How to do the classification of Screw Taps?
Classification of Screw Taps
1. By Driving Method: Hand-operated screw taps and machine-mounted screw taps
2. By Processing Method: Cutting screw taps and roll-form (extrusion) screw taps
3. By Processed Thread Type: Metric coarse-thread screw taps, metric fine-thread screw taps, pipe-thread screw taps, etc.
4. By Shape: Straight-flute screw taps, spiral-flute screw taps, and spiral-point screw taps
5. By Tapping Direction: Right-hand thread screw taps (for clockwise threading) and left-hand thread screw taps (for counterclockwise threading)
Straight-Flute Screw Taps
Straight-flute screw taps offer the best versatility and maximum rigidity among common screw tap types. Therefore, they are the first choice for processing materials with high hardness (e.g., quenched steel with a hardness of over 40HRC) and materials that produce powder-like chips (e.g., cast iron and cast aluminum).
Spiral-Flute Screw Taps
Spiral-flute screw taps are particularly suitable for processing **blind-hole threads** (also known as blind holes), as chips are discharged upward during processing. Due to the helix angle, the actual cutting rake angle of the screw tap increases as the helix angle becomes larger.
Experience shows:
– When processing high-hardness materials, a smaller helix angle (usually around 30 degrees) is preferred to maintain the screw tap’s rigidity and extend its service life.
– When processing non-ferrous metals (e.g., copper, aluminum, magnesium, zinc) with lower hardness, a larger helix angle (usually around 45 degrees) is recommended to enhance cutting sharpness and improve chip discharge.
Tapered-Flute Screw Taps
During threading, chips are discharged forward, making tapered-flute screw taps the top choice for processing through-hole threads. In design, an oblique cut is made at the cutting edge of a straight-flute screw tap using a grinding wheel—this means the rigidity of tapered-flute screw taps is comparable to that of straight-flute screw taps.
Roll-Form (Extrusion) Screw Taps
Unlike the previous three types of cutting screw taps, roll-form screw taps create internal threads in pre-drilled holes through **plastic deformation of the material** (via extrusion molding). For this reason, they are not suitable for processing overly hard materials.
Key Advantages
No chips are generated during processing, which eliminates approximately 90% of common processing issues (e.g., chip clogging or damage to thread surfaces caused by chips).
Limitation
Due to the extrusion molding process, fine grooves form on the top of the internal thread teeth. Thus, roll-form screw taps are not suitable for applications requiring high airtightness (e.g., threaded holes in pressure vessels or fluid pipelines).
