Keeping a sharpening stone perfectly flat and even is fundamental for achieving consistently sharp edges and maintaining the correct blade geometry. An even sharpening stone ensures that the entire edge of your blade makes proper contact, leading to superior sharpness and preventing uneven wear.
Why Stone Flatness Matters
Over time, repeated sharpening creates wear patterns on a stone, typically forming a concave "dish" in the center where most of the work occurs. An uneven stone can lead to:
- Uneven Edges: Blades sharpened on a dished stone will have inconsistent bevels and may not achieve optimal sharpness.
- Difficulty Setting Angles: Maintaining a precise sharpening angle becomes impossible on an irregular surface.
- Ineffective Sharpening: Parts of the blade might not make proper contact with the abrasive, leading to slower and less effective sharpening.
- Damage to Blades: In extreme cases, deep dishes can cause nicks or damage to the blade during sharpening.
The Essential Tool: The Truing Stone or Lapping Plate
The primary tool for flattening a sharpening stone is a truing stone, also known as a lapping plate or flattening stone. These are typically made from harder, more abrasive materials than the sharpening stone itself, such as:
- Diamond Lapping Plates: Often metal plates with embedded industrial diamonds, available in various grits. They are highly effective, durable, and work on virtually any sharpening stone.
- Silicon Carbide Stones: Coarse silicon carbide stones (e.g., 120-220 grit) are excellent for flattening other stones.
- Silicon Carbide Grit on a Flat Surface: Loose silicon carbide abrasive powder can be used on a perfectly flat surface like a piece of thick glass, granite, or a ceramic tile.
Step-by-Step Guide to Flattening Your Sharpening Stone
Here's how to effectively flatten your sharpening stone, ensuring it remains perfectly even:
1. Preparation
- Wet the Stones: Ensure both your sharpening stone and truing stone/lapping plate are thoroughly wet. For waterstones, soak them as usual. For oilstones, apply a generous amount of honing oil. This helps to carry away the abrasive swarf.
- Mark the Stone (Optional but Recommended): Use a pencil to draw a grid pattern or several lines across the surface of your sharpening stone. These marks will act as indicators, disappearing as you grind down the high spots, letting you know where you've been and when the stone is truly flat.
2. The Flattening Process
- Place the Truing Stone: Position your truing stone or lapping plate squarely on top of your sharpening stone.
- Apply Consistent Pressure: Apply light, consistent pressure across the truing stone.
- Use a Circular Motion: Begin moving the truing stone over the sharpening stone. It is highly effective to use a circular motion to wear down your sharpening stone. This motion should be deliberate and systematic.
- Cover All Edges: As you execute these circles, draw the circles with your truing stone in such a way that it hangs over all the edges of the stone as you pass over them. This critical step ensures that the very edges of your sharpening stone receive good contact and are ground down evenly, preventing the formation of a raised perimeter and ensuring it gets good contact with every part of the whetstone.
- Rotate and Distribute: Periodically rotate your sharpening stone 90 or 180 degrees to ensure even wear across its entire surface. Vary your circular motions to cover all areas.
- Monitor Progress: Continue grinding until all the pencil marks you drew earlier have disappeared. This indicates that the surface is now uniformly flat. For heavily dished stones, you might see the marks disappear from the edges first, gradually working towards the center.
- Check with a Straightedge: For ultimate precision, use a metal straightedge to confirm the stone's flatness. Place the straightedge across the stone in various directions; there should be no gaps visible beneath it.
3. Cleaning and Maintenance
- Rinse Thoroughly: After flattening, rinse both stones thoroughly under running water to remove all abrasive slurry and grit.
- Inspect and Store: Inspect your sharpening stone for any remaining imperfections. Store it properly to prevent warping or damage.
Choosing Your Flattening Method
| Method/Tool | Pros | Cons | Best For |
|---|---|---|---|
| Diamond Lapping Plate | Fastest, most durable, works on all stones | Higher initial cost, can be aggressive | Frequent flattening, hard stones, large stones |
| Silicon Carbide Grit/Powder | Very effective, affordable, customizable grit | Can be messy, requires a perfectly flat base | Budget-friendly, specific grit requirements |
| Coarse Silicon Carbide Stone | Good value, effective for most stones | Wears down itself over time, less durable | Regular maintenance, medium-hard stones |
Practical Tips for Longevity and Even Wear
- Flatten Regularly: Don't wait until your stone is deeply dished. Flattening frequently with light passes is easier and extends the stone's life.
- Rotate Your Stone: During sharpening, try to use different areas of your stone. Rotate the blade's position or the stone itself to distribute wear more evenly.
- Use Consistent Pressure: Apply uniform pressure when sharpening to prevent localized wear spots.
- Keep it Clean: Regularly clean your sharpening stone to prevent swarf build-up, which can impede its cutting action and contribute to uneven wear.
By consistently applying these techniques, you'll ensure your sharpening stones remain perfectly flat, providing an optimal surface for achieving razor-sharp edges every time.
