How to sharpen the twist drill

Drilling is a common process in mechanical processing, and twist drill is an indispensable tool, so what are the techniques for grinding twist drill?


First, let’s understand the wear of twist drills:

Wear 1: Chisel edge wear

Wear 2: Flank wear

Wear 3: Landing surface wear

As shown below:



The common top cutting edge shapes of twist drills are:


(1)Cone type, as shown below:


Features and effects:

Grind the flank surface into a conical surface, so the flank angle from the outer circle closer to the center part is larger drill shank adapter;


General use


(2) Plane type, as shown below:



Features and effects:

Grind the second flank face into a flat surface;

Easy to grind;


Mainly used for small diameter drill bits;


(3) Three-sided type, as shown below:



Features and effects:

There is no chisel part, so the centering degree and the expansion of the hole are also small;

Three-sided surface grinding;


Used for drilling with high positioning accuracy;


(4) Helix shape, as shown in the figure below:




Features and effects:

In order to increase the relief angle near the center of the drill bit, an unconventional spiral is formed on the basis of conical surface grinding;

The chisel edge is S-shaped, so it has good centering and machining accuracy;


For high-precision drilling processing;


(5)Arc cutting edge type, as shown below:




Features and effects:

The cutting edge is ground into an arc shape to reduce the cutting load;

Good processing accuracy and surface roughness;

When the through hole is processed, the bottom surface changes little;


For cast iron and light alloy; For cast iron plate; Steel;


(6)Candle type, as shown below:




Features and effects:

The cross-section is in the shape of a candle, so the centering degree is good, and the impact is small when the drill is cut out;


For thin plate drilling processing;


Sharpening of the chisel edge:

The rake angle of the cutting edge of the drill is smaller as it approaches the center of the drill, and the rake angle is negative at the chisel edge..During cutting, the center part squeezes the material, and the cutting resistance generated accounts for 50%-70%. The cross knife grinding is very effective in reducing the cutting edge of the drill, discharging the chips generated in the chisel edge part, and improving the machinability..


(1)XType, as shown below:




The axial load is greatly reduced and the penetration is improved.Effective when the core diameter is large;


General processing, deep hole processing;


(2) XR type, as shown below:



The penetration is slightly worse than that of the X type, but the cutting edge strength is high, the work piece material has a wide application range, and the service life is long;


General processing, stainless steel processing;


(3)SType, as shown below:





Easy to grind, generally used more;


General processing of steel, cast iron and non-ferrous metals;


(4)NType, as shown below:




Effective when the core diameter is large;


Deep hole processing; 

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