Why doesn't Tormek replace stone with a CBN wheel?

[Sharpco]

CBN wheel has several advantages. No need truing, No wear out, Alway same grit......

And, if it is made of a non-rusting material, it can also be used with water.

But Tormek has not replaced the stone with a CBN wheel.

Why?

Is there a drawback to the CBN wheel?

[Ken S]

Good question.

As you state, CBN wheels are always the same grit (after a very brief wear in period). Traditional Tormek thinking was one grinding wheel. Originally this was with a natural stone mined nearby. These were finer grit. Many years ago, these were replaced with the present manmade aluminum oxide SG stones. These are coarser, but could be modified with the stone grader to be finer. One stone could serve both purposes. In fact, when skillfully used, middle gradations are possible. Having several degrees of coarseness would require purchasing several CBN wheels.

Interchangeable wheels is a fairly new concept with Tormek, only since 2010. I believe Tormek may be moving in the direction of CBN wheels. The T2 uses diamond wheels. The diamond wheel is single grit; that's why there are two available. Several forum members, including me, have purchased third party CBN wheels. Mine are 80 and 180 grit. They work very well for heavier grinding, such as reshaping turning tools. For me, the SG is still my go to sharpening wheel.

I suspect that Tormek may eventually include CBN wheels as accessories, like the SB, SJ, and DWC-200 (the coarser diamond wheel for the T2). At this point, I do not believe there is adequate market demand to justify the cost of adding CBN wheels to the product line.

Incidently, adding Honerite Gold to the water takes care of rusting with steel wheels and reducing bushings.

Ken

[cbwx34]

I'm kinda thinking like Ken... it may eventually be offered... at least as an option.  I don't grade my stone all that often, (although it is a nice feature to have)... so could maybe get away with just one.

Only things I would wonder about are longevity and cost vs. the "traditional" stone.  Also, one downside to diamond stones, and I'm thinking CBN might be similar, is if you damage them, for example using too much pressure can basically "strip" the stone... no recovery like a regular stone.

I really need to get one and experiment.  Maybe next year.... 

[Herman Trivilino]

CBN wheel has several advantages. No need truing, No wear out, Always same grit......

I think Tormek would not consider that last one to be an advantage. They market their premiere grindstone, the SG-250, as something whose grit can be changed.

And is it really true that there's no wear out of a CBN. Perhaps negligible wear when sharpening knives, but what about axes, lawn mower blades, and hedge clippers?

[cbwx34]

Not directly Tormek related... but some interesting comments on CBN wheel use...

https://youtu.be/zI4wLWoZ9Vs

[GKC]

I think that Sharpco poses an excellent question.  It can be taken as "Are CBN wheels better for the Tormek?" and as "If CBN wheels are better, why hasn't Tormek offered two CBNs as an alternative to the SG-250?"

On the first question, I and most of the dry-grinders I know (mostly turners) have gone over to CBN on dry grinders for tool shaping and sharpening purposes.  In dry grinding they have three important advantages (over stones): negligible heat, excellent balance and alignment, and constant diameter.

The first two of those are not an issue on the Tormek, so the main advantage on a Tormek would be the constant diameter.  This is not a big deal if you don't mind adjusting as the stones shrink.
 
With that said, I recently got two CBN wheels for my T8 (from Woodturners Wonders; they have several Tormek-compatible 10" CBN wheels with 12mm arbors in various grits).  That is because, for one of my recent uses of the Tormek (repeatable grinds on scandi carving knives), the constant diameter is very important to me.  Also, though they can be used wet with an anti-rust agent, they are designed to be used dry, which is easier on my lovingly made custom knife handles.

While, as Herman notes, Tormek would not see having a constant grit as an advantage (relative to the variable grit SG-250 and SB-250), I don't find swapping wheels to take any longer than re-grading the stones, so that factor is a wash for me.

And an advantage on the Tormek (that isn't much different from stones in dry grinding) is speed: I have found that a coarse CBN is a lot faster than the SB-250 graded coarse.  Probably similar to the Tormek diamond stones.

Now on the second question, why Tormek doesn't introduce CBN wheels, I agree that Tormek should (and probably will) come out with CBN wheels, but given the fairly narrow application, I can see that it would not be a priority for them.  They have just introduced the diamond wheels, and CBN might complicate their marketing. 

Which is to say, I sense that the main reason we don't have CBN wheels from Tormek is Tormek's general prioritization, for marketing reasons, of simplicity over optionality.  This might be good marketing.  They might be concerned that if they give people choices, people will perceive the Tormek system as too complicated. I think that they are slowly getting over that, as shown by the new wheels and other innovations in the past few years, but it does seem to be like a big slow-moving ship.  In the meantime, the option is there in the aftermarket.

[cbwx34]

One thing mentioned in the video I linked... he claims that "mild or high carbon steels will clog the CBN grit and cannot be removed, which will ruin the wheel"  (1:26)... and that only... quality high speed steel or carbide can be sharpened on them.  That true?

[GKC]

I have seen this warning before, mostly in connection with high heat grinding with both diamond and CBN abrasives. 

I have also seen people report that it is not an issue.  Some confusion comes from the vagueness of the term "high carbon steel".  A fairly thorough review by Reed Gray (aka "robo hippy") seems to conclude that the culprit is not HCS per se, but non-hardened HCS.  So, for most cutting tools there should be no problem.  Gray also notes that a run over a clogged wheel with an HSS tool will clean it up.  Gray gives some comments at the following link, but his full report is available on his website.

https://sawmillcreek.org/showthread.php?246501-CBN-grinding-wheels-and-the-steels-they-are-suitable-for

It has not been an issue with me.  So far I only sharpen high carbon steel knives on my CBN wheels on the Tormek, and there is no clogging at all.

