Some experience with DMT sharpeners

Nov 25, 1999
<center><font size=4>DMT sharpeners.</font></center>
<center><small>Patr 1 of 2</small></center>

The questions about different sharpening devices sometimes are asked here and on General Discussion Forum, so I decided to share my experience on sharpening equipment I have tried and/or I'm currently using.
First in this series let be DMT sharpening surfaces. It is well known that diamond is king of cutting. This is the hardest known material in the world, no one natural or man made material can beat it in hardness and as result - in cutting abilities. So it is a good idea to use diamond as abrasive material to obtain controlled steel removing from cutting edges what we usually call sharpening.

Construction. Diamond Machining Technologies (DMT) sharpening surfaces are created embedding diamond powder with strictly calibrated grain size onto steel surface using electrolyte nickel.
<small>Please click thumbnails to open enlarged image in separate window</small>
<a href="" target="_blank"><IMG align=right SRC="" border="3"></a>Most of DMT sharpeners (but not all) have diamond particles embedded onto steel surface perforated with round holes about 3 mm in diameter. These holes are filled wit plastic which makes up the sturdy base under relatively thin (about 1 mm) steel plate. This way steel plate is connected to plastic base near indestructibly, I can't imagine situation when it could be torn off. The interrupted sharpening surface have some advantages: first of all it allows to save some diamond powder what allows to reduce production costs and as result - price. Another advantage - interrupted surface is less prone to clogging - is not so important because diamond sharpening surfaces are in their nature much less prone to clogging than ceramic or natural counterparts. All things in this world have two sides, the disadvantage of interrupted surface appears when you have to sharpen very small blade or blade with very sharp pointy tip. For such occasions DMT makes some their sharpeners in Machinist version with some deal of continuos surface.

Grits. All DMT sharpening surfaces are divided to four groups depending on grit. Each group is marked in different color.
X-Coarse surfaces are marked with black color. Diamond particles size 60 microns makes grit 220. This kind of abrasive provides very fast and efficient steel removing what allows to restore heavily damaged edges or to reprofile the edge with minimal effort.
<a href="" target="_blank"><IMG align=right SRC="" border="3"></a>Coarse surfaces are marked with blue color. Particles have size 45 microns (grit 325) what provides efficient cutting to restore very dull or lightly damaged edges. If only light edge reprofiling is required this surface is quite enough.
Fine surface are marked with red color. Particles with 25 microns (grit 600) leave very sharp working edge which matches both heavy and precise cutting tasks. This surface could be considered as basic sharpening tool.
<a href="" target="_blank"><IMG align=right SRC="" border="3"></a>Extra-Fine surfaces are marked in green color. 9-micron particles (grit 1200) leave really hair-popping edge. This surface is ideal for your favorite knife fine-tuning.
Quite frequently asked question: does the finest grit leave polished edge? In my experience Extra-Fine DMT leaves the edge which I couldn't assume as polished, at least it is not shiny. Think the reason is in abrasive particle density but not in dimensions. However, literally few strokes on Arkansas whetstone or fine ceramics let your edge shine after sharpening on green DMT sharpening surface.

<center><small>to be continued...</small></center>

[This message has been edited by Sergiusz Mitin (edited 07-29-2000).]
<center><font size=4>DMT sharpeners.</font></center>
<center><small>Patr 2 of 2</small></center>

Some particular sharpeners I have tried and used (and use currently).

<a href="" target="_blank"><IMG align=right SRC="" border="3"></a>Diamond Whetstones are intended for working bench sharpening, 6-inced ones are quite enough for even large knives. Basic version comes with wooden case equipped with rubber discs on bottom side to prevent sliding when working. Honestly I'm regretting to waste this nice case with water and removed metal particles, so I always remove my coarse whetstone from this case when working.
Budget priced and, by the way, more practical version is mounted on durable plastic base also with non-slippery rubber discs on bottom side and transparent plastic cover. Whetstone as itself can be removed from plastic base, this allows me to use the same plastic base working with coarse whetstone removed from wooden case.

<a href="" target="_blank"><IMG align=right SRC="" border="3"></a>Double Sided Diafold is near the ideal for field conditions. It folds into plastic handle like butterfly knife. It's weight is comparable with lightweight knife's one but it's 4 inches long sharpening surface allows to resharpen quickly even pretty large knives. Additional advantage - you have two grits in one compact and lightweight package and you can work even without sturdy base like table or working bench. This one at my photo has Fine/Extra Fine grits but for outdoors conditions I could recommend rather Coarse/Fine one.

