Tool Sharpening Tips and Techniques

 

I've found that there are two types of carvers when it comes to tools. Those that see the tool as just a means to carve the wood, and those that see the wood as a chance to use the tool. I fall into the later category. With a bent blade, the first type sees this as a loss of carving time, while the second type sees this as a chance to reshape the tool. Now you may fall into the first type, but even if you don't really like messing with your tools, you will find a great deal more freedom when you develop the skills to fix and reshape your tools. So here goes. When I started carving, I was extremely frustrated with sharpening. I finally found that practice was what made the difference. Sharpening a tool is not rocket science, its being able to hold the tool in the same position repeatedly while going through the sharpening process. The other part is having some basic knowledge about edge shapes. If you are at all mechanically inclined, and can visualize what the edge looks like, then you have all you need. Pictures make all the difference, but text editors don't do them, and I'm no good at doing that funky ASCII art. So here are words for some basic principles. 1. The shallower the angle (smaller), the sharper the knife edge. Conversely the shallower the angle, the weaker is the edge. So for choking done trees, you need a much steeper angle then for shaving your beard. Angles in books are nothing more then general guidelines. If you are too shallow, then the knife cuts great, but gets dull quickly. If too steep, then the knife cuts less great, but does it for a lot longer before resharpening. As you continue wood carving, you will form opinions about what that angle should be based on the particular tool, the wood being carved, and your own particular style. Don't agonize too much over the proper angle. "Good-enough" goes a long way here, but I like 27.43 degrees. 2. It is the microscopic edge (the leading edge) which determines how sharp the blade is regardless of the angle used. That's why you can shave with an axe that's well sharpened. Once you have an appropriate angle, all of your effort is to make this microscopic edge; clean, polished, and true. How this is accomplished is where you get all of the differences of opinion. 3. You can sharpen your knife with a flat rock found in the back yard. It will turn out just fine. But, it will take a lot of work, and it will be a pain. You will need to buy some things to make your job easier. What you buy though is wide open. It mostly depends on: - $ or $$$$ - Are you high tech or low tech (new fangled vs old fashioned) - You like hand tools or power tools. - You just want it sharp, or you want to perfect the craft of sharpening. - Big workshop or small box in the hall closet --> I am a cheap, low tech, tool sharpener with a garage (part of it at least, the rest keeps filling up) Now, since you have no opinions, and are looking for specifics, I will give you my idea of the basics you should have. This is roughly in order of priority. 1. a double-sided carborundum stone at least six inches in length. This can be found in any hardware store. This is your basic stone for reshaping and establishing the edge. It has two sides, a rough side, and a medium side. Note: you will need to use oil or water or spit to keep the pores clean while cutting (see 2 below). For these stones I find spit best. Oil is too messy, and water soaks right through too quickly. 2. a soft Arkansas stone, again at least six inches in length. These are a little harder to find, but any store that handles knives will have one of these. You should get a small bottle of honing oil for the stone. It usually comes with the stone. The oil keeps the particles of metal from getting embedded into the pores in the stone (the little crystalline cutting edges which do the work) and clogging them up. You can use any light oil for the job, including cooking oil. Water or spit works too, but I like to stay consistent with a stone. 3. a honing strop (sp). This you make your self. Instructions below. 4. polishing compound for the strop. These look like big fat Crayons. It is a polishing powder mixed with wax to hold it together. You rub it on the surface of your strop, or on some cotton or felt power sharpeners. You can find this at many hardware stores hidden away someplace. Also you can find it at jewelry supply and some auto supply stores. It comes in different colors (the color of the powder used). They have different hardness and polishing characteristics. The box they come in will give you some guidelines. I've just always used the red rouge and never really experimented with the rest much. You don't need much. It goes a long way I still have the original set after 20 years (but I don't use power buffing tools much). 5. two good flat files. A medium one, and a fine one. By good, I mean not too small, and one with a decent handle. At this point you have everything you need. It's about as cheap as you can go. From there on, you are getting into specialty items which can make things easier or faster. You can get: - harder Arkansas stones for finer polishing - specialty ceramic stones instead of Arkansas - Japanese water stones instead of Arkansas - Diamond surfaced stones instead of Arkansas - cotton and felt polishing pads for a bench grinder - belt sanding rigs replacing the carborundum - water bath power sharpeners - bench grinders for fast reshaping and blade making - $$$$ Ok, now how do you fix the point on your new knife. I have not had much success with bending the points back. If you have a hammer and a solid surface (like a metal anvil) you can try hammering it flat. It will still need some fix-up, but not as much. With your file, file off the bent point. When it starts to get flat, you can switch to the rough carborundum. Work on it until all of the bend in the metal is gone and you have only the original "plane" of the blade. Then its decision time. You said it was a roughout