Insert tooling has changed the face of modern woodworking. Helical jointer cutterheads and insert lathe tools allow you to rotate a dull or chipped edge to a brand new cutting face instantly. But eventually, all four edges run out. In this deep-dive, we examine the economics and physics of sharpening insert tooling.
Shear Cut and Insert Orientation
Unlike traditional straight jointer knives that slap the wood flat-on, insert cutterheads seat the carbide at a shear angle (usually 15 degrees). This creates a slicing cut, similar to skewing a hand plane. The shear geometry drastically reduces noise, power consumption, and tearout—especially on difficult wood grain. But to maintain this advantage, the insert’s rake and clearance angles must remain perfectly aligned.
Honing vs Replacing: The Math
A pack of ten replacement C3 carbide inserts costs around $35 to $50. While this is reasonable, a woodworker who turns or joints daily will go through inserts quickly. Can you sharpen them? Yes, but only on the flat top face. Never attempt to hone the beveled edges, as this changes the cutting circle diameter, causing uneven cut lines in jointer tables.
Step-by-Step Honing Process
- Remove the insert from the tool block and clean off all pitch and wood resin using a solvent.
- Place a 1200-grit (or finer) diamond plate on a flat surface. Apply a drop of mineral oil or lapping fluid.
- Press the flat face of the insert firmly against the diamond plate. Keep your fingers flat to avoid rounding the corners.
- Perform 5 to 10 light strokes. The diamond abrasives will polish the carbide face, bringing a fresh, sharp apex to all cutting borders simultaneously.
To learn more about carbide properties, read our cornerstone article The Complete Guide to Carbide Woodworking Tools. For an example of premium carbide tooling in action, view our Whiteside 1950 Router Bit Review.
For replacement inserts and accessories, browse the inventory at Lee Valley Tools.
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