Diamond Drill Bit Selection Chart

Drill Bit Designations

G12, G14 & G15 Very tough, free cutting, high-quality diamond grit, high concentration,and high penetration rates obtainable.
G11 & G10 Very tough, free cutting, high-quality diamond grit, high concentration, and very good penetration rates obtainable.
G9  & G8 Tough, free cutting, good-quality diamond grit, high concentration, and very good penetration rates obtainable.
G7  Tough, reasonably free cutting, good-quality diamond grit, medium to high concentration, and good penetration rates obtainable.
G6 Medium hard, reasonably free cutting, good-quality diamond mixed grit, medium concentration, and reasonable penetration rates obtainable.
G5 Hard soft tough fairly free cutting, good-quality diamond grit, low concentration, and reasonable penetration rates obtainable.
G2 & G4 Hard, fairly free cutting, reasonable-quality diamond grit, low concentration, and lower penetration rates obtainable.
G1 Very hard matrix, good-quality diamond grit, high concentration, and lower penetration rates obtainable.

 


Selection Chart

 

Click on image to enlarge.

 

Notes: 

As a simple guide, the harder the rock type ie: the closer it approaches 10 on the Mohs scale, the higher the series of drill bit should be used. It must be recognised, however, that many other factors affect the selection and use of the series drill bit.

  • Diamond size:  General rule of thumb, the harder the rock, the smaller the diamonds. Smaller diamonds should not be specified for drilling badly broken ground.
  • Number of diamonds is a very important factor in determining how well a drill bit will cut smaller diamonds. higher concentration = more cutting points.

 

In-hole Drill Bit Sharpening 

This can be done in various ways:

  1. Reduce the flushing volume to retain the cuttings at the drill bit face for a longer period.
  2. Reduce the RPM whilst maintaining weight on the drill bit until penetration increases.
  3. Increase the weight on the drill bit whilst maintaining the RPM. 

ALL THE ABOVE IN-HOLE SHARPENING TECHNIQUES MUST BE CARRIED OUT BY COMPETANT DRILLERS TO AVOID DAMAGING OR BURNING IN THE DRILL BIT

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