Manufacture of telecommunications cable core units

Forming a core unit from telecommunications conductor units of twisted together conductors in which the units are first changed in relative positions laterally of their passline and then are passed between two rollers to form them into a curved array. The positions of the units in the array influence their final positions in the core unit as they move towards a core unit closure device. Hence as the positions in the array change because of the positional change in relative positions of the units upstream from the array, then the units change in relative positions in the core unit by extending backwards and forwards around the core unit axis.

This invention relates to the manufacture of telecommunications cable core 
units. 
A telecommunications cable is constructed with a core comprising one or 
more core units, each having a multiplicity of twisted units of 
conductors, each unit conventionally being a twisted pair of conductors. A 
core may be formed as a single core unit of twisted pairs, e.g. fifty or 
one hundred pairs, or larger cores, i.e. up to thirty-six hundred twisted 
pairs, each comprise a plurality of core units. The twisted pairs are 
stranded together to form a core unit with the conductors of each pair 
twisted together with a predetermined lead to the twist, i.e. the distance 
taken along the pair for each conductor to complete a single revolution 
along its path. This distance is normally referred to as the "twist lay" 
of the pair. There are different twist lays provided for the twisted pairs 
in a core unit with a pair having a particular twist lay being adjacent to 
other pairs of different twist lays. Care is taken, so far as is 
practicable, to ensure that pairs of equal or similar twist lays are 
separated from each other. The reason for this arrangement is an attempt 
to maximize the communications performance of the cable, e.g. to lessen 
pair-to-pair capacitance unbalance, to reduce cross-talk between the pairs 
and to lower the coefficient of deviation of mutual capacitance of pairs 
in the cable. To reduce the pair-to-pair capacitance unbalance and to 
improve cross-talk, suggestions have been made to move the conductor pairs 
relative to one another as they progress towards a stranding machine for 
stranding them into a core unit so that in the finished core unit, the 
conductor pairs change in relative positions and distances apart. In a 
suggested method for changing the relative position of conductor pairs as 
they move towards the stranding machine, the conductor pairs enter a guide 
arrangement which comprises a system of horizontal guides movable 
horizontally and located in vertically tiered fashion. This method was 
first suggested by S. Norblad of Telefonaktiebolaget L.M. Ericsson, in a 
paper entitled "Capacitance Unbalance Telecommunications Networks" read 
before the International Wire and Cable Symposium in 1971. 
Further methods of changing the relative positions of the conductor pairs 
have also been suggested. These include the method and accompanying 
apparatus which is described and claimed in U.S. patent application Ser. 
No. 637,594, filed Aug. 3, 1984 (Canadian Application No. 459,921 filed 
July 27, 1984), and entitled "Manufacture of Telecommunications Cable Core 
Units" in the name of J. N. Garner. In that patent application, apparatus 
is described for forming a core unit in which a plurality of position 
changing means are provided for conductor units, each position changing 
means operating to change the position of a conductor unit across the 
feedpath relative to other units. In this apparatus, each position 
changing means comprises a guide and means to reciprocally move the guide 
across the feedpath. The position changing means are disposed in series 
with one another along the feedpath with their reciprocating means 
overlapping one another in a view taken along the feedpath and the 
arrangement of position changing means is such that each guide is aligned 
for unobstructed passage of a conductor unit as it moves along the 
feedpath. 
Thus although suggestions have been made to move the conductor pairs 
relative to one another in the finished core unit, it still remains 
necessary to use a stranding machine to provide a core unit in which the 
twisted conductor units move around the axis of the core unit as they 
extend along its length. This type of assembly of core unit is preferred, 
because it provides a more positive assembly of the conductor units in a 
core unit and also enables the finished cable to be flexed either during 
spooling or laying into operating position by virtue of the fact that the 
conductor units extend angularly around the core unit. 
