An SP tap, commonly known as a spiral point tap or sometimes a "gun tap," is a specialized type of thread-cutting tool engineered to efficiently create internal screw threads in through-holes. Its distinctive design focuses on driving chips forward out of the workpiece, preventing chip accumulation in the flutes.
Understanding the Spiral Point Tap Design
The design of an SP tap is ingeniously simple yet highly effective for specific tapping operations. It is fundamentally a straight flute tap, but what sets it apart is a unique gash located at its front. This gash is ground at a diagonal angle to the straight flutes and is strategically positioned at the cutting chamfer of the tap. This particular geometry is responsible for its exceptional chip evacuation capabilities.
Key design elements include:
- Straight Flutes: Unlike spiral flute taps, the flutes run straight along the tap body.
- Spiral Point (Gash): The defining feature, this angled cutting edge at the tap's nose "shoots" chips forward.
- Cutting Chamfer: Where the gash is located, facilitating the initial thread cutting and chip formation.
This design ensures that as the tap cuts, the chips are curled and propelled ahead of the tap, through the unthreaded portion of the hole and out the other side.
How SP Taps Work
When an SP tap begins to cut, the spiral point design engages the material. The unique angle of the cutting edge at the point creates a shearing action that curls the material into a tight, manageable chip. Instead of accumulating in the flutes, these chips are pushed forward by the tap's rotation and the gash's geometry. This continuous forward chip evacuation is crucial for maintaining a clean cutting action and preventing chip interference.
For a visual understanding of tap geometries, you can explore detailed diagrams here.
Key Advantages of Using SP Taps
SP taps offer several significant benefits, particularly in high-production environments and specific material applications:
- Efficient Chip Evacuation: The primary advantage is the forward chip removal, which prevents chip packing, a common issue with other tap types.
- Reduced Tap Breakage: By eliminating chip accumulation in the flutes, less torque is required, significantly reducing the risk of tap breakage, especially in hard materials.
- Faster Tapping Speeds: The clear chip path allows for higher cutting speeds and feeds, boosting productivity.
- Improved Thread Quality: Less interference from chips results in cleaner, more accurate threads with better surface finish.
- Better Coolant Flow: The straight flutes and clear chip path allow coolant to reach the cutting zone more effectively, aiding in cooling and lubrication.
Common Applications
SP taps are the preferred choice for a wide range of industries and materials, primarily for through-hole applications where chips can exit the bottom of the hole.
Typical applications include:
- Automotive Manufacturing: For creating threads in engine blocks, chassis components, and other parts where through-holes are common.
- Aerospace Industry: Precision threading in light alloys and steels where chip management is critical.
- General Machining: Ideal for production runs in materials like steel, stainless steel, cast iron, and aluminum.
- Fixture and Tooling Production: Used for creating fastening points in various jigs and fixtures.
- Electronics Enclosures: Threading in metal casings for mounting components.
SP Tap vs. Other Tap Types
To further understand the role of SP taps, it's helpful to briefly compare them to other common tap types.
| Feature / Tap Type | SP Tap (Spiral Point) | Spiral Flute Tap | Hand Tap (Straight Flute) |
|---|---|---|---|
| Chip Evacuation | Pushes chips forward | Lifts chips upward | Collects chips in flutes |
| Hole Type | Through-holes | Blind holes | Through & Blind (general) |
| Strength | Very strong | Strong | Good |
| Cutting Action | Aggressive, fast | Smooth, controlled | General purpose |
While SP taps excel in through-holes, spiral flute taps are designed to lift chips out of blind holes, and standard hand taps (with straight flutes) are general-purpose tools suitable for both but may struggle with deep holes or certain materials due to chip packing.
Choosing the Right SP Tap
Selecting the appropriate SP tap involves considering several factors:
- Workpiece Material: Choose taps with coatings (e.g., TiN, TiCN, AlTiN) and geometries optimized for the specific material's hardness and abrasiveness.
- Hole Diameter and Depth: Ensure the tap size matches the pre-drilled hole.
- Machine Type: SP taps are well-suited for machine tapping due to their robust design and chip evacuation.
- Coolant System: An effective coolant delivery system is vital to maximize tap life and thread quality.
By understanding the unique design and advantages of the spiral point tap, machinists can significantly improve efficiency, reduce tool wear, and achieve higher quality threads in appropriate applications.
