C.B.N. coated for T7

[Ken S]

Excellent articles, Grepper. Thanks for posting them.

Ken

[grepper]

Wow!  Fast! Amazing.  CNC CBN machining:

https://www.youtube.com/watch?v=4XIZQFMYUzk

While you are at it, check out this series of 9 videos.  More show up on the right as you watch each one.  Really cool and impressive stuff!:
https://www.youtube.com/watch?v=5HBLocw7GyE

[Ken S]

I can see where one of these wheels might be a useful adjunct for some Tormek users. CBN seems more suited to high speed steel than "regular" high carbon steel.

The EZYlock shaft has made using multiple grinding wheels time efficient. Whether or not using multiple wheels is cost efficient depends on the kind and volume of work involved. In my case, mostly chisels, planes and knives, the CBN wheels do not seemto be cost efficient. If I had a sharpening business involving alot of harder steel, or a large tool budget, I would acquire at least one. If I did a lot of turning, I would seriously consider one.

In any case, it is nice to know that we have that option either now or in the future.

Ken

[Rob]

it certainly looks an interesting technology.  I predict as it passes from niche, premium, novelty into general circulation, it's price will drop through the floor and in 5 years from now be significantly more common.  It does look like there are many advantages.

[Herman Trivilino]

Weird that the wheel designed for mounting on a Tormek T7 is only 40 mm wide instead of 50 mm.

Also, what's the need for the Tormek water trough and low speed? Why not mount an 8-inch wheel on a high speed grinder, add a BGM-100, and off you go?

Rob, this is an alternative to your Sorby!

[Ken S]

This is just a guess. I suspect the narrower grinding wheels are really designed to stay balanced with much higher motor speeds. Actually, for the two T4 fans on the forum, 40mm represents a same size replacement.

For reshaping high speed turning tools, I would think the CBN wheels would work quite well. A turning club  could easily split the cost. The set up could be used wet or dry. The coarse grit would give an agressive cut, tempered by the Tormek's slow speed for control. That seems a very civilized way to work.

The EZYlock shaft allow a quick change to the SG wheel for sharpening any carbon steel turning tools or a final smoothing cut, thus giving the user the best of  both worlds.

Playing the devil's advocate, a Tormek T4 is not  much more than a cheap eight inch grinder and a BGM-100. In fact, the eight inch CBN wheels are considerably less expensive the tens and the T4 is better built than most grinders. CBN eight inch wheels are available with 12mm holes for the T4. They will also work with the T7 as well as any wheel worn down to eight inches. (Yes, they are only 40mm wide instead of 50mm, however, thatis still wider than regular dry grinder wheels.) The T4 has plenty of pep to reshape a turning tool with a coarse grinding wheel. In fact, my initial tests found that the T4 and T7 have essentially equal cutting speed with high speed steel and the SG wheel.

Ken

Ken

[grepper]

Herman, if you check around the 'Net you will see folks are using exactly the setup you describe.  They say it sharpens very fast, runs hotter than the Tormek but not too hot to hold in your hand.

One dude complained that his CBN wheel had slightly dished so he obviously had an older type matrix composite wheel rather than a plated steel wheel.

One place said the CBN wheels work just fine on the Tormek just slower, so it is a perfectly acceptable option especially if you have a Tormek and not a bench grinder.

You would not need the water trough, but it wouldn't hurt and while there is no stone dust from the wheel it would catch steel dust from the blade which is sort of nasty stuff in it's own right.

[Ken S]

I like the idea of using a CBN wheel wet. Very Tormek cool, and it catches all themetal grindings. Looking at what all sticks to the magnet in the water trough, there is plenty of stuff I would prefer not fly around. A coarse wheel on a Tormek should give an acceptable speed of grinding.

When I tested Norton 3X 46 and 80 grit wheels on the Tormek, I was very pleased with the cutting speed.

Ken

[Ken S]

Grepper, Yoshio Odate designed dished diamond plates for sharpening plane blades with camber. You dude friend may have come up with a solution for matching the sweep of a gouge or the camber of a plane blade. With nine CBN wheels with differing amounts of hollow, he would have a set of gouge plates!

Ken

[Rob]

Weird that the wheel designed for mounting on a Tormek T7 is only 40 mm wide instead of 50 mm.

Also, what's the need for the Tormek water trough and low speed? Why not mount an 8-inch wheel on a high speed grinder, add a BGM-100, and off you go?

Rob, this is an alternative to your Sorby!

Yes the thought had occurred to me.  But from a logical standpoint I'm also struggling to see the sense in mounting a wheel where the technology allows cooler grinding at faster speeds to be mounted on a Tormek.  Surely, the appropriate motor for such a wheel is pretty much anything which spins fast?  Point being you then get a solution to the "elephant in the room" which is shaping HSS or even those tricky  very hard steel planar blades dare I imagine??

The Tormek's speed is married in design wedlock to the water bath.  The two are inextricably linked, the water being the solution to overheating and the speed being the solution to water being centrifugally thrown off the stone.  THE big advantage (it seems to me) with this CBN tek is being able to shape which means fast steel removal which means speed is your friend.  The fundamental change this tek brings is cool grinding at fast speed which is an enabler for rapid shaping of hard steels.  Thus, the thing which carrys it need only satisfy one function...speed.

Now I'm not saying don't use it with a Tormek.  If someone has already invested then why on earth not?  I'm just saying that the primary ingredient to shape (remove steel fast) is speed.  Tormek beautifully solved the problem of overheating (a side effect of speed) with their solution but the price paid is efficiency in shaping.

