Sharpening chisels & plane blades

Chisels and plane blades need to be sharp to cut wood fibres cleanly rather than tear them out. A keen edge allows for greater precision, smoother surfaces and significantly less effort, giving you better control and better results.

Contents:

Flattening the back, sharpening the bevel and honing
Plane blades – The Lie-Nielsen Method
Template for setting bevel angles on a honing guide
Honing guides

Flattening the back, sharpening the bevel and honing

For chisels and plane blades to perform properly, the back of the blade must be perfectly flat. On new tools, the back may not be completely flat or may still show coarse grinding marks from manufacture. To achieve a sharp cutting edge, these marks need to be removed and the surface refined.

Depending on the depth of the grinding marks and the flatness of the blade, the back may first require coarse flattening. Western chisels and plane blades can be flattened on a diamond block. In most cases, it is sufficient to flatten the front two-thirds of the back. After this initial preparation, the back only needs to be honed on the finest sharpening stone.

Place the back of the blade at a 90° angle to the long side of the diamond block.
Position the cutting edge as close as possible to the opposite edge of the sharpening surface.
Using light pressure, move the blade back and forth across the stone, guiding it with your fingers.
Shiny areas indicate where the back is making contact with the stone; darker areas have not yet been touched. The most important areas are the first approx. 3 mm behind the cutting edge and the outer edges.
After this initial flattening, refine the surface on finer stones, for example 1000 and 6000 grit, using the same motion until no scratches remain.

Japanese blades can be flattened on diamond blocks or using a steel lapping plate and silicon carbide powder.

On the lapping plate, work the blade with silicon carbide powder and water under relatively high pressure. A piece of wood makes it easier to apply even pressure. As you work, the abrasive breaks down into a fine slurry that also produces a polishing effect.

Flattening the back in this way is generally only necessary once on a new tool. Flat, properly trued honing stones should be used for this process. Afterwards, the back only needs to be honed on a fine sharpening stone.

Sharpening the bevel

Next, sharpen the bevel. Depending on the intended use of the tool, the bevel angle will generally be between 23° and around 40°. To check the angle, we recommend using a bevel gauge or small protractor.

► The smaller the bevel angle (1), the lower the cutting resistance — but also the more delicate the cutting edge. A larger bevel angle (2) increases cutting resistance but produces a stronger edge. Finding the ideal bevel angle is therefore a matter of balancing the type of wood, the way the tool is used and the quality of the steel.

The basic technique is much the same as for sharpening knives. Start by sharpening the bevel on a 1000-grit stone. Place the blade on the stone at a slight diagonal and move it back and forth in smooth, straight strokes while keeping the bevel angle constant.

Avoid tilting or rocking the blade. Use the entire surface of the sharpening stone to work efficiently and ensure even wear.

Honing

Next, hone both the bevel and the back on a 4000- or 8000-grit stone. For greater honing efficiency and a mirror-polished edge, rub a Nagura stone over the honing stone to create a very fine abrasive slurry.

Rocking the blade while sharpening produces an unsuitable convex bevel (1). A similar rounding effect can be caused by high-speed felt polishing wheels, which we do not recommend.

With plane blades, sharpening the blade alone is not enough. The edge of the chip breaker also needs to be flattened on the sharpening stone so that it sits flush against the blade and prevents shavings from becoming trapped underneath (2).

Maintaining a consistent angle is generally easier with thick Japanese blades because of their larger contact area. The marks left on the stone can also indicate whether pressure is being applied evenly. A honing guide is useful for maintaining the bevel angle precisely.

Plane blades – the Lie-Nielsen method

Lie-Nielsen Toolworks, manufacturer of high-quality metal hand planes, developed this sharpening method in collaboration with David Charlesworth to produce exceptionally sharp plane blades quickly and with relatively little effort.

Start by polishing the back of the plane blade using the ruler trick. Place a thin steel ruler along one long edge of a fine honing stone, then polish the very front of the blade back along the opposite long edge of the stone (1).

Next, hone a micro-bevel, or secondary bevel, onto the primary bevel (2). For example, a smoothing-plane blade may have a 25° primary bevel and a secondary bevel a few degrees steeper, such as 30°.

Using a honing guide and a homemade angle-setting jig (see below), first grind the primary bevel on a coarse sharpening stone or diamond block.

After adjusting the honing angle to the desired final bevel angle — 30°, 35°, 40° or 45° — hone the secondary bevel on a finer stone, for example 1000 grit (1). Only a few strokes are required. The result should be an extremely narrow secondary bevel.

To polish the secondary bevel, around ten strokes on a 6000-grit honing stone are sufficient.

Finally, use the ruler trick to polish the back with 10–20 strokes.

When resharpening, simply hone the secondary bevel and polish the back again using the ruler trick. Over time, the secondary bevel will become wider, increasing the area that needs to be polished. When this happens, regrind the primary bevel periodically on your coarsest stone to reduce the secondary bevel and make subsequent sharpening quicker again.

Alternatively, you can use a honing guide with self-adhesive abrasive paper mounted on a granite plate (2).

Chisels can also be sharpened using the Lie-Nielsen method. However, the ruler trick must never be used on chisels. The back of a chisel must remain perfectly flat because it serves as a reference surface during precision work.

Template for setting bevel angles on a honing guide

Stop block
Bench-top stop
Honing guide

Placing a wooden spacer between the stop block and the cutting edge increases the bevel angle, for example when honing a secondary bevel (4).

Cambered plane blades

A perfectly straight cutting edge is desirable for most planing tasks. When planing wider surfaces, however, the sharp outer corners of the blade can sometimes leave visible tracks in the wood.

This can be avoided by introducing a slight camber across the cutting edge or by gently rounding the outer corners of the blade.

Honing a slight camber

As a rule of thumb, the corners only need to be relieved slightly more than the thickness of the shaving you intend to take — around 0.05 mm for a smoothing plane (1).

For heavier cuts, such as with a scrub plane, the cutting edge is cambered across its full width (2).

Special honing guides with a cambered roller (3) make it possible to produce a slight, controlled camber while maintaining the bevel angle accurately.

Honing guides

Honing guides usually use two jaws to hold the blade securely and allow straight-edged blades to be sharpened repeatedly at an accurate, consistent angle. Depending on the design, they can also accommodate short, irregular, tapered or Japanese blades, as well as slightly cambered or skewed blades.

There are two main types:

1. Side-clamping honing guides

Characteristics

The back and side edges of the blade serve as the reference surfaces.
Best suited to machine-made chisels and plane blades with accurately parallel and square sides, such as Western chisels.
Blades with very thick side edges may not fit the jaws.
Easy to handle, with no horizontal clamping screws getting in the way.
Long clamping surfaces provide a secure hold.

2. Top-clamping honing guides

Characteristics :

The back and top face of the blade serve as the reference surfaces.
Particularly suitable for handmade chisels and plane blades whose sides may not be perfectly parallel or square, such as Japanese chisels.
Suitable for tapered chisels.
More time-consuming to set up because the angle must be set manually.
Also suitable for skewed bevels.