3M 15 micron diamond paste in action

3M sell a wide range of abrasives to consumers, from sand paper sheets to diamond hand laps and lapping films. However, they do not sell their stropping pastes on the consumer market.

Luckily a fellow knife nut works as a physical engineer. This gave me the chance to test some 3M diamond polishing paste, called Diapat. (Diapad – with a d – seems to be their name for the diamond hand laps.) This paste is available in micron sizes ranging from 15 micron to 0.3 micron. Since the effects of the coarsest stuff were hopefully the easiest to see, I picked the 15 micron diamond paste.

I had no spare leather strops anymore, so I only tested the paste on balsa. First I made a pretty horizontal scratch pattern on the edge using the 1000 grit stones.

Edge after 1000 grit stones before stropping with 3M 15 micron diamond paste on balsa.

I then did 500 stropping strokes.

Edge after 25 stropping strokes with 3M 15 micron diamond paste on balsa.

Edge after 50 stropping strokes with 3M 15 micron diamond paste on balsa.

Edge after 100 stropping strokes with 3M 15 micron diamond paste on balsa.

Edge after 250 stropping strokes with 3M 15 micron diamond paste on balsa.

Edge after 500 stropping strokes with 3M 15 micron diamond paste on balsa.

What I saw was a gradual abrasion of the edge. The stuff did not appear to leave 15 micron wide scratches, but the 7 micron scratches made by the 1000 grit stones were gradually removed. I didn’t understand quite what was happening, but clearly the stuff was abrasive.

And, judging the pictures, it did not cause a lot of burnishing. (Which, in a way, was also surprising, since it felt just as sticky as the Wicked Edge pastes.)

It then occurred to me that I could perhaps get a higher quality image by removing the knife from the clamp and using the microscopes in a more traditional way. (I should have thought of that much earlier; a few other people make better pictures than I do by using their microscope in this way.)

And yes :-) .

Edge after 500 stropping strokes with 3M 15 micron diamond paste on balsa.

Now the scratches made by the 3M paste are much better visible. They are most prominent at the top of the edge: I had some problems maintaining an exact angle.

Then it occurred to me that the scratches made by the 3M paste might well have the same width as, or even be wider than, those made by the 1000 grit stones. They just appeared less deep than the 1000 grit scratches.

In Photoshop I cut out an area of the photograph representing 0.2 mm (200 micron) of the edge and then magnified it 4 times. Below is the result.

0.2 mm portion of the edge after 500 stropping strokes with 3M 15 micron diamond paste on balsa, blown up several times. I counted 18 scratches.

I counted the number of scratches and came to 18. That means each scratch is about 200 micron / 18 = 11 micron wide.

Not bad for a 15 micron paste. Finally practice behaves according to theory :-).

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