Method and cable anchor assembly for anchoring plastic coated rope

A cable anchor assembly is disclosed as well as a method of using the assembly for anchoring plastic coated rope in oil well drilling derricks and the like for alternatively carrying a load on the rope and also for allowing the rope to be selectively slipped or fed through the cable anchor assembly for replacement thereof, the assembly including a snubbing drum having a circumferentially formed groove with an included angle in the range of about 130 degrees to about 165 degrees, more preferably in the range of about 150 to about 160 degrees and most preferably about 160 degrees, the groove also being formed with preferably at least two, more preferably at least three to four turns, and most preferably about three turns for engagement with the rope about the drum in order to normally support a substantial portion or more preferably the entire rope load while still permitting the rope to be selectively slipped or fed through the assembly, the clamp means including a grooved insert for engaging and clamping the rope with reduced clamping force.

FIELD OF THE INVENTION 
The present invention relates to a cable anchor assembly and a method of 
use for such an assembly in anchoring plastic coated cable in oil well 
drilling derricks and the like while allowing the cable to be selectively 
slipped or fed through the cable anchor assembly, for example to replace 
the cable. 
BACKGROUND OF THE INVENTION 
A large number of designs for cable anchors have been disclosed in the 
prior art to form a "dead-end" coupling for securing a cable against a 
load carried on an oil drilling derrick or the like. The cable is commonly 
formed from wire and is trained or roved about a crown block and traveling 
block in the derrick to raise and lower the drill pipe and casing by means 
of the cable. 
Massive loads tend to be present in deep drilling operations and it is 
accordingly important for the cable anchor to be able to carry them. 
It is also common practice to provide a supply drum for additional cable 
which is slipped or fed through the cable anchor for replacing the cable 
roving in the derrick, usually after the cable experiences substantial 
wear. 
A cable anchor assembly of this type was disclosed in U.S. Pat. No. 
2,282,685 issued to Timbs on May 12, 1942. The cable anchor assembly of 
that patent included a snubbing drum and associated clamping means 
arranged between the derrick and the supply drum for operation in the 
manner generally referred to above. 
U.S. Pat. No. 2,488,070 issued November 15, 1949 to Spalding further 
disclosed the combination of a weight indicator or load cell employed in 
combination with a cable anchor assembly to indicate the amount of load 
carried on the cable. 
Still further refinements in cable anchor assemblies have been provided in 
the prior art. For example, U.S. Pat. No. 3,973,435 issued August 10, 1976 
to Decker disclosed a cable anchor assembly including the formation of 
fluting or spiral grooving in a cylindrical surface of the snubbing drum 
with the cable being arranged within the groove. 
Such cable anchor assemblies have been found to be satisfactory 
particularly where bare wire cable is employed with metal-to-metal 
engagement existing between the cable and snubbing drum and between the 
cable and clamp. 
However, more recently, there has been a tendency to employ plastic coated 
cable or rope in applications other than oil well drilling for a number of 
reasons set forth, for example, in U.S. Pat. No. 3,824,777 issued July 23, 
1974 to Riggs. That patent disclosed a stranded wire rope including a 
heavy viscous lubricant in its core with the outer portions of the rope or 
cable being impregnated or coated with plastic. This cable is commonly 
referred to as plastic filled valley (PFV) rope or cable and has been 
found to be desirable for use in drilling applications for a number of 
reasons. Initially, use of the internally lubricated rope or cable avoids 
the need for externally applying grease to the cable. Furthermore, plastic 
coated cables such as the PFV rope referred to above increases wear life 
or ton miles in drilling operations and the like while also protecting the 
wire from the environment, including corrosion effects, etc. 
However, the use of plastic coated rope in drilling operations has been 
found to be incompatible with cable anchor assemblies designed for use 
with bare wire cable. lnitially, decreased frictional engagement with the 
drum and with the clamp exists because of the plastic-to-wire engagement 
and also because of the tendency for the plastic coated rope to maintain 
its cylindrical shape in cross section when wound about the drum and 
carrying a heavy load. 
A number of design variations were considered in development of the present 
invention in an attempt to overcome this problem and to assure that the 
load is secured by the cable anchor assembly while still permitting the 
rope to be slipped through the cable anchor assembly as desired or 
necessary. 
For example, in some instances, it was found necessary to remove a portion 
of the plastic coating in order to obtain normal metal-to-metal engagement 
between the rope and drum for developing sufficient friction. 
It has also been found that additional turns of rope could be formed about 
the drum for the same purpose. However, the additional turns of rope 
unduly increased the axial length of the drum making the cable assembly 
more bulky and tending to interfere with the drilling operation. At the 
same time, the presence of additional turns about the drum also interfered 
with the slipping or feeding of rope from the supply drum. 
Still another expedient for overcoming this problem was the provision of 
increased clamping surface associated with the drum for securing the 
plastic coated cable. However, this was also found to be generally 
undesirable because of the tendency for clamps to deform the cable and 
prevent its proper operation as roving associated with a derrick. 
Accordingly, there was found to remain a need for substantial improvements 
in the cable anchor assembly in order to firmly secure the rope and carry 
the full load, without damage to the rope, while also permitting the rope 
to be selectively slipped or fed through the cable anchor assembly when it 
was necessary for example to replace rope in the derrick. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
cable anchor assembly and method for alternatively carrying a load in well 
drilling derricks and the like while also allowing the rope to be 
selectively slipped or fed through the cable anchor assembly. 
