Final report, CBN grinding wheels

[cbwx34]

We've been using CBN wheels for over half a year, on a few hundred knives by now.

Do you have a grit preference?  (The.... If you could only buy one.... question).

And do you finish on a CBN (prior to stropping if any), or switch to a waterstone?  (Guess the easier question... what's your "CBN use" procedure)?

Thanks.

[wootz]

Do you have a grit preference?  (The.... If you could only buy one.... question).

Speaking of knife sharpening (not woodturner' tools), if you could only buy one CBN wheel, get #1000, and not necessarily the 10" Tormek-ready; cheaper 8" CBN wheels work fine on both T4 and T7/8/2000, you only need a bushing to fit the Tormek shaft - the bushing specs are here:
http://knifegrinders.com.au/05Equipment_CBN.htm

On the CBN wheel #1000, we can set edge on most of the knives.
With the grossly dull knives, you can set bevel on rough SG or SB, then continue on #1000.

And do you finish on a CBN (prior to stropping if any), or switch to a waterstone?

The edge you get on #1000 can be deburred and finished on the Tormek leather wheel with a honing compound; we do it on paper wheels.
For regular knives you do not need a finer grit in between.
Safe queens go through a combination of SJ and paper wheels.

... what's your "CBN use" procedure?

It is in the "Sharpening Procedures" section on our website, e.g. see there "Stainless steels, mainstream" or "Tool and high-end steels" etc
http://knifegrinders.com.au/06Procedures.htm

[cbwx34]

Ah.... very cool.  Thanks!   

[larcal]

Thank you Ken and Wootz for your thoughtful answers.

Have partially looked over Dave Schweitzers videos but so far seen no mention of the clogging issue and it's solution but will keep looking. Guess I'd like to ask if either of you have tried declogging by his method and if it does in fact work and is fairly easy?

And there is this possible discrepancy in the way I read your experience if you guys would care to comment.

Ken says the clogging only happens with "mild steel", a term usually applied to low carbon steel up to max carbon of .3% that can not be heat treated. He has no problem with high carbon heat treated steel chisels that are probably in the 1% or more carbon camp but do not, I'm guessing) have any of the special additions like tungsten, molybdenum.

While you, Wootz, seem to experience that it is necessary to have these "metalurgical alloys" to avoid clogging and that any normal high carbon, even the very high 2% ones, will present problems without them. And as you say, even the CBN leaflet warns against high carbon.

So is interesting as to why Ken has no problem, or I'm misinterpreting this some how

Glad to see that you both agree Stainless steel blades are fine on CBN.

Other good and interesting points made in both posts

[wootz]

We saw CBN wheel performance decrease after conventional rusting steels, both low and high carbon (e.g. 1095), on a couple of occasions, and 1095 clogged worse.

On the other hand, Japanese high carbon, well tempered  hard steel kitchen knives cause no problem, similar to Ken's chisel.
So it is not only about Carbon contents, go guess. Temper might matter, as Ken suggested.

Solution in the leaflet is to wash in kerosene with a brush - so as soon as we noticed that, we ran the CBN wheel with the Tormek water trough filled with Turpentine, and brushed it with a tooth brush... This saved the wheel, but turpentine discoloured the trough.

Given their cost, and the trouble of cleaning, we generally avoid sharpening rusting steels on the CBN wheels, so far so good.

[Ken S]

Excellent post, Wootz. CBN is designed for hard steels. The SG is designed for carbon steel. I don't think of either as a universal wheel, although the SG was the only wheel for the Tormek for many years.

Ken

[wootz]

Tormek-ready CBN Wheels from WoodturnersWonders for less than the cost of stone wheel, all grits. Haven't tried them myself yet, but affordability is a true breakthrough.

https://woodturnerswonders.com/collections/spartan-affordable-cbn-wheel-1/products/spartan-10-cbn-wheel-5-8-arbor

[Ken S]

My pet peeve with this company is not their products. I have never used them, so I have nothing negative to say about the wheels. My pet peeve is how they are photographed. The edges look like they taper. They should be square with the sides of the wheel. I believe they are, however, one would not know that from looking at their photographs.

Good commercial photographers solved this problem the better part of a century ago. The answer is to use a longer lens and make the photograph from farther away to flatten the perspective. Ring photographers deal with the same possible distortion, as do portrait photographers. How many times have we seen a portrait shot too close, so that the subject's nose appears too large.

Grumble, grumble. The photo just hit a pet peeve.

Ken

[wootz]

So true about the photo, Ken, that I even asked Ken Rizza at the WoodturnesWonders, though about other Spartan wheel, and he assured they are square.
But you never know till get one yourself...

[grepper]

Is that a plastic wheel?  No rust?

How is the CBN attached?  Electroplated to an aluminum ring around the plastic wheel?  Steel ring around plastic wheel (rust?)?

If it is a plastic wheel with a plastic hub, any issues with hub wear?  I know some folks remove the wheel after each use. 

[wootz]

The wheel surface is electroplated CBN on steel, and center is made of nylon - the latter drops the cost.

[Ken S]

I use CBN wheels wet or dry. I think the water mess problem with Tormek grinding is overhype and mostly a result of sloppy technique. No one seems to mention the mess of dry grinding dust. Minor spillage of water is easily controlled and contained. Dry grinding metal dust may not be so easy to contain.

