Tuesday, April 24, 2007
Drawknives, The Other Half
By the other half, I am, of course, referring to the back. To get a sharp edge on any piece of metal, both surfaces must be properly shaped and polished. There are a couple of different ways to flatten the back of a drawknife depending on whether it will be used bevel up or down. Anytime that a tool is perfectly flat (as opposed to a gently rounded) it will dig into the wood and will be difficult to control. To relieve this problem, all you need is a gentle rounding of the surface. If the tool is going to be used solely with the bevel down, the back surface can be flattened like a chisel. Easier said than done! In the photo above, you can see that I use a small grinding wheel to "hollow grind" the back of a blade to make the flattening easier. I alternate between stoning the back and grinding away the flat spots that appear, avoiding grinding the edge. By keeping the back of a bevel down knife flat, you make sharpening more certain, however, I use most of my blade bevel up, which means that I must gently round the back. To do so, I flatten the back just as I would for a bevel down blade. At the end of the process, I strop both the back and the bevel with a leather strop on a block of wood. I charge the strop with green honing compound. Most importantly, when I strop, I try to maintain the proper geometry just like with the stones. Any rounding will occur because of the deflection of the leather, and it is plenty. I don't spend huge amounts of time trying to perfect my blades, instead, each time that I grind and hone, I try to improve it. Experimentation is key to getting the geometry and results that work best for you. Remember to test whatever process you come up with by shaving some softwood endgrain, it will tell you volumes about what you've actually achieved.