Paul Sellers talks about the practical limits to sharpening woodworking tools like planes and chisels:
As I have said, we have become something of an obsessive bunch when it comes to the different elements of working wood; sharpness has become more and more obsessive. Now we are not talking about the violin maker seeking sharp levels for clear tone from the wood and who uses wood so soft, unsharp gouges and planes would bruise rather than cut the fine surfaces he strives to achieve. His standards parallel the levels needed for severing tissue by the surgeon’s hand, not the bench joiner chopping mortises and cutting a few dovetails.
It’s unfortunate that since the demise of ordinary craftsmanship we now turn to guru wood writers and not wood-wrights. Woodwrights are no longer there to give us our information of course. It’s true too that the sources of information become more and more questionable. Three recent sources of information teaching on sharpening techniques I tracked back to tool catalog and online sales people selling products for sharpening. Most of the information they have is not new but regurgitated. Each phase of sharpening change marks another saleable product and so we see Japanese water stones added to carborundum stones, Arkansas stones and Washita stones and then came diamonds and abrasive films, diamond paste and flattening stones. The list goes on.
We have survived the different gospels of scary sharp and micro-bevel methodology and are emerging to this very simple reality. As long as you start the cutting edge somewhere around 30-degrees and polish it out it will cut well. If you you sharpen to around 1200-grit it will cut most anything you need in woodworking. If you sharpen to a polished edge of around 15,000-grit you can slice the most delicate of materials effortlessly, but 98% of the time that’s far from necessary. What am I saying? I’m saying that we generally sharpen to task but often sharpen to a higher level because it’s not much extra effort. We all know after a few efforts at sharpening that the greatest effort comes at the start of the process when we have to regain ground to get through a fractured and dulled edge and back to a productive cutting edge. That said, it’s not a big deal, just a few extra strokes on the coarse diamonds gets you there. So, if that is the case, why do we sharpen to higher levels than are usually needed. Well, it is a fact that the more polished the two plains forming the arête for a cutting edge are, the sharper the edge is but the stronger the edge is too. As I said, the extra effort is worth the work because it’s so quick and effective. It’s not so much what we do to the edge to establish it but what we do to the edge after we have prepared it for work. Taking the chisel to the surface of the wood to work the wood begins an immediate process of edge reduction we now know is edge fracture but was once called wear. No matter the steel, edge fracture occurs at some level but some steels fracture more readily than others. What we often do not realise is that it is impossible to find a steel that both takes and retains an edge and at the same time has a level of durability we can rely on forever. All edges wear away by fracture and constantly need restoring.