I use Honerite Gold at the standard dilution of 1:25 with water. That and careful drying with a light coat of oil at the end of the session has cured the rust problem for me.

Personally, I like the idea of inexpensive CBN wheels for turners. A coarse CBN wheel would make quick work of reshaping. Do a quick change with the EZYlock to the SG for sharpening. You have the best of both  worlds.

Wheel wear with nylon? I would expect more wear than with steel. However, the Tormek bushings are nylon, and work fine. Part of our thinking is back in the high speed dry grinder era. I would expect sealed steel bearings in a Baldor grinder. It lives in a much more stressful environment. I suspect the nylon bushing area of the wheels will probably last as long as the CBN grit. At the price, they can be replaced more often, if needed. (If one is wearing out wheels with any grinder in business, the revenue produced should certainly cover new wheels as needed.)

Ken

[wootz]

I asked our Australian woodworkers what steels should be avoided on CBN wheels and they said unhardened only.
They gave me a long list of tool and knife steels they grind on CBN wheels, but in one word - any steel is OK except poorly hardened - the latter will gum up the grit. Tungsten carbide is another exception, but for a different reason - better done on diamonds.
Well, we have to conclude that the manufacturer's leaflet coming with the CBN wheels is incorrect in saying that high carbon steels should be avoided.

BTW, Ken Rizza at the WoodturnesWonders has sent me a 10" Tormek-ready Spartan CBN wheel, and delivered it would cost me less than a stone wheel bought locally. If it is as flat and square and round as promised, you won't want a stone wheel any more.
The Spartan CBN wheel won't be cooling as well on regular bench grinders as its fully aluminum counterparts, but that has no bearing on the low-speed Tormek.

For a new generation of Tormekers, the problem will be to find a Tormek machine on sale stripped of the stock wheel.

[Ken S]

"If it is as flat and square and round as promised, you won't need a stone wheel anymore."

That's a lot of ifs. Not only that, those ifs cannot be easily corrected by routine maintenance with the TT-50 Truing Tool. And, unlike the SG-250 stone wheel, CBN (and diamond) wheels are single grit. Putting together a multigrit sharpening system with CBN is not difficult, however, it requires purchasing several wheels.

I have three CBN and one diamond wheels. Each has a purpose, and fulfills that purpose well. Like my modified Norton 3X wheels, most of the CBN wheels are coarser grits (80 and 180)  primarily for reshaping woodworking tools. They do this very well and quickly. I think a 180 grit CBN wheel would be a good investment for an active turner. I would recommend switching to a stone wheel and leather honing wheel to complete the sharpening, especially before making the finish cuts.

For rough grinding of high speed steel, the SG-250 is no match for a CBN wheel. For harder steels, it is no match for the SB-250, CBN or diamond. For a highly polished edge, it is no match for the
SJ-250. The SG-250 is primarily designed for high carbon steel. It performs this function very well. Unlike the more exotic wheels, when it wears, it is easily retrued. It can be graded to function as several grits. It can sharpen high speed steel. HSS is not its forté, however, until ten years ago, it was the only wheel available for the Tormek and did trooper service. While it does not match the Tormek SJ-250 4000 grit stone for the ultimate, highly polished edge, it comes reasonably close without the several hundred dollar additional cost.

I have read several reports of CBN wheels wearing out of flat and square. My ten inch 180 grit CBN wheel is slightly out of round. It still functions. As I recall, Wootz, your original CBN wheel soon wore out of flat.

Please do not misunderstand me. I am a proponent of CBN wheels. They have some significant advantages for some Tormek users. As they evolve, they will be a larger part of kit for Tormek users. They are certainly long lasting. For the average Tormek home user, this may be a lifetime. I would not say they last forever. With the right grit, they may work very well for a professional knife sharpener. Please note that even the T2, designed for simplicity of operation with a 600 grit diamond wheel, has an optional second (320 grit) diamond wheel. In my home workshop, trying a suggestion by Sharpen a Dull Wit, I ground a knife into a "cake knife" by removing the bevels. I then resharpened it with the T2 and 600 grit wheel. Sixteen double passes on each bevel did the job. In my home shop environment, this amount of time is no problem. For a professional, this would be unacceptable. A busy sharpener would switch to a second, coarser wheel for initial sharpening. (Ordinarily I would have used the SG or SB stones graded coarse.

For a garden variety Tormek user like me, I believe the standard issue SG wheel is still the most practical, cost efficient choice for a one wheel shop. For those who might read this in the future, I would add that the Tormek is an innovative, evolving and expanding technology. At some point, CBN, diamond, or something else may become the standard "stone". Until that time, I believe the obituary for the stone wheel is premature.

Ken

[cbwx34]

I'm still a bit confused...     maybe this was answered somewhere, but why CBN over diamond?  Going by what I've read on the interweb... diamond is generally cheaper, and CBN was used only where diamond couldn't be (usually when heat is an issue, if I understand it), and that diamond in general performed better.  Yet all the aftermarket stones (with the exception of the new T-2 stones), seem to be CBN.

So, what's the reason(s) for CBN over diamond?