While stranding machines are obviously very efficient in producing the 
required core unit structure, they are of complex construction. A core 
unit take-up reel is required which needs to be rotated not only around 
its own axis, but also around the axis of the machine so as to 
simultaneously provide the stranding action of the stranding machine and 
also take-up the core unit after its formation. The take-up reel, 
especially when partially or almost completely loaded with core unit, has 
substantial weight and thus provides a substantial moment of inertia as it 
is rotated around the axis of the stranding machine to provide the 
stranding action. To provide for such a rotational movement, stranding 
machines are very heavily built and are expensive to manufacture. In 
addition to this, because of the location of the take-up reel and the need 
for it to rotate about two axes, it is an extremely tedious and time 
consuming operation for a completely loaded take-up reel to be removed and 
for a succeeding and empty reel to be located within the stranding 
machine. 
It is an object of the present invention to provide a method and apparatus 
for forming a core unit which avoids the use of a stranding machine while 
causing conductor units to extend around the core unit at an angle to its 
length. It is also an object of the invention to provide a method and 
apparatus which, while avoiding the use of a stranding machine, enables 
the core unit so formed to be assembled directly onto a take-up reel which 
is rotating in one direction only or alternatively, enables the completed 
core unit to be moved directly in line or in tandem with apparatus which 
provides the core unit with either a surrounding sheath or shield or a 
jacket material or both. 
Accordingly, the present invention provides apparatus for forming a core 
unit from telecommunications conductor units each formed of twisted 
together insulated conductors comprising, in a downstream direction along 
a passline for the conductor units, a position changing means for changing 
the positions of laterally spaced-apart conductor units across the 
passline and relative to other conductor unit, conductor unit array 
forming means comprising at least two rollers having rotational axes one 
downstream from the other with opposed peripheral surfaces of the rollers 
spaced-apart one on each side of the passline, each surface changing in 
diameter along its length with one surface having its smallest diameter 
and the other its largest diameter at a position intermediate its axial 
ends, the positions and configurations of the surfaces being such that 
together they are operable to position the conductor units in an array as 
the conductor units move towards, past and then beyond the rollers, the 
array extending in two planes in a section taken across the passline, the 
rollers enabling the conductor units to move across the array dependent 
upon the positional charge caused by the position changing means; and core 
unit forming means for causing convergence of the conductor units in the 
array to bring them together with the relative positions of the conductor 
units changing in the core unit as they extend along the core unit, each 
conductor unit extending around the core unit axis alternately in opposite 
directions as influenced by its movement across the array. 
In a preferred construction, the position changing means is operable for 
continuous operation to move the conductor units across the passline in a 
continuous fashion. In a further preferred arrangement, one of the rollers 
has a concave peripheral surface and the other a convex peripheral 
surface. 
The invention also provides a method for forming a core unit from 
telecommunications conductor units each formed of twisted together 
insulated conductors, the method comprises (a) moving a plurality of 
conductor units in laterally spaced relationship along a passline while:- 
moving the laterally spaced conductor units into an array across the 
passline, the array of controlled configuration extending in two planes in 
a section across the passline, and moving each conductor unit alternately 
in opposite directions across the passline independently of other units at 
a position upstream from the array so that each conductor unit moves 
alternately in opposite directions across the array and the conductor 
units move laterally relative to one another in the array; and (b) causing 
the conductor units in the array to converge as they continue along the 
passline so as to bring them together to form the core unit with the 
relative positions of the conductor units changing in the core unit as 
influenced by their relative positions in the array and with each 
conductor unit moving around the core unit axis alternately in opposite 
directions as it moves along the core unit and as influenced by its 
movement across the array. 
By the use of the apparatus and the method according to the invention, 
conductor units are caused to move around the axis of the core unit as 
they extend along its length. While the conductor units will not 
continuously move around the core unit axis in a single direction, as in 
conventional constructions, nevertheless the advantages obtained by 
conventional core unit construction will be obtained with a core unit made 
in the inventive manner. Movement of the conductor units in opposite 
directions around the axis of the core unit formed by the inventive method 
and apparatus provide the angular orientation relative to the axial 
direction so as to enable the core unit and the finished cable to be 
flexed in the acceptable fashion. In the core unit made by the method 
according to the invention, if sufficient lateral movement is provided for 
each of the conductor units in the array, then each conductor unit as it 
extends axially may also move around the core unit axis for almost a 
complete revolution in each direction.

