Flattening the Sole (Lapping)

A flat sole is essential for accurate hand plane work. Even vintage Stanley planes often need sole flattening.

Why Sole Flatness Matters

Any deviation from flat—twist, cup, or bow—transfers directly to your work. A concave sole won't cut in the middle. A convex sole rocks and can't maintain consistent depth.

The Lapping Process

  1. Check flatness with straightedge and feeler gauges
  2. Mark sole with marker or layout fluid
  3. Rub on 80-grit sandpaper adhered to flat surface (plate glass or granite)
  4. Check progress—high spots wear first
  5. Progress through 120, 220, 320 grit for smooth finish
You don't need the entire sole perfectly flat—just the toe, heel, and areas immediately around the mouth. Many professional plane tuners leave a slight hollow in the middle.