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Screw taps for hard machining

Screw tap for hard thread machining

In order to reliably process hardened steels with a hardness of 48 HRC or higher when thread cutting, a screw tap must have a negative ground chip geometry.

The straight design of the screw taps is made possible by the fact that short chips are produced during thread cutting in hardened steels and the chip does not have to be removed via the geometry on the screw tap. Therefore, there is only one geometry in both blind and through holes.

Learn more about the ATORN screw taps.

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Cutting materials and coating for screw tapping in hardened steel

The ATORN screw taps for machining hard threads in the hardness range of 45–55 HRC use the cutting material HSSE-PM. In the hardness range of 55–65 HRC, however, only ATORN screw taps in the solid carbide version are still functional.

The ATORN screw tap has the greatest effect in the thread cutting of hardened materials in the hardness range of 45–63 HRC with a TiCN coating.


Reinforced core and negative special geometry

Basically, the ATORN screw taps are equipped with a long cut of type D as well as negative chip geometries. The long cut shape D on the screw tap ensures an optimum cut distribution.

Thanks to the multi-tooth technology and reinforced core geometry, a long service life can be achieved. However, one disadvantage of the long cut shape is the large amount of space required by the screw tap in the component.


The process of hard thread tapping - helpful tips

Note the thread depth: Despite the optimisation of the tool geometry, in this hardness range only a maximum thread depth of 1.5 x D can be achieved with ATORN screw taps. If you want to achieve higher thread depths, you can use our ATORN thread milling cutters for this purpose.

Lubrication and cooling: Use a high-quality thread cutting oil when thread cutting. Without such a cutting oil, the process reliability cannot be fully guaranteed.

Cutting speed: You can achieve the ideal service life with our ATORN screw taps for the machining of hardened steel at the following cutting speeds:

  • Screw tap <55 HRC HSSE-PM TiCN 3–5 m/min
  • Screw tap >55 HRC solid carbide TiCN 1–3 m/min.
Core hole optimisation: Screw taps for hard machining must counteract high forces, which is why minimising the cutting forces is very important. A core hole optimisation increases the hole for the screw tap insert. In practice, the dimension is increased by +0.1 mm in the M4-M16 range. In addition, the service life can be optimised in series production by exploiting the upper tolerance limit.