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It is commonly known that sharp
tools are in fact safer tools. This is because when you are
using a sharp tool there is generally less effort and force
involved to cut or drill something, and this generally results
in fewer accidents as a result. But getting your tools into a
condition that you could call "sharp" can be tough without the
right equipment. After reviewing the Veritas Mk.II Honing Guide
recently on this site, I found a need for a larger diamond stone
than the one I currently had. So I searched the various diamond
stone manufacturers and eventually settled on the DMT 10" stone
I will review here. It was large enough and wide enough for my
sharpening needs and does seem to have favorable reviews from
existing owners.
After having used this stone for
about 6 weeks now, I believe I have enough qualitative data and
results to form this review, so let's get to it!
The DMT DuoSharp Diamond Stone
So I purchased the W250FNCB model DuoSharp stone from
Amazon.com. At the same time I also ordered the special base
that is available for these "stones", also made by DMT. The stone,
as its title suggests is made from diamonds, which are known to
be one of the hardest materials available to us at this time
(researchers have now discovered a harder natural material and
have constructed harder materials in the lab, however these are
not readily accessible or easily manufactured etc). There are
other manufacturers that make diamond sharpening stones. Perhaps
the most well known is Eze-Lap, and we have reviewed some of
their products here on the site previously. They are very good
in their own right too. Using a diamond surface has obvious
advantages over other softer materials we commonly find in
sharpening stones; aluminum oxide, natural stone and ceramic
etc.
Firstly, because diamonds are
significantly harder than any tool steel we will use on them,
there is going to be very little wear of the diamond surface of
the sharpening stone (or at least very slow wear which will see
a diamond stone last many years of heavy use). This has big implications when it comes to
sharpening stones. The result of this ultra-hard diamond surface
is virtually zero pitting, hollowing or grooving as compared to
softer sharpening materials. You do not have to worry about
moving the blade or tool being sharpened evenly across the stone
to reduce the chance of pitting or hollowing occurring in one
area, nor do you have to spend time flattening a stone that may
have developed some of those problems. Secondly, because of diamond's
hardness, you can sharpen a tool much faster than you can with
other materials and with less force or pressure exerted. A couple passes on a diamond stone might be the
equivalent of a couple dozen on other stones. Third, it is not essential to
use a lubricant or fluid when sharpening on a diamond stone,
although it does help remove the swarf or material abraded from
the tool surface. Not a lot, if any will be abraded from the
diamond stone itself. This particular brand of diamond stone has
a design that helps remove debris, which we will look at
shortly. So you can say goodbye to messy oils and the smells
they produce. You can clean this product with water, or use
water during the sharpening process if you wish.
DMT Stone Construction
The folks over at DMT make some claims as to their products
description, all of which would appear true after having used
the stones for some time now. To begin with, DMT uses
monocrystalline diamonds in their product, as opposed to the
more inferior polycrystalline types found in stones of less
quality or price. What's the difference? These two pictures
certainly help explain it...
As you can see, monocrystalline
diamonds are larger, single structure pieces, as opposed to
polycrystalline which is a diamond structure piece made up of
multiple, smaller diamond fragments that are bonded together.
You can imagine what might occur to the polycrystalline diamonds
over time and use. Their bondings make break down, leading to
fragmentation and a "worn" surface. Monocrystalline on the other
hand would only wear or "fail" significantly if the hole diamond
piece is dislodged from its holding surface, which is much less
likely. DMT uses the monocrystalline diamonds in its products,
and while I cannot verify these are indeed better in the long
run (you would need a pretty good microscope), the logic makes
sense. The diamonds are imbedded approximately two thirds of
their height into the nickel bed. This provides an excellent
hold on the individual diamond stone while still leaving plenty
of diamond surface above the nickel bed for sharpening purposes.
 The
diamonds themselves are bonded to a machined, flat steel plate
within a bed of nickel. Underneath this steel plate is the bulk
core of the stone, constructed from hardened plastic. For models
which have two grit types, like the one reviewed here, a second
diamond layer is found on the reverse side, with the plastic
core sandwiched in between. For this stone, DMT offers their
"interrupted" surface construction. These are the small round
"pits" (recessed dots) you can see throughout the sharpening
surface. These are added primarily to collect abraded metal
created during the sharpening process and to remove and contain
it away from the diamond surface. This way the diamond surface
does not "clog" with metal and require constant cleaning or
re-abrading of the surface for it to continue functioning (like
you have to do on a high speed dry grinder when metal becomes
imbedded in the wheel). Cleaning couldn't be easier. Just wash
the stone down with clean water and it is ready to go again for
next time.
