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Spear Point Tool |
Side view |
Top View |
The Spear Point Tool's cutting edge is sharpened using a platform jig such as the Tormek SVD-110.
SVD-110 Platform Jig |
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General Guidelines |
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Angle |
Recom. |
Comments |
| α1 | 40° |
click on the gray block to see more I've measured angles on tools in the range 35° to 80°, but 40° works well for me. |
| α2 | 40° |
The top angle needs to be <90° so that the tool can be used as a scraper for corners, though I've measured angles on tools which range from 60° - 95°. |
If grinding this on a high speed grinder or sander, be sure to manage the temperature so that the temper is not lost due to overheating.
| High Carbon Steel |
Temperature control is critical for high carbon steel. Tempering will be lost in the steel if heated until it is blue (~550°F / 300°C). Cool by dipping as needed in water. Dr. Larrin Thomas noted in his book, Knife Engineering: Steel, Heat Treating, and Geometry (2025), The lack of sparks or color changes is no guarantee that the edge was not overheated. Therefore, sparks are not necessarily a sign that heat has or has not been generated in the steel. Color changes can occur from overheating of steel in grinding, but during grinding, the surface is being removed, and the affected volume can be relatively small. Therefore a color change is not always observed. Microhardness measurements of edges sharpened with a belt sander show a drop in hardness at edge. This results from “over-tempering” the edge by heating it above its original tempering temperature. |
| High Speed Steel |
Cool by dipping as needed in water. |
| Steel with Carbide Insert |
DO NOT cool by dipping in water. This will cause the carbide to crack due to shocks.
It is also recommended to use a high grit wheel for sharpening carbide as lower grits can cause cracks in the edge leading to it being far more crack-ridden and brittle. (Lower grits can be used for shaping the edge -- see also, Grindstones and Other Sharpening Media - Quick Selection Guide.) |
