How we sharpen
Having a sharp knife or any other carving tool is one of the most important
necessities of carving. A dull blade will tend to slip off the wood and cut
you more easily than a sharp blade. A sharp blade will penetrate the wood
rather than jump off into your hand. A dull blade will cause you to lose
interest in your carving. Need I say more?
As I meet carvers in our store and in my travels, I find that many, many
carvers do not know how to sharpen. There are many schools of thought on
this subject and I am not here to criticize anyone's methods. I am fond of
saying in my sharpening seminars that if you can use a rock that you pick
up off the ground and get your tools sharp with, then that is great.
We sharpen hundreds and hundreds of tools and I am going to share some of
the techniques that we use to sharpen. We don't have the time to spend on
long and complicated methods of sharpening and I am sure that you want to
spend less time sharpening and more time carving.
So here goes. I am going to try to give you with enough knowledge so that
you can approach sharpening with more confidence but there is nothing like
experience.
I will start the main course by talking about
bevels first.
The bevel is that shape taken by the thick, supporting metal of the blade as
it thins down to the fine cutting edge, which actually penetrates the wood.
It can be flat, rounded or hollowed along its length, and there may be a
bevel on one or both sides of the cutting edge. The bevel on a woodcarving
tool is in effect a wedge, which cuts and pries fibers apart against
resistance. As wood fibers from different species of trees bind together
in different densities and strengths, differences in the wedge-like quality
of the bevel are required to deal with this resistance efficiently.
Beginners who tend to sharpen only the very edge only, producing a
secondary bevel that gradually thickens in size often neglect the importance
of the bevel. This also happens if a blade is not stropped "flat" along
the bevel and I call that "rounding". Blades will be sharp but have trouble
slicing through the wood because the blade was held at an angle when
stropped and produced a secondary bevel. This unwanted secondary bevel can
only be removed by re-sharpening the blade and creating a new bevel. Most
carvers prefer that the bevel on carving knives extend almost the entire
width of the blade but not so that the blade is weakened. The set of a
carving tool is the angle at which the bevel has been ground on a blade -
how long or short it appears. Carvers usually talk about longer or shorter
bevels, rather than an actual angle, because this is how they appear.
Invariably, a bevel will be set on a carving tool when it leaves the maker,
whether it has been sharpened further or not. The grinding may be part of
an automated process in some factory, or involve a skilled person using a
grinding wheel. But this bevel angle, pre-set by the manufacturer, is not
necessarily the one that is wanted by the carver. There are various
circumstances in which a different angle - a longer or shorter bevel -
may be desired.
One problem with pre-sharpened tools is that while the bevel may indeed be
set at a useful angle, it may not be the most useful working angle for the
needs of that particular carver. Someone buying a woodcarving tool for the
first time may assume that the shape of the bevel found on the blade is the
correct angle for the tool and can not be altered. It may be the correct
set of bevel, but then again, it may not be.
If the angle of bevel you need is different from the one, which has been
ground onto the tool, then the bevel will need re-setting first. There are
2 factors working against each other in the set of the bevel. As the bevel
becomes longer and the wedge effect sharper, the tool, in theory at least,
is able to work its way through the fibers of the wood with less effort.
But the cost is in the loss of strength - there is less metal to buttress
the cutting edge. As the bevel becomes longer, the cutting edge becomes
weaker until the fibers of the wood may be hard enough to damage the
cutting edge. This is where Flexcut tools have an advantage. Their long,
thin bevels have held up longer than any other tools we have worked with.
The strength of the metal in these tools is excellent. But it stands to
reason - for any tool - hard woods require a shorter bevel . This is a
good place to remind you that for soft wood you need a sharp blade. A
dull edge will crush or push aside the fibers before cutting through them.
If a carving tool is not cutting easily or satisfactorily - even though
the edge appears to be sharp as possible - it may the that the bevel
length needs adjustment to be a little longer or shorter. What is being
sought at the end of the day is the longest, and therefore the sharpest,
bevel compatible with strength.
