Hand tools in practice. Compression in chisel work

We are starting a series of articles focused on the practical aspects of working with hand tools. First up: woodworking chisels. Many beginner woodworkers see the chisel as a crude tool, lacking any attachments that help control its movement—like a sole, fence, or depth stop. However, in my opinion, it’s a versatile tool that can be used with great precision, provided we understand the principles of using it correctly. Often, it’s thanks to the chisel that we can create tight-fitting, gap-free joinery. I won’t go into definitions or classifications of chisels here. I will focus solely on the practical aspects of working with these hand tools. The first topic is the compression effect when working with a chisel. But before diving into compression, let’s start with a few words about the chiseling process itself.

Wood Chiseling

One of the basic woodworking techniques in hand tool joinery is chiseling. On our blog, you’ll find an article dedicated to mortise and tenon joints – Hand Tools Needed for Mortise and Tenon Joints – Bensari Workshop – which discusses the practical aspects of chisel use, as well as tools for marking wood. I also recommend the article Basic Woodworking Tools – Where to Start? – Bensari Workshop, where you’ll find information on chisels, marking tools, and sharpening accessories useful for chiseling. The success of chiseling depends on several factors:

• precision in marking the wood,
• the sharpness and bevel angle of the chisel,
• the type of chisel used,
• the skill of using a chisel.

What is wood chiseling?

Chiseling involves methodically cutting away wood to shape it or to create a woodworking joint such as a dovetail, mortise and tenon, etc. There are two main types of cutting: slicing and splitting (to be covered in future posts). Chiseling can be done using just the chisel or with a mallet—a special hammer, traditionally with a wooden head. Before chiseling, you must mark the wood with lines and indicators that allow precise shaping. Another crucial step is clamping the wood in a vise. If this isn’t possible, you should not chisel freehand—it’s a matter of both safety and quality. Chisel gradually and methodically.

What is wood compression when striking a chisel with a mallet?

One key concept in understanding chisel work is compression—the spreading of wood fibers as the chisel penetrates the material. Compression is responsible for many of the errors in precise joinery. It can destroy previously marked lines and ruin your joint. While it may seem obvious, there are a few simple technical principles worth understanding to counteract it.

How to use a wood chisel correctly?

Imagine working with a chisel that has two symmetrical bevels. Striking it with a mallet will generate symmetrical compression, as shown in figure 1A.

 

The top of the figure shows a side view of the chisel; the bottom shows a top-down view of the board (green color). The red line is the chisel line, usually marked with a knife, and the point where the chisel is applied. In the lower part of the drawing, you see the mark left by the chisel after a mallet strike. Fig. 1A shows a symmetrical mark from a double-bevel chisel, while Fig. 1B shows an asymmetrical mark from a single-bevel chisel. Symmetrical compression occurs because the force direction (blue arrow) aligns with the chisel’s cutting direction (purple arrow—assumed to be the bisector of the bevel angle for simplicity). With a single-bevel chisel, things get more complicated. Contrary to what some believe, a single-bevel chisel does not follow the flat (mirror) side. Its cutting direction aligns with the bevel’s bisector, causing it to veer left (purple arrow). Since the mallet’s force direction differs from the chisel’s natural cutting direction, two things happen:

• the effective chisel path lies somewhere between the mallet strike direction and the chisel’s natural direction,
• compression becomes asymmetrical, as shown in Fig. 1B and the photo below.

 

It’s worth noting that an experienced woodworker knows the path of a chisel is also affected by the grip strength and control over the tool. Holding the chisel firmly and steadily can help align its movement with the mallet’s force—but only to a limited extent. The chisel will always tend to “drift” (in this case, to the left). Other factors that influence compression include bevel angle and wood hardness. The steeper the bevel, the greater the compression.

What are the rules for using a chisel?

Here are a few key rules for effective chisel work:

1. Hold the chisel firmly—don’t let it take over!
2. With light taps, compression is minimal and doesn’t affect the outcome. Build a wall from the flat (mirror) side of the chisel—known as a **knife wall**. The larger it is, the more it resists compression.

 

Start with gentle vertical taps. After each one, remove the wood on the bevel side. Repeat until you create a clean groove without damaging the marked line.
3. Start chiseling slightly next to the line—about 1/16” away. Compression won’t destroy the line this way. Even if it closes slightly from the force, you can easily restore it.

 

Once you reach the right depth, make one or more vertical cuts, removing thin shavings to approach the line. Since there’s almost no resistance from the bevel side, compression will be minimal or invisible.

 

 

4. If you’re working on fine detail, use a chisel with the smallest bevel angle available (e.g., 20–25 degrees).

In summary, one of the fundamental skills in chisel work is minimizing the impact of compression on your joinery. That’s why it’s crucial to understand how compression arises and how to reduce it. Only then will working with hand tools be both efficient and satisfying.