Multi-Surface Stone
This particular model DMT stone, the W250FNCB offers two
sharpening surfaces. These are color coded to indicate the grit
rating of each surface. DMT uses their own color coding chart,
and this particular stone is coded blue for one side and red for
the other. Small round color dots can be found on each side of
the stone to quickly identify which grit surface you are using.
The blue coded surface indicates a grit/mesh rating equivalent
to 325 mesh (45 micron). This surface is for "quickly sharpening
a neglected edge". On the other side of the stone is the red dot
indicated surface which is equivalent to 600 mesh (25 micron).
This is to put a "keen edge on a maintained tool". Duosharp
bench stones are also available offering a coarser (220 mesh /
60 micron) surface indicated by a black dot, or a finer (1200
mesh / 9 micron) surface indicated by a green dot. Other DMT
products (not DuoSharp stones) are available with coarse 120
mesh (silver), and finer 2200 mesh (white) and 8000 mesh (tan)
surfaces.
So the W250FNCB model here has
the 325 and 600 mesh surfaces... A good compromise between
coarse initial sharpening requirements on a pre-formed edge,
while offering a more refined surface by using the 600 mesh
surface on the reverse side. Different combinations of surfaces
are also available in the DuoSharp line.
In Use
Since I have used diamond stones before, I had some idea of
what to expect. It is commonly known, or at least complained
about in various forums, that the person's new diamond stone
doesn't seem to sharpen as fast as it did the first few times
they used it. This is NORMAL folks! Look at the image of the
diamonds again above. Notice the sharp top points or tips of
each diamond crystal. On new stones these sharp tips give a
rough look and surface feel to the stone. You can imagine that
these sharp tips will round over fairly quickly for the first
few uses, especially since near the top of each tip there is
very little material beneath it. As these tips wear down,
sharpening seems to slow down, and it certainly does slow down,
but this is normal for a new diamond stone. There is a certain
"breaking in" period where the very top tips of each crystal are
worn down. Sharpening slows a little, and the stone actually
becomes smoother as a result (better for honing anyway) but
sharpening is still much faster than with other stones because
of the diamond's hardness. So with this in mind, I reserved
making any judgement on this product until I had put the stone
through a break-in period (usually only about half a dozen uses
or so it seems).
Now, a quick U-turn on the flow.
Back to the stone holder I mentioned earlier, called the "DuoBase".
This basically holds the DMT stone up off the bench (knuckle
saving) in its cradle and with its included eight rubber feet
underneath, it goes a long way to preventing the stone slipping
on the bench as you use it. The one DuoBase will accommodate all
DuoSharp line stones. On the reverse side is a handle. I
thought, great, I can carry it around a little easier, but then
wondered why you would need a handle to carry a fairly light
sharpening stone anyway? It turns out that this handle is also a
way to hold the stone for running it over a large surface that
may be immobile or not easily manipulated. I haven't really
found a need to use it this way as yet, perhaps sharpening mower
blades while still installed on the mower or blades on a much
larger cutting machine? Whatever the use, the DuoBase is a handy
accessory if you don't have any other method to secure the stone
and it is reasonably priced too, all things considered.
The DMT DuoBase with the W250FNCB Stone in place
Now, back to the stone and
sharpening. I have been primarily using it for sharpening my
hand chisels and bench plane blades. WEith a width of 2 5/8"
(67mm) it is capable of sharpening pretty much all my hand plane
blades and chisels. The extra width makes things easier when it
comes to sharpening. These is nothing worse than trying to
balance a large/wide hand plane blade on a narrow sharpening
stone and constantly having it slide off the edge as you try to
move the blade evenly across a the stone. No such problems here.
The extra width is great for use of sharpening jigs that have a
wide roller wheel too, like the Veritas Mk. II jig. It also has
a generous length of 8" (203mm) providing enough room to really
put in nice, smooth, and long sharpening strokes. The stone is
3/8" (9.5mm) thick, but that doesn't really have much effect on
sharpening, only to ensure there is no flex in the stone itself,
which there isn't.
