The planer knife (jointer or thickness planer) largely decides how clean the surface comes out: whether you get torn grain, lines or “waves”. In this guide we explain briefly and technically how to choose the material, how to read the dimensions, what the sharpening angle does, and how to mount and maintain a set of knives.
1. What the L × H × S dimensions mean
Every classic planer knife is described by three dimensions, for example 400 × 30 × 3:
- L – length along the cutting edge (equal to the width of the cutterhead: 260, 300, 400, 410, 500, 640 mm etc.);
- H – height of the blade (usually 20, 25, 30 or 35 mm);
- S – thickness (on classic jointers and thickness planers, usually 3 mm).
2. Material: DS, HSS 18% W or carbide
The material decides how long the edge lasts between sharpenings and on which wood species it is worth using.
| Material | Hardness | Recommended for | Strengths | Limitations |
|---|---|---|---|---|
| DS (chrome alloy steel) | ~59–60 HRC | spruce, fir, pine, lime, poplar | low price, easy to sharpen, shock-resistant (knots) | dulls quickly on hardwood |
| HSS 18% W (1.3355 / T1) | 62–64 HRC | beech, oak, ash, hornbeam; volume production | keeps its hardness when hot, long interval between sharpenings | higher price than DS |
| Carbide (T.C.T. / HW) | far above steel | boards, laminated or abrasive wood; electric planer blades | very slow wear | brittle on impacts and knots, sharpened only with a diamond wheel |
Simple rule: for softwoods and occasional work choose Pilana DS; for hardwoods and daily production go for Pilana HSS 18% W – the extra cost pays back through fewer stops for sharpening.
3. Sharpening angle and cutting angle
This is where most confusion happens. On a classic jointer there are two different angles:
- Sharpening angle β – the angle of the ground bevel of the knife (Fig. 1). It is set when sharpening. Typically around 35° for softwoods and 40° for hardwoods: a larger angle gives a sturdier edge that does not chip in hard wood.
- Cutting angle – the inclination of the knife relative to the wood, determined by the design of the cutterhead, not by the knife. You do not change it by buying a different knife.
Straight knives or a spiral (helical) cutterhead?
“Spiral” is not another type of long knife. A spiral (helical) cutterhead is a separate head fitted with many small reversible carbide inserts arranged in a spiral. It cuts more quietly and tears less on interlocked grain, but it means replacing the cutterhead. A classic cutterhead uses straight knives – and with these, surface quality depends on material, sharpening and setting.
4. Correct mounting – the set matters
- Replace or sharpen the whole set (2, 3 or 4 knives) at once. The knives must have the same height and the same weight, otherwise the cutterhead vibrates and marks appear on the surface.
- Clean the slot and the wedge of resin and dust before mounting – a chip under the knife changes the edge projection.
- Set the projection of each knife with a ruler or setting jig so that all edges reach the same cutting circle (Fig. 3).
- Tighten the bolts gradually, from the middle towards the ends, to the torque in the manual. Worn square-head bolts should be replaced – see our jointer wedge bolts M6–M12.
5. Sharpening and signs the knife needs replacing
- Signs of dullness: “fuzzy” surface on softwoods, tear-out on hardwoods, more noise, harder feeding, shiny burn marks.
- Sharpening is done only on the bevel, on a machine with coolant, keeping angle β. Overheating “burns” the steel and the edge no longer holds.
- After each sharpening the height H decreases. When it falls below the minimum allowed by the machine or wedge, the knife must be replaced.
- Small nicks (from nails or knots) on a single knife can be offset by shifting the knives in the set sideways, until the next sharpening.
Frequently asked questions
Which size should I order if I don’t know the machine model?
Measure the old knife (L × H × S) and check the cutterhead length. Send us the dimensions or a photo of the knife next to a ruler and we will tell you the right option.
Can I fit HSS 18% W knives on any jointer?
Yes, if the L × H × S dimensions match. The material does not change mounting, only the edge life.
Is HSS worth it if I only plane fir and spruce?
For occasional work on softwoods, DS is enough and more economical. HSS 18% W shows its advantage on hardwoods and high volumes.
Is the price for a set?
For Pilana planer knives the price shown is per piece. For a cutterhead with 2, 3 or 4 knives, adjust the quantity in the cart.
💬 Which knives do you use on your jointer now – DS or HSS? Tell us in the comments which species you work with and we’ll tell you which option is worth it.