knife. Not knowing what it looks like, but clueing off the word roughout, I'm figuring that a pointy type end is not real important. If so, you are almost home free. You just resharpen the end to make it match the rest of the blade. - well no, not really because you will find that you are going to put an entirely new edge on the blade anyway which take some time. If you think you want a point back on, or want to reshape the end, then you are going to do some major surgery. This is the real hard part - it takes faith - take the edge off your knife with the rough stone so you don't cut yourself while reshaping. Have faith, you will get the edge back on. With your file, filing perpendicular to the edge, file the point until the shape looks right. You can use the rough stone here too. You aren't trying to put an edge on, just to get the shape (profile) right. Ok, now how to resharpen. I would use this as an opportunity to practice. This will take about 30 minutes, so get a good flat surface, and a chair to sit in. You are going to go rough side, medium side, soft Arkansas, and strop. You want to develop control and consistency. You want to experiment with pressure, and with different postures of hands and body which help the consistency. Some people use a round-and-round motion when sharpening. I just do a sweep in one direction - cutting edge leading rather then trailing. I will use a round-and-round motion when I want to take off metal faster, particularly at the start, but then switch. This is personal preference (and it works for me) Ok, here is where the visualizing comes in. What your are doing is grinding a face on your blade. In the books and instructions, this face looks nice and flat, but because you can't keep the blade at exactly the same angle your face will be more rounded. The flatter the better (consistency). As you are working you blade, stop, wipe it off and take a good look at the edge. If you have a good magnifying glass, use it. Also, get a black magic marker and go over the edge with it. Then go back to the stone for a little. Stop, and look at the edge. You can see real clear where you are grinding and where you are not. Bright light helps too. You will likely get a bias in the blade from change in angle as you move it across. This means that one side is at a different angle then the other, or that the front or back of the knife is at a different angle. Try to minimize this bias. To test the knife, use your fingernail rather then shaving your arm. Push the edge across your thumb nail as if it was the sharpening stone (not a slice or saw motion). Don't push down on the knife, let the weight of the knife be the pressure. When it starts to get sharp, it will "grab" the nail rather then slide over it. This is rather dramatic, and you will know it when it happens. Also slide the edge of the nail along the knife edge feeling for smoothness. You can feel the slightest micro-nicks this way. Do this slowly and cautiously. We don't want to cut ourselves. You will spend the most time on the rough stone. Your are going to remove a lot of metal. Stay with it until it starts to catch your nail, and has a good face on the edge. Figure 15-20 minutes here (but it depends). Next go to the medium. You want to make sure to keep the same face angle. The magic marker works well here. You are also smoothing the scratches from the rough stone. You are done here when the edge starts to look polished, and there is a significant increase in sharpness. If you "think it feels a little sharper", then you aren't done. If you aren't making progress, then you are probably changing the angle and are trying to grind a new face. This is the mistake I always made. With a magic marker and a magnifying glass this is real obvious. With the Arkansas stone, you want to finish the polishing of both the edge face and the edge edge. Watch your angles here. Check yourself. You will see some improvement in the sharpness as measured on your thumb nail, but it will be more refined. Keep going as long as you see increased progress. Use the magnifying glass and watch the edge. When you think you are ready, You want to put about 5-10 strokes on each side at a steeper angle - just slightly steeper, say 5 degrees. This puts on your micro-cutting edge. It is this micro edge that you will be reconditioning as you resharpen your knife while carving. You don't have to go back to this major resharpening as described here until you no longer have success in touching up the micro edge. The strop and Arkansas stone will be your tools for the touch-up. Wipe the knife, and then under a bright light gently press the knife almost flat on your thumbnail. If you have done the job right, you will see the extreme edge appear to bend (the reflected light lets you see this). The part that is bending is called the "wire edge". It is very thin, and is an artifact from the sharpening process. If used this way, it will break off causing micro-nicks (can't see them, but can feel them with the nail). We use the strop for this. Take the strop, and lay the knife flat on it and use some pressure pushing it against the strop. Then draw the knife with the edge trailing (else you cut the leather strop) across the strop switching from side to side. 10 strokes usually does it. If you test the knife for sharpness on the thumb nail, you should see a dramatic increase in sharpness. Keep stropping until it doesn't improve. Use this same procedure to touch up your knife while carving. When you don't feel an improvement, then go back to the Arkansas and re-do the micro-edge. Eventually you have to go back and put the face back on. How often depends on the steel, the original face angle, and the carving. Re-doing the face is never as dramatic as putting the original face on the tool. Much faster. The knife should now catch immediately in your thumb nail. It doesn't skid at all. You are doing this with little or know pressure. The weight of the blade is all it takes. If your are unsure of