Chisels are fundamental tools that, when tuned, are a joy to use. Many texts provide details on a plethora of different chisels available, but I have found myself using only a small selection of fine tools. This is a relief for those putting together their hand tool list; limit the chisels in your tool collection, then spend your money on fine tools you will actually use. In this article, we will explore bevel-edged chisels and mortising chisels.
When I refer to bevel-edged chisels, I include in that group both the “bench chisels” and “firmer chisels”, as long as they have bevelled edges. Bench chisels are shorter versions, usually fitted with a socket type of handle that features a hoop at the top end to resist chipping. Firmer chisels usually have a tang-style wooden handle with hoops at the top and bottom ends to reduce splitting.
When buying a set of chisels, consider the length of the handle, shape of the handle, shape and length of the blade, steel composition, durability, the feel in your hand and, of course, price.
I studied under James Krenov in 1994. Jim used a set of short bevel-edged chisels made in Sweden by the E.A. Berg Company. Jim did not have large hands, so he found tools that felt good, were the right length for him, that held a good edge. The steel was carbon steel, nothing fancy, just good honest tools. I find many chisels have excessively long blades, forcing me to hold only the blade while paring, which is undesirable. Today I enjoy the use of Japanese chisels for their physical size and excellent edge; these shorter tools just fit right, for me. I use two sets of chisels – one burly set for general purpose work, and one set for fine work, where my best edge is essential.
When it comes to edge tools, there is always a lot of discussion about steel. There are a wide range of options out there, ranging from carbon steel, to carbon steel alloyed with metals to resist deformation, to bi-metal blades made with soft steel for the blade body, mated with very hard, fine-grained carbon steel at the cutting edge.
Inexpensive chisels are generally cast from carbon steel and then ground into shape. These tools tend to suffer from a rather large grain structure and relatively soft blades. Blade hardness is defined by the Rockwell “C” hardness scale. The Rockwell test applies a known force to a 120° diamond cone causing a dimple in the chisel blade. The penetration depth in the subject steel is directly read out on a dial indicator that displays a higher number for harder steel. Woodworking chisels typically range from RC58 to RC64. At the high end of the scale, there is a possibility that the steel may become brittle.
Rockwell “C” 58 is the usual starting point for chisels: hard enough to take and hold a reasonable edge, but soft enough to resist cracking. If you are handy with your wet stones, you can achieve good results, but you will be back to the stone more often.
High carbon steels contain between 0.5 and 1.5 percent carbon. Some tools employ alloys such as chromium, vanadium, and molybdenum to increase the toughness of the steel, while reducing edge softening if the tool is overheated. I use German-made, Two Cherries chisels for my day-to-day work because they take a reasonable edge, are moderately hard at RC61, they resist chipping, and the cost is reasonable. I do not like their handle design because the tools roll off of my bench. The real downside is that you cannot obtain that super-keen edge with the above-mentioned alloys. The large grain size created by alloying with chromium causes a serrated edge when viewed at a micro level. This leads to micro-fractures during use and inevitably a loss of keen edge performance. However, these chisels will work all day with very little degradation of that reasonably sharp edge due to the toughness of the steel.
A2 steel works about the same – tougher and harder than simple carbon steel, but the edge is somewhat limited by the trade-offs taken for toughness. A2 contains about 1 percent carbon, 5 percent chromium and 1 percent molybdenum.
So why do most people have a reverence for old tools? Why do so many old-timers say that edge tools used to be much better? The answer is most likely in the manufacturing method; the chisels may well have been forged. This process tends to keep the grain structure small, allowing the maker to achieve a keen edge with carbon steel tools.
Japanese chisels are made of two metals. The body of the tool is made of relatively soft steel, while the back that forms the cutting edge is made of hard, high carbon steel. These are forged tools that take and keep a keen edge. The hardness at the edge is typically Rockwell “C” 64, which is very hard. The fine grain of Japanese tools is superb, resulting in a very fine edge that is the best I have used.
The Japanese chisels really shine when it comes to hand work such as paring. The experience is hard to describe – find someone with these tools, and try paring some dovetails, and then you will see and feel the difference.
Bevel-edged chisels are ground to a primary angle of 25°. Remember that your six-inch Aluminum oxide grinding wheel will create a concave grind angle, which means the effective cutting angle will be less than 25°. Therefore, I grind my chisels at 27 to 30°. The absolute angle is not critical. If you are chopping bubinga, make the angle more obtuse – there is nothing to say you cannot grind the tool to 32°.
Do not grind your Japanese chisels with a 6″ wheel creating a hollow grind. I actually made this error a long time ago; the result was that I weakened the tool, and my chisels chipped excessively. I like to re-establish the 25° primary bevel on my Japanese chisels by honing the entire bevel on a 1000 grit water stone. If you have difficulty holding the tool flat, use a Veritas honing guide; it is perfect for this job. I then create a micro-bevel at about 27° using my 4000 grit water stone and move on to some 3 micron, then 1 micron diamond paste on a maple block.
I think everyone should have a ¼” and a 3/8″ mortising chisel. These tools are very sturdy, and feature a very thick trapezoidal (in section) body from front to back of the blade. Mortise chisels are meant to be struck hard, and then used as a lever to remove the waste. They are ground at a stout angle with a primary bevel of 35°. Adding a micro-bevel makes an effective cutting angle of about 37°.
Leave the front edges of your mortising chisels sharp after flattening the back of the tool. This is essential to allow the edges to cut the fibres within the mortise during the lever operation following chopping.
Handle size is important if you are whaling away at a mortise – the German tools have massive hornbeam handles that will take a serious blow while also ensuring that you will strike the tool and not your favourite woodworker. These tools are referred to as registered mortise chisels. They feature wooden handles with hoops top and bottom, and a leather “shock washer” to reduce vibration.
The British Sorby registered mortise chisel is another design that is favoured for its relatively small size. If you are put off by the sheer size of the Two Cherries or Hirsh tools, have a look at the Sorby tools which also use hoops top/bottom and a shock absorbent leather washer.
Learn to chop a mortise by hand; it is very rewarding. I often clean up the sides of my mortise by paring with a bevel-edged chisel before fitting a tenon.
So, to finish, buy a few chisels, and build your set as time and budget permit. Take the time to flatten and polish the back side of the tool to a mirror finish. Make room in your kit for a couple of Japanese dovetail chisels, which are triangular in section to aid access to tight dovetail corners. Buy a few good tools rather than an inexpensive eight-piece set, and enjoy the experience.