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JOEL Joel's Blog

Diamond Sharpening - Introduction


Diamond Sharpening - Introduction 4In the past 30 years sharpening with diamond stones has gotten more and more popular. Some teachers, notably Paul Sellers have been huge advocates of the technology, and more and more people are using diamonds for some of all or their hand sharpening needs. The largest US maker of diamond stones for sharpening, and one of the best is DMT and lately we have started to stock most of their entire range. This is the first of two blogs on diamond sharpening, this entry being about the issues involved, and the next part about with my personal experiences with the stuff.

30 years ago the major complaints about diamond stones were that the stones weren't flat enough for precision sharpening, the stones didn't last, and you could not get a finished edge from one. The major positives about the technology were that the rise of exotic alloys in woodworking tools such as A2 and D2 increased the demand for a sharpening media what could handle these tough materials with speed. Also diamond stones didn't need lubrication or flattening.

Another popular application of diamonds in sharpening is to charge a plate with diamond paste, which turns the plate into a fine abrasive stone. This works great,especially for very fine grits. This is an old method of sharpening that has been applied to woodworking tools for the past ten or twenty years.

In addition to directly sharpening stones another very popular use of diamond stones is to flatten waterstones. It's a quick method and works great with one major problem. The problem is that the way you make a diamond stone is by taking a flat piece of steel, sprinkling diamond dust of a specific grade on the plate, and then nickel plating the entire plate, rocks and all, to cover the stone. The plating bonds the diamonds to the plate. When you use a diamond stone to flatten a waterstone, the water stone particles are abrasive and wear away the the plating that keeps the diamonds on the stone - so the diamond stones work slower and slower. In the photo (taken with my inexpensive not very sharp USB microscope) on the right you can see the plating surrounding the diamond particles like irregular halos.Diamond Sharpening - Introduction 5

When sharpening diamonds produce a coarser edge than does the same grit waterstone. There are two reasons for this. Diamonds, like most abrasives have a nominal grit assigned to the stone. The grit - 220, 600, or 1200 or so mesh is the maximum size of the diamond particle. This is the same with all abrasive stones - there is a nominal abrasive grade and an actual variance on the particles. Lower quality stones will have a greater grit variance but all diamond stones have some variance. With regular waterstones the second you start sharpening, any large grit particle shatters, and all the particles start to round over and wear. So very quickly you get an even scratch pattern that we associate with the grit of stone. Diamonds, which cut fast, don't shatter (very much) and the larger diamonds on plate scratch the edge deeper, and don't get worn down. The end result is that for the same grit stone, the diamond scratch pattern is a fair amount coarser. But, because the diamonds don't break down, very fine diamond pastes can sharpen quickly and for a long time.

Pre-diamond my basic sharpening sequence for waterstones was, Hollow grind, use a 1000 grit stone to create the wire edge, then chase it with first a 4000 or 5000 stone, followed by an 8000 grit or better finishing stone. For harder Japanese tools I stop there, for Western steels which are typically softer I follow with a plain, untreated leather strop.

The question now is what's an appropriate sequence of diamond stones? Do I need as many? of what size? DMT makes two basic styles: the original DuoSharp with spots of diamonds on plastic substrate, and the DiaSharp which is a continuous diamond surface on a precisely flattened steel substrate. For woodworking tools the steel plate is the way to go - it's what they were designed for. They do weigh a ton, are more expensive than the earlier stones, and are overkill for knives and other non-precision tools. I like large stones, but the weight of the steel stones has kept me on the 8" size, not the 10". A fair number of customers like the 6" length because it's a lot less expensive, and much lighter. To keep the stones from slipping around a bench we stock the absolutely fab non-skid mat or a magnetic holder that comes with 12" stones and has the advantage of lifting the stone off the bench for more clearance.

DMT does manufacturer, and we offer, an 8000 grit (extra-extra-fine) DiaSharp, but as I am chock full of finishing stones I haven't tested it. In the next part of this series I will take a closer look at diamonds and start getting into practical experiences. I've got two goals here - the first is figure out if I can get an edge that is the equal to or better of the edges I get using oil or water stones. The next goal is to figure out what's the fastest way of getting there. Finally, and make that three or four goals, can diamonds be used on my carving tools and are they an improvement on what I am already using? The last goal and let's just say, amongst my many goals, is answering the question: are diamonds a good solution for sharpening kitchens knives and other things that I get regularly asked to sharpen?
Click here for Part Two
Join the conversation
12/11/2014 Mark Hagy

Thank you. You consistently deal with issues which directly impact our lives as woodworkers, providing thoughtful and well founded advice and suggestions. You help all of us learn and grow in the experience which we all enjoy, working with wood.