Now it could be that as Ken says, this low grit version (80 wasn't it) is so abrasive that a fast speed is in fact redundant and therefore the Tormek is a perfectly acceptable motor upon which to drive it.  It's a pretty exciting idea for those with investment already sunk because of course it protects the investment already made in jigs.  I rather suspect that due to cost it's less likely to excite new buyers though.  If you combine the cost of CBN and a new Tormek you're probably heading towards a $1K aren't you?

I think if I hadn't already gone down the linisher style tool for my shaping needs of turning tools I would probably seriously investigate those wheels.  Very interesting indeed.

Last question:  They're made of steel right?  Then the abrasive is electrolitically applied???  If they were used with the water trough in situ, would there be a rust risk to the wheel?

[Rob]

I've thought of another too.  You cant true them right?  So if there's any lack of concentricity on the Tormek shaft you're sunk because you cant calibrate the circumference of the wheel to the USB with the diamond dresser.  That holds equally true for any other grinder of course.  I'm guessing the Tormek shaft does run true and any wobble we (quite often) see in the stone is actually because it's stone and either not seated properly or needs truing.  So maybe that's not such a biggy after all.  Think I've talked myself out of that.  Bottom line, putting a CNC machined wheel on a Tormek (any grinder in fact) shaft will quickly reveal if it's out of true :-)

[Ken S]

Very good posts, Rob, worthy of thought.

I certainly see your point where speed is of the essence or when someone is starting very specialized sharpening without a lot of previous investment. While a CBN wheel with a high speed grinder would make quick work of a planer blade sharpening or reshaping a turning tool, it could also convert a chef's knife to a paring knife with equal dispatch.

That brings us back to the balance between efficiency with a few operations and versatility. A related balance, as you mention, is between cost and return in both revenue and time.

Regarding a wheel or shaft running out of true, needing to dress a conventional grinding wheel initially and from time to time is baked in the cake. The same is true when bench stones wear. CBN wheels are manufactured to high concentricity standards and are expected to maintain those standards throughout useful life.

Shaft runout iis another story. It is easily checked, either mounted or unmounted. This can be done with a simple feeler gage set up or with a relatively inexpensive dial indicator. If in doubt, this is a quick and easy job for a local machine shop.

Costwise, I agree with your figure, Rob. However, one should consider a T4 as a lower cost alternative. A new T4 and a CBN wheel would cost around $600 US, and would get the job done in a home or small business shop. I am not talking about an industrial environment. For a part time operation the T4 combo offers a lot of firepower and versatility for not much investment. And, should demand warrant adding a T7 later, the jigs will all interchange.

My family is awakening. I will write more later.

Ken

[Rob]

Interesting Ken.  Your extra experience with the T4 keeps reminding me to consider it as I've not gone there given the T7.  Also the comment you make about the knife disappearing fast.  Do you believe these CBN wheels are so abrasive that even at slow grinding speeds they would remove steel very very fast, even HSS?
And your comments about shaft runout are of course spot on....I went up a blind alley on that and realised where I had been only at the end :-)
And the rust thing?

[Ken S]

Good question. Rob. I emailed one of the manufacturers with the question about using them wet. He replied that they work either wet or dry. He made no mention of rust, although I will pursue the question further.

I found that using the 3X wheels on the T4 produced significantly faster cutting than either the SG or Sb wheels. I admit, the test was not exhaustive and there may well be other factors involved. I placed identical 3/8" (10mm) square HSS metal lathe cutting bits in the SE-76 jig and ground for five minutes with heavy pressure. With the 80 grit wheel I ground almost an entire new bevel in five minutes. I achieved this same amount of grind with the 46 grit wheel in four minutes. The SG wheel ground about two third of that in five minutes. The SB did less well. (The SB may require a lighter touch to avoid glazing. I need to do further testing and would welcome advice from SB users.)

in all cases, the finish was surprisingly smooth. I have not tested enough to be certain, but I believe using a lighter touch with all wheels would produce a more controlled and slightly smoother cut. So, to answer your question, my best guess not based on actual testing is that the coarser wheels can be controlled. A follow up with the leather honing wheel loaded with valve grinding compound might add enough polish. Following with the SG wheel and honing compound would certainly provide the polish. I would change the water in the trough before following up with the SG wheel and I only use valve grinding compound with a separate leather honing wheel.

Regarding the T4, I do not plan to sell my T7 and switch. However, in hindsight, given my actual use over the years, if I had that experience at the time of initial purchase and if the T4 had been available, I would have purchased the T4 instead of the T7. (That assumes, rightly or wrongly, that I would have had the wisdom to be realistic in my needs, which is debatable.) I do not see either choice as a bad choice. Besides, the rest of the system works with either model. I would choose the T4 for its strengths rather than to save money.

The 3X wheels do not have all the advantages of either the SG or the CBN wheels. They are one inch (25mm) wide. The largest diameter is eight inches (200mm), just like the T4 or some of the well worn T7 wheels. They do wear down, just like the Tormek wheels and will need to be trued occasionally. As they are designed for initial more coarse work, I do not see the truing issue as a major condition. I want the finer wheels to be very true, They are not a substitute for the SG. They do remove metal quickly with high speed steel in a very controllable way. they work wet, and, being ceramic, do not rust. They are also relatively inexpensive, around $50US each. They require a simple homemade adaptor to fit the 12mm Tormek shaft. I can post instructions for this if there is interest.

For the cost of a BGM-100, they provide the occasional user with a workable coarse wheel alternative with the benefits of the Tormek, water cooled grinding, spark free and dust free. While they might work dry, I am quite content to enjoy the benefits of the water cooled Tormek.

Ken

[Rob]

That's quite the experiment you've conducted there Ken :-)  You're becoming a "freelance innovation tester" for all things of a sharpening nature.  Thanks for that, interesting feedback.