The apparatus according to the invention is particularly useful for a 
tandem or "in-line" operation for twisting individually insulated 
conductors together into conductor pairs and then for forming these 
conductor pairs into a core unit. 
As shown in the embodiment, twenty-five conductor pairs 10 (FIG. 1) each 
formed from two twisted together individually insulated conductors, are 
drawn from twenty-five reels 12 of the conductor pairs in conventional 
fashion. A core unit 14 is formed at the downstream end of the apparatus 
by passing the conductor pairs through a closing die 16 which draws the 
conductor pairs together and a binding head 18 at which position a binding 
material is closed around the drawn together conductor pairs to hold them 
together in conventional manner. The closing die forms part of a core unit 
forming means 24 for causing divergence of the conductor units into a core 
unit. 
Disposed between the reels 12 and the means 24 are a position changing 
means 20 and a conductor unit array forming means 22. The position 
changing means and the conductor unit array forming means ensure that the 
conductor pairs are moved relative to each other and in such a fashion 
that the finished core unit has conductor pairs extending around its axis 
alternately in each direction as the conductor units extend along the 
length of the core unit. 
The position changing means 20 and a guide means 26 which precedes it are 
of the construction described in a copending U.S. patent application Ser. 
No. 637,594 filed Aug. 3, 1984 (Canadian Application No. 459,921 filed 
Jul. 27, 1984) entitled "Manufacture Of Telecommunications Cable Core 
Units" in the name of J. N. Garner. 
The guide means 26 comprises a roller 28 which is freely rotatably mounted 
upon a machine frame (not shown) and the roller is provided with a 
plurality of annular grooves (not shown) as described in the 
aforementioned application. As can be seen from FIG. 1, the conductor 
pairs are fed from the reels 12 and through the guide means. Each 
conductor pair is disposed in its own individual groove in the roller 28 
so as to maintain the conductor pairs separate from one another as they 
approach the position changing means 20. 
As shown by FIGS. 2 and 3, a plurality of position changing means 30 are 
provided for the conductor pairs, one position changing means for each 
pair. The position changing means are all housed within a straight sided 
frame 32. The position changing means are disposed in two groups, one 
vertically above the other, with the position changing means in each group 
lying in series with one another along the feedpath for the conductor 
pairs. Each position changing means comprises a guide 34 for a conductor 
pair. This guide, as shown by FIG. 4 has a guide passage 36 that is formed 
with two side wings 38 attached with rivets 40 to an endless moving means 
for the guide, the moving means comprising a flat plastics belt 42 through 
which the rivets 40 pass. The endless moving means also comprises a chain 
44 which extends between the ends of the belts as shown in FIG. 7. Each 
endless moving means has a horizontal flight 45 formed by the belt 42 and 
the associated guide 34, the belt mounted around two pulleys 46 at the 
sides of the machine frame to proceed as two flights 48 towards a sprocket 
50 around which the chain 44 passes. The endless moving means overlap one 
another, as shown particularly in FIG. 3, and the arrangement is such that 
each guide is aligned for unobstructed passage for its conductor pair as 
the pair moves along the feedpath. This clear passage for movement is 
achieved by disposing the horizontal flights 45 of the belts 42 of each 
group of position changing means at different vertical levels as shown by 
FIG. 3. In practice, with the lower group, the horizontal flights are 
displaced progressively vertically upwards from one changing position to 
the next in the downstream direction of the feedpath by locating the 
pulleys upwardly from each position changing means to the next on supports 
55 (see FIG. 5). In contrast the horizontal flights of the upper group are 
displaced vertically downwards in a downstream direction of the feedpath. 
The horizontal flights of the two groups oppose each other across the 
feedpaths and approach each other progressively in a downstream direction. 