It is a further object of the invention to provide such an improved cable 
anchor assembly and method of operation through the use of a snubbing drum 
having a spiral groove formed on a cylindrical surface of the drum for 
receiving the cable, the groove being formed with an included angle in the 
range of from about 130 to about 165 degrees, more preferably in the range 
of from about 150 degrees to about 160 degrees and most preferably an 
included angle of about 160 degrees, the groove also being formed with a 
number of turns for engagement with the cable about the drum, the number 
of turns being selected for preferably supporting a substantial portion 
and for more preferably supporting approximately 100 percent of the load 
whereby a clamp means associated with the drum normally provides a safety 
factor in the cable anchor assembly. 
It is also an important object of the invention to form the groove with a 
radius approximately equal to the nominal radius or one-half the nominal 
diameter of rope contemplated for use with the drum. It is to be 
understood that sometimes the cable anchor assembly of the invention may 
be used with rope of a different size. However, the cable anchor assembly 
of the invention must be used with rope of the contemplated nominal size 
to realize full advantages of the invention. It is also noted that plastic 
coated rope of the type contemplated for use in the invention is normally 
somewhat oversize, typically up to about seven percent over its nominal 
size. With the groove radius being approximately true to its nominal size, 
a "pinch effect" is produced between the groove and rope to maintain 
desired frictional engagement therebetween. 
Thus, with the cable anchor assembly being contemplated for use with 
plastic coated rope ranging in (nominal) diameter from about 7/8-2 inches, 
the drum is formed with grooving of corresponding nominal size. This 
feature is of course combined with the included angle of the groove and 
number of rope turns about the drum, as discussed above and below, for 
establishing overall frictional engagement between the rope and drum of 
the cable anchor assembly. 
It is a further object of the invention to provide an improved cable anchor 
assembly and method of operation as disclosed above wherein the groove is 
formed with preferably two to four turns, more preferably three to four 
turns and most preferably about three turns for engagement with the cable 
about the drum. 
The precise number of turns varies of course depending upon the relative 
angles with which the cable enters and leaves engagement with the drum. 
For example, in a preferred embodiment as disclosed below, approximately 
one quarter turn of cable about the drum is present for this purpose. 
Accordingly in that embodiment, the groove is shown with about three and 
one quarter turns in engagement with the rope about the drum. 
As is also set forth in greater detail with relation to the preferred 
embodiment described below, the combination of the snubbing drum and 
additional clamping means is employed with the cable load normally being 
substantially carried by frictional engagement of the cable with the drum. 
In such an arrangement, the clamp means serves as a safety factor for 
assuring proper operation of the cable anchor assembly. Furthermore, 
although the cable anchor assembly is adapted for use with plastic coated 
cable of a specified size and strength, the safety factor provided by the 
above combination permits safe operation of the cable anchor assembly even 
with plastic coated ropes of other size although use of plastic coated 
cable other than that of the nominal size and type particularly specified 
is not recommended or authorized. 
It is yet another related object of the invention to provide an improved 
design for the clamp whereby the clamp includes an insert for engaging the 
plastic filled cable, the insert preferably being formed with spiral 
grooving to permit clamping of the cable with reduced clamping force. This 
in turn assures that the cable load is properly supported while further 
serving to prevent the possibility of damage to the cable in the cable 
anchor assembly. 
Additional objects and advantages of the invention are made apparent in the 
following description having reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings and particularly to FIG. 1, the invention is 
directed toward a cable anchor assembly generally indicated at 10 also 
contemplated for carrying out the method of operation of the invention. 
The cable anchor assembly 10 is illustrated in conjunction with an oil 
drilling derrick generally indicated at 12. The oil drilling derrick 12 
includes a crown block 14 and a traveling block 16 as conventionally 
employed on a tower shown in broken lines at 18 for raising and lowering a 
drilling unit generally indicated at 20. 
During operation of the oil drilling derrick 12, the drilling unit 20 is 
raised and lowered by means of cable or rope 22 operating in conjunction 
with the crown block 14 and traveling block 16. The rope 22 is of heavy 
construction in order to support the massive loads typical in drilling 
units such as that indicated at 20. Accordingly, the rope is susceptible 
to wear and must be replaced at regular intervals. For that purpose, the 
rope 22 on the oil drilling derrick 12 is an integral extension of rope on 
a supply drum 24. At the same time, the other end 26 of the rope is wound 
about and secured to a take-up drum 28 which stores excess rope from the 
derrick 12 when the traveling block 16 is raised and supplies additional 
rope necessary as the traveling block 16 is lowered. 
To facilitate operation of the derrick 12, the rope 22 passes from the 
supply drum 24 through a clamp mechanism 30 and is then wound about a 
cylindrical snubbing drum 32 described in greater detail below. As is also 
described in greater detail below, the snubbing drum 32 and clamp 
mechanism 30 are adapted during normal operation of the derrick 12 for 
providing a "dead-end" anchor for the rope 22. At the same time, the clamp 
mechanism 30 and snubbing drum 32 are also adapted to permit the cable 22 
to be slipped or fed from the supply drum 24 to the derrick when it is 
necessary to replace the cable on the derrick. 
From the snubbing drum 32, the rope 22 passes upwardly to the crown block 
14 and is then trained about sheaves 34 and 36 in the crown block and 
traveling block respectively to form roving generally indicated at 38 for 
suspending the traveling block 16 from the crown block 14. 
After forming the roving 38, the rope 22 passes downwardly from the crown 
block 14 for engagement with the take-up drum 28. 
As is conventional in such derrick units, the crown block 14 is mounted 
upon a structural portion 40 of the tower 18 in order to support the 
weight of the drilling unit 20 when it is attached to the traveling block 
16. 
