The optimal angle for a flint to strike steel to produce a good spark while retaining as much of the flint's edge as possible typically falls between 45 to 60 degrees.

• 45 to 60 Degrees: This angle allows for sufficient friction to shear off small particles of steel, which oxidize rapidly upon contact with the air, producing a spark. At this angle, the force applied is enough to create a spark without unnecessarily blunting the flint too quickly.

Tolerances:

• Too Shallow (Less than 45 degrees): If the angle is too shallow, the flint might not create enough friction with the steel, resulting in weak or no sparks. Also, the flint might skip off the steel rather than scraping it effectively.

• Too Steep (More than 60 degrees): If the angle is too steep, the flint will dull quickly because the force is concentrated more directly into the flint, causing it to wear down faster. This setup might also reduce the efficiency of spark production.

Edge Retention: To maximize the flint's edge retention:

• Material Quality: Use high-quality flint or synthetic alternatives like agate or ceramic, which are harder and retain their edges longer.

• Technique: Apply consistent, controlled pressure when striking. A sudden, hard strike can chip or significantly dull the flint's edge. A lighter, controlled strike can help in maintaining the edge for longer.

• Angle Adjustment for Different Steels: The hardness of the steel can affect the optimal angle. Harder steels might require a slightly different angle, but generally, staying within the 45 to 60-degree range will work well for most situations.

• Practice and Experimentation: The exact optimal angle might also depend on the specific flint and steel combination you're using, so some experimentation might be necessary to find the perfect balance for your setup.