the feel of this, get a razor and test it on the nail. This should be your benchmark. Now, how to make a strop. Get a 14-16 inch piece of 1x2 pine. Carve a decent handle in the first six inches, and leave the rest flat. Now get a chunk of leather at least 8-10 inches long and 2 inches wide (and not real thin). Glue the leather onto the rest of the stick. White glue or contact cement work fine. Clamp or weight the thing down to set overnight. When set, use a sharp knife to trim off excess leather. Take the polishing compound as described above and rub it all over the leather putting on a reasonable coat. Every so often I will scrap off the old stuff and put on a fresh coat. Well, there you have it. Chris Nelson Duane: Any sort of buffing with any type of wheel/strop/buffer will EVENTUALLY round off a tool's edge. That is because the is always a little deflection of the buffing wheel as it comes off the tool,... as sort of depression... that rounds the tool edge ever so slightly. The buffing wheel, though, rounds the edge off less than, say, a stitched cloth wheel. Unless of course, the person at the "handle end" of the tool is causing the tool to contact the felt wheel at too "blunt" an angle. I watch my students buff their tools on my felt wheel, and honestly, sometimes I just cringe. They may as well just push the "sharp" edge right into the wheel, the way they are attempting to buff the tool. When a tool's cutting angle becomes blunt from buffing, it is a very simple matter to take the tool to the bench stone, dress the edge with a few stroke, take the burr off with slip stones, and buff the edge to a fresh, sharp finish. I can do this in less than 3 minutes in a pinch. No sharpening system is EXACT, especially when it comes to buffing. This is because the person who holds the tool is not EXACT (like a machine) and also because buffing wheels/strops deflect. Instead of trying to find something that is EXACT, try your best to develop the SKILL you need to keep your tools in shape. It takes practice, but the effort is worth it. Just accept the fact that ONCE IN A WHILE you will have to reshape the edge on your bench stone to bring the cutting angle back to specs. It's a fact of life where sharp edges are concerned. Hope this helps. Bill Judt Grande Prairie, Alberta, Canada One of the major advantages of felt is that it will deform to the shape of the applied object - it has some "give" to it. How much it will round (or deform) the edge depends on the amount and aggressiveness of the compound applied, the angle at which the edge is introduced, the length of time in contact, and the force with which you apply the edge to the wheel. With that out of the way, yes it will round your edge, but how much and how soon depends on your individual sharpening practices. I personally use two cardboard wheels to sharpen with, one charged with 220 grit aluminum oxide abrasive and lightly coated with wax. The second is plain cardboard with slots across the face, and a buffing compound, usually white rouge applied, for honing. I use the grit wheel for normal sharpening, which is only required occasionally, unless an edge becomes damaged. I use the honing wheels for final honing and light touchup. This is on all knives and the outer bevel of all sweeps and gouges, including vees. The commercial name of this system is Frizzell's Razor Sharp, but I have seen similar under other names. I also use a muslin buff, a fairly stiff one, as a final touch to remove all traces of rouge from the edge and on the inside of gouges. I know many professional carvers who use felt wheels, but always in conjunction with some sort of hard wheel, most frequently a conventional grinding wheel. If you use felt, eventually the edge will round enough that you must go back to something else to flatten it. If, however, your edge will cut a thin curl across the end grain of a piece of basswood, that is a curl thin and smooth enough to curl near full circle before breaking, it is suitable for carving. Regardless of all the theories and pundits - myself included - the ultimate standard in sharpening has to be the ability to cut clean and smoothly, without requiring excessive force. Jim From: Graeme Vaughan (vaughan@webnet.com.au) The best information I have received on sharpening (after a good deal of reading and asking and trying) is from Les Miller at the recent Working with Timber show here in Melbourne (Les also produces videos on this and other subjects but I don't have the contact details - sorry! perhaps some other Ozwoodie can help).Advice as follows: The sharpening process is best divided into three parts: grinding or setting the bevel honing stropping or polishing 1.Grinding For this you will need a soft start bench grinder with an 8 inch white Aluminum oxide wheel (NOT the Silicon Carbide wheel which is sold with most bench grinders), 46 grit and rated K or J for hardness. The wheel is large, quite coarse and soft. The reason for this is that it enables material to be removed quickly without heating the tool and ruining the temper. There is no need to dip the tool in water to cool it as it remains cool throughout the process. To clean and true the wheel do not use diamond sticks etc, but use a silicon carbide dressing stick as this keeps the wheel true. You will also need a tool rest which adjusts to any angle. Daniel Starbuck's point about maintaining the bevel is absolutely spot on. It is very difficult to maintain the correct angle freehand. 2. Honing For honing, use a diamond impregnated steel plate or Arkansas slate slipstone (the former is preferred). Use WD40 to keep the stones clean. For plane blades, chisels etc, use a bought or shop made holder to keep the blade at the correct angle to the plate. See any good sharpening book on the techniques. Hone the flat side of single bevelled tools first. 3. Stropping For this you will need a leather wheel and polish rouge. There are power strop systems available for power drills. Hope this helps. Cheers. Graeme