To commence operation of the derrick 12, or when the supply drum 24 is 
replaced, the rope 22 is threaded in the manner described above. The clamp 
mechanism 30 is then engaged with the rope so that the snubbing drum 32 
and clamp mechanism 30 provides the necessary dead-end anchor to support 
the weight of the drilling unit 20. As will be described in greater detail 
below, the present invention particularly contemplates design of the 
snubbing drum 32 so that a substantial portion of the weight or load 
(preferably 100%) of the drilling unit 20 carried by the rope 22 is 
supported by the snubbing drum 32 with the clamp mechanism 30 being 
available as a safety factor in the cable anchor assembly 10. 
Thereafter, the drilling unit 20 is raised or lowered by rotation of the 
take-up drum 28 in normal operation. 
Because of the massive weights involved in the drilling unit 20, the rope 
22 is susceptible to wear after certain intervals of operation and is 
periodically replaced in what is commonly termed a "slip and cut" 
operation. This is accomplished by releasing the clamp mechanism 30 and 
slipping or feeding the rope 22 through the clamp mechanism 30 and around 
the snubbing drum 32. At the same time, the cable is also fed through the 
roving 38 to provide a new length of rope 22 between the cable anchor 
assembly 10 and the take-up drum 28. The worn or used rope is then removed 
and, with the fresh rope being secured to the take-up drum 28, operation 
of the derrick 12 is resumed as described above. 
The present invention particularly contemplates the use of plastic coated 
rope or cable such as the PFV wire referred to above and described for 
example in the Riggs Patent referred to above. That patent is incorporated 
as though set out entirely herein in order to provide a complete 
disclosure of the plastic covered rope contemplated for the invention. 
The cable anchor assembly 10 is described in greater detail below having 
additional reference to FIGS. 2-4. As may be best seen by combined 
reference to FlGS. 2-4, the snubbing drum 32 is mounted upon a base 42 and 
includes a cylindrical portion 44 formed with a spiral groove 46. As may 
be best seen in FlG. 2, the rope 22 passes horizontally from the supply 
drum 24 (see FIG. 1) for engagement with the clamp mechanism 30. The rope 
is then wound about the snubbing drum 32 in engagement with the spiral 
groove 46 for a selected number of turns as described in greater detail 
below. Thereafter, the rope 22 exits the snubbing drum in a generally 
vertical configuration for passage to the crown block 14 (see FIG. 1). 
Because of the relative arrangement of the supply drum 24 and passage of 
the cable to the crown block of the derrick, the rope is wound about the 
snubbing drum 32 a predetermined integral number of turns plus an 
additional quarter turn to permit connection with both the supply drum 24 
and the derrick 12. 
It is of course apparent that the arrangement of the supply drum 24 and the 
derrick could result in a different fractional turn on the snubbing drum. 
Thus, although the following description refers to a quarter turn in 
accordance with the embodiment of FIGS. 1-4, the integral number of 
complete turns about the snubbing drum is of particular importance in 
connection with the present invention. 
A load sensor 48 is also coupled with the cable through the snubbing drum 
32 for determining the instant load on the rope cable 22 in a generally 
conventional manner as set forth in greater detail for example in the 
Spalding Patent referred to above which is also incorporated herein by 
reference. The construction of the oil drilling derrick 12 is of course of 
conventional construction. At the same time, the features of the cable 
anchor assembly 10 discussed above are also generally in accordance with 
the prior art. In that regard, it is further noted that certain standards 
have been developed with specifications for certain features of the cable 
anchor assembly depending upon parameters such as the weight of the 
drilling unit 20. In the United States, these standards are established by 
the American Petroleum Institute (API). 
The size or diameter of the drum 32 is selected according to a number of 
parameters. Generally, the maximum drum size is selected to maintain 
compactness of the cable anchor assembly. Its minimum diameter is 
particularly selected for preventing excessive bending and possible damage 
to the rope. Furthermore, frictional engagement between the rope and drum 
has been found to depend on the number of turns of rope about the drum 
regardless of the drum diameter. 
Therefore, and in accordance with common practice, the diameter of the drum 
is approximately twenty times the diameter of the rope. In the cable 
anchor assembly of FlGS. 2-4, with the rope having a nominal diameter of 
1.75 inches, the diameter of the drum 32 is approximately 31 inches. 
When bright wire cable was replaced by plastic coated rope as noted above, 
it was found that the plastic coated rope did not have the same frictional 
engagement with the cable anchor assembly 10. Initially, whereas the 
bright wire cable relied on metal-to-metal contact with the snubbing drum, 
the plastic coated rope naturally involved plastic-to-metal contact. At 
the same time' it was found that the bright wire cable tended to "flatten 
out" when it was wrapped around the snubbing drum 32 under a heavy load as 
provided by the drilling unit 20 (see FIG. 1). The plastic coated rope, 
particularly as described in the above noted patent, tends to resist such 
deformation or flattening out even when it is a wound around the snubbing 
drum 32 under a heavy load. At least for these two reasons, the plastic 
coated rope has been found to exhibit a substantially different 
coefficient of friction requiring modification of the cable anchor 
assembly 10 in order to permit the same load of the drilling unit 20 when 
plastic coated rope is employed as indicated at 22 in FIG. 1. Numerous 
modifications were attempted during development of the present invention 
to adapt the cable anchor assembly 10 for use with plastic coated rope. 
As one expedient, it was found that removing a portion of the plastic 
coating permitted metal-to-metal contact with the snubbing drum 32 so that 
the plastic coated rope performed generally similarly as the bright wire. 
However, removing the plastic coating was found to be undesirable since it 
destroyed the Integrity of the plastic coated rope, weakened the rope for 
use on the derrick and also exposed the metal strands to the environment 
including corrosion factors and the like. 
