Which tool or method is advised against using for sharpening shear dies?

Using mechanical devices to sharpen shear dies is advised against because these tools can remove material too aggressively and may lead to an uneven edge or even damage the die. Shear dies require precise geometry and a sharp edge to ensure they function correctly during operation. Mechanical devices may not provide the level of control needed to maintain the necessary tolerances and surface finish that are critical for effective cutting.

On the other hand, hand filing and light grinding are generally acceptable methods for sharpening shear dies, as they allow for more precise adjustments and refinements in the edge profile. This precision is crucial in maintaining the integrity and performance of the shear dies, as a well-sharpened die contributes significantly to the quality of the cut and the lifespan of the tool.