CBN wheels for sharpening

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Natlek

Joined
Jun 9, 2015
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Well , my USA friend is coming soon here .Time to make some order ..... ;) Anybody use this CBN wheels for sharpening knife or for any other task knife related ? Did they worth that money ? Only I know that they a good for sharpening any kind of drill bits ?

 
When I was a machine rebuilder we used these wheels to sharpen the carbide scrapers that we scraped in ways and gibbs. I always liked the surface these wheels left on the carbide tips of the scraper. No grind lines, just a shiny smooth surface and razor sharp edge that would last hours of shaving softer steel. Some of the guys would lightly free hand sharpen their pocket knives daily on these wheels to keep the edge perfect.
 
I've used one in the past for sharpening but belts work better imho...
 
They are great for sharpening and repairing carbide tools and drills. There is no reason to sharpen a knife on one, because (As razor-edge pointed out) a belt does that just fine.
 
Many times cheaper, and belt sharpening is simpler.

It is like asking if a laser will light a candle. Yes, but a match does just as well.
 
According to the video, CBN grinding is much cooler, not requiring that the blade be dipped in water to keep the edge cool.
 
Nathan the Machinist said:
Belts are friable so can do the job with less heat. CBN would be a good way to burn your edge.
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Australians use them for stainless, tool and hard alloy steels ?

We use a sequence of CBN wheels of progressive grits to edge your premium blade, followed by a rock-hard felt wheel loaded with fine diamonds, and thanks to all wheels having exactly the same diameter, and precise angle control as the blade is worked on progressive grits and honed, we get crisp bevels and an exceptional hair-splitting and hair-whittling edge
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it would depend on what speed you used them at... on a 1750 rpm bench grinder it can certainly burn your edge and get really hot. I know from experience. If you use it on a watercooled or even just slow speed 'tormek' like machine like above then yes it would work fine. But for me, I always a have a bunch of extra belts from grinding primary bevels that are not fully used up and still do a great job for the secondary bevels (edges) and I already have a water cooling system set up similar to Nathan's so I have the best of both worlds. If you try the CBN wheels, keep us posted =) Aaron Gough also uses one I think... check his youtube channel on 'making knives the high tech way' and it shows him sharpening.
 
@razor-edge-knives , sharpened edge on my HSS blades last much longer when I sharpen them with diamonds compared to stone and ceramic belts sharpening ? CBN will CUT any kind of carbides will not tear them from matrix.... ?
 
WhitleyStu said:
When I was a machine rebuilder we used these wheels to sharpen the carbide scrapers that we scraped in ways and gibbs. I always liked the surface these wheels left on the carbide tips of the scraper. No grind lines, just a shiny smooth surface and razor sharp edge that would last hours of shaving softer steel. Some of the guys would lightly free hand sharpen their pocket knives daily on these wheels to keep the edge perfect.
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Carbide will destroy a CBN wheel in seconds. The wheels you used we're most likely diamond. We have a slow speed diamond lapping wheel for carbide at work. It uses magnets to hold diamond coated discs on the hub. The grinder is about 30 years old and is most likely where Rod Neilson got the idea for his disc grinder set up.
WhitleyStu said:
When I was a machine rebuilder we used these wheels to sharpen the carbide scrapers that we scraped in ways and gibbs. I always liked the surface these wheels left on the carbide tips of the scraper. No grind lines, just a shiny smooth surface and razor sharp edge that would last hours of shaving softer steel. Some of the guys would lightly free hand sharpen their pocket knives daily on these wheels to keep the edge perfect.
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mike-E said:
Carbide will destroy a CBN wheel in seconds. The wheels you used we're most likely diamond. We have a slow speed diamond lapping wheel for carbide at work. It uses magnets to hold diamond coated discs on the hub. The grinder is about 30 years old and is most likely where Rod Neilson got the idea for his disc grinder set up.
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No, with all due respect, the wheels were CBN. I bought and mounted these wheels in the shop. We used them at higher speeds.
 
WhitleyStu said:
No, with all due respect, the wheels were CBN. I bought and mounted these wheels in the shop. We used them at higher speeds.
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But you're using resin bonded wheels I imagine and not cheap pvd coated wheels like being discussed here.
 
kuraki said:
But you're using resin bonded wheels I imagine and not cheap pvd coated wheels like being discussed here.
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Very possible... once we found a product we liked we would tell with the company and they would keep them in stock. The wheels we had lasted a very long time with lots of use.
 