Additional modifications included the use of multiple clamp mechanisms such 
as that indicated at 30 for engaging the plastic coated rope. However, 
these arrangements were found to be relatively cumbersome. In addition, 
when the clamp mechanisms were tightened against the plastic coated cable 
sufficiently to take-up the additional load, they tended to cause damage 
to the rope, thereby preventing its proper operation on the derrick. 
Yet another modification involved axial extension of the snubbing drum 32 
to permit additional turns of rope about its cylindrical portion as 
indicated at 44 in FIGS. 2-4. Obviously, if sufficient additional turns of 
rope about the snubbing drum were employed, the load of the drilling unit 
could be supported. However, the provision of additional grooving in the 
snubbing drum unduly increased its axial length making the cable anchor 
assembly 10 generally cumbersome and difficult to handle. At the same 
time, as additional turns of rope were employed about the drum, it also 
became more difficult to slip or feed the rope about the drum during cable 
replacement as described above. 
These difficulties in substituting plastic coated rope for the earlier 
bright wire cable are described in detail in order to permit a more 
complete understanding of the invention which is set forth immediately 
below as a means for facilitating use of the cable anchor assembly 10 with 
plastic coated rope while maintaining the relatively compact configuration 
for the cable anchor assembly 10, particularly the snubbing drum 32, and 
also assuring the capability of slipping or feeding the rope through the 
cable anchor assembly 10 as necessary for cable replacement. At the same 
time, the present invention also contemplates the provision of a safety 
factor within the cable anchor assembly 10 for further enhancing its 
operation in conjunction with oil drilling derricks, such as that 
indicated at 12 in FIG. 1, and the like. 
Substantial testing developed the following parameters for the present 
invention in connection with the snubbing drum 32. Initially, the size of 
the groove 46, particularly its radius and included angle were found to be 
of critical importance. As is best illustrated in FIG. 5, the groove 46 is 
formed with a uniform radius of curvature along its length as indicated at 
50. The included angle of the groove is indicated at 52. 
The radius 50 of the groove 46 is of course related to the particular size 
of plastic coated rope contemplated for use with the cable anchor 
assembly. Generally, it is necessary for the radius 50 of the groove 46 to 
be selected in order to provide frictional engagement between the surface 
of the groove 46 and an extended surface portion of the plastic coated 
rope. At the same time, it is necessary that the radius 50 of the groove 
46 is selected so that the rope can be slipped or fed about the snubbing 
drum 32 during replacement as described above. 
As noted above, the groove is preferably the same size as the "nominal" 
size of the rope 22 in order to produce a "pinch effect" between the rope 
and groove. However, as is indicated by the following test data, some 
variance is possible between groove size and nominal rope diameter 
although not recommended for optimum performance of the invention. 
At the same time, it has been found that the included angle 52 for the 
groove 46 is particularly important for insuring proper frictional 
engagement with the plastic coated rope and at the same time allowing the 
plastic coated rope to be slipped or fed through the groove 46 during 
replacement. 
The number of turns formed by the groove 46 about the cylindrical surface 
of the snubbing drum 32 is of related importance in this regard. As noted 
above, it is generally desirable to avoid excessive numbers of turns in 
order to allow the snubbing drum 32 to be as compact as possible and also 
to still allow the plastic coated cable to be slipped through the entire 
length of the groove 46. 
In accordance with drum sizing, it has been determined in accordance with 
preferably about two to four turns, more preferably three to four turns 
and most preferably about three turns of the groove 46 are necessary for 
engagement with the rope about the circumference of the snubbing drum 32. 
Here again, it is noted that the number of turns referred to in this 
regard are defined to include that portion of the groove 46 which is in 
actual contact with the rope 22. Also, it is again noted that a fractional 
turn, for example one quarter turn as illustrated in FIG. 2 is necessary 
to accommodate for the direction in which the cable 22 approaches the 
snubbing drum 32 from the supply drum 24 and the direction in which the 
cable 22 exits the snubbing drum 32 toward the derrick (also see FIG. 1). 
In any event, it has been found in accordance with the present invention 
that, in the embodiment of FIGS. 1-4, at least three turns, or three and 
one quarter turns are most preferred to assure proper frictional 
engagement between the groove 46 and the rope 22 while still allowing the 
rope 22 to be slipped or fed through the groove for replacement. 
At the same time, it was found necessary to form the included angle 52 
within the range of from about 130 degrees to about 165 degrees. 
Preferably, frictional engagement between the groove 46 and rope 22 is 
best maintained if the included angle 52 is maintained within the range of 
about 150 degrees to about 160 degrees and most preferably at about 160 
degrees. 
With the preceding values being established for the snubbing drum 32 and 
the spiral groove 46, the groove 46 is selected (preferably) for 
supporting a substantial portion (more preferably 100 percent) of the load 
on the rope 22. As will be made more apparent in the test results set 
forth below, the meeting of that goal depends upon various factors in the 
selection of the plastic filled cable and the particular design of the 
snubbing drum 32 and clamp mechanism 30. 
The specific construction of the snubbing drum 32 and clamp mechanism 30 is 
illustrated in FIGS. 2-4 and 6-8 and is described in greater detail below. 
The snubbing drum 32 is fabricated to withstand contemplated loads with the 
cylindrical portion 44 being mounted on the base 42 generally in 
accordance with prior art constructions also described in greater detail 
within the references noted above. Accordingly, the patents referenced 
above are incorporated herein as though set forth in their entirety to 
assure a more complete understanding of the invention. 
With the cylindrical drum portion 44 being arranged on the base 42 for 
receiving the plastic coated rope 22 in its groove 46, the load sensor or 
test cell 48 is also conventionally interconnected between the cylindrical 
drum portion 44 and the base 42 for measuring the instantaneous load on 
the cable. Here again, the interconnection and function of the load sensor 
48 in the present invention is similar to that described in the references 
noted above. 
