Final report, CBN grinding wheels

[wootz]

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?

Not that puzzling if you imagine yourself an owner of a factory producing grinding wheels, and streamlining profits is your major concern.
You know that CBN has higher heat and impact resistance than diamonds - and this is important for high RPM grinders which are your principal consumer base. With them in view, you commission a CBN technology, and as a side-line you also make wheels for Tormek-like slow grinders. Having an additional diamond wheels line for slow rotary grinders just isn't that profitable, i guess.

What has been said in this thread, is better read together with Curt's thread https://forum.tormek.com/index.php?topic=3259.0
All read and thought over, hardly can it be summarised better than Ken did a post above.

[cbwx34]

Not that puzzling if you imagine yourself an owner of a factory producing grinding wheels, and streamlining profits is your major concern.
You know that CBN has higher heat and impact resistance than diamonds - and this is important for high RPM grinders which are your principal consumer base. With them in view, you commission a CBN technology, and as a side-line you also make wheels for Tormek-like slow grinders. Having an additional diamond wheels line for slow rotary grinders just isn't that profitable, i guess.

What has been said in this thread, is better read together with Curt's thread https://forum.tormek.com/index.php?topic=3259.0
All read and thought over, hardly can it be summarised better than Ken did a post above.

Makes sense.

Hopefully, Curt (OBR) will post a followup in that other thread.

[Ken S]

Thanks, Wootz. You have been the original forum pioneer with CBN. Like you, I hope Curt (OBR) will continue posting on his CBN journey. We all benefit from having posts from different backgrounds. You, with a high end sharpening service; Curt as a high energy farmers market weekend warrior, and me as a curious home shop sharpener.

From what I have learned, if CBN works better at high speeds, and diamond wheels are less costly to manufacture, I think Tormek shows good engineering by choosing the less costly product which suits the slow speed Tormek. I was surprised at the cost of the Tormek diamond wheel. The prices seem very reasonable to me. Not cheap, but fair. Tormek has chosen a product ideally suited to the Tormek machines at a reasonable price.

I would be curious to know the reaction when Tormek first introduced the man made SG grinding wheel as an alternative to the locally mined natural stone. The SG stone is coarser than the nstural stone. My uninformed guess is this was the original impetus for the stone grader.

Ken

[AKMike]

I haven't read any further, but one CBN wheel manufacturer claims that the pure carbon in diamond wheels forms carbides with the other elements in steel, destroying the diamonds. http://www.optigrind.com/page_2538178.html

Mike

[Ken S]

Mike,

I have not found definite proof, however, I suspect the carbon problem is from the high heat produced in high speed grinding. The slow speed (approximately 100 RPM) of the Tormek is very different than the 1725 to 3450 RPM world of dry grinders.

I am glad you brought up the question. We need more documentation. The costs of designing, research testing, and manufacturing the T2 with the diamond wheel must be substantial. I can not imagine Tormek choosing diamond for the wheel if there was a carbon/carbide problem which effected grinding at Tormek speeds. I wish Tormek would share more of its decision process in choosing diamond.

Ken

[Stickan]

Hi,

This happens only with high-speed grinders. CBN wheels are designed to mainly be used on bench-grinders.

Sincerely,
Stig

I haven't read any further, but one CBN wheel manufacturer claims that the pure carbon in diamond wheels forms carbides with the other elements in steel, destroying the diamonds. http://www.optigrind.com/page_2538178.html

Mike

[Ken S]

This discussion of CBN and diamond wheels illustrates my idea about trying to apply high speed dry grinding thinking to the Tormek.

I have downloaded the instruction booklets of the clones. The safety portions give away the high speed dry grinding thinking. A grinding wheel turning at 3450 RPM requires more stringent safety precautions than a wheel spinning at 100 RPM. That is why high speed grinders require guards, spark guards, eye shields and cooling buckets. (That same dry grinding thinking, and cost, are why clones are still using rust prone regular shafts eleven years after Tormek converted to stainless steel.)