The bevel can have three different contours from the heel to the edge:
hollow (concave), rounded (convex) and flat. There are several reasons
why a flat bevel is the most desirable although I have been told by
several carvers that they prefer hollow ground. They also claim that
hollow ground is easier to sharpen.
Hollow bevels - a hollowed contour comes from applying the bevel to a
circular grinding wheel which grinds its own shape into the metal. It is
thought, by some carvers, that a slightly hollow-ground bevel is a better
option than a truly flat one, as the blade is free to follow the cutting
edge. With this benefit, however, comes 2 disadvantages. The first is the
inherent weakness in a hollow bevel. As the hollowness encroaches on the
cutting edge, the angle of the bevel becomes more acute. The edge becomes
sharper and sharper, but - being less supported - weaker and weaker.
Secondly, a hollowed bevel rides up on the edge of a cut, say when setting
in, and working feels awkward and inaccurate compared with a truly flat
bevel. Leaving a hollow bevel is not necessarily a quicker way of
sharpening a carving tool either. With correct grinding, it takes the same
amount of time to flatten across the whole bevel - so making the edge
stronger and lining up more accurate - than sharpening from heel to edge.
Rounded bevels - some hollowness, or concavity, towards the center of the
bevel is preferable to a rounder or convex bevel. A rounded bevel is
produced by altering the angle at which the blade is presented to the
grinding wheel - lifting and lowering the handle. At the cutting edge,
the rounded bevel has the opposite, obtuse, profile to that of a
hollow-ground tool, with two effects. In the first place, a thicker wedge
of steel has to be pushed into the wood, involving more effort. Secondly,
the carving tool will start to cut the surface of the wood with its handle
positioned higher than would the same tool with a flat bevel. In other
words, a rounded bevel gives a greater cutting angle. The lower this
angle, the more control a carver has when cutting - the carver's hands will
rest on the wood and work more surely. The higher the cutting angle, the
more awkward and uncontrolled the cutting becomes. The exception to the
rule comes in the long and short bent gouges. A slight rounding is
acceptable as an extension of the bent or 'rounded' shape of the tools -
helping to jig the edge through their hollow cut.
Flat bevels - cut most efficiently and contribute the greatest amount of
strength to the edge for its sharpness, compared with hollowed or rounded
bevels. The cutting angle can be accurate and low; and the bevel will
self-jig along the face the edge is cutting. It is no more trouble to
sharpen a flat bevel than any of the other shapes.
Some carvers, as we so often mention, sharpen only the very edge of their
carving tools, producing a small secondary bevel or artificial rounding.
This in effect thickens the wedge of the metal, as the angle of the
secondary bevel must be greater than the primary one. The secondary bevel
gets longer with each sharpening, increasing the cutting angle of the tool.
Eventually the tool will need re-grinding. Remember, this is a carving
knife, not a pocket knife. You want the knife to slice through the wood.
NUMBER 1:
Once a tool is sharp, DO NOT re-sharpen unless you break,
chip or otherwise want to re-shape the blade. Once the blade is sharp,
only strop it after that either by hand with a leather strop or with a
buffing wheel.
NUMBER 2:
Sharpening materials. As I have said, anything will do.
We use a diamond hone when sharpening by hand because the ease of use. It
is used like file and it makes no difference which way you go against the
edge. You can use stones to sharpen. There are lots on the market. We
use a sanding belt when sharpening mechanically. It doesn't matter what
you use as long as you get a wire edge or wire bur on the edge of the
blade. Wire edge? What is that? Hang on. I will cover this and more
later on.
NUMBER 3:
Stropping Materials. The most
common material in a strop is leather. A thin piece of leather is glued to a board and the
tool is pushed up and down this leather. Some kind of strop abrasive is
applied to the leather to assist in returning the razor edge to the blade.
There are several kinds of materials used in mechanical buffing and I will
cover these materials later and tell you what works best for me.
