Thread: Cheap Chinese diamond sharpening plates

Thanks Ilya for sharing that information.

I like this size diamond plate. I keep a fine and a coarse in my coat pockets for touching up woodturning scrapers.

The ones I got haven't kept their bite as long as well known named brands, but for the price you can buy half dozen at a time...[emoji23]

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Originally Posted by NeilS

The ones I got haven't kept their bite as long as well known named brands, but for the price you can buy half dozen at a time...[emoji23]

My thought exactly... I don't hand sharpen too much, and they last long enough for me. For many things I just use the CBN wheel on slow grinder. By the way, I plan to see under the microscope what sort of edge I get with that CBN wheel as well.

Ilya, was it a metallurgical microscope? - obviously should be...
I realised it is first time I see industrial diamonds under magnification - lack of uniformity in the grain size stuns - am I getting right that the grit is determined by the size of the larger crystals?

This is just a "generic" but very good microscope... For those who knows optics a bit, it can do both dark field and bright field images. I actually posted a mix of those, bigger particles looked better in dark field, and smaller particles in bright field.

Regarding the grit - I am not sure. Grit tables that I found on the internet mention average particle size. But logically, the worst scratches will be left by the biggest particles.

Thank you for posting this, mate. I use these cheap plates for de-clogging and conditioning Tormek and Japanese stone wheels after truing, do the job well and last long - now just fascinated by your images, the larger crystals look pretty much like natural raw diamonds, plainly beautiful

To say "average" means that there are smaller and larger particles in the mix. One question is: How many?
I'll guess that it is increasingly difficult (expensive?) to remove larger and smaller particles to be left with mostly one exact size.
Tedious, but measurements and analysis for mean and standard deviation would show the proportions of smaller and larger particles.

Thank you very much for both the pictures and the numbers. Good piece of photomicroscopy.

Originally Posted by Ilya

This is just a "generic" but very good microscope....

Could you please give us some details?


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Variation in particle shape (as seen in Ilya's images) is as important as size range.

https://books.google.com.au/books?id...0sizes&f=false

But, at the prices we are paying now, and the purposes we wood workers are putting these abrasives to, this is not critical for us.





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[QUOTE=NeilS;2047399]Could you please give us some details?
/QUOTE]

It is "standard" for many labs, but certainly would be too expensive for home use - Olympus BX51 with 5 objectives from 5x to 100x magnification. The finest grits are imaged at 100x.

[QUOTE=Ilya;2047421]

Originally Posted by NeilS

Could you please give us some details?
/QUOTE]

It is "standard" for many labs, but certainly would be too expensive for home use - Olympus BX51 with 5 objectives from 5x to 100x magnification. The finest grits are imaged at 100x.

Thanks Ilya.

Yes, definitely well out of the price range of the average woody.

And, definitely a magnitude better than my old Olympus CHK.... sigh!


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Got my hands on the new DMT D8C (Coarse) sharpening stone, and looked at it under the microscope. The stated size of the diamomds on the DMT chart is "325 mesh, 45 micron" This is pretty close to what I saw, with quiet a large spread of the sizes - from 30 to 55 microns, and I would say most particles are actually around 30-35 microns. I guess, for coarse grids it is not as critical as for finishing grits.

These size particles would probably correspond to the Chinese 600 grit (in original post I had 400 grit with 70 micron particles and 800 grit with 35 micron particles).
Good news is that the density of the diamonds on those Chinese plates is not less than what DMT has. The strange observation is that the "height" of the particles (from the surface to the top) on the Chinese plates is noticably less than what DMT has. Chinese stones have particles that look more like "flakes", whereas DMT looks more close to spherical shape (so I expect them to cut better). Maybe the process of diamond fabrication is different, or maybe they are not diamonds at all, hard to say. Another unknown is the quality of the attachment of the particles to the base - I suppose that time will tell.

I would be interested in seeing the difference between monocrystal and polycrystal plates. What type are the plates you have looked at above?

Quote>Some diamond stones use what are called “polycrystalline diamonds”, while others use “monocrystalline diamonds”. The surface of polycrystalline diamonds are very rough, covered with tiny points and sharp edges. These edges fracture during use, exposing new sharp edges. This is great for very fine polishing pastes but not so great on diamond sharpening stones. The diamonds get smaller as they break up and your 300 grit stone quickly becomes something entirely different. That’s why the better quality diamond stones are made with monocrystalline diamonds. These are more expensive to produce, but they maintain their size and shape during use. It takes a very long time for this type of diamond stone to wear out.

From this link BlogWS13

He is not an expert on the subject but he does explain the difference between the two types.

Thank you for providing a link - useful info also about the fluid to use. Good point about monocrystalline vs polycrystalline. It is usually impossible to say if the diamond is monocrystalline by using just a microscope. The guy in your link shows an extreme case of a good diamond vs poor diamond (almost non-crystalline). For the plates I looked at I can clearly see nice facets on the diamonds from both the DMT and Chinese plates, meaning that they are likely crystalline.

To complete this review for the time, I have used these plates to sharpen some chisels. They are cheap Bahco chisels, which nonetheless serve me well. I used Veritas guide. Some observations:
1) The 80 grit plate is really rough, can remove a lot of material.
2) I changed the angle on the chisels, so it took a bit of time to sharpen on the roughest grit.
3) Once the angle was set, going through all the grits was very quick. They cut pretty well, nothing to complain about, and no obvious deterioration after doing a couple of chisels.
4) Quite expectedly, after the last grit the bevel still shows the scratch marks, since the diamond size is 7 microns. Microscope shows scratches of the order of 7 um. True mirror finish will be below 1 micron.
5) For my use I will be finishing sharpening with diamond lapping films from lee valley (the finest goes down to 0.5 micron and gives very nice finish). Will probably do a test of those when I get a new set, as mine are pretty worn out.

Photo is only at 10x magnification.