Overview
This protocol describes a repeatable procedure for blade touch-up using a softwood (such as Hinoki or Sugi) wood lap loaded with α-alumina (Ra ≈ 50 nm) or DND (Ra ≈ 30 nm) powder , PVP (Polyvinylpyrrolidone) binder and a light viscosity oil (VG10: ISO viscosity grade 10). It is intended for fine touch-up (de-burring / re-activating edge) rather than full sharpening.
Materials & consumables
- Preferred: Dense, well-dried Hinoki (Japanese cypress) board with fine comb/longitudinal grain (prepared lap). Hinoki's denser cells and finer grain provide greater stability and more consistent abrasive retention than sugi.
- α-Al2O3 powder (Ra ≈ 50 nm class), and/or DND powder (detonation nano diamond, 30 nm class).
- PVP solution in ethanol (1–3% w/v) for temporary fixation.
- Light mineral oil, ISO VG10 (thin oil) for moisture/wetting.
- Low-lint pulp wiper (e.g. Kimwipe S-200) for the wet and dry wiping steps. "Low-lint" is sufficient for this procedure since any remaining lint is removed during the wet-wipe stage.
- Thick polyethylene bags; silica gel (optional).
- Personal protective equipment: respirator/mask, safety glasses, gloves.
Step-by-step procedure
- Preparation of the lap: Clean the softwood surface. Condition by cross-hatch rubbing (four directions, bias/"aya" pattern) with a mating softwood board to produce a uniform micro-texture. Remove large debris.
- Apply PVP: Spray or brush a thin film of PVP in ethanol (1–3% w/v). Allow a short flash period (a few minutes) until the surface becomes slightly tacky; do not fully dry to powder redistribution.
- Disperse abrasive: Evenly sprinkle the α-alumina or DND powder across the lap. Gently tap or brush to distribute. Remove loose excess by light tapping or low-pressure air blow.
- Oil wetting: Using a low-lint pulp wiper with a very small amount of VG10 oil, lightly stroke the lap to create a thin, even film. Avoid puddles — the intent is a slight wetting to soften the contact.
- Touch-up motion: Hold the blade at the working angle +0.5–1° and perform short, light strokes (1&endash;5 passes). Use minimal pressure. In practice, using a lap stroke in a large diagonal (about 15–25° from the blade axis where 0° is parallel to the edge) with two alternating pull directions (pulling the blade across the lap in one diagonal direction, then the opposite diagonal) gives especially clean removal of micro-burrs while avoiding micro-rounding of the apex. Test frequently on scrap or check edge visually/microscopically.
- Inspect & repeat: Verify burr removal and edge sharpness. If needed, repeat steps 2–5 in small increments.
- Clean the lap: Wipe the lap with a VG10-damp low-lint pulp wiper to collect adhered metal particles; follow immediately with a dry low-lint pulp wiper to minimize residual oil.
- Lap recondition: Pair-rub the lap against another softwood board (same grade) in the four-direction bias pattern to dislodge any embedded carbides and restore texture.
- Final cleaning & storage: Repeat oil-damp wipe then dry wipe. Place lap in a thick PE bag with optional silica gel; seal for storage.
Operational notes & parameters
- PVP concentration
- 1–3% w/v in ethanol is a useful starting range. Too thin: powders run; too thick: clumping.
- Oil amount
- Very small ― apply via a wiped cloth; one or two drops across the lap surface is often sufficient for a 100×40 mm area.
- Pressure & strokes
- Minimal pressure; short strokes. Monitor with loupe or microscope after each set.
Safety: Nanopowders and metal swarf are hazardous if inhaled. Use appropriate PPE and local ventilation. Dispose of metal-loaded wipes according to local regulations.
Microscopic checks
- Abrasive distribution uniformity on the lap surface.
- Edge micro-geometry: check for micro-rounding vs retained apex.
- Burr cross-section: cut vs stretched morphology.
This protocol emphasizes repeatability and gentle action; parameters should be adjusted with small, documented trials on scrap blades before use on valuable knives.