NUMBER 4:
Begin Sharpening. It should be
obvious by now that you will be sharpening the bevel. So let us begin.
As I mentioned back up yonder, you must get a wire edge or wire bur to
have a sharp edge. A wire edge is produced when the metal gets very thin
along the edge. This means that you will sharpen the blade (the bevel) until a wire
edge is produced evenly along the edge. Then you will turn the
blade over and sharpen the other side until the wire is produced from
that side. The wire edge is actually on the other side of the
edge you are sharpening. I feel along the opposite side of the blade
to check the wire edge while I am sharpening. When you finish one side
and turn the blade over, you are, so to speak, pushing the wire edge to
the other side.
The IMPORTANT thing to remember here is to sharpen evenly. That is to say,
you want metal removed the same all along the blade. If you don't, you
will end up hollows and high places in your blade. So no matter what
method you use to sharpen, even pressure should be applied during the
whole process. This works well with a new blade but sometimes you will
have an older tool that already has high and low places in it. This is
where using a diamond hone comes in handy. It is easier to adjust the
pressure on different parts of the blade with the filing motion than on,
say, a flat stone.
Once you get the wire edge (both sides), you will strop or buff the tool
to remove the wire edge and it is ready to use.
Simple, right? Well, let us carry on with some very important details.
Take out your pocket knife and you will notice that it has a very small
or short bevel. This is because you use it mostly for cutting string,
boxes, and so on. But a carving knife should have, except for special,
conditions, a longer bevel. We extend the bevel almost the whole width
of the blade. This allows the blade to slice through the wood. A shorter
bevel, such as on the pocket knife, will have a tendency to stop or hang
up after a short penetration into the wood.
You are, as I have said, sharpening the bevel. This applies to gouges,
v-tools, and veiners. A bevel doesn't extend very far up the shank of a
gouge simply because you are not attempting to slice through the wood as
you do with a knife. A shorter bevel works better with harder wood and
a longer bevel works better with softer woods.
V-TOOLS Carvers have the most problems
sharpening and keeping sharp v-tools. I will try to give you some pointers here to help but
the best teacher is experience.
Here is the most important thing to remember about v-tools: a v-tools is
two chisels joined together in the middle. When you think about the
v-tool in this way, it becomes simpler to think about sharpening two
chisels. First one chisel and then the other. The point, or the V, will take care
of itself if you sharpen evenly.
You need parallel lines for a v-tool. This means that you need an even
amount of metal from tip to the other. Sometimes v-tools come from the
maker with thin or thick places in the blade and, of course, v-tools can
wear unevenly. Take a look at the top of both sides and try to determine
with your naked eye if the metal looks even. If it is obvious that it is
not, grind down both sides until they look even. You may have to grind
a lot of metal off.
Now that you have parallel lines, sharpen one side and then the other. I
lay small v-tools in the crook between my thumb and forefinger and use my
diamond home to sharpen. This way I can observe the process easily and
can control the amount of pressure and where I want to apply pressure. I
sharpen one side until I can't see any light along the edge and then I
turn it over and sharpen the other side.
I have read and heard that you must round off the tip but I don't find this
necessary on hand v-tools. Perhaps it might be necessary on some of the
larger mallet tools. I have found that if you attempt to round off the
tip or point, you will end up with a veiner instead of a v-tool.
TROUBLES WITH V-TOOLS:
(1)dipping out near the center. This can be caused
by sharpening un-evenly and creating a thin place in the metal near the
center. You will have to grind the blade down again to get your parallel
lines again. This can also be caused by bad metal from the maker because
they used cheap metal or the tempering process created a "cold" spot at that
point. Re-grind.
(2)a heel or sharp metal at the tip or center. This is caused by the
same reasons at mentioned in (1) above. Same solutions apply.