12/11/2014 John Willman
I have been using diamond stones for several years now and I have found that I like to use a 300 grit and then either a 600 or 1000 grit diamond stone for establishing the micro bevel and then finish on an 8000 grit water stone. I have an 8000 grit DMT stone and I don't think it polishes nearly as well as the water stone.
12/11/2014 Tico Vogt
I purchased a DiaSharp 8,000 stone at the Woodworkers Showcase in Saratoga Springs this last March. The owner of the company told me that it would initially produce a rougher scratch pattern until a certain amount of work was done on it, that particles needed to wear down a bit to be at the truly 8,000 grit polishing level. In the meantime he suggested using it for flattening chisel backs to reach that stage. So far I'm less than thrilled: I have other media for the purpose of flattening chisels, etc. I don't want to experiment on my honed microbevels to see if the stone has reached the point where it is what it claims to be.
So, I will stick with the excellent micro-abrasive 3M paper that I get from TGWW to do the final polishing on my planes and chisels. The results are fantastic.
12/11/2014 Chuck Hart
I use a 1000 DMT stone and finish with a 15K ceramic stone. I bought a DMT 8000 stone and I am very dissatisfied with the stone, so much so I sent it to DMT to have it checked. Their engineer told me the stone was well broken in but the stone does not produce a slurry therefore it doesn't leave a polish. That statement was pure BS. I like the 1000 stone but find I can get a better polish with 1200 sandpaper. I use it because it is fast. Then finish with better stones.
12/11/2014 Mr Ronald Carl Dennis
In July of last year ( or the year before ) I purchased DMT's 8000 grit 8 inch sharpening media. I have been very pleased with the media's performance and the resulting impact on my woodworking.

I've abandoned strop honing on leather due to rounding and adopted 3M's 0.5 micron PSA film on float glass instead. Uber sharp!
12/11/2014 Mr Ronald Carl Dennis
In July of last year ( or the year before ) I purchased DMT's 8000 grit 8 inch sharpening media. I have been very pleased with the media's performance and the resulting impact on my woodworking.

I've abandoned strop honing on leather due to rounding and adopted 3M's 0.5 micron PSA film on float glass instead. Uber sharp!
12/12/2014 Bob Black
I've started using Brent Beach's system with a double faced 10" coarse diamond plate for rough shaping. I can use the shop made blade jigs on the diamond plate thus having very good control of the bevel angle. Beach is the only place I have ever seen that actually tests the honed edge and reports on the relative sharpness.Everyone else says "lasts twice as long"or "three times sharper" with nothing to back up the statement. In the Beach method finish honing is done on 3M Microfinishing Film, 15, 5 and .5 micron. On his list of suppliers of the 3M Film the first supplier on the list it "Tools for Working Wood". Beach isn't selling anything. Making the jigs can be a bit tedious. The website is a bit cumberson but it covers a lot of material. I've been very pleased with the results if get on cutting tools, primarily plane irons.
12/13/2014 Bruce Wedlock
Regarding flattening water stones, does the water stone slurry wear away the nickel plating holding the diamonds? So the slower cutting is a result of a loss of diamonds? Or are the actual diamonds worn more with a water stone than with steel?
Great question. the slurry wears away the plating. There might be some wear on the diamonds but I am pretty sure it's the plating. I have a plate I can't find at the moment which would show this one way or another. There also might be a point at which depending on the diamond shape, the wear on the nickel doesn't loosen the diamonds. Many people use diamond flattening plates, they work great, and even if they slow down they are still useable years later.
A coarse plate we use for steel only is about 7 years old and going very strong.
12/14/2014 Steve
re: Wearing out a diamond plate by flattening a waterstone

I recall one of the DMT guys saying a while back that it depends on the diamond grit, because the nickel plating is different on fine vs. coarse stones: Using a fine grit plate as a waterstone flattener will wear it out, while a coarse grit plate will keep working indefinitely.

The big Dia-Flat lapping plates are obviously designed to explicitly withstand use as a waterstone flattener.
I've been using my Dia-sharp plate for going on eight years now, and it still works fine. I use it for all my edge tools (plane irons, chisels, carving tools, etc.) followed by a fine Arkansas stone and a strop.

I do use it for all my kitchen knives, too, and it works very well. I just hone each bevel on the diamond stone until I get a wire edge and then use a sharpening steel to smooth it all out.
12/24/2014 John Walkowiak
I have been using the DiaSharp plates for a long time, and a couple years ago I bought the 8,000 grit plate. This was after reading that Mary May used it for sharpening her carving tools. I figured if it was good enough for her tools it would be good enough for mine also. I am extremely pleased with it, and the rest of the plates. I do strop after the 8,000 grit, and end up with a mirror finish. I don't have the space in my shop for a dedicated sharpening station and the plates don't take up much room and are not messy to use. It is true that they don't leave as polished a finish like some other methods, but the proof is in how it works, not how your reflection looks.
01/14/2015 Lee Laird
I have the Dia-Flat plate and use it for both flattening my water stones as well as the backs of chisels that need refurbishing. Works great and I've had it for well over a year and while I can tell the area that has flattened chisel backs, doesn't "bite or grab" as hard as the area that hasn't seen steel, it doesn't seem to have slowed either process. I have three other steel plate diamond "stones" that were purchased 2000-earlier, and after a decent amount of use (and slightly strange results) I decided to test each with a good straight edge, and they all failed! Moral is, just like you would do with water stones or oil stones, verify they are flat BEFORE use.

One question about the cool sounding MagnaBase is whether the magnetic pull is enough to make the tools to be sharpened, stick to the plate with any meaningful pull? Will it cause the sharpening action to possibly feel stilted?
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The opinions expressed in this blog are those of the blog's author and guests and in no way reflect the views of Tools for Working Wood.