A-SFT-SUS

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Spiral flute tap for stainless steel

Keita Ono | OSG Corporation Product Development Engineer

Unstable chip evacuation is the leading cause of tapping issues. OSG’s high‑performance, multi‑purpose A‑Tap series delivers excellent chip evacuation while accommodating a wide range of work materials. However, the high ductility of stainless steel makes chips difficult to break, frequently resulting in chip entanglement that can cause tap breakage or poor internal thread accuracy.

To address these challenges, OSG developed the A‑SFT‑SUS spiral flute tap for stainless steel. Designed to deliver stable machining and higher productivity when tapping stainless steel, the A‑SFT‑SUS is available in seven sizes from M3 to M12 and was launched in March 2026.

Chip Entanglement: A Key Challenge in Stainless Steel Machining

Stainless steels—particularly SUS304 and SUS316—are highly ductile and tend to form long, continuous chips. During tapping, these chips can wrap around the flutes or shank, leading to tap breakage or dimensional inaccuracies (Figure 1).

Figure 1. Example of chip entanglement during tapping.

Removing tangled chips often requires machine stoppages, making chip entanglement one of the primary obstacles to efficient and automated tapping operations. To overcome this issue, the A‑SFT‑SUS incorporates the following optimized design features.

Flute Geometry Optimized for Stainless Steel

The A-SFT-SUS’ flute geometry has been specifically optimized to match the cutting characteristics of stainless steel. This design enhances chip evacuation, promotes smooth chip flow and significantly reduces chip entanglement.

Optimized Shank Length

When long chips collide with the holder face, chip flow becomes unstable. The A-SFT-SUS’ optimized shank length helps stabilize chip movement and suppress chip entanglement, improving overall machining efficiency (Figure 2).

Figure 2. A-SFT-SUS’ smooth chip evacuation mechanism improves productivity.

Dramatic Reduction in Machine Downtime Machine stoppages were evaluated using an A‑SFT‑SUS M8×1.25 tap to machine 500 holes at a depth of 2D in SUS316, compared with a conventional tap (Figure 3).

Figure 3. Comparison of chip entanglement frequency.

The A‑SFT‑SUS recorded seven stoppages, while the conventional tap experienced 20 stoppages, representing an approximate 65% reduction in machine downtime.

Chip entanglement often creates a negative cycle of machine stoppage, manual chip removal and restart. Reducing stoppages directly improves operational efficiency and supports automation.

Outstanding Tool Life

Improved durability reduces tool replacement frequency, contributing to greater productivity and labor savings. Figure 4 compares tool life when machining SUS316.

Figure 4. Tool life comparison in SUS316.

The A‑SFT‑SUS continued machining beyond 2,000 holes, while the conventional tap broke after 498 holes, demonstrating a fourfold or greater improvement in tool life.

Cutting Data

SUS304 (Vertical Machining Center)

Figure 5. The A‑SFT‑SUS demonstrates consistently high durability.

SUS304 (Horizontal Machining Center)

Figure 6. Even on a horizontal machining center, the A‑SFT‑SUS suppresses chip jamming and edge chipping, remaining usable after 1,000 holes.

SUS316 (Vertical Machining Center)

Figure 7. Stable, high durability is achieved even with the small M4×0.7 size.

Pilot Hole Diameter and Recommended Cutting Conditions

Because stainless steel generates tough, difficult‑to‑control chips, the pilot hole diameter should be set as large as permitted by the internal thread specification.

Typical examples:

  • M6 × 1: Recommended pilot hole Ø5.1 mm
  • M10 × 1.5: Recommended pilot hole Ø8.6 mm

Recommended cutting speed: 5–10 m/min

Conclusion

The A‑SFT‑SUS delivers clear, measurable benefits for customers machining stainless steel.

Key advantages include:

  • Reduced machine stoppages
  • Less manual chip removal
  • Improved machining stability and productivity
  • Extended tool life, reducing tool consumption

By delivering these benefits, the A‑SFT‑SUS supports labor savings and reduced environmental impact, making it an ideal solution for sustainable, high‑efficiency stainless steel machining.

For more information on OSG’s A-SFT-SUS spiral flute tap for stainless steel