Well a quick look would tell you. Is there more than a single brazed layer of grit on a steel wheel? Carbide wears CBN fast enough to wreck a wheel like in the OP. But a resin bonded wheel has much more depth of abrasive so can grind quite a bit before wearing out. That's why a 6" resin bonded wheel is hundreds of dollars and a pvd wheel isn't.

Whether it's more cost effective to use CBN or diamond to grind carbide depends on the exact application and where current costs are but when I was doing it daily we never used anything but resin bonded diamond, even though we had CBN wheels for both the little Mitsuis and big Okamotos.
 
Natlek, these guys don't make knives with high carbide volume steels at 70hrc. That's when the CBN wheel would really make a difference.

I had a lot of difficulty putting an edge on a knife in Rex 121 at 70-71rc with norton blaze ceramic belts and it was a very low quality burnished edge.

I used a CBN Waterstone and it was like 1095 on a king stone

High carbide volume with hardness in the lower 60s rc is no big deal, but at hardness pushing the 70s rc the abrasive really matters.
 
DeadboxHero said:
Natlek, these guys don't make knives with high carbide volume steels at 70hrc. That's when the CBN wheel would really make a difference.

I had a lot of difficulty putting an edge on a knife in Rex 121 at 70-71rc with norton blaze ceramic belts and it was a very low quality burnished edge.

I used a CBN Waterstone and it was like 1095 on a king stone

High carbide volume with hardness in the lower 60s rc is no big deal, but at hardness pushing the 70s rc the abrasive really matters.
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It is not about hardness of blade , it s about DID ceramic on belt cut carbides and + it s generate a lot of heat so you need coolant ? CBN will cut vanadium carbides surely and only 40 % heat goes on steel ???
WHY edge on my HSS knives last much longer when I sharpen them with diamonds ?
I don t know...I still think that they are better/faster/safer then ceramic belts ...google this company knifegrinders

Boron nitride is a compound of boron and nitrogen with a chemical formula of BN. When its crystalline structure is cubic, its abrasive cutting qualities are analogs to diamonds. The only harder abrasive particle is diamonds, but CBN will hold its integrity at higher temperatures than diamonds. The really juicy plum in the CBN pudding is thermal conductivity. The most common material used in grinding wheels for tool sharpening is aluminum oxide, which is not a good thermal conductor. Because of this, 90% of the heat from grinding with aluminum oxide ends up in the work piece. CBN is a good conductor of heat, so only 40% of the heat goes into the tool being ground. The rest goes into the wheel, which, being metal, is a good conductor of heat. Thermal properties are so good that there is very little sparking when grinding with CBM and the tool is usually cool enough to touch. Because of this superior thermal conductivity, CBN will dry grind tool steel where diamond wheels will be ruined if used dry.
There are some drawbacks to CBN wheels, the first being expense. The typical 6″ or 8″ wheel costs between $150 and $250. The other drawback is that they will only grind hardened tool steel: mild steel will ruin them. They really work best on high-speed steel but will do fine on carbon tool steel that is Rockwell C scale 55 or above. I feel the expense for even one wheel is justified by the fact that most people will never need to replace it and a good aluminum oxide wheel costs between $50 and $75 and wears out. A solid compromise is to keep a 46-grit aluminum oxide wheel on the left side of your grinder and mount an 80-grit CBN wheel on the right. Do your mild steel and rough tool grinding on the aluminum oxide and final tool grinding on the CBN.

Because there is no danger of the wheel exploding, you can mount CBN wheels at a higher level, giving better visual acuity. If you are also running an aluminum oxide wheel I would not do this, however.Using CBN wheels is quite a different experience. There is no vibration, there is no shower of sparks and there is not even really loud noise. Only light pressure against the wheel is required. It is all very sedate, and the finished grind is performance art. On scrapers the burr is uniform, working as well as, or better than, one raised on an aluminum oxide wheel. I even grind carving tools on the 80-grit CBN without burning them.
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As someone who has actually done CNC grinding in steel with real proper CBN grinding tools I can tell you it is very easy to overheat the steel. Even under flood coolant. Anyone telling themselves the steel is going to stay cool has never done it. While sharp fresh CBN may, it doesn't stay sharp forever. Grinding tooling has to fracture and break down to stay fresh. This is called being friable. The wheel construction and abrasive all play a roll here but I'm telling you people that in the real world, a not completely new CBN grinding wheel is going to get your work hot. It just does. And in practice a ceramic grinding belt setup on an automatic grinder can grind pounds of steel without even much sparking, the resulting swarf a bronze (not burnt) color.
 
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