Smoky Mountain Woodcarvers 

 

7321 LAMAR ALEXANDER PKWY     TOWNSEND, TN  37882               800-541-5994    865-448-6350    

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Sharpening-How We Do It!


 

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.......

 

 

 


How we sharpen


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