Past posts have suggested that the Tormek could be improved by using sealed bearings instead of nylon bushings. This is another example of high speed dry grinding thinking. In a low speed, wet environment, the nylon bushings do not rust. An older non stainless shaft and nut may be solidly connected with the grinding wheel by rust, especially from poor housekeeping or lack of yearly regreasing. I have never heard of a shaft freezing to a nylon bushing. How many of us have old SuperGrinds with shafts rusted tight to the grinding wheel, but otherwise working perfectly?

Much of the consumer grinding world thinks in high speed dry terms. It is important to recognize this thought prejudice.

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

Today had first customer folder ground on this wheel, a Benchmade Osborne S30V - the wheel is all-round perfect – flat, square, and round.
The best flatness of all CBN wheels I have. Affordability is a true breakthrough.

Challenge with this particular blade was that it came with an uneven bevel out of the box, by 1mm higher at the tip:


Fixing defects like that is demanding to the flatness of the wheel - the result is pretty good:


Having ground the bevel on the Spartan CBN #1000 wheel, refined the edge on a sequence of paper wheels from 5 micron diamonds, down to 0.5 micron diamonds.
Final edge sharpness is 45 BESS, hair-whittling.

Can definitely recommend the Spartan CBN wheels.

[grepper]

Which sharpness tester are you using Mr. Wootz?

[wootz]

PT50 1st issue in the workshop.
Have to admit, Mr. Grepper, I still learn a lot from your posts on the BESS forum

[Jan]

Having ground the bevel on the Spartan CBN #1000 wheel, refined the edge on a sequence of paper wheels from 5 micron diamonds, down to 0.5 micron diamonds.
Final edge sharpness is 45 BESS, hair-whittling.

Can definitely recommend the Spartan CBN wheels.

Wootz, your BESS sharpness 45 gf is an excellent result!

Following the BESS definition it means that your edge is as sharp (and also as thin) as a standard DE razor blade. The apex width is surely in the submicron region.

Based on prof. Verhoeven measurements the edge width of Gillette DE razor blade was about 0.3 microns.

J.F.Sackman paper reported that the edge width of Wilkinson DE razor blade was about 0.1 micron.

Jan

[wootz]

True, that's the best reading for the S30V steel I ever got, usually I get a score between 60-80 - that blade must have been very well tempered.

Not sure if you guys have played with them yourselves, but both the Gillette & Wilkinson DE razors score anywhere between 25 to 35 on the PT50 and PT50B with little consistency. Although in the specs the PT50 & PT50B resolution is at +/- 5, it is true in the over 50 segment of the BESS scale; these instruments lowest meaningful reading is somewhere at 30, and you cannot trust any score under.
Not that it is written somewhere or Mike told me - just came obvious to me from trying razor edges.

It is therefore only possible to say more or less confidently that the edge apex width is in the 0.2 micron range where the score is under 80-90, and that it is probably in the vicinity of 0.1 micron, where the score is 20-60.

For true submicron measurements, a PT50A or KN100 is needed.
I realise that these notes are not pertinent in here, just haven't registered at the BESS forum yet, still in the reading mode there.

[Jan]

Recently ToddS on bladeforums.com has shown perfect SEM images of different brands of razor blades. He claims that the average edge width is about 0.1 micron.

This is in full agreement with Sackman paper, A Close Shave, published in Physics in Technology, vol. 9, already in 1978!

Jan

[grepper]

The 45 gf reading is very impressive, Mr. wootz!  Excellent job of sharpening there. 

Are you using test clips or the media holder on the PT50?

I'm surprised by that 25-35 gf reading on the Gellette's.  If memory serves, that's sharper than your average Feather DE blade.

I learn from you too Mr. wootz.  One big happy family. 

[wootz]

... spooled certified media.
What surprises you, I believe only tells us that the PT50 and PT50B are unreliable in the lower range of the BESS scale under 50.

All our edges score between 50 and 90 on PT50, i.e. between 0.1 and 0.2 micron, and there is nothing amazing about it. Miracles aren't allowed in my workshop - only consistent angle is while sharpening and deburring.
Absolute angle value is of no concern, but maintaining the same angle through the sharpening session is.
Steel type and temper bring the edge closer to either 50 or 90.