The Influence Of The Length Of The External Edge Of Gun Drill On The Roughness Of The Hole
Jan 25, 2019

The grinding angle of the gun drill has a great influence on the quality of the inner hole. However, in some special situations, the change of the length of the cutting edge inside and outside the gun drill will play a leading role in the quality of the inner hole. An example is given below.

1. Workpiece information

Workpiece material: Q235, hot rolling state;

Workpiece outline size: φ20 (outer diameter)*100 (length)

Machining inner hole size: φ10×90

Machining Requirements:  Hole Accuracy 10 0.025; Roughness: Ra0.8

Machining Machine Tool: ZSK2115*500*4


Second: The influence of tool edge change on machining quality

  1. Standard gun drill: φ10standard angle gun drill with equal length of inside and outside edges, TiN coating (see figure below)


    Machining effect: The roughness of inner hole is very poor and scratches are serious. The size consistency is very poor, the inner hole is strong and the size range is about 0.1 mm.

    See the following effect chart:


    See Part Section Photo:


    Long Outer Edge Gun Drill: External Edge Length is Super Long, Length is about 1/3D, TiN Coating (see figure below)


    When processing, the same parameters such as speed, tool amount and oil pressure are adopted, but the processing effect is greatly improved.

    Machining effect: Inner hole roughness: Ra0.4-Ra0.8

    The dimension consistency is good, the dimension range is about 0.02mm, and the linearity of the inner hole is very good.


    In conclusion, in the processing of some low carbon steel with low carbon content, the use of long external edge gun drills can significantly improve the processing quality of inner holes. Roughness and dimensional accuracy requirements can be considered for use.

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