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Putty Knife |
Overview
The Putty Knife's edge is shaped on a belt sander (preferred) or bench grinder.
Side View |
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He could tear up an anvil with a wet noodle. Unknown Shop Teacher |
The leading edge is ground to be straight across, and 90° to the edges. There is no thinning of the leading edge to form a blade (as with a scraper).
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.) |
