DMT dia-sharp scratches.

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SKOOKUM_KUSHU

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Apr 20, 2021
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First, I’ve read other forum posts about what may be the same issue but the image hosting sites have taken the original images down so it’s impossible for me to tell. I started sharpening a Leatherman Charge Titanium (S30V blade) with some new Dia-sharp stones and noticed what looks like small hairline scratches in the metal (or at least removed diamond). I was fairly conscious of the pressure I was using, not more than the weight of the multi tool and maybe my hands. The problem was more pronounced as the fineness of the grit increased. The worst offenders are the extra fine and extra extra fine stones. Is this normal? Have I damaged (or ruined) my stones? It looks like the tip of the blade gouged in slightly but my fingernail can’t detect any sort of defect on the surface.

It’s hard to make out in the pics, but I’m talking about the hairline scratches that catch the light, not the duller, wider marks.

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Plated diamond hones will always show these scratches after they've been used. More noticeable if sharpening wear-resistant steels with hard carbides (like S30V), of which the carbides are much harder than the nickel plating itself. It's generally nothing to worry about, so long as the hone is used with relatively moderate-to-light pressure, as is the norm for these plated hones. Used as such, they'll last a long time.

Sometimes the apparent 'scratches' might also be trails of embedded metal left behind from blades sharpened on the hone. Some low-alloy stainless steels, like 420/440-series for example, will cling to a diamond hone's surface in this manner. It's a good reason why it's generally better to use some lubrication (water or oil) on the hone for sharpening - more so, if some major grinding is to be done. The lubrication helps prevent the metal swarf from clinging so tenaciously to the surface.
 
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The DMT HardCoat stones resist scratches a bit bit better. Depending on the steel, they will still show scratches after a bit of use.
 
Diamond hones work best dry, no lube required. If/when they load up, you can clean them with dish soap and water, or use something like BreakFree CLP, which has worked for me for several decades. You can spread a thin coat over the hone and wipe immediately, or even better, leave it on a few hours or overnight, then wipe clean with a soft cloth.
 
I got new stones a few weeks back, and I have noticed the same massive scratching on the EF plate in particular. I used a cheap smith & wesson knife to break it in, so I'd imagine no hard carbides like there would be in S30V, etc.

The quality of these plates is NOTHING like it was 10 years ago. I have an EF that's 10-12 years old, and it is perfectly smooth and doesn't get scratched up like this newer one. The newer one also has imperfections on the surface that do not appear to be diamonds. When the edge hits them, I get a nice dull spot. It doesn't seem like something that's going to go away with breaking in. I'm very disappointed.

As long as you can see metal coming off when you pass the blade over the surface, the stone is not "ruined;" it still has diamonds and will cut steel
 
Diamond stones require very light pressure, this is a common mistake most new to diamonds make.

In addition, when the stones are new, they have a very aggressive action with many fresh diamonds protruding out of the matrix. Should be broken in with an older junk knife or a piece of hardened steel to smooth out the diamond surface.

I have used oil mineral oil, or sometimes water on my DMT stones for many years, work much better than dry. The lub floats way the steel particles as you abrade the knife edge.

Regards,
FK
 
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