DMT breakin and diamond loss?

B

bgentry

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Aug 3, 2009
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I recently got some 8x3" DMT diasharp plates. These things very different from the stones and ceramics I've used in the past. So far I'm enjoying them, though they're so loud! I'm frankly kind of shocked every time I use one.

In any case, on the Coarse plate, I've noticed that when I wipe my finger over the plate, after using it for a while, my finger comes away with gray steel dust *and* sparkly little powder of diamonds. Sometimes it's just a sprinkle, other times I get a lot of diamond versus metal.

I'm used to regular stones so I'm used to pressing down with maybe 3 to 5 pounds of force. I've caught myself pressing a little too hard here and there, but not for long. Generally I'm using maybe the weight of my hands. Perhaps 1 to 2 pounds? I've also tried nearly no weight, but when I do that the blade chatters on the plate and skips. There's a fine line of almost no pressure to stabilizing pressure that keeps it from skipping.

Anyway, I want to make sure that what I'm seeing is normal break in, as opposed to me ruining my plates by using a few pounds of pressure.

Thanks for any advice. :)

Brian.
 
Brian,

Hard to say, but I will tell you that they will seem to smooth out over time. I have never seen any sparkling debris on my stones...I am not sure about that.

I generally use very low pressure, but on some big jobs...I will admit to using some elbow grease and never noticed what you are saying. To be clear, it is a bad idea to ever use more than perhaps a pound of force.

As for the knife skipping on the stone...that also is odd. However I do recall my C stone did have a pimple (for lack of a better term) on it that I used the spine of the knife to break off. That was about 25 years ago and the stone is still going strong;)

Today if I got one with a "pimple" like this, I would send it back. Perhaps you should contact DMT, they have a fantastic warranty, I hear (never used it but have friends that have).
 
The sparkly stuff you're seeing might not be diamond dust, could just be flakes of metal cut just-so - hard to say without a microscope, and even then... Under magnification the particles on diamond plate are not reflective.

They do tone down a bit (quite a bit actually) with some use, and I've found a sprinkle of soapy water works wonders on my diamond stones.

DMT service I'm sure varies - took nearly six months to replace a defective interrupted surface stone I sent back to them.
 
Synthetic diamonds are black so I don't think you are seeing diamonds removed. It's also very clear when diamonds are coming off, you will get obvious smoothing of the plate and prior the surface takes a milky and worn appearance where they are coming off.

DMT stones feel very different for the first 10 sharpenings then will start to smooth out and produce better edges and scratch patterns.
 
I struggled for a while, with that skipping & chattering on very coarse hones. I found it's much easier to control & avoid that, by using somewhat of a draw stroke (slicing, at a diagonal), 'pulling' the blade down & across the face of the hone. The skipping & bumpiness is much harder to regulate, if the blade is pushed in a direction perpendicular to the edge. Every little surface imperfection on the hone will catch the edge, and cause the blade to pitch forward in angle. Very hard/impossible to regulate pressure that way, while still maintaining flush contact.

As mentioned, the hones will smooth out with some use. And using some soap & water or similar surface lube can make it much easier, with good feedback too.
 
All the input is very appreciated.

Interesting that the diamonds are black and "not reflective". That's exactly the opposite, on both counts, of what I had assumed.

I've drug my fingernail across the portions of the plates that I've spend the most "grinding time" on and compared that to the rest of the plates, and I don't feel a big difference. So maybe I'm being light enough to at least not damage them. Yay.

Regarding the chattering or skipping: HH reminded me that this was more of an issue on the XXC diasharp than on the C. It happens on both, but again, it's when I'm using almost zero pressure and not really guiding the blade with a second hand. When I add some stability to the blade by using a second hand, I can eliminate the chatter more easily.

The other thing is what phase of grinding I'm in. When setting a new bevel, I think of the first part as "breaking the corner", as you're exerting force on the upper corner of the bevel and flattening it out, producing a new flat plane that eventually intersects the entire edge bevel. Breaking the corner feels and sounds very different than grinding on a nice flat plane. In turn, this corner tends to catch on the surface much more easily and "skips" or "chatters" if you don't use the right stabilizing force. I hope this makes some kind of sense.

I'm sort of amazed at the grinding power of the XXC. Two knives I've tried so far have both had the choil area of the edge ground incorrectly. Both had very narrow bevels in the last 1/2 to 1/4 inch, and different angles in this area. I nearly fully repaired one of them in perhaps 3 minutes of careful grinding on the XXC. It's not perfect, but I think getting "perfect" would require regrinding the entire edge bevel. The point is how quickly it went from obviously wrong to almost right. I'm quite impressed.

Brian.
 
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