Once you have sharpened your v-tool, remove the wire edge from the inside
of the blade and you are ready to use it. I find that a leather shoe
string does quite well for smaller v-tools. Just place the string on the back side
of the v-tool and pull briskly. This should rid the back side of any burs that are
there. Repeat as many times as need. For most v-tools we use a stiff canvas
buffing wheel. The corner of a block of wood will also work as well as a leather
wheel that has been shaped to form a thin edge that fits in the v-tool.
KEEPING THE V-TOOL SHARP:
When you strop your v-tool, pull each side (one
chisel and then the other) down the strop with the cutting edge away from
you. Remove any burs on the inside as mentioned above. A good buffing
wheel will be the best method.
Practice - practice - practice!
LIGHT IS YOUR BEST FRIEND WHEN SHARPENING
Light is your best friend because of a simple law of physics: light only
reflects off flat surfaces. This means that if you have a dull place on
the edge, light will reflect off of this dull place or flat place. So,
try to sharpen in direct sunlight or very good lighting. You can rotate
the blade around and look for "sparkles" or other indications of light
being reflected off of a dull spot. You can also use this principle to
see the wire edge. You will be able to see how uniform the wire edge is
and determine if further metal removal is required. The wire edge will also
hide a dull place by being thinner than the dull spot. I usually jam the tool
into a block on wood to break off any wire edges that might be there. This
will show up the flat or dull places along the cutting edge.
NUMBER 5:
Power Sharpening.
HEAT IS YOUR ENEMY WHEN POWER SHARPENING
If you could sharpen at 100,000 rpm and not burn your tool, that would
certainly work. This means that a very expensive, water-cooled, slow
moving wheel arrangement is not required. You only need to concern
yourself with getting the wire edge and not burning your tool.
We have found that using an al oxide sanding belt provides the easiest
and quickest way to sharpen. We use an 80 grit sanding belt. 80 grit?
You have to be kidding? No, we use 80 grit because of what I just told
you: to reduce heat. The larger particles on the belt allow heat to
escape more readily into the air rather than into your blade. We use the
belt on a small Delta sander and it does a wonderful job. Some practice
is required as so not to remove too much metal but anyone can do it.
Note: when sharpening a knife with power, always push the point away from
you so that the heat is forced toward the handle which acts as a heat sink.
A gouge is rotated on the belt along the bevel and you can feel inside the
blade for the wire edge. I will cover power stropping a little later.
A grinding stone, the kind you get with your bench grinder, can also be used
to sharpen but I don't recommend it because of the extreme heat. I have
seen lots of tools sharpened this way and I am not criticizing this method:
just not recommending it; especially for beginners.
NUMBER 6:
Stropping.
Learning how to keep a tool sharp by stropping will be far more useful to
you than just learning to sharpen. With this in mind, I will spend more
time on stropping than I did on sharpening.
HAND STROPPING.
Most carvers use a leather strop to keep an edge on their tools. There are
other materials such as a nylon ribbon which will also work very well.
You can buy a leather strop, they are not expensive and last a long time,
or make one yourself. The leather should be very thin and have the fuzzy
side out but either side will work. The leather should be thin to reduce
rounding the blade (I will cover rounding shortly). We glue the leather
to a narrow thin piece of board with enough board exposed to serve as a
handle. You will also need some type of strop abrasive such as al oxide
powder. We use 1000 grit powder and also Yellowstone. The abrasive
assists in cutting the metal while you strop to return the razor edge.
You don't want to use a lot but enough to slightly cover the surface.
The abrasive also assists you in spotting tracks. A nick or dull place
in the blade will show up as a "track" in abrasive on the leather.
When you spot a track, just keep stropping until the track disappears.
How often should you strop? As often as you need to. I recommend stropping
your tools before you start carving each day to remove any moisture that
might have collected over night on the blades. Usually you will want to
strop about every 45 minutes to an hour while carving but this will depend
on what kind of wood you are carving and how you use your tools. You can
usually tell when a tool is getting dull because it will tend to drag as
you cut.
HERE IS THE IMPORTANT PART OF THIS SECTION!!