The one issue with this stone,
especially with the recessed dot design, is that it is not
terribly suited to tools that have a small or sharp point, like
those found on small carving tools or small lathe gouges. These
points can drop into the recessed dot areas and prevent a smooth
pass over the diamond surface, so this particular stone cannot
"do it all" so to speak. DMT do make a DuoSharp stone with a
small continuous surface of diamond at one end of the stone to
accommodate these smaller/pointed tools. Model numbers for those
are WM8EF and WM8FC. But since I havent used or tested those I
will not comment further.
Ok, the actual sharpening... The
only real way I can tell you how good, or otherwise, this
product is, it to explain the speed at which something is
sharpened. We all know it is possible to sharpen a tool equally
well or to the same degree of "sharpness" on a diamond stone as
it is on a refined aluminium oxide or other type of "softer"
stone. The difference is in the speed, or time it takes to get
there. The results I give you are only qualitative. I is hard to
setup an experiment for detailed testing without the use of
multiple machines, and then there are many variables that can
affect the outcome. My simple test was to take two chisels of
the same brand, same size and type. Both were in need of
sharpening. So first, I put them on the dry grinder just to
rough grind the bevel so each chisel was fairly similar in its
surface grind (as far as I could tell by eye anyway). Then I
went to work with the DMT DuoSharp stone, using it on one of the
chisels, while sharpening the other chisel on a basic, standard
aluminum oxide stone (with two grit surfaces as well) with each
surface probably even slightly coarser than the diamond stone. I
used water as the carrier for the DuoSharp, and oil for the AO
stone and sharpened both chisels using the Vertias Mk II honing
guide.
Without babbling on too much... I
refined each chisel to a similar looking edge. The results...
About 25 minutes of work on the Al Oxide stone... About 5
minutes of work on the DMT. This was total time, not actual
sharpening only time, but as you can see, there is a large
difference in the times to refine each chisel to a similar edge,
starting from a similar point. There is no doubt that Diamonds
are able to abrade a surface much quicker, and with less effort
than other "softer" sharpening stones. This does not account for
the cleanup time required for the al oxide stone, or any time to
resurface it later down the track either. I know which one I
would be reaching for!
Conclusion
Well, we probably already know that Diamond stones work
faster to sharpen our woodworking tools. And yes, to get them
ultra sharp like some of us like them, they will need further
refinement after sharpening on this stone. I have a leather
wheel and diamond paste which quickly takes care of that, among
other sharpening contraptions! But perhaps you wish to know how
it compares against other diamond stones? Long story short,
forget all those budget diamond stones or sharpening sticks you
see being sold here and there for next to nothing. They are
often poorly made with low quality, polycrystalline diamonds and
don't do a particularly good job. There is a marked difference
between the lower end and higher end of the diamond stone market
in terms of quality and sharpening results. Against another
quality diamond stone product, the Eze-lap, I would say the DMT
has it beat, but only slightly. Both stones produce great
results, but the Eze-lap doesn't have the recessed dots for
clearing material away from the surface. You can see it building
up, which no doubt slows the sharpening down, if only
marginally. On the other hand, the Eze-lap's continuous diamond
surface allows it to be used with small and pointed tools,
something which this particular DMT model stone does not. Both
are great products, so think about what you intend to sharpen on
the diamond stone before you decide which to go for. But if you
have the money, this particular DMT stone (it retails for around
US$100 - Feb '09) is well worth it in my
humble opinion.
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DMT W250FNCB Photos
All photos copyright onlinetoolreviews.com. Use without prior
written permission prohibited
The W250FNCB, with its coarse face showing, as indicated
by the blue dot.
The reverse side of the stone with the fine face
showing, indicated by the red dot.
Closeup of the coarse surface with the recessed dots for holding
swarf and abraded material.
Sharpening a small chisel with bevel down.
No water used here on the stone.
With water added to the stone, the swarf is more easily
removed from the diamond surface. the heavier particles find their way
into the recessed dots while the lighter particles become suspended in the
water.
Yes you can flatten the back of the chisel too quite
easily with this diamond stone.
Cleanup couldn't be easier. Just wash it down with water
and it is almost like new again!
A shot of a bevel sharpened on the DMT W250FNCB diamond
stone. This chisel is now very useable, but for the ultimate in sharpness,
more finer honing and polishing will be required.
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