How to Sharpen CPM S90V

[James]

My very first knife was the Benchmade 940-1, which is made with CPM S90V. A couple years later I got the Generation Pro 3 sharpener. Of course, I practiced on my kitchen knives before I decided to sharpen my Benchmade. Of all the super steels, S90V is arguably the hardest to work with. I made several horrific mistakes. First, I had to mount the knife in the low-angle extender, meaning at rest the stones only go halfway up the blade and not beyond the edge. One slip and your blade is forever scarred. Now, whenever I sharpen a knife with the low-angle extender, I use masking tape to tape up the blade all the way to the shoulder so that only the edge and the bevel are exposed. No exceptions.

Secondly, I lost patience trying to get the knife super sharp, so I backed down to a coarser grit. Big mistake. The grit was too coarse, and I left deep scratches in the bevel, not to mention all the scratches I made by not being careful and taping up the blade.

I never did get the blade as sharp as I wanted because normal grit progressions don’t apply to S90V. Over time, my blade became a beater, which saddened me because I paid more than $300.00 for the knife. I sent the knife back to Benchmade, and they replaced the blade for only $30.00. The new blade was stonewashed and not a satin finish the way it was originally.

The blade was reasonably sharp, but the tip was completely rounded over. After using my Wicked Edge sharpener for three years, I finally knew what I was doing. The secret to sharpening any knife is knowing which grit to start with. Rounded points are easy to fix, but that’s another topic. I started with a 1,000 grit stone and kept at it until the edge was sharp and the point had been fixed. This took me three hours.

After that I progressed to a 1,500 grit stone. I have never been able to raise a burr with S90V, so I relied on my touch. Again, I kept at it for almost three hours. Now the edge was very sharp, After that I progressed to 2,200 grit and kept at it for nearly an hour. At this point, the knife was so sharp I could drop a piece of paper on the edge, and the paper was cut cleanly in two pieces. Time to move on to 3,000 grit. By now, I didn’t need to put so much time into sharpening because I was merely homing the edge.

I wasn’t satisfied with the edge just yet, so switched to 6 micron diamond lapping film. I think I gave the blade 30 strokes before switching to 3 micron diamond lapping film. The nice thing about diamond lapping film is that it is still a powerful abrasive, but it also polishes the edge to mirror finish. I progressed to 1.5 micron diamond lapping film, and then finally to 0.1 micron diamond lapping film. The edge was wicked sharp, but I wanted to take it two steps further.

I switched to Nano cloth using 0.050 micron diamond slurry. After that, I progressed to 0.025 micron diamond slurry. The knife turned out perfectly. To be honest, I never saw a knife so sharp. I even showed it to my dentist. He said it was sharper than his scalpel. I could shave with it if I really had to, but it would definitely leave serious razor burns.

I hope this helps.

James Weil

• This topic was modified 3 years, 9 months ago by Marc H.
• This topic was modified 3 years, 9 months ago by James.

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