Operating Parameters: Bit Load
for Geotechnical Core Bits
The types of geotechnical core bits that are discussed in this technical data sheet include:
 Surface-set diamond (natural),
 TSP – Thermally stable polycrystalline diamond (synthetic),
 PDC – Polycrystalline diamond compact (synthetic) – also known as “Pax-set”,
 Saw tooth tungsten-carbide,
 “Carbide-chip” tungsten-carbide.
Bit load requirements for surface-set diamond bits
The maximum bit load or “weight-on-bit” (WOB) to be applied to a surface-set diamond bit is calculated by
multiplying the number of diamonds set on the bit face by a maximum load factor. The relationship between the
maximum load factor and the diamond size / diamond grade are illustrated in the table below:
DIMATEC
Diamond Size Range
4/5 SPC*
6/8 SPC
10 SPC
15 SPC
25 SPC
50 SPC
Maximum Load per Diamond Crystal
as a function of DIMATEC Natural Diamond Grade
Grade AA
Grade P2
Carbonado Grade
6.8 lbs
4.3 lbs
3.1 kg
2.0 kg
7.7 lbs
5.0 lbs
3.5 kg
2.3 kg
8.3 lbs
6.3 lbs
5.6 lbs
3.8 kg
2.9 kg
2.6 kg
8.8 lbs
6.8 lbs
4.0 kg
3.1 kg
9.2 lbs
7.2 lbs
4.2 kg
3.3 kg
9.7 lbs
7.7 lbs
4.4 kg
3.5 kg
-
*SPC = “Stones per carat”
Example
The maximum permissible bit load for a T2-76 Surface-Set Core Bit with 354 diamonds of 50 SPC Dimatec “Grade
AA” natural diamond set on the bit face is given by: (354 diamonds) x (9.7 lbs/diamond) = 3,434 lbsF (or 1,561 kg).
Bit load requirements for TSP-set and PDC-set bits
The bits in this group are set with large synthetic diamond cutting elements that require the use of relatively high,
sustained bit loads. When applied in appropriate formations, they often provide rates of penetration that are
considerably higher than surface-set diamond bits.
Higher bits loads are necessary to maintain the sharpness of the individual TSP or PDC cutters, particularly in
formations of medium hardness. Insufficient bit loads will cause the cutter elements to become glazed and
polished. As a result, the bit’s penetration rate will be reduced to virtually zero. However, applied bit loads should
not be so high as to exceed the manufacturer’s recommended maximum load rating for the core barrel and drill
string in use.
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Dimatec Inc. ● Operating Parameters: Bit Load for Geotechnical Core Bits
For Triangular-TSP or Cubic-TSP core bits, the recommended bit load is approximately 100 to 125 lbs force (45 kg
to 57 kg) per TSP element mounted on the bit face.
Maximum and Minimum Recommended Bit Loads for
Triangular-TSP and Cubic-TSP Core Bits (kg)
6000
5130
4845
5000
4560
4275
3990
Bit Load (kg)
4000
3705
3420
3825
3135
3375
2850
3000
2565
2925
2280
3150
Min
2700
1995
2000
4050
3600
2475
2250
1710
2025
1425
Max
1800
1140
1575
1350
1000
900
1125
0
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
No. of TSP Elements on Bit Face
Maximum and Minimum Recommended Bit Loads for
Triangular-TSP and Cubic-TSP Core Bits (lbs)
12000
11250
10625
10000
9375
10000
8750
Bit Load (lbs)
8125
9000
7500
8000
8000
6875
7500
6250
7000
5625
6000
6500
5000
6000
Min
5500
4375
5000
3750
4000
8500
4500
3125
4000
2500
Max
3500
3000
2500
2000
2000
0
20
25
30
35
40
45
50
55
60
65
70
No. of TSP Elements on Bit Face
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75
80
85
90
Dimatec Inc. ● Operating Parameters: Bit Load for Geotechnical Core Bits
For PDC (Pax-set) core bits, the recommended bit load is approximately 550 to 770 lbs force (250 kg to 350 kg) per
PDC element mounted on the bit face.
Maximum and Minimum Recommended Bit Loads for
PDC (Pax-Set) Core Bits (kg)
6000
5250
5000
4200
Bit Load (kg)
4000
3500
3750
3150
2800
3000
3000
2100
1750
2000
Min
2500
2250
2000
1400
1050
Max
1500
1250
1000
1000
750
0
3
4
5
6
8
9
10
12
15
No. of PDC Elements on Bit Face
Maximum and Minimum Recommended Bit Loads for
PDC (Pax-Set) Core Bits (lbs)
12000
11550
10000
9240
8250
7700
Bit Load (lbs)
8000
6930
6160
6600
6000
4620
4000
5500
Min
4950
3850
4400
3080
Max
2310
3300
2750
2000
2200
1650
0
3
4
5
6
8
9
No. of PDC Elements on Bit Face
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10
12
15
Dimatec Inc. ● Operating Parameters: Bit Load for Geotechnical Core Bits
Bit load requirements for “saw-tooth” type tungsten-carbide core bits
Bit load is a function of the total length of the tungsten-carbide cutters that are mounted on the face of the bit. Each
of these tungsten-carbide cutters possesses a single cutting edge. The maximum bit load is determined by finding
the sum of the linear length of cutting edge on all of the cutters on the bit face and multiplying that sum by a
constant of load per unit length of cutting edge.
The formula that is used to calculate the maximum bit load (F) for any “saw-tooth” type tungsten-carbide core bit is
given as:
Where:
F = The calculated maximum bit load expressed in kilograms.
D = The outside set diameter of the bit crown expressed in millimetres.
d = The inside set diameter of the bit crown expressed in millimetres.
n = The number of tungsten-carbide cutting blades mounted on the bit face.
Bit load requirements for “carbide-chip” type tungsten-carbide core bits
In the case of carbide-chip core bits, bit load is a function of the bit face bearing area. That is, the actual contact
area of the bit face with the formation being drilled. The maximum recommended bit load per bit face bearing area
2
2
is 0.35 kg/mm (500 lbs/inch ).
The formula that is used to calculate the maximum bit load (F) for any “saw-tooth” type tungsten-carbide core bit is
given as:
Where:
F = The calculated maximum bit load expressed in kilograms.
D = The outside set diameter of the bit crown expressed in millimetres.
d = The inside set diameter of the bit crown expressed in millimetres.
n = The number of full waterway canals across the bit face kerf.
w = The typical width of the waterway canals expressed in millimetres.
Technical Data Sheet TD110
Revision 0
Document Release Date: February 1, 2013
The technical application data in this document is intended as a basic guideline for the selection of the appropriate tools for your job. As drilling
conditions and the capabilities of drilling equipment vary considerably from site to site, it is impossible to define absolute parameters for the
application of our drilling tools. Some experimentation on the part of the end user may be required as parameters outside of those recommended in
Dimatec’s product literature may be applicable. Every effort has been made to ensure the accuracy of the data contained in this document.
Dimatec Inc. cannot accept any liability due to errors or omissions in the data that we provide. Dimatec Inc. is constantly working to improve our
products and therefore reserve the right to make changes to materials, specifications, prices and technical data without prior notice.
Dimatec Inc. • 180 Cree Crescent • Winnipeg, Manitoba, Canada R3J 3W1
Telephone: Toll-Free 1-866-202-5875 (Canada and US) or (204) 832-2828 • Fax: (204) 832-4268 • E-mail: [email protected] • Website: www.dimatec.com
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