The advantages for this arrangement are as discussed in the aforementioned 
application. 
Each of the endless moving means is movable independently of the others. 
For this reason, each position changing means is provided with its own 
reversible stepper motor 52 (see FIGS. 2, 3 and 7). All of the stepper 
motors 52 are mounted remotely from the horizontal flights by being 
attached to upper and lower panels 54 of the machine stand. Each motor is 
directly drivably connected to a sprocket 50 which engages with its 
respective chain 44 as shown by FIG. 7. The drive motors may be driven at 
the same speed as each other whereby the guides 34 move along their 
horizontal flights at the same speed but out of phase with each other. 
However, in this embodiment the drive motors are driven at speeds which 
are slightly different from each other so that the positional relationship 
of all of the guides is continuously changing while reducing the 
possibility of a set pattern of movement of the guides 34. 
A reversing means is provided for each drive motor 52 to cause its belt 42 
to reciprocate. As shown by FIG. 7, and more clearly described in the 
aforementioned application, the reversing means for each direction of 
movement of a belt 42 comprises a magnet carried in one leg of a head 58 
which is U-shaped in side elevation (not shown). The other leg carries a 
magnetic field receiving means in the form of a coil (not shown) affected 
by inductance of the magnetic field created by the magnet. Each coil sends 
signals into an electrical circuit (not shown), the strength of the 
signals dependent upon the strength of the magnetic field induced in the 
coil and produced by the magnet. A trigger device in the form of an arm 60 
is secured to and projects sideways from the chain 44 so as to be aligned 
with the gap in the head 58. The position of the arm on the chain is 
dictated by the position required to influence the magnetic field, i.e. by 
a location within the gap when the guide 34 is at the end of its movement 
on the horizontal flight of its belt in the appropriate direction. 
In use of the position changing means, the conductor pairs 10 are fed to 
their individual changing means 20 in the manner described with reference 
to FIG. 1. Each conductor pair is passed through a respective guide 34 and 
proceeds from there around two in series arrangement rollers 62 prior to 
passing to the conductor unit array forming means. As the conductor pairs 
move along their feedpaths in spaced positions through the position 
changing means, the independent motors 52 rotate at their own speed, 
possibly controlled by a computer, so as to move the belts 42 to 
reciprocate the guides horizontally. During this movement, each of the 
conductor pairs passes both over and under horizontal flights of the belts 
42 of position changing means in its own group, as shown by FIG. 2. In 
this figure, the paths of only six conductor pairs 10 are shown for 
clarity. Movement of the guides 34 independently of other guides 
continuously changes the relative positions of all of the conductor pairs 
as they pass through the position changing means. Thus as conductor pairs 
pass around the arrangement roller 62, their positions in the plane of 
contact with the rollers are dependent upon the positions of the pairs at 
any particular time moving through the guides 34. The relative lateral 
movement of conductor pairs will be discussed below. 
While the position changing means is useful for producing positional change 
of conductor units in the finished core unit, any progression of conductor 
units around the axis of the core unit as they extend along its length is 
a random occurrence and takes place in a localized region. In the 
aforementioned application Ser. No. 637,594, the progression around the 
core unit was provided by a stranding machine in conventional fashion. In 
the apparatus of the present invention however, the stranding machine is 
replaced by the conductor unit array forming means 22 which simplifies the 
structure of the apparatus and also simplifies the reeling of cable core 
and removal of filled reels and their replacement. 
To be able to provide for any movement of each conductor unit around the 
core unit axis in progressive fashion, then the conductor unit array 
forming means must produce movement of each conductor pair not only in one 
plane as with the position changing means, but also in a second plane in a 
cross-section taken along the passline. To achieve this two planar 
movement of each conductor pair, the forming means 20 operates to convert 
the planar arrangement of the conductor pairs as they issue from the 
rollers 62 into a two planar array 72 in a section taken across the 
feedpath. Thus any lateral movement of any conductor pair as produced by 
the position changing means, will be translated into a movement across the 
array in two directions. 
