Carbide

The guide bushing supports the gun drill at the entry point of the workpiece. It prevents the drill from whipping or deflecting during the first few millimeters of engagement, which are the most critical for hole straightness. I have spent years selecting and maintaining guide bushings for different applications, and the right bushing choice is one of the most important tooling decisions in deep hole drilling. Guide Bushing Material Selection The most common bushing material is hardened tool steel, typically A2 or D2 tool steel hardened to 58 to 62 HRC. It provides good wear resistance at moderate cost. For high production or abrasive materials, I use carbide bushings. For soft materials where marking is a concern, I use bronze bushings. ...

I use carbide for production and HSS for prototypes. That rule of thumb has served me well across hundreds of jobs, but the real answer depends on material, volume, hole geometry, and your shop’s tolerance for risk. Gun drills are made from either carbide or high-speed steel. Each has distinct advantages, and picking the wrong one costs time and broken tools. Here is what I have learned from running both in production. ...

I use TiAlN-coated carbide for steel and DLC for aluminum. That combination covers about 80% of what I drill. The tool material and coating are critical for gun drill performance. Get the combination wrong and the drill wears fast, holes drift, or surfaces come out rough. I have tested enough bad combinations to have a strong opinion on what works. Tool Material Options Carbide Grades Most gun drills use carbide. It offers the best balance of wear resistance and toughness. ...