Dulling Characteristics

Possible Problems

Possible Corrective Actions

Broken Inner inserts

1 . Too Much Weight on Bit

2. Too Soft of a Bit

1. Reduce Weight on Bit

2. Select a Harder Bit

Broken Gage Inserts

1. Too High Rotation Speed

2. Too Soft of a Bit

1 . Reduce Rotation Speed

2. Select a Harder Bit

Worn Inserts

(Flat Crested Wear)

1 . Too Hard of a Bit

2. Too High Rotation Speed

3. Not enough Weight on Bit

1 . Select a Softer Bit

2. Reduce Rotation Speed

3. Increase Weight on Bit

Lost Inserts

(Gage/NTG)

1. Erosion due to Over-drilling

2. Erosion due to “Air-Blast”

1 . Reduce Weight on Bit

2. Increase Rotation Speed

3. Increase Nozzle Size

Worn Bearing

1. Low Air Volume to Bearings

2. Too much Weight on Bit

3. Plug Air Passages

1. Check System for Leaks.

2. Check Compressor Output

3. Check bit Clogged Air Tubes

4. Reduce Nozzle Size

5. Reduce Weight on Bit

Bit Body Erosion

1. Too High Air Volume

2. Hole Cave-In (Back Ream)

1. Reduce Compressor Output

2. Select a Back Reaming Bit

Worn Shirttail

1. Failing to Clear Cutting

2. Bit Worn Undersize

1 . Check Compressor Output

2. Reduce Rotation Speed

3. Reduce Water Injection Rate

Single Worn Shirttail

(On one Lug)

1. Bent Drill Pipe

2. Cross Threaded Bit

1. Check Drill String

2. Inspect Bit Connection

Grooves Formed Between Inserts

(Same Row)

1. Over Drilling

2. Too Hard of a Bit

1 . Reduce Weight on Bit

2. Increase Rotation Speed

3. Select a Softer Bit