As can be seen from FIG. 1 and more clearly from FIGS. 8 and 9, the array 
forming means comprises two rollers 64 and 66. The roller 64 is disposed 
with its axis of rotation slightly upstream from that of roller 66 with 
the rollers disposed one on each side of the passline. The outer 
peripheral surfaces of the two rollers vary in diameter along their axial 
lengths as shown by FIG. 9. In the case of roller 64, its outer peripheral 
surface 68 is of concave curvature whereas the surface 70 of roller 66 is 
convex. As is clearly seen from the figures, especially FIGS. 9 and 10, 
the rollers are disposed so that their surfaces while opposing one another 
do not in fact form a nip between them for the conductor pairs to be moved 
along the passline. In contrast, the rollers coact so that the surface of 
each roll urges the conductor pairs against the surface of the other roll 
as it passes between them so as to form a curved array 72 of the conductor 
pairs as they issue downstream from the roller 66. This curved array is in 
contrast to the flat array which exits from the rollers 62 and, as can be 
seen from FIG. 14 particularly, has two ends which turn upwardly. The 
spacing apart of the rollers 64 and 66 in the manner shown, ensures that 
movement of the conductor pairs can take place laterally of the array as 
they move into and between the rollers so that the conductor pairs may be 
moved relative to each other. In addition to this, with the rollers curved 
in opposite directions as described, the coaction of the rollers urges the 
conductor pairs into a specific position against each roller, that 
position being dependent upon the position and direction of movement of 
each conductor pair as it moves into contact with the roller 64. In 
contrast, if the rollers had a relationship tending more towards a nip for 
passage of the conductor pairs, then movement of the pairs transversely of 
the array could not take place and also there might be a tendency for the 
conductor pairs to bunch together in between the rollers so as to follow a 
path of least resistance as they move towards the closing dies. 
The array 72 issuing from between the rollers 64 and 66 then continues 
towards the core unit forming means 24 for the conductor pairs. As shown 
particularly by FIG. 11, the means 24 comprises an upstream profile die 74 
with orifice 75 and a further profile die or dies 76 with orifice 77, 
these dies 74 and 76 which are for the purpose of guiding the conductor 
pairs in the array 72 into a more closed position in which they are 
aligned with the closing die 16 which causes final convergence of the 
conductor pairs to form the core unit 14. As may be seen from FIG. 11, the 
two profile die orifices 75 and 77 are somewhat elongated vertically so as 
to form more of an elliptical or oval shape as distinct from a circular 
orifice shape. In order to bring the conductor pairs into alignment with 
the closing die orifice 78 so as to fill it without distorting some pairs 
more than others in the closing die orifice, it is essential that the 
profile die orifices 75 and 77 have their centers disposed upwardly from 
the closing die orifice 78. As a result of this, as the array of conductor 
pairs moves into the orifice of die 74, the upturned side portions of the 
array engage the sides 80 of the orifice with the center of the array 
engaging towards the bottom regions of the orifice. The conductor pairs at 
the upwardly turned side edges are then directed more towards the upper 
regions of the profile die orifice 77 as these regions are lower than 
those of the die orifice 75. Hence the conductor pairs move more towards 
the upper regions of the dies as they progress from one die to another 
until upon reaching the closing die orifice 78, the conductor pairs engage 
around the whole of the peripheral surface of the circular die orifice in 
natural alignment with the orifice as they pass into it. The bunching 
together of conductor pairs at this stage, of course, ensures that the die 
78 is filled by the pairs. 
As will now be described, the relative movement of the conductor pairs in 
the position changing means and the formation of the array in the array 
forming means causes the conductor pairs to follow a path around the axis 
of the core unit as the core unit is being formed. This progression of 
conductor pairs from position changing means and into the finished core 
unit will be described with reference to two pairs only. The action of 
these two pairs is typical of all other pairs passing through the 
apparatus and into the core unit. 