<a href="" target="_blank"><IMG align=right SRC="" border="3"></a>Diafold Serrated Knife Sharpener allows to cope with either serrated edges and plain ones. With plain blades it can be used simply as sharpening steel. So if you have your outdoors knife with serrated or combined edge - take in the field this one instead of Double Sided Diafold or to complete with it.

<a href="" target="_blank"><IMG align=left SRC="" border="3"></a>Don't you believe these sharpeners are good and don't want to pay pretty high price for untested equipment? No problem, buy DMT Mini-Sharp and test it! I'm sure you will get to like it's advantages and go to another DMT sharpeners. However, this diminutive folding sharpener has not only advertising and testing functions. You can sharpen pretty decently medium to large sized folder or smaller to medium sized fixed blade. Maybe this will take a bit more time and effort only. Wherever I'm going away from my house for more than one day my fine grit Mini-Sharp is always with me.

How to work with? It's simply:
* First and foremost, improve your free-hand sharpening skills. No one device can replace them. Alternatively you can buy DMT Aligner set, it works like well known GATCO or Lansky similar equipment. The main difference is you can use Aligner clamp also with DMT bench stones.
* Use water only for lubrication. If you haven't water - work on dry stone.
* Don't apply much force, let diamonds to do their job and they will do it.
* Don't worry about wear out and the loss of sharpening surface's flatness. The abrasive layer is extremely thin and even being worn out it can't change working plane noticeably.
And this is all! It's really simply...

Durability. When I tried my first DMT sharpener (it was Double Sided Diafold) I was initially embarrassed: sharpening first dozen knives it lost cutting aggressiveness quite noticeably form each knife to another! But after about dozen or so knives were sharpened it's cutting abilities didn't changed more and they are consistent so far, for almost 2 years. This lose of cutting aggressiveness was nothing else than break in. The same way works each diamond sharpener, in fact out of the box the new DMT Extra-Fine grit sharpening surface cuts almost like Fine one, Fine cuts almost like Coarse etc. After you will sharpen 10-20 knives, depending on knife size and steel hardness, you will see sharpener's true cutting abilities.
My second older DMT Coarse Diamond Whetstone serves me for more than year and after break in period it doesn't display any noticeable wear.
Believe me, testing knives I use my sharpeners hard and frequently.

Drawbacks. Quite impressive price... But here I could quote some proverb used in my country: "Greedy pays twice and works triply". First he buys cheap thing (first work and first payment), when he convinces this cheap thing is really cheap and throws it away (second work) and now he buys decent thing (third work and second payment)

Conclusions. May I skip them this time?
If you would have some questions I'm glad to answer them.

Sergiusz Mitin
Lodz, Poland

[This message has been edited by Sergiusz Mitin (edited 07-29-2000).]
I've been using these also for a number of years and have found them to work very well.
Usually if edges are not to dull within a couple passes on each side of edge your back in bussiness. Also find it much more convient to put micro-serrated eddge on a standard knife blade, rather than a carry a serrated edge knife. A standard blade sharpened with a DMT or similar diamond hone nearly duplicates cutting results of tough material.

ANOTHER Great review!!

I have 2 DMT's and LOVE them.Super tools!

Thanks! Barry
I have the new duo sharp. So far, I'm very impressed. It was my first DMT and now I'm sold on them. DMT is the way to go for me.

I have the 6" DMT stones in every color/grit available and I love them. But, in defense of the other diamond sharpeners out there, I have used the Ezelap sharpeners with equally great results as well. And they are cheaper. After using diamond hones, you just dont want to go back to a regular stone, unless you are trying to get that polished edge. In fact, some of the new stainless steels out there really cannot be sharpened with anything other than a diamond stone.

Danbo, soul brother of Rambo
I have a DMT pocket hone(fine) I bought 14 years ago I still carry it. I've learned some things during that time:keep the hone clean for best results,you can file down small chips in your teeth with diamonds,and diamonds are a knive's best friend. I have probably sharpened a couple miles of blade with mine and it's no where near retirment.
Your short and seemingly simply question is pretty hard to answer certainly

It is no way to measure cutting speed objectively when sharpening free hand. Indirectly we could assume it as the opposite to stroke number required to obtain the same sharpening effect, right?
Well, DMT diamond sharpening surfaces cut noticeable faster than each natural or ceramic abrasive (excluding ceramic-diamond abrasives where diamond particles are embedded into ceramic base). Proportion would be such: the stroke on 6" long DMT surface provides the same sharpening effect as on 8" long very good ceramic (the same grit of course) and 10" long so-so ceramic.

