An optimised cutting geometry for universal use in a wide range of materials allows customers the opportunity to significantly reduce their tap stock usage, according to supplier Iscar.

Normally, taps are the easiest and most convenient tools for threading holes. When using a tap, generally no special operator skills are necessary. The cycle time is very short compared to the mill-thread tool, and the tool prices are very attractive.

Ensuring the best threads means picking the correct tap

In order to achieve proper thread quality, shops have to take several factors into account.

At the very first stage of choosing the correct tap, we must determine the application type. Basically there are several popular tap geometries which refer to specific applications:

• Gun-point type: used on through-hole applications. The left spiral on the lead of the tap pushes the chips forward and creates a smooth cutting process. Shallow flutes ensure optimised tap rigidity and strength, as well as good lubrication flow.

• Straight flute type: used on through and blind hole applications as well. Suitable for short chip materials.

• Spiral flute type: used on blind hole applications. The helical flute ensures correct chip flow direction, which is out of the hole, providing a smooth cutting process and eliminating the chips stacking on the tool or the bottom of the hole. (See Figure 1 in photo gallery.)

• Cold forming type: this type differs from cutting taps. The thread is created by plastic material deformation. There are no chips created from the machining process. This type can be used on materials with tensile strength not exceeding 1200n/mm2.

• In the second stage, the material to be machined is key. This will guide the correct tap surface treatment and coating:

• TiN coated: the TiN coating has a hardness of approximately 2,300HV and is temperature resistant up to 600C. This makes it an excellent coating for general applications.

• Steam tempered: the steam tempered has a Fe3O4-oxyd-coating, which reduces the friction between the tool and the workpiece and prevents cold welding.

• Nitrated: recommended surface treatment for machining hard wear/abrasive materials such as grey iron, aluminum alloys with high silicon percentage (more than 10%).

• For example, to machine a stainless steel part, we need a gun-point tap made of HHS-E high cobalt HSS steel with a steam tempered treatment. On the other hand, for machining grey iron we will need a straight flute tap with nitrating treatment.

The compete article can be accessed online at http://www.etmm-online.com/machining_accessories_cutting_tools/articles/435638/

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