We are, as I have said too
many times, sharpening the bevel and stropping the bevel. This means that
you must strop the whole length of the bevel. This is very important when
stropping knives. You must keep the knife blade flat when stropping. This
will prevent creating a secondary bevel or rounding.
Rounding will occur if you hold the blade at an angle when stropping. When
held at an angle, the blade will not touch the whole width of the bevel.
After some period of time a secondary bevel is created or when examined
closely, the edge appears somewhat rounded. I have had many carvers bring
me knives which they say are sharp and indeed will even shave the hairs on
my arm. But they complain that these knives don't cut very well. This is
because they have rounded the edges by improper stropping and created a
secondary bevel higher up on the blade. You can take these rounded knives
and rotate them in strong light and notice how the light tends to play or
roll along the edge.
You need to exert enough pressure on the knife blade while stropping to
keep the blade flat but not enough pressure to cause the blade to push
down into the leather.
Always push the knife along the strop with the cutting edge trailing. In
other words, don't push the cutting edge into the leather. I usually
make about 8 or 9 trips up and down the strop or more if I find tracks.
I try not to remove the blade from the leather when changing directions
because this helps me keep the blade flat. I just turn the blade over
when I reach the end and start back the other direction with the blade
still on the strop.
When stropping gouges, just roll the bevel back and forth on the strop.
Since we don't sharpen the inside of gouges, don't strop there. There can
be burs on the inside and they can be removed by a folded piece of leather.
Chisels and v-tools are stropped by drawing them along the strop with the
bevel flat. Since a v-tool is two chisels joined together, strop both
"chisels". Remove the burs on the inside of v-tools with a piece of folded
leather or a leather shoe string.
POWER STROPPING:
There are several kinds of materials used in power stropping or buffing
including cloth, leather, paper, rubber and felt. Again, I am not here
to criticize anyone's method or product. I am sharing our methods and
products with you and you will need to find out what is best for you.
We find that a heavy, mutli-layered cloth wheel works the best for us.
All of the other materials, including thin cloth wheels, intend to round
the tools off if not used with extreme caution. We use this heavy cloth
wheel because it is easy to use, doesn't round our tools off, and reduces
the danger of burning. The multi-layered wheel dissipates the heat and the
heavy cloth allows us to buff easily by "giving" just enough to surround
the blade and we don't worry about the amount of pressure on the blade. I
turn a gouge or v-tool straight up and down along the edge of the wheel
to remove any burs on the inside. Usually just a touch or two will remove
any burs. I hold the knife at about the 4 o'clock position ( the wheel
is turning toward me) and hold it with both hands and keep my elbows
locked into my sides. Don't turn either edge of the blade into the wheel.
Just buff along the bevel. I rotate a gouge back and forth along its
bevel and I just hold a chisel straight on.
We have this wheel mounted on a 3450 rpm bench grinder. Remember, heat is
your enemy when sharpening - not speed.
This method works as well on all tools including gouges, v-tools and knives.
Just remember to respect a moving device and a sharp blade. When buying and
using any buffing wheel, ask about safety requirements.
We use an al oxide abrasive in a wax-base to apply to our wheel. We use the
green because it is best for returning the razor edge to the tool. Doesn't
take much. I usually add more to the wheel if I feel like it is taking me
longer to buff than normal or if I am working with just-sharpened tools and
need to remove the wire edge.
We have found that this method is fast, forgiving and gives the best results.
Our goal is to get to carving. How about you?
TESTING YOUR SHARPENED TOOLS:
I keep a couple of pieces of wood around to test my tools after I sharpen them. One way
to know that you have a sharp tool is to check the cut. The cut you make should be perfectly
smooth. Any scratches or other deformities in the cut will indicate you are not through
sharpening yet. I also cut across the end grain for a better test. Most tools, even when dull,
will do a fair job when cutting with the grain. When I test a v-tool, I cut an s-shaped curved so
that I can check all sides of the tool and to show results when I cut across grain. Look down
into the channel you have just cut and see if it is perfectly smooth.
To be continued.......
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