The clamp mechanism 30 includes a housing portion 54 which is an integral 
portion of structural fabrication 56 for the snubbing drum 32. Inserts 58 
and 60 (also see FIGS. 6-8) are arranged within the clamp mechanism 30 for 
directly engaging the cable 22 and are urged into clamping engagement with 
the cable 22 by means of a clamping plate 62. The housing portion 54 and 
clamping plate 62 are configured for receiving the inserts while also 
being interconnected by means of bolts 64 which are rotated under measured 
torque loads for causing the inserts 58 and 60 to enter into clamping 
engagement with the cable 22. 
The clamp mechanism 30 is also sized relative to the selected plastic 
coated cable being used in a particular application. In particular, the 
inserts 58 and 60 are formed with cylindrical inner surfaces 66 (see FIGS. 
6-8) which generally conform with the diameter of the selected plastic 
coated cable. In addition, the cylindrical inner surfaces 66 are formed 
with grooves 68 which provide for better clamping engagement of the 
inserts 58 and 60 with the plastic coated cable. 
For example, with the cable having a nominal diameter of about one and 
one-half inches, the grooving 68 is preferably formed with a depth of 
about one sixteenth inch and a width of about one-eighth inch. The 
grooving 68 is also preferably machined in the manner of a square bolt 
thread a may be best seen in FIG. 6, with a pitch of about four threads 
per inch. 
The major advantage of the clamp mechanism 30 over prior art clamp 
mechanisms resides in the grooving 68 which permits decreased torquing of 
the bolts 64 while still maintaining clamping engagement of the inserts 58 
and 60 with the plastic coated rope. Here again, it is noted that the 
clamp mechanism 30 is preferably present in the cable anchor assembly 10 
to provide a safety factor with the groove 46 carrying substantially the 
entire rope load. However, in different applications, it is of course 
contemplated that additional loading may be encountered and the clamp 
mechanism 30 is designed to resist that additional load. 
The construction of the cable anchor assembly 10 and its method of 
operation for anchoring plastic coated rope is believed to be fully 
apparent from the preceding description. However, a number of tests for 
different combinations of cable anchor assemblies and plastic coated rope 
are set forth below to facilitate a more complete understanding of the 
invention. 
In the following tests, plastic coated rope was employed having a nominal 
diameter of either one and one half inches or one and three-fourths 
inches. The plastic coated rope was obtained from Greening Donald under 
the trade designation "REGULAR LAY 6X26 PFV". Results for the various 
tests are set forth below. 
TEST I 
In this test, a cable anchor assembly constructed as illustrated in FIGS. 
2-4 was employed with plastic coated rope having a nominal diameter of one 
and one half inches. The diameter of the snubbing drum 32 was 31 inches. A 
deadline load was applied to the cable 22 as indicated at T.sub.1 in FIG. 
2. In the clamp mechanism 30, the inserts 58 and 60 were approximately 
nine inches in length with six clamping bolts being employed as indicated 
at 64 in FIG. 2. The bolts 64 were standard 7/8 inch machine bolts. 
With the plastic coated rope being a nominal one and one half inch 
diameter, the groove 46 in the snubbing drum was formed with four and one 
quarter turns in engagement with the cable 22 as illustrated in FIG. 2. 
The groove 46 also had a uniform diameter of one and three quarter inches 
(a radius of seven eighths inches) with an included angle of 160 degrees. 
The plastic coated rope was installed as illustrated in FIGS. 1 and 2 with 
the bolts 64 being tightened to a predetermined torque level. The deadline 
load T.sub.1 was then varied with readings being taken of the load cell 
load T.sub.2 after intervals of one minute, two minutes, three minutes, 
four minutes, etc. These time intervals were selected because when loading 
at T.sub.1 occurs, it takes a period of time for partial loading to occur 
at T.sub.2 due to the coefficient of friction between the PFV wire rope 
and the grooves in the anchor. A four to five minute time period was 
determined to be sufficient during testing so maximum pull at T.sub.2 
could be recorded. 
Results for this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
20,000 300 300 300 -- 
40,000 -- -- -- -- 
60,000 900 1100 1150 1200 
80,000 2200 2300 2400 2450 
100,000 3600 4000 4200 4300 
120,000 5100 5800 6100 6300 
130,000 6600 7050 7350 7600 
______________________________________ 
The dashes appearing in the table indicate no further loading after the 
initial time period was recorded. 
TEST II 
The conditions of TEST I were repeated except that a film of 10 W motor oil 
was applied to the surface of the snubbing drum 32 and the spiral groove 
46 to simulate conditions often encountered in the field. 
Results from this test were as follows: 
______________________________________ 
Deadline Load 
Sensor Load T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 4 Min. 
5 Min. 
______________________________________ 
130,000* 17,200 17,300 17,375 17,400 
-- 
130,000* 17,900 18,000 18,000 18,000 
-- 
130,000* 12,300 12,600 12,650 12,700 
-- 
150,000 -- -- -- -- 13,500 
______________________________________ 
*T.sub.1 load of 130,000 lbs repeated. 
TEST III 
The conditions of Test I were again repeated except that plastic coated 
rope having a nominal diameter of one and three-fourths inches was 
employed. The snuffing drum 32 as dry and generally free from oil. 
In this test, the plastic coated rope was "one and three-fourths inch 
REGULAR LAY 6X19 PFV". 
The results of this test were as follows: 
______________________________________ 
Deadline Load 
Sensor Load T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 4 Min. 
