Taps - Gating forms
The chamfer is the beveled area at the tip of the cutting part at Gewindebohrer de. In this area, the thread teeth are not yet fully formed, but only gradually reach the full diameter and the desired shape. The lead is defined by its length. The number of thread turns over which the lead extends is specified.
The thread teeth in this area do all the cutting work when cutting threads, the other thread teeth are only used for guidance. This also means that the individual lead teeth must be able to withstand the greatest load. Choosing the right lead shape for a specific cutting application is the basis for both good results and optimum tool life, and therefore for good efficiency in thread cutting.
The lead forms for taps are standardized according to DIN 2197. A distinction is made between six lead shapes, which are marked with letters from A to F. Form A stands for the longest lead with 6 to 8 threads, while form F is extremely short with 1 to 1.5 threads. This shape is a special gate that is only used in exceptional cases in practice.
Which chamfer shape is the right one depends on the type of core hole and the material. Shorter lead shapes are suitable for blind holes that do not go through the workpiece but end in the material. Through holes can also be machined with very long gates. Although this reduces the load on the individual gate tooth, it also increases the required torque.
The type of flute is also closely linked to the lead shape. Shape A always has straight flutes, shape B straight flutes with a peel cut, which rolls the chip tightly and guides it in the cutting direction. Shapes C to F can have straight flutes or helical flutes.
Form A
- long: 6 - 8 courses
- straight grooved
- for short through holes
Form B
- medium: 3.5 - 5.5 threads
- straight fluted with skiving cut
- for through holes in medium and long-chipping materials
Form C
- short: 2 - 3 courses
- straight fluted and spiral fluted
- for blind holes in medium and long-chipping materials
- for through holes in short-chipping materials
Form D
- medium: 3.5 - 5 gears
- straight grooved and helix angle 15°
- for blind holes with long thread run-out
- for short through holes
Form E
- extremely short: 1.5 - 2 gears
- straight grooved and helix angle 15
- for blind holes with very short thread run-out
Form F
- extremely short: 1 - 1.5 grooves
- straight grooved and spiral grooved
- for blind holes with very short thread run-out
- Avoid as far as possible
Note:
Short chamfer produces thread depths close to the bottom of the hole.
Long chamfer reduces the load on the cutting edges (recommended for materials with high strength)
Long chamfer increases the required torque.