FIG. 13 shows, as dots, the positions of all of the conductor pairs 10 at a 
specific time as they emerge from the position changing means 20. At that 
time, two of the conductor pairs 1Oa and 1Ob are in positions 82 and 84 
respectively as shown by FIG. 13. Both conductor pairs 10a and 10b are 
moving towards the left hand side of FIG. 13 with conductor pair 10a 
having only just commenced movement in that direction and conductor pair 
1Ob almost at the end of its movement before returning in the opposite 
direction. 
At some later time, and with the conductor pairs moving laterally at 
different speeds, conductor pair 10a has now reached position 84 towards 
the end of its movement towards the left. At this stage, conductor pair 
10b has completed movement towards the left and is at some intermediate 
position 86 of movement towards the right. 
The corresponding positions 80, 82, 84 and 86 for movement of the two 
conductor pairs across the array 72 and as they pass through the dies 74 
and 76 are shown in FIGS. 14, 15 and 16. 
The positions of conductor pairs in the array and as they pass through the 
profile dies 74 and 76 have some control over their position in the 
finished cable core unit. The final position of each of the pairs is, of 
course, also dependent upon the pressure applied to them in a lateral 
direction by other pairs as they approach and enter the closing die 18. 
Hence, not only is each pair moved progressively in one direction and then 
in the other around the axis of the core unit as it extends along the core 
unit, but also its radial position in the core unit is automatically 
determined. This is illustrated by the positional movement and the path 
followed by conductor pairs 10a and 10b as they turn around the core unit 
axis along an axial length of the core unit. In FIG. 17, conductor pair 
1Oa follows the path 88 around the core unit between the two positions 80 
and 84 while moving radially inwards and outwards randomly through the 
core unit. As with all other conductor pairs, pairs 1Oa and 1Ob move 
almost completely for 360.degree. around the core unit axis before 
changing direction. As positions 80 and 84 in FIGS. 13 and 14 are almost 
at opposite ends of one complete direction of movement, then in FIG. 17, 
pair 10a substantially completes movement in one direction and almost one 
complete revolution around the core unit axis. 
On the other hand, conductor pair 10b in completing one direction of 
movement and then commencing to move in the opposite direction between 
positions 82 and 86, does in fact move to its limit position 90 in one 
direction as it moves along path 92 in FIG. 17 between the corresponding 
positions 82 and 86. 
As may be seen, it is impossible for any conductor pair 10 to form a 
complete revolution about the cable core axis before changing direction of 
movement around the axis. Passage of the closed together conductors in the 
core unit through the binding head 18 effects wrapping of a binder tape in 
conventional manner around the core unit and holds it in substantially 
circular cross-sectional shape. 
The above embodiment shows that with the use of apparatus and a method 
according to the invention, conductor pairs in a finished core unit may be 
caused to follow a path which extends around the axis of the core unit as 
the pairs move along the core unit and without use of a stranding machine. 
It follows that the core unit is provided with the degree of flexibility 
which is required to enable it to bend and without placing undue strain on 
the conductor pairs. 
As can be seen from FIG. 1, after movement of the core unit through the 
binding head, it is reeled onto a reel 94. Because the apparatus causes 
the conductor pairs to move around the axis of the core unit as described, 
there is no reason for the reel 94 to be rotated around any axis 
additional to its normal rotational axis 96. Thus the reel 94 is merely 
rotated around its own axis by a motor 98 and for this purpose may be 
merely held in bearings at its ends in a fixed position machine frame. It 
follows therefore that it is a simple matter to remove a filled reel and 
to replace it with an empty reel for a further reeling operation in a 
short space of time. In addition to this, and as shown by the modification 
of FIG. 18, there may be two or more reels disposed side-by-side such as 
reels 94 and 100 and, upon the reel 94 being filled with core unit, then 
the core unit issuing from the closing die is fed onto the reel 100 
without stopping operation. 
