A secondary bevel does not have one exact, fixed angle; instead, it is always ground at a steeper angle than the primary bevel. For instance, if a primary bevel is 25 degrees, the secondary bevel would typically be anything from 26 degrees upward.
Understanding Secondary Bevel Angles
A secondary bevel, often referred to as a micro-bevel or microbevel, is a small, slightly steeper bevel applied to the very edge of a tool, such as a chisel, plane blade, or knife. This additional bevel is ground on top of the existing primary bevel. Its primary purpose is to create a stronger, more durable cutting edge that retains its sharpness for longer, while also making subsequent resharpening quicker and more efficient.
The crucial characteristic of a secondary bevel is that its angle must be higher than that of the primary bevel. As an example, if a tool's main cutting edge (primary bevel) is established at 25 degrees, the secondary bevel is typically applied at an angle that is slightly greater, starting from 26 degrees upward. This slight increase in angle at the very apex of the edge provides crucial support.
Why Use a Secondary Bevel?
Incorporating a secondary bevel offers several distinct advantages for tool users:
- Enhanced Edge Durability: The steeper angle at the edge tip provides more material to support the cutting edge, significantly reducing the likelihood of chipping, rolling, or folding, especially when working with tougher materials or during heavy use.
- Expedited Sharpening: When the tool eventually dulls, only the tiny secondary bevel needs to be refined. This saves considerable time and effort compared to regrinding the entire primary bevel and removes less precious material from the tool.
- Optimized Performance: This two-stage bevel allows for a relatively thin primary bevel, which reduces cutting resistance, combined with a robust, long-lasting cutting edge for superior performance.
- Versatility: The angle of the secondary bevel can be adjusted based on the specific application or material, allowing for customization between fine cutting tasks and heavy-duty work.
Common Secondary Bevel Angle Ranges and Examples
While the exact angle is flexible, the principle remains constant: the secondary bevel is always steeper. Here's a general guideline for common applications:
| Primary Bevel Angle | Typical Secondary Bevel Range | Purpose / Application |
|---|---|---|
| 20° | 25° - 30° | Fine woodworking, paring chisels, delicate cuts |
| 25° | 26° - 35° | General-purpose chisels, plane irons, good balance of strength and keenness |
| 30° | 35° - 40° | Heavy-duty chisels, axes, tools for tough materials |
- Note: The specific range for a 25-degree primary bevel, as mentioned, can be 26 degrees upward, depending on the desired durability and application.
How to Apply a Secondary Bevel
Setting a secondary bevel is a straightforward process once the primary bevel is established. Here are the key steps:
- Establish Primary Bevel: Ensure your tool has a well-formed primary bevel at the desired angle (e.g., 25 degrees).
- Increase Angle Slightly: Using a sharpening jig, angle guide, or freehand technique, increase the sharpening angle by a few degrees (e.g., from 25° to 28° or 30°).
- Hone the Edge: Apply this slightly steeper angle to the very edge of the tool on your chosen sharpening medium (e.g., a sharpening stone or strop).
- Form a Micro-Burr: Continue honing until a tiny burr forms along the entire length of the cutting edge on the opposite side. This indicates the secondary bevel has met the other face of the edge.
- Remove the Burr: Finish by removing the burr through careful stropping or very light passes on a fine abrasive at an even slightly higher angle or by honing the back of the tool briefly.
For more detailed guidance on sharpening techniques, including setting bevels, you can explore resources like the Wikipedia article on Sharpening.
