Dull Grading 

Dull grading the condition of a rock bit when it comes out of the hole is an important field operation that is often overlooked.

At many mines, the decision to change the bit is left up to the driller, with very little guidance given.  

This means that most bits get changed after they're completely worn out, and after they have been operating at low efficiency for a length of time.  

The operator can save a great deal of money by establishing a program of close examination and grading of used bits, and by applying some simple rules based on this information.

Collection of Dull Graded Drill Bits

Significantly reduced penetration rate at the end of a bit's life is inevitable when the cutting structure becomes ineffective either through breakage or wear.

Bit grading provides an evaluation of the performance and dulling characteristics of the bit based on the drilling practices used.  When done as a matter of routine, this simple procedure yields data that can significantly lower drilling costs and increase efficiency.

Dull bit valuations can be made quickly, but it is important that this data be gathered by someone with reasonable judgment and accuracy.

Examinations include both the cutting structure and the bearings.  Bit life does not need to be totally exhausted before dull grading.

The purpose of grading is to determine the condition of the dull bit and to assess what is happening to the bit while in use.

In grading a dull bit, its condition is best recorded using a simple but accurate code.  A complete grading chart is here.

Properly graded bits along with a completed bit record of the well drilled is an important part of evaluating a drill bit's performance.  Without this information, knowing what to do to improve performance is, at best, a shot in the dark.

The bottom line:  when properly collected and recorded, data gathered from dull rock drill bits yield exceptionally valuable information about what should be done to correct unprofitable practices, including helping to choose proper bits in the future.

Related Pages:

API Standards:  API standards, including pin sizes for drill bits and acceptable tolerances for rock bits and pdc bits.  

Atlas Copco:  Atlas Copco bit selection guide, examples of shirttail protection, and TCI and steel tooth cutting structure. 

Button Bits:  Button bits offer several advantages over PDC drill bits: they are less expensive and can withstand higher impact.

Drag Bits:  Drag Bits manufactured as one solid piece of alloy steel offer greater durability and reliability.  Available in step and chevron styles for hard rock drilling.

Dull Grading:  Dull grading drill bits is important but often overlooked.  This process provides valuable information for proper bit selection.

IADC:  The IADC classification system for tooth and button bits explained as well as dull grading codes and what they mean.

IADC Classification:  The IADC classification system for PDC bits:  pictures and explanation of what it means and how to use it.

PDC Cutters:  Because of PDC cutters, PDC bits drill sixty-five percent of total footage.  Their shearing action is more efficient than the crushing action of tricones.

PDC Drill Bits:  Available in either matrix or steel bodies, PDC drill bits  offer higher rate of penetration than tricones in many different formations.

Tricones:  With the exception of cutting structure, tricone bits are designed in the same manner regardless of manufacturer. 

Well Completion Bits:  Well completion drill bits from Atlas Copco in both tooth and button bits.  Bear Claw, Hurricane, Aardvark, and PDC diamond mill bits from KC Bit & Supply.

Return from Dull Grading to Types of Drill Bits

Return to Atlas Copco

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