reduced as some of the high areas between scratches are abraded away.  New, shallower scratches are created in previously smooth areas.  Some burr material was caught and torn away.

From a more macro perspective, I think it can be compared to running a piece of cheese over a box grater, first with a heavy passes and then with lighter passes.

Anyway, here are three images.  First image; heavy pressure.  Second image; lighter pressure.  Third image; many passes with very light pressure.

I find the third image most curious compared to the first two.  I would have thought that many very light passes would further smooth the finish, but that does not appear to be what occurred.  Maybe even the opposite.

Keep in mind that this was just one test, in a pretty much uncontrolled environment.  But, if I were to form any conclusions from this single test, I would conclude that a couple of light passes seems to smooth the surface some, but further passes do not, and may even be regressive.

What do you think?