Final answer:
To sharpen a saw blade, a triangular file is the best choice as it enables precision and maintenance of the correct angle. This file's shape suits the saw teeth gaps and offers control over the sharpening process.
Step-by-step explanation:
To sharpen the dull edges of a saw blade and achieve the proper angle set, the best tool would typically be a triangular file.
A triangular file is designed with three sharp corners which make it suitable for filing in between the teeth of a saw blade, while maintaining the correct sharpening angles.
Using a triangular file allows for precise control of the sharpening process compared to other tools like a bench grinder, which might remove too much material and damage the saw. It is important to use the file properly, gently pushing it along the edge of the saw teeth, taking care not to apply excessive pressure.