CBN grinding wheel for knife grinding?

CBN wheels are about as good as it gets for getting a wheel to hold up for long amounts of grinding hard steel on a surface grinder. They're a pain to true up but when you get them running true they grind and grind and grind longer than any rock wheel without needing to be redressed.

In regard to knife making, the only thing I could see them being useful for is surface grinding the flat portions of hardened blades. On soft material they load up rather quickly and require redressing, and the grits they come in and how they're structured make material removal rather slow compared to belt abrasives.

ETA: They are also rather expensive. I remember pulling one out of the tool crib once when I was new in that particular shop and it wasn't an hour later the dept manager was in the tool room asking who/what/why ~$500 for a little 6" wheel IIRC.
 
If I were going to surface grind 100 blade batches on an automated surface grinders it would be my choice hands down.
 
So the question I'm spinning for a while :thumbup:
[video=youtube;wgpuN6GXKfY]https://www.youtube.com/watch?v=wgpuN6GXKfY[/video]
 
yea, Now I am curious, why don't we have CBN belts available thenstead of the Norton blaze SG type alumina ceramic abrasives seems like it would be more effective. I was grinding a knife on a 2x72 at full speed with a Norton Ceramic 36 grit and was thinking there has to be something more effective.
 
I suspect cost and lack of industry application more than anything.
 
http://www.uddeholm.com/files/TB_grinding-english.pdf
Materials in the Uddeholm Vanadis range, for example, contain a large quantity of vanadium carbides. To cut through a vanadium carbide requires an abrasive that is harder than aluminium oxide or silicon carbide. CBN wheels are therefore recommended as first choice for grinding this material. The fact that, despite this, material can be removed from Uddeholm Vanadis steel by grinding with aluminium oxide or silicon carbide is due to the fact that it is the material enclosing the carbides that is ground away, so that the carbides are torn out of the basic material of the steel. However, this occurs at the price of high wear of the grinding wheel and a risk of poor grinding performance."
VSM-BA970X-CBN......belts cca 150$ :o
http://www.teraskonttori.fi/easydata/customers/teraskonttori/files/hiomatarv/VSM_BA970X_CBN_erittain_koville_ja_hauraille_materiaaleille.pdf
I followed the occasional discussion on this subject and on other forums , still all the discussion turns to the same :D
My question is, would it be possible to use OptiGrind CBN Grinding Wheel suitable for Tormek , grinding small tihn blades which are HT and basic pre grinding...Of course PM steels
https://www.dictum.com/en/sharpening/grinders-accessories/sharpening-devices-for-grinders/704887/optigrind-cbn-grinding-wheel-oe-250-x-40-mm-super-fine
 
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The long and short of it is we don't need CBN for knifemaking.

An 8"X1.5" wheel cost $200 - That is about the minimum size that would work for knifemaking. I haven't seen any CBN wheels larger than 8".
All you can do with one is make hollow grinds - and the 8" hollow will work on small blades. A 1/8" blade will make a .6" hollow grind.
They are only a very thin bonded layer of CBN on steel - This can easily be damaged by misuse.
There is no repair for a damaged wheel - One slip and $200 is out the window.
They are only really useful for sharpening high hardness tooling, tungsten, or carbide - this is what they are made for.



(I won't say they don't exist, but I have never seen a large flat disc that was completely covered in CBN. 2-3" is all I have run across. Larger discs are either rim coated for slitting, or have a 1/2" raised lip that surface grinds.)

If you have your heart set on using a very hard abrasive, try diamond belts, wheels, discs, and polishes. I have not seen an off the shelf 2X72 diamond belt, but they can be made up by places like Eastwind Diamond. A 60 grit 2X72 industrial grade belt probably would cost several hundred bucks a belt. Normally, they are used on expanded rubber drums up to 8" diameter. Use on a belt grinder may greatly shorten the abrasive life because of the flexing.



I have a 6" diamond expandable drum setup that I will likely put in the new shop. It is run wet and used for shaping and polishing stones and glass. On the other side of it is a 100 grit 6X1" diamond wheel. That sucker will re-sharpen even the toughest carbide tooling.

Years ago, I had a 10" diamond flat lap that I donated to the local Gem and Mineral society along with a bunch of other lapidary equipment. The flap lap might have had some knife use, but the lapping discs cost about $50 each. They came in grits from 60 to 3000
 
They work fine on hard stuff that reduces to tiny powdered particles - Glass, rock, ceramics. On these things the diamonds crystals shatter off minute pieces of the object. If you look at the grind with magnification, you will see millions of tiny spalls.

On steel and other metals, unless the metal is extremely hard, it doesn't shear the metal away but instead abrades/melts it away. This will quickly glaze the wheel in a coating of soft metal and the cutting stops. Removing the metal from the wheel greatly shortens the wheel's life.
With steel, the softer ferrite matrix that the martensite and carbides are in can actually grab the diamond crystals and pull them out of the grinding wheel.

When using diamond and things like CBN on metals - only grind hardened steel, and the harder the better. Grind wet with a surfactant in the coolant. Speed can vary depending on what you are grinding, but generally, the faster the better as long as you can keep it cooled.
 
That's basic idea...I got some Elmax in 2,5 mm(0,098 inch) and like to try make some slipjoints.
When steel are cutt ,surface grind ,basic grind 45 degrees and HT it's no need to hollow grind too much....but because it is thin , tough and small overheating was the next worry.
I began to take an interest in CBN wheels as a good option....that's the whole story :)
 
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