5 Min. 
______________________________________ 
20,000 0.0 0.0 0.0 0.0 0.0 
40,000 0.0 0.0 0.0 0.0 0.0 
60,000 0.0 0.0 0.0 0.0 0.0 
80,000 0.0 0.0 0.0 0.0 0.0 
100,000 0.0 0.0 0.0 0.0 0.0 
120,000 0.0 0.0 0.0 0.0 0.0 
130,000 0.0 0.0 0.0 0.0 0.0 
140,000 0.0 0.0 0.0 0.0 0.0 
______________________________________ 
TEST IV 
The conditions of Test III were again repeated except that only one and one 
and one-fourth turns of cable were employed about the snubbing drum 32. In 
this test, the plastic coated cable was identified as "one and 
three-fourths inch REGULAR LAY 6X39 PFV". 
The results for this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
20,000 1150 1150 1150 -- 
30,000 1600 1650 1700 -- 
40,000 4100 4150 4200 -- 
50,000 7000 7100 7150 -- 
60,000 10000 10100 10150 -- 
70,000 11400 11200 11000 -- 
______________________________________ 
Comment: The cable slipped with T.sub.1 equal to 70,000 lbs. 
TEST V 
The conditions of Test IV were repeated exactly except that the bolts 64 
were retorqued to 300 lbs. 
The results of this test are as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
50,000 9300 9400 9500 -- 
60,000 12100 12400 12550 -- 
70,000 15100 15500 15700 -- 
______________________________________ 
Comment: No slip occurred with T.sub.1 equal to 70,000 lbs. 
TEST VI 
The conditions of Test IV were again repeated but with two and one-fourth 
wraps of cable about the snubbing drum 32. The drum was again dry and free 
from oil. 
Results for this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
30,000 0.0 0.0 0.0 0.0 
40,000 250 250 250 -- 
50,000 550 650 700 -- 
60,000 1100 1200 1300 -- 
70,000 1700 1900 2000 -- 
______________________________________ 
TEST VII 
The conditions of Test I were again repeated except that only one and one 
quarter wraps of cable were employed on the snubbing drum 32. As in Test 
I, the surface of the drum was dry and free from oil. 
The results of this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
10,000 450 -- -- -- 
17,000 450 -- -- -- 
20,000 4100 -- -- -- 
0-20,000* 4200 -- -- -- 
25,000 7300 -- -- -- 
30,000 10000 -- -- -- 
35,000 13100 13300 -- -- 
40,000 15600 15800 -- -- 
______________________________________ 
*The 20,000 lb test was repeated with the load applied very rapidly to 
simulate shock loading that may occur in normal drilling operations. 
TEST VIII 
The conditions of Test I were again repeated except with two and one-fourth 
wraps of cable around the snubbing drum 32. 
The results of this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
11,000 500 -- -- -- 
12,000 500 -- -- -- 
20,000 1000 -- -- -- 
25,000 2300 2400 -- -- 
30,000 4000 -- -- -- 
35,000 5500 -- -- -- 
40,000 7000 -- -- -- 
0-40,000* 8600 -- -- -- 
______________________________________ 
*The 40,000 lb test was repeated with the load applied very rapidly to 
simulate shock loading that may occur in normal drilling operations. 
An additional series of tests was conducted to determine the optimum range 
for the included angle of the groove and also to determine the preferred 
number of turns of rope engaged about the drum 32. In addition, these 
tests included "slip and cut" testing to determine the ability of slipping 
or feeding additional rope through the cable anchor assembly for 
replacement in the derrick as described above. 
in all of the following Tests IX-XXVII (as in the previous tests above), 
plastic coated rope identified as PFV REGULAR LAY 6X39 wire rope 
manufactured by Greening Donald. In Tests IX-XVII, the plastic coated rope 
had a nominal diameter of one and three quarter inches. In each of these 
tests, the drum had a diameter of 32 inches. The diameter for the groove 
was 1 and 3/4 inches. Accordingly, in Tests IX-XVII, the only variables 
were the included angle of the groove and the number of turns of plastic 
filled rope about the drum. Accordingly, these two variables are initially 
set forth in each of the following tests followed by dynamic load test 
results and comments relating to certain of the tests. 
TEST IX 
Included Groove Angle--165 degrees 
Number of Rope Turns--Four and One-fourth 
Results for this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
130,000 0 -- -- -- 
______________________________________ 
Comment: No load at T.sub.2 was observed after five minutes. In Test IX a 
in all of the other tests set forth herein, the included angle for the 
groove is determined as the approximate included angle along the length o 
the groove about the circumference of the snubbing drum. 
Test X 
Included Groove Angle--165 degrees 
Number of Rope Turns--Three and One-fourth 
Results for this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
130,000 0 -- -- -- 
______________________________________ 
Comment: No load at T.sub.2 was observed after five minutes. 
TEST XI 
Included Grove Angle--165 degrees 
Number of Rope Turns--Two and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
50,000 200 -- -- -- 
60,000 300 350 -- -- 
70,000 900 900 -- -- 
80,000 1300 1300 -- -- 
90,000 1800 1825 -- -- 
100,000 2500 2600 -- -- 
110,000 3100 3200 -- -- 
120,000 3700 3850 -- -- 
130,000 4400 4525 -- -- 
______________________________________ 
TEST XII 
Included Groove Angle--158 degrees 
Number of Rope Turns--Three and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
130,000 0 -- -- -- 
______________________________________ 
Comment: No load at T.sub.2 was observed after five minutes. 
