My introduction to sharpening hand tools was rudimentary because the shop in which I worked was equipped mostly with power tools with carbide-tipped blades. When they became dull, one of us would take them to Luke’s Machinery on Notre Dame where they were sharpened and honed on a machine.
Our workshop did have a bench grinder with a #80-grit wheel on one side and a #120-grit on the other. The grinder was capable of sharpening chisels and other tools made of high-speed steel, but it was powered by a motor that ran at 3,500 rpm, which was far too fast for hollow grinding a woodworking chisel on a hard-stone wheel. Any attempt to sharpen a tool ended in disaster, as the heat produced by the high revs turned the steel blue-black, indicating the temper had been removed from the cutting edge, effectively ruining the steel.
The only person in the shop who could successfully sharpen a tool on the high-speed contraption was an experienced cabinetmaker named Eric, who eschewed hollow grinding because it took too long to create a good cutting edge. Instead, he would hold the beveled edge of a chisel lightly against the side of the #120 wheel, removing sufficient steel to create a burr on the opposite side without overheating the chisel. He took off the burr by rubbing the back of the chisel over a sheet of #320 silicon carbide wet/dry sandpaper glued to a sheet of plate glass. He’d spit on the paper to “lubricate the surface and increase the carbide’s cutting ability.” With the burr removed, he’d create a fine micro-bevel on the cutting edge by moving the chisel a few times across the face of a sheet of #1000 wet/dry paper also pasted to the plate glass.
Eric had developed this simple sharpening technique because it saved precious time and created a cutting edge sufficient for his purposes, usually chopping out mortises or shaving wood from hand-cut dovetails. The secret to his method was experience, knowing exactly how much pressure to place on the chisel’s bevel to obtain a usable edge without overheating the steel. I eventually learned to sharpen a chisel using Eric’s technique and still use it today, though I’m sure it would make many woodcarvers or chefs blanch.
Needless to say, woodcarvers and chefs require tools with extremely sharp edges to cleanly sheer wood fibres or chop food into thin slices for various purposes. Every carver or chef has his or her special technique for sharpening the tools of their trades.
Carvers who use knives to produce three-dimensional pieces sharpen the entire blade or the bevel, depending on the tool of their choice. This can be accomplished in myriad ways; however, an effective method is to strop the tool on a homemade belt made from a strip of hardwood with leather glued to its surface. The leather is charged with a honing compound that produces a razor-like edge after about a dozen strops on both sides of the knife. Re-grinding is not generally required unless the cutting edge is nicked by a bit of stone or steel embedded in the wood, a particular problem when re-cycled material is carved or when carving certain woods. Teak, for example, has a high natural silica content that blunts a keen edge quickly, while African ebony causes severe blunting because of its density, requiring frequent re-sharpening and honing.
One inexpensive and effective method to redefine a flat or beveled knife edge is to grind it on rigid plastic sanding discs that sell for less than $10 and can be chucked into a battery-operated or plug-in 3/8-inch reversible drill. I have seen woodcarvers who demonstrate their art at shows use this technique to grind and hone edges. The drill is held in an upright position by hand or by a homemade jig; the knife is held flat or, depending on the micro bevel, at about 20 degrees in relation to the disk. 220-grit sandpaper is used to remove deep scratches or nicks while 1000-grit is excellent for general sharpening.
Honing is accomplished by holding a knife on a disk with a piece of leather glued to the surface. As with a strop, the leather is charged with a honing compound available from Lee Valley or on the Internet. For safety reasons, the drill should be reversible so that the knife’s keen edge faces away from the operator no matter what side is being sharpened.
(Next week: part 2)