In a second embodiment shown in FIG. 19, the reels are dispensed with and 
the core unit after passage through the binding head 18 is then passed 
through apparatus for completing manufacture of the cable with the core 
unit forming the whole cable core. The bound core unit is fed into 
apparatus 102 for folding a core wrap 104 around the core unit and for 
placing a metal shield or sheath 106 onto the core unit prior to extruding 
a jacket around the unit by the extrusion head 108. The apparatus for 
providing the core wrap, sheath and jacket are of conventional 
construction and do not require description. 
The possibility of applying a core wrap, sheath and jacket in tandem with 
core unit formation also makes it possible to tandemize the above 
operation with the twisting of individually insulated conductors into 
conductor pairs when incorporated with apparatus as described in U.S. 
patent application Ser. No. 565,634 filed Dec. 27, 1983 (Canadian 
Application No. 444,295, filed Dec. 23, 1983) and entitled "Forming Cable 
Core Units" and in the names of J. Bouffard, A. Dumoulin and M. Seguin. As 
described in application Serial No. 565,634, in the second embodiment of 
FIG. 19, the reels of conductor pairs are replaced by a plurality of 
twisting machines 110, i.e. one for each conductor pair 10. These machines 
110 may be of conventional construction and each have two reels of 
individual insulated conductor. The two conductors of each machine are 
twisted together as they leave the machine. The twisted pairs then pass 
through a tension reducing means which enables the twisting machines to be 
placed in tandem with the core unit forming means. The tension reducing 
means comprises two cylinders 112 and 114 which are rotating at a 
peripheral speed greater (e.g. 5% greater) than the draw speed of the 
conductor pairs into the closing die 78. As described in application Ser. 
No. 565,634, the cylinders do not drive the conductor pairs along their 
feedpath. Instead, the areas of contact between cylinders 112 and 114 and 
conductor pairs are merely sufficient to assist in drawing the pairs 
through the apparatus with some slippage because of the excess peripheral 
speed of the cylinders. The degree of grip of the conductor pairs upon the 
cylinders and which thus controls the amount of assistance provided by the 
cylinders in drawing the conductor pairs from the twisting machines, is 
dependent upon the degree of tension in each conductor pair downstream 
from the cylinders. 
Hence, when there is a small tension in any pair downstream from the 
cylinders, the cylinders provide no assistance in drawing the pairs 10 
because the grip upon the cylinders is unsubstantial. If downstream 
tension increases, thereby increasing this grip, the cylinders provide a 
degree of assistance corresponding to the degree of grip. Of course, 
immediately this assistance is given, the downstream tension reduces 
thereby reducing the degree of grip and thus of cylinder assistance. The 
cylinders thus reduce the tensions downstream to enable the conductor 
pairs to be formed, at low tension, into the core unit. The operation of 
the tension reducing means which enables the twisting operation to be 
tandemized with the core unit forming process is described in detail in 
application Ser. No. 565,634. 
It is clear therefore that the invention provides not only a core unit 
having conductor pairs extending around its center to provide the normal 
flexibility for a core unit, but also simplifies the operation of the 
apparatus, i.e. it enables reels to be replaced simply and quickly or it 
enables the core unit to be formed in tandem with the cable finishing 
processes. Clearly, greater core and cable flexibility is provided if each 
conductor pair extends around the core unit axis for almost a complete 
revolution. However, it is preferred that the movement around the core 
axis of each pair subtends an angle of at least 180.degree. with the core 
unit axis. In particular, extremely good flexibility is obtained with the 
angle at least 270.degree.. In addition to this, it is also clear that 
each conductor pair moves through the core unit completely independently 
of other conductor pairs and as dictated by the use of the position 
changing means in addition to the array forming means. Each conductor pair 
in fact follows a path around the core unit through inner and outer radial 
positions so as to lie close to any other conductor pair for only short 
distances of the core unit. Thus the apparatus provides improvements in 
the electrical characteristics such as in mutual capacitance or lowering 
the coefficient of deviation of mutual capacitance between the pairs and 
lessening outer pair capacitance unbalance. The independent movement of 
the conductor pairs throughout the core unit also leads to a reduction in 
cost.