TEST XIII 
Included Groove Angle--160 degrees 
Number of Rope Turns--Two and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
50,000 100 100 -- -- 
60,000 125 150 -- -- 
70,000 250 300 -- -- 
80,000 450 500 -- -- 
90,000 700 800 -- -- 
100,000 1500 1700 -- -- 
110,000 2100 2450 -- -- 
120,000 3100 3300 -- -- 
130,000 3900 4100 4800 -- 
______________________________________ 
TEST XIV 
Included Groove Angle--160 degrees 
Number of Rope Turns--Three and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
50,000 0 0 -- -- 
70,000 0 0 -- -- 
90,000 0 -- -- -- 
100,000 0 -- -- -- 
110,000 0 -- -- -- 
120,000 100 -- -- -- 
130,000 100 -- -- -- 
______________________________________ 
Comment: In Tests IX-XI, where the included angle was 165 degrees, it was 
relatively difficult to advance to slip or feed the plastic filled rope. 
By contrast, in this test as in Test XII and all other successive tests 
with an included angle of about 160.degree. or less, it was relatively 
easy to slip or feed the plastic covered rope in a "slip and cut" 
operation. 
TEST XV 
Included Groove Angle--154 degrees 
Number of Rope Turns--Two and One-fourth 
Results of this test were as follows: 
______________________________________ 
Deadline Load 
Sensor Load T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 4 Min. 
5 Min. 
______________________________________ 
40,000 150 200 -- -- -- 
50,000 225 275 -- -- -- 
60,000 400 400 -- -- -- 
70,000 750 1000 -- -- -- 
80,000 1600 1900 -- -- -- 
90,000 2800 3100 -- -- -- 
100,000 3800 4100 -- -- -- 
110,000 4800 5000 -- -- -- 
120,000 5600 5700 -- -- -- 
130,000 6200 6400 6500 6600 6700 
______________________________________ 
TEST XVI 
Included Groove Angle--150 degrees 
Number of Rope Turns--Three and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
50,000 0 0 -- -- 
60,000 0 0 -- -- 
70,000 0 0 -- -- 
80,000 0 0 -- -- 
90,000 0 0 -- -- 
100,000 50 100 -- -- 
110,000 100 150 -- -- 
120,000 200 225 -- -- 
130,000 300 300 -- -- 
______________________________________ 
In the test 0-130,000, the 130,000 lb. load was applied very rapidly to 
simulate shock loading that may occur in normal drilling operations. 
TEST XVII 
Included Groove Angle--150 degrees 
Number of Rope Turns--Two and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
40,000 50 75 -- -- 
50,000 100 175 -- -- 
60,000 300 350 -- -- 
70,000 625 850 -- -- 
80,000 1250 1500 -- -- 
90,000 2000 2300 -- -- 
100,000 3000 3300 -- -- 
110,000 4000 4200 -- -- 
120,000 4800 4800 -- -- 
130,000 5700 6000 6100 6200 
0-130,000 7000 7100 7400 -- 
______________________________________ 
TEST XVIII 
Included Groove Angle--145 degrees 
Number of Rope Turns--Three and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load T.sub.2 (lbs) 
Deadline Load T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
40,000 0 0 -- -- 
50,000 0 0 -- -- 
60,000 0 0 -- -- 
70,000 50 100 -- -- 
80,000 100 100 -- -- 
90,000 150 150 -- -- 
100,000 150 175 -- -- 
110,000 200 250 -- -- 
120,000 350 400 -- -- 
130,000 500 625 700 800 
______________________________________ 
TEST XIX 
Included Groove Angle--145 degrees 
Number of Rope Turns--Two and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load 
Deadline Load 
T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 4 Min. 
5 Min. 
______________________________________ 
30,000 0 0 -- -- -- 
40,000 150 175 -- -- -- 
50,000 400 550 -- -- -- 
60,000 900 1000 -- -- -- 
70,000 1400 1500 -- -- -- 
80,000 2000 2200 -- -- -- 
90,000 3000 3200 -- -- -- 
100,000 3900 4150 -- -- -- 
110,000 4900 5150 -- -- -- 
120,000 5200 6050 -- -- -- 
130,000 6750 7100 7300 7500 7600 
______________________________________ 
TEST XX 
Included Groove Angle--141 degrees 
Number of Rope Turns--Three and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load 
Deadline Load 
T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
40,000 0 0 -- -- 
50,000 0 0 -- -- 
60,000 25 25 -- -- 
70,000 25 25 -- -- 
80,000 375 375 -- -- 
90,000 375 375 -- -- 
100,000 375 375 -- -- 
110,000 400 400 -- -- 
120,000 450 475 -- -- 
130,000 500 550 600 625 
0-130,000 600 -- -- -- 
______________________________________ 
TEST XXI 
Included Groove Angle--141 degrees 
Number of Rope Turns--Two and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load 
Deadline Load 
T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 4 Min. 
5 Min. 
______________________________________ 
30,000 0 0 -- -- -- 
40,000 100 125 -- -- -- 
50,000 250 300 -- -- -- 
60,000 500 600 -- -- -- 
70,000 1000 1100 -- -- -- 
80,000 1650 1950 -- -- -- 
90,000 2500 2800 -- -- -- 
100,000 3550 3800 -- -- -- 
110,000 4400 4600 -- -- -- 
120,000 5400 5700 -- -- -- 
130,000 6500 6800 7000 7100 7200 
0-130,000 -- 8000 -- -- -- 
______________________________________ 
TEST XXII 
Included Groove Angle--136 degrees 
Number of Rope Turns--Three and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load 
Deadline Load 
T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 4 Min. 
