1. ROLLING CUTTER BITS Rolling Cutter Bits
Steel Tooth (milled tooth)
Carbide Tooth (tungsten carbide insert)
Introduced in 1909 by Howard Hughes
2 - cone bit
Not self-cleaning

2. Tungsten Carbide Insert Bit
Milled Tooth
Bit

3. ROLLING CUTTER BITS
The three-cone rolling cutter bit is by far the most common bit
Large variety of tooth design and bearing types
Maximum use is made of limited space
Cone offset to stop rotating periodically to scrape the hole like (PCD) bits
It increases drilling speed but tooth wears faster. (4 for soft, 0 for hard)

4. ROLLING CUTTER BITS
Shape of teeth: long widely spaced steel teeth are used for drilling soft formations
As the rock type gets harder the tooth length and cone offset must be reduced to prevent tooth breakage
Tooth action = Scraping and twisting
Zero offset cones action = Crushing
Smaller tooth allows more room for the construction of stronger bearings

5. Classification of Tricone Bits
(a) Milled tooth cutters
(b) Tungsten carbide insert cutters
Hard facing on one side of the tooth allows self sharpening
Chipping tends to keep tooth sharp
Intermeshing is advantageous.
Heel teeth = outer-raw very difficult job it wears it leads to out of gauge bit (hole)

6. Example tungsten carbide insert cutter used in rolling cutter Bits

7. ROLLING CUTTER BITS Improvements 3 - cone bit (straighter hole)
Intermeshing teeth (better cleaning)
Hard-facing on teeth and body
Steel Tooth (milled tooth)
Carbide Tooth (tungsten carbide insert)
Change from water courses to jets
Tungsten carbide inserts
Sealed bearings
Journal bearings

8. ROLLING CUTTER BITS Advantages
For any type of formation there is a suitable design of rock bit
Can handle changes in formation
Acceptable life and drilling rate
Reasonable cost

9. Proper bottomhole cleaning is very important
Fluid flow through water courses in bit

10. Fluid flow through jets in the bit (nozzles)

11. ROLLING CUTTER BITS Milled Tooth Bit (Steel Tooth)
Long teeth for soft formations
Shorter teeth for harder formations
Cone off-set in soft-formation bit results in scraping gouging action
Self-sharpening teeth by using hard-facing on one side
High drilling rates - specially in softer rocks

12. Milled Tooth Bit (Steel Tooth)

13. ROLLING CUTTER BITS Tungsten Carbide Insert Bits
Long life cutting structure in hard rocks
Hemispherical inserts for very hard rocks
Larger and more pointed inserts for softer rock
Can handle high bit weights and high RPM
Inserts fail through breakage rather than wear
Tungsten carbide: very hard, brittle material

14. Tungsten Carbide Insert Bits

15. Roller Cone Bearings

16. Bearings Ball Bearings (point contact) Roller Bearings (line contact)
Journal bearing (area contact)
Lubrication by drilling fluid or . . .

17. Bearings Sealed Bearings (since 1959) Journal Bearings (area contact)
Grease lubricant (much longer life)
Pressure surges can cause seal to leak! Compensate?
Journal Bearings (area contact)
Wear-resistant hard surface on journal
Solid lubricant inside cone journal race
O - ring seal
Grease

18. Grading of Dull Bits How do bits wear out?
Tooth wear or loss
Worn bearings
Gauge wear

19. Grading of Dull Bits How do bits wear out?
Steel teeth - graded in eights of original tooth height that has worn away
e.g. T3 means that 3/8 of the original tooth height is worn away

20. Grading of Dull Bits Broken or Lost Teeth
Tungsten Carbide Insert bit
e.g. T3 means that 3/8 of the inserts are broken or lost

21. Grading of Dull Bits How do bits fail?
Bearings: B3 means that an estimated 3/8 of the bearing life is gone
Balled up Bit
Cracked Cone

22. Grading of Dull Bits How do bits fail?
Washed out Bit
Lost Cone

23. Grading of Dull Bits How do bits wear out?
Gauge Wear:
Bit is either in-Gauge or out-of-Gauge
Measure wear on diameter (in inches), using a gauge ring
BIT
Examples:
T3 – B3 - I
T5 – B /2
GAUGE RING