On the other hand DMT sharpening surfaces cut somewhat calmer than non-interrupted diamond ones. Subjectively I could evaluate about 15-20% less cutting speed but noticeable better controlability of each stroke. In any case working on DMT I have not subjective feeling of "crazy cutting" what sometimes occurs working on some another diamond sharpening surfaces. Especially these no-names. I think the diamond particle calibration precision is the key here and this is also supported with the interrupted sharpening surface.

Just my subjective opinion

Sergiusz :

[cutting speed]

Indirectly we could assume it as the opposite to stroke number required to obtain the same sharpening effect, right?

Yes, that is what I was thinking. You could simply take a test piece of metal, weigh it on a very precise balance and work on it awhile and see how much metal is removed as indicated by its mass loss. I think I'll try that out if I can get a loan of a digital balance.

Interesting notes, first comments I have read along those lines in a quantitative manner. Personally I have found that they cut much slower than Japanese waterstones. The reason is simply that I can press very hard on my SiC waterstone, if I do the same with the x-coarse DMT I would most likely damage it.


[This message has been edited by Cliff Stamp (edited 08-01-2000).]
I'm afraid the test you proposed is not enough to determinate certainly cutting speed as sharpener evaluation parameter. You should add some terms to keep consistent:
* stroke length - this would be easy, enough to mark start and finish lines on sharpening surface,
* pressure - this would be a bit harder to keep consistent but also possible. Would be enough to put the same weight on test metal sample when pulling it along each stone,
* speed - yes, maybe it could seem silly but in my subjective opinion the cutting efficiency somewhat depends on speed I'm making my strokes with,
* the square where metal sample contacts the whetstone - I have no ideas how to keep it consistent.
In my opinion too much parameters to keep consistent to make this test strictly scientific and reliable.

I can't to compare with Japanese waterstones because I never tried one. But you are right as to pressure, diamond sharpening surfaces (I think no one made would be exception in this matter) do not like too much pressure applied. You can't break diamond particles as themselves, but you can to break them out of nickel plating. This is the weaker point of this kind of sharpening surfaces.
Hands down much less sensitive to applied pressure are ceramic-diamond sharpening surfaces (diamond abrasive particles embedded into ceramic matrix) but they are fairly expensive. Many years ago I had 6x2" double-sided (aprox. fine/extra fine) ceramic-diamond whetstone made in former Soviet Union. Mmmm, what the sharpener it was! I'm very unhappy it is not with me now.
Sergiusz, you should not focus on the random variations from stroke to stroke. What you should always be comparing are two means and the variation in the means will be far less than the variation in any of the sample strokes because random variations tend to cancel each other out. If they didn't then they wouldn't be random.

To get specific, assuming the strokes are influenced by normal variations, then the means will be more stable by a factor of 1/sqrt(n), as compared to any particular stroke, where n is the number of strokes. Therefore if the pressure varied by 25%, the mean pressure would be stable to within 2.5% if I did 100 strokes and less than 1 percent if I did 1000 which was about the number I was thinking of.

It is trivial to determine the variance in the means as well, you don't have to take it for granted you could simply repeat it a few times and see how the means vary. I have done this will all the tests I do to verify the mean variance is less than the significance level.

You can then average these means to reduce the variation further, which has the same effect of taking a sample that much larger.

Or you could just time yourself.

David Rock

AKTI Member # A000846
Stop when you get to bone.
I think time is probably the most sensible way to rank a stones speed of metal removal. It is how I formed the rough ranking I have now of the stones I currently own and what you really want to know - how long will it take. The problem with using it in a quantitative sense is time until what happens? Of course over time all you have to do is time your blade sharpenings. If you do it enough times you will get a stable result. However that is a bit too long for me so I would like a more direct way.

I think I might try marking out some sections on a mild steel bar and just recording the number of strokes and time (to be able to judge fatigue) to reach that level of wear. One thing I am unsure of is how directly proportional these rankings would be to the steels used in knife blades.