5 Min. 
______________________________________ 
40,000 0 0 -- -- -- 
50,000 0 0 -- -- -- 
60,000 25 25 -- -- -- 
70,000 75 100 -- -- -- 
80,000 125 125 -- -- -- 
90,000 150 150 -- -- -- 
100,000 475 475 -- -- -- 
110,000 475 500 -- -- -- 
120,000 650 700 -- -- -- 
130,000 750 800 875 900 925 
0-130,000 1000 -- -- -- -- 
______________________________________ 
TEST XXIII 
Included Groove Angle--136 degrees 
Number of Rope Turns--Two and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load 
Deadline Load 
T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 4 Min. 
5 Min. 
______________________________________ 
30,000 225 225 -- -- -- 
40,000 350 400 -- -- -- 
50,000 650 750 -- -- -- 
60,000 1200 1300 -- -- -- 
70,000 2400 2600 -- -- -- 
80,000 3300 3400 -- -- -- 
90,000 4200 4400 -- -- -- 
100,000 5200 5400 -- -- -- 
110,000 6200 6450 -- -- -- 
120,000 7300 7600 -- -- -- 
130,000 8400 8600 8800 9000 9100 
0-130,000 -- 10000 -- -- -- 
______________________________________ 
TEST XXIV 
Included Groove Angle--132 degrees 
Number of Rope Turns--Three and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load 
Deadline Load 
T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
40,000 0.0 0 -- -- 
50,000 0.0 0.0 -- -- 
60,000 25 50 -- -- 
70,000 100 100 -- -- 
80,000 125 125 -- -- 
90,000 125 125 -- -- 
100,000 150 200 -- -- 
110,000 225 225 -- -- 
120,000 275 325 -- -- 
130,000 425 575 700 800 
0-130,000 925 1050 -- -- 
______________________________________ 
TEST XXV 
Included Groove Angle--132 degrees 
Number of Rope Turns--Two and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load 
Deadline Load 
T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 4 Min. 
5 Min. 
______________________________________ 
30,000 300 300 -- -- -- 
40,000 425 450 -- -- -- 
50,000 775 900 -- -- -- 
60,000 1350 1500 -- -- -- 
70,000 2225 2450 -- -- -- 
80,000 3125 3350 -- -- -- 
90,000 4100 4350 -- -- -- 
100,000 5125 5400 -- -- -- 
110,000 6200 6500 -- -- -- 
120,000 7200 7800 -- -- -- 
130,000 8600 9150 9475 9700 9850 
0-130,000 10150 10850 -- -- -- 
______________________________________ 
TEST XXVI 
Included Groove Angle--121 degrees 
Number of Rope Turns--Three and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load 
Deadline Load 
T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
40,000 0 0 -- -- 
50,000 50 50 -- -- 
60,000 75 75 -- -- 
70,000 75 75 -- -- 
80,000 100 100 -- -- 
90,000 125 125 -- -- 
100,000 200 250 -- -- 
110,000 300 400 -- -- 
120,000 600 900 -- -- 
130,000 1700 1850 2000 2100 
0-130,000 2100 2450 2650 2800 
______________________________________ 
TEST XXVI 
Included Groove Angle--121 degrees 
Number of Rope Turns--Two and One-fourth 
Results of this test were as follows: 
TEST XXVII 
Included Groove Angle--121 degrees 
Number of Robe Turns--Two and One-fourth 
Results of this test were as follows: 
______________________________________ 
Sensor Load 
Deadline Load 
T.sub.2 (lbs) 
T.sub.1 (lbs) 
1 Min. 2 Min. 3 Min. 
4 Min. 
______________________________________ 
20,000 0 -- -- -- 
30,000 75 -- -- -- 
40,000 200 700 -- -- 
50,000 1300 1400 -- -- 
60,000 2200 2400 -- -- 
70,000 3000 3350 -- -- 
80,000 4400 4600 -- -- 
90,000 5500 5900 -- -- 
100,000 6750 6800 -- -- 
110,000 8250 8900 -- -- 
120,000 10100 10800 -- -- 
130,000 11900 12300 12400 -- 
0-130,000 13000 13700 13700 -- 
______________________________________ 
A comparison of the results from the above tests, particularly Tests 
IX-XXVII, confirms the preferred parameters set forth above. In 
particular, in Tests IX and X, it was somewhat more difficult to slip and 
feed the plastic coated rope than in the subsequent tests. With the 
included angle being greater than 165 degrees, it became much more 
difficult if not impossible to slip or feed the plastic coated rope in the 
manner described above as being necessary for proper operation of the 
cable anchor assembly of the invention. 
The more preferred included angle for the groove was in the range of 150 
degrees-160 degrees and most preferably about 160 degrees as demonstrated 
in Tests XII-XVII. In this range, a substantial portion or preferably 100 
percent of the rope load could be supported by the drum without reliance 
upon the clamp. 
As the included angle ranged downwardly toward 130 degrees, the remaining 
load (T.sub.2) which is necessarily taken up by the clamp became 
relatively excessive. Note in particular from Test XXIV that, with three 
and one-fourth wraps of rope about the drum and with an included angle of 
about 132 degrees, the load cell load (T.sub.2) approached 1000 lbs. which 
is considered a relative maximum in terms of the present invention. By 
contrast, Test XXVI also included three and one quarter turns of rope 
about the drum with an included angle of 121 degrees, resulting in loads 
ranging unacceptably from above 1000 to almost 3000 lbs. 
At the same time, these tests indicate that it is possible to operate with 
as few as two and one-fourth turns. However, three and one quarter to four 
and one-fourth turns are preferred and three and one quarter turns are 
most preferred. 
Accordingly, there has been described a preferred cable anchor assembly and 
method for anchoring plastic coated cable in oil drilling derrick 
applications and the like. Numerous variations and modifications are 
believed apparent in addition to those specifically set forth above. 
Accordingly, the scope of the present invention is defined only by the 
following appended claims.