Diamond Sharpening

There are many different abrasive systems used to produce sharp edges on tools, be that sandpaper, abrasive grits, waterstones, oil stones, or diamond stones (among others).  They all have one thing in common, and that is very hard precisely sized particles suspended or retained in a soft matrix.

The quality of the hard particles goes a long way towards the quality of the abrasive.  Strange as it may seem at first glance, this even applies to diamond – there is diamond, and then there is diamond.  For example, the diamonds need to be bound securely into a parent material, if not they come loose, and not only are lost, but can really gouge the tool as well.  Also too, you can have a few diamonds, or a lot, evenly sized diamonds or not, and diamonds that are strong and durable, or ones that easily shatter and shear.

I have sourced some diamond stones from Professional Woodworkers Supplies which have a good name for quality and durability.  They are DMT Diasharp stones, and the ones I have chosen are double sided, so are the equivalent of 4 diamond stones.

For some reason, DMT only categorise their stones as fine, coarse, extra-coarse etc, which is rather frustrating when trying to compare apples with tomatoes. However, I have been able to determine what the equivalent is across all abrasive types, by finding out what the size of the abrasive particles are, which means it is easy to switch and swap between all the different abrasives and still be working “through the grits”. This earlier article of mine on comparing abrasive systems spells it out in a table form.

From the DMT website, I was able to determine the actual particle sizes:

Stone Mesh Micron Effective Micron
Ex Ex Coarse 120 120 40
Ex Coarse 220 60 20
Coarse 325 45 15
Fine 600 25 8
Ex Fine 1200 9 3
Ceramic 2200 7 ?
Ex Ex Fine 8000 3 1

*I have amended this list in light of recent discussions with the Technical Director for DMT, and the effective micron size now listed is based on the size of the exposed diamond, which is what is doing the cutting and not the size of the diamond in total (2/3 of which is buried in the Nickle plating).

Just out of interest, the concept of “Mesh” originates from a sorting method for determining the particular particle size, by passing it through a number of sieves (meshes), with increasing holes per inch (and therefore decreasing hole sizes) until the particle can go no further, so it’s size is known.

Oh, and fwiw, 1 micron = 0.001mm = 0.00004″

When flattening something (whether that be sharpening, or sanding), you start off with a particle size (or grit) which is coarse enough to remove the existing structures and scratches caused by the tooling.  Depending on how rough the surface is to start will determine what is the correct grit to start with, and you keep working till the original machining marks are replaced completely with the scratches from that original grit. You then move onto the next higher grit, and work to remove the scratches from that previous grit.  Rinse and repeat through all the grit sizes until the final finish quality is achieved.  As you work up the grits, less and less material needs to be removed.  One thing I find annoying, is the manufacturers rate their abrasives based on the average grit size.  The problem with that is although the average is all very well, if you have a few much larger particles, they will cause some individual serious scratches which will remain in the project unless you return to a heavier grit and start again.  The better quality the abrasive, the less of a problem there is.

Oh, and one other myth – rubbing two abrasives together to produce a finer grit is just that – a complete myth. Imagine the individual particles of abrasive as tiny chisels.  Do you get a better, sharper, finer chisel by ramming it into another?  No- all you get is a blunt, chipped or broken edge which renders the tool useless.  Same with abrasives.

So onto the sharpening with diamond.  Diamond chips are just another collection of micro chisels.  These are securely bound in a base of metal for the simple reason that because diamond is so durable, you want to keep the diamond particles around as long as possible.  If they are not worn out, why get rid of them?!

The two diamond stones I chose are double sided.  One has an extra coarse side and a coarse side, and the other stone has a fine and extra fine side.  The equivalent in ISO sandpaper is 240, 320, 600 and 2000.  Unfortunately, I feel this already demonstrates a problem, that too many intermediate grits are being skipped.  400, 800, 1200, 1500.  This may explain why when I was using these stones, I found the final result less than the perfection I was hoping for.  Not a fault of the stones themselves, but more may be needed to really perfect the finish.  The lower two were fine, and the jump from 320 to 600 not too extreme, but going from that to 2000 was too much.  However, once you understand micron sizes, it is easy to switch from one material to another.  In this case, I’d probably stop at the fine diamond stone, and switch over to the Japanese waterstones to finish the process. (1000, 2000 and 6000, or in grit sizes: 14, 7.5 and 2). (Update, I now have a better understanding of the grading of diamond stones from the Q&A with the Technical Director for DMT, which covered this point, and demonstrated that there is much less of a jump in the effective micron sizes than I realised)

Part 2 will document the stones in use.

3 Responses

  1. Appreciate the good words regarding DMT in several of the articles I have found. If there is anything in the way of information I could supply to you or help with any subject matter I would be happy to assist you if I am able to.
    Regards, Stan.

  2. […] Diamond Sharpening (stusshed.com) […]

  3. […] sheets that go from 30µm, down to a miniscule 1µm.  That is the same particle size as the extra-extra fine diamond stone from […]

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