AD-MICRO

Advanced small diameter carbide drill for stable, high-precision machining

Seiya Uchida | OSG Corporation Product Development Engineer (Drill Division)

On July 23, 2025, OSG Corporation unveiled its latest A Brand innovation: the AD-MICRO, a small diameter solid carbide drill designed for exceptional precision, durability and versatility. Building on the legacy of the WX-MS-GDS and MRS-GDL series, the AD-MICRO introduces a significantly expanded lineup and enhanced performance across a wide range of materials and machining environments.

Expanded Product Lineup

The AD-MICRO series is available in two length variations: 4D and 10D, with diameters ranging from Φ0.5 to Φ3.0 in 0.01 mm increments. This fine gradation enables precise hole adjustments and optimized pilot hole preparation. With 502 items in total, the lineup represents a more than 1.5-fold increase over the 316 items offered in previous models, providing users with greater flexibility and control.

Precision Engineering

Engineered for high-accuracy machining, the AD-MICRO features a coated cutting diameter tolerance of 4 μm and a shank diameter tolerance of 3 μm. Combined with the 0.01 mm increment lineup, this precision ensures consistent hole quality and minimizes variation, even in complex small-diameter applications.

Versatility Across Materials

The AD-MICRO series was developed with a focus on stable, uninterrupted machining of stainless steel. While previous models could process stainless steel, challenges such as sudden chipping and tool breakage persisted, especially in external coolant environments involving small diameter and deep-hole drilling. To address this challenge, OSG completely redesigned the flute and cutting edge geometry, resulting in a new drill shape that offers superior resistance to breakage and chipping. This newly engineered geometry also improves rigidity at the cutting edge and enhances overall tool strength, making the AD-MICRO suitable for a wide range of materials, including carbon steel, hardened steels and titanium alloys that demand high wear resistance.

Advanced Cutting Edge Design

Machining stainless steel presents unique challenges due to its low thermal conductivity and tendency to work harden, which concentrates heat and stress at the cutting edge. Its ductility also increases the risk of adhesion and edge damage. To counter these effects, all sizes of the AD-MICRO series feature cutting edge honing—a chamfering process that strengthens the edge and reduces chipping (figure 1).

Figure 1. Front view and structural diagram of the AD-MICRO.

While honing improves durability, it can reduce sharpness and bite. To maintain cutting performance, OSG applies thinning across all sizes. Thinning shortens the chisel edge and introduces a rake angle, improving bite, reducing thrust and enhancing chip evacuation. Despite the technical difficulty of applying thinning to small-diameter tools, AD-MICRO achieves stable thinning down to Φ0.5 mm, enabling high-precision, uninterrupted machining.

Shoulder Edge Guard (SEG)

As illustrated in figure 1, the AD-MICRO drill incorporates SEG to the outermost edge of the drill tip. SEG stands for Shoulder Edge Guard, a technique designed to suppress chipping at the drill’s shoulder. During machining, cutting speed (Vc) is calculated as: Vc = (π × DC × n) / 1,000, where Vc is the cutting speed in meters per minute, D is the drill diameter in millimeters, and n is the spindle speed in revolutions per minute. This formula shows that cutting speed is zero at the drill’s center and highest at its outer edge—where heat and stress are most concentrated. This makes the outer edge especially vulnerable when machining tough materials like stainless steel. While honing helps, the intersection of the honed surface, margin and relief areas remains a weak point. SEG addresses this by applying a precisely controlled micro-chamfer, enhancing edge rigidity without compromising sharpness or increasing machining load.

KeptA Coating

Coating plays a critical role in enhancing a drill’s wear resistance, heat resistance, and surface lubricity. The AD-MICRO features KeptA coating, a proprietary solution developed by OSG for small-diameter machining. As shown in figure 2, KeptA offers a smooth film surface and strong adhesion to the carbide substrate, promoting efficient chip evacuation and minimizing delamination. Its superior wear and heat resistance contribute to extended tool life. Uniform coating thickness is also critical for maintaining drill precision. KeptA’s smoothness and consistency enable accurate diameter control, ensuring reliable performance in demanding applications.

Figure 2. Surface coating comparison between the AD-MICRO and a conventional product. KeptA is a registered trademark of OSG Corporation.

Cutting Data Figure 3 compares tool life between the AD-MICRO 4D and a conventional OSG drill during SUS304 machining on a CNC automatic lathe. The conventional tool showed early edge chipping and significant adhesion, while the AD-MICRO exhibited no notable damage and delivered stable, long-lasting performance.

Figure 3. Machining data for SUS304.

Figure 4 presents a comparison between the AD-MICRO 10D and a competitor’s product during SCM440 machining on a vertical machining center. The AD-MICRO demonstrated excellent stability and performance not only in stainless steel but also in materials requiring high wear resistance.

Figure 4. Machining data for SCM440.

Conclusion

The AD-MICRO series expands machining possibilities through its comprehensive lineup, broad material compatibility and high tool precision. Its stable chip formation and durability support unmanned operations, such as those on automatic lathes. As OSG’s latest A Brand small diameter carbide drill, the AD-MICRO is engineered to deliver optimal performance across demanding applications.

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