It might be that I haven't had a problem because I am only working with hardened steel and I don't grind on CBN at high speeds / temperatures.  I have CBNs on a slow speed dry grinder, and obviously speed is not an issue with the CBNs on my Tormek.  I wouldn't try to do serious shaping on non-HSS on a CBN wheel, that might cause clogging.

Gord

[Ken S]

I think the real question with CBN wheels should be why are they not made for the Tormek.

CBN wheels are primarily designed and marketed for eight inch high speed dry grinders and woodturning tools. While they may also work with the Tormekto some extent, that is a marketing after thought. Even my three D-Way CBN wheels, which I have used successfully with my Tormek, are not really designed for the Tormek. They can be used wet (with a rust inhibitor) or dry with the Tormek. D-Way's reducing bushing works equally well with the T4 or T7/8. This works well, but would work better if made made from stainless steel. (Of course, it is designed for high speed dry grinders).

The last I knew, using the woodturnerswonders wheels wet would void the warranty. Has this changed?

The main argument for CBN vs diamond wheels seems to be problems with diamond at high grinding speeds (heat). The slow speed of the Tormek motor negates that constraint.

I believe the discussion about CBN wheels really began because Tormek has never offered a true coarse wheel. Many dry grinders use 46 and 80 grit wheels. These are much more coarse than the 220 grit of the SG or SB. I think the frustration which started the CBN desire was a product of the frustration from slow grinding of operations like turning tool reshaping or planer blade resharpening.

I would like to see Tormek offer a true coarse grit wheel. I would like to see Tormek realize how useful diamond wheels are with the T4. Looking ahead, I see Tormek with diamond and Original wheels. I would be surprised to see CBN wheels in the Tormek lineup. Keep in mind, I have no crystal ball......

Ken

[cbwx34]

I have seen this warning before, mostly in connection with high heat grinding with both diamond and CBN abrasives. 

I have also seen people report that it is not an issue.  Some confusion comes from the vagueness of the term "high carbon steel".  A fairly thorough review by Reed Gray (aka "robo hippy") seems to conclude that the culprit is not HCS per se, but non-hardened HCS.  So, for most cutting tools there should be no problem.  Gray also notes that a run over a clogged wheel with an HSS tool will clean it up.  Gray gives some comments at the following link, but his full report is available on his website.

https://sawmillcreek.org/showthread.php?246501-CBN-grinding-wheels-and-the-steels-they-are-suitable-for

It has not been an issue with me.  So far I only sharpen high carbon steel knives on my CBN wheels on the Tormek, and there is no clogging at all.

It might be that I haven't had a problem because I am only working with hardened steel and I don't grind on CBN at high speeds / temperatures.  I have CBNs on a slow speed dry grinder, and obviously speed is not an issue with the CBNs on my Tormek.  I wouldn't try to do serious shaping on non-HSS on a CBN wheel, that might cause clogging.

Gord

Thanks for the reply.

I know some also feel that way about diamond stones (not necessarily Tormek wheels)... that lower end steels will destroy them for various reasons.  Hasn't been my experience... I'm sure there's a number of variables involved.

Good info!

[Ken S]

Gord,

i don't think we have enough hard evidence about grinding non hss with CBN. I have ground my Carbon steel sharpening chisels with CBN wheels, and have not noticed any ill effects. I also recall Dave Schweitzer saying that clogged CBN wheels can be easily restored by grinding on a piece of hss.

Ken

[Ken S]

CB and Gord.

I have a secret weapon for grinding carbon steel....my Original SG wheel!

Ken

[GKC]

The last I knew, using the woodturnerswonders wheels wet would void the warranty. Has this changed?

Ken

This has not changed, but when I bought mine I asked them why, and they said it was because the water could cause corrosion.  So, I see no reason why they couldn't be used wet with Honerite or Tormek ACC-150.  If I ever want to use mine wet, that is what I will do. (From his videos it looks like Vadim is using his wet, so I assume he is using some anti-corrosion compound.)

Gord

[Ken S]

Gord,

I think you are correct. It is hard to get a straight answer on this. I think the vendors are reluctant to authorize wet use with anti corrosion for fear of complaints from those foolish or lazy enough to leave the wheels in the troughs between sessions. I question whether or not careful use would actually cause any damage. I would be interested in learning about manufacturer's test using the wheels wet with ACC.

I would also like to learn about these tests on the Tormek DWF-200 and DWC-200 diamond wheels. Although they are officially designed for only dry use with the T2, I have found that they work seamlessly with the T4.

Ken

[RichColvin]

I seem to remember that CBN wheels work best at higher speeds than the Tormek (i.e., 1,500+ rpm).  I do know that certain grinding functions work best at high speeds and some work best at higher pressures (applied to the grindstone). 

In addition, diamond is significantly harder than CBN (like 2x as hard).  The reason CBN is used on grinders where high heat is generated in the grinding process is that diamonds can melt when used to grind steels at high temperatures.  CBN doesn't do that, and that is why it gets used in many grinding operations.

In any regard, I'd tend to believe that Tormek have used research and good judgment to go with diamond stones in lieu of CBN.

Kind regards,
Rich