Guide bush

A guide bush is described, having a bush-holder and a quill integral with the bush support. The device has a clamp capable of rotating a workpiece, means for opening and closing the clamp and regulating means adapted to monitor the opening and closing means in order to compensate for changes in the dimensional tolerances of the workpiece, wherein the bush regulating means are adapted to operate the opening and closing means of the clamping means very quickly as a direct result of variations in the dimensional tolerances of the workpiece in order to provide a substantially constant pressure of the clamp on the workpiece. The bush is for use with a machine tool such as a travelling headstock automatic lathe.

FIELD OF THE INVENTION 
The invention relates to a guide bush. 
More specifically, it relates to a guide bush notably designed in 
particular for use with a machine tool such as a travelling headstock 
automatic lathe. 
DESCRIPTION OF THE PRIOR ART 
A guide bush is known of the fixed type, housed inside a support block by 
means of a bush-holder support, which has a quill integral with the 
bush-holder inside which a workpiece to be machined can be accommodated 
and rotatably supported. 
This type of bush has the following disadvantages. 
Firstly, where a workpiece having significant, notably positive, variations 
in dimensional tolerances, in other words where there are large increases 
in the outer diameter of the workpiece in certain areas, there is a risk 
of jamming which causes the workpiece to become wedged inside the bush or 
even causes variations in the angular speed of the workpiece in relation 
to the tool. 
In the opposite case, i.e. in the presence of negative dimensional 
variations, that is when a workpiece has substantially localized 
reductions in its outer diameter, the machined product acquires an outer 
diameter that differs from the desired diameter (generally larger) due to 
displacement from the centre of the workpiece due to lateral thrust of the 
tool thereon. 
Rotating bushes are available which, while they naturally prevent the risk 
of jamming, have the major disadvantage of transferring to the finished 
product any geometric faults existing on the workpiece as supplied. 
Finally, adjustable bushes are known which have clamping means associated 
with a nut on which an outer, manual force can be applied. Again, this 
type of bush only very partially overcomes the above-mentioned problems. 
Although this adjustable bush makes it possible to overcome the 
dimensional variations of the workpiece to be machined, roughly and in a 
given series, permanent adjustment is impossible. 
OBJECTS OF THE INVENTION 
It is an object of the instant invention to overcome the above-mentioned 
disadvantages by providing a guide bush capable of overcoming all the 
variations in dimensional tolerances which can occur on a workpiece to be 
machined or between one workpiece and another, without outside 
intervention, that is in quasi automatic and permanent manner, by ensuring 
that geometric faults have no effect on the finished product. It is also 
an object of the present invention to provide a guide bush which makes it 
possible to machine finished pieces, machined to tolerances that are 
smaller than those of the workpiece. 
BRIEF SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a guide bush, 
notably designed to equip a machine tool such as a travelling headstock 
automatic lathe of the type comprising: 
a bush-holder adapted to be positioned with respect to said lathe, 
a quill integral with the bush holder and comprising clamping means adapted 
to receive and rotatably guide a workpiece to be machined, 
means for opening and closing the clamping means so as to adjust the 
clamping of the latter on the workpiece, and 
regulating means adapted to monitor the opening and closing means in order 
to compensate for positive and negative variations in dimensional 
tolerances of the workpiece, 
wherein the said regulating means are capable of instantaneously actuating 
the means for opening and closing the said clamping means as a direct 
result of variations in the dimensional tolerances of the workpiece being 
machined, in order to provide a substantially constant pressure of the 
clamping means on the workpiece. 
More particularly, the adjustment means of the invention are mechanically 
controlled by the workpiece itself. 
It should also be noted that these adjustment or regulating means are 
driven by an oscillating rotating movement of the sheath, sensitive to 
said variations in the dimensional tolerances of the workpiece.

DETAILED DESCRIPTION OF THE INVENTION 
A preferred embodiment of a guide bush of the invention is described 
hereinbelow with reference to FIGS. 1 to 3. 
The guide bush of the invention, which is generally allocated the reference 
numeral 1, is adapted for use with a machine tool such as a travelling 
headstock automatic lathe, not shown. For this purpose the bush 1 is 
housed at least partly inside a block support BS in which a tool carrier P 
with a tool O firmly mounted thereon, preferably by screwing, and being 
composed in the example shown in FIG. 1 of an interchangeable machining 
wafer, is able to move along a transverse axis Y1. 
The guide bush 1 has a bush-holder 2 which is firmly mounted on the block 
support BS. 
A quill designated by the reference numeral 4 is mounted inside this block 
support BS. The quill 4 is moveable rotatably about a longitudinal axis of 
rotation X1 which is perpendicular to the transverse axis Y1 in the 
embodiment shown. 
Coaxial clamping means 6, capable of receiving and rotatably guiding a 
workpiece or stock bar to be machined B, are housed inside the quill 4. 
This workpiece B is on the one hand driven rotatably about the axis X1 in 
the direction of rotation shown by the arrow RB on FIG. 2, and on the 
other hand advanced transversely along the axis X1 in the direction shown 
by the arrow ATB in FIG. 1. The workpiece B is thus driven in rotation and 
transversely in relation to the bush 1 and in relation to the tool O by 
conventional drive means, not shown. Since the means for driving the 
workpiece B are not the object of the present invention, they will 
consequently not be described in greater detail. 
The bush-holder 2 has an outer sleeve 8 made of a metallic material which 
has a slit 9 passing therethrough which is partially filled with a 
synthetic material such as silicone. This material forms a resilient and 
tight sealing tongue 9a which in particular permits the radial extension 
of the outer sleeve 8 which, since it is housed directly inside a boring 
10 provided in the block support BS, can be fixed therein. 
The bush-holder 2 also has an inner sleeve 12 which is housed and wedged 
inside the outer sleeve 8. For this purpose the inner sleeve 12 has a 
tubular body 13 of frustroconical outer shape, which engages inside a 
corresponding frustroconical boring provided directly in the outer sleeve 
8. 
At one end of the body 13 the inner sleeve 12 has an end or base 14 which 
is threaded on the outside and onto which a notched nut 18 axially 
abutting against a side flange of the outer sleeve 8 is screwed. By 
pushing against the outer sleeve 8, the nut 18 exerts traction on the 
inner sleeve 12 and notably on its tubular body 13. Because of the conical 
connection constituting a wedge between the two sleeves 8 and 12, this 
traction makes it possible to exert a radial thrust on the body 13 towards 
the axis X1. 
In order to achieve this, the inner sleeve 12 has resilient slits 16 
provided longitudinally by milling directly in the body 13 up to the 
threaded end or base 14. Sealing tongues 16a, also made of a synthetic 
material such as silicone, are injected into the slits 16 and serve the 
same function as the tongues 9a of the outer sleeve 8. It will be noted 
that the parts of the slits 9 and 16 that are left empty are arranged so 
that they coincide so as to permit passage of a lubricant, the latter 
being carried across the bush support 2 as well as towards the outside and 
the inside of the sheath 4 via a supply channel H provided in the block 
support BS. For this purpose, the bush-holder 2 is angularly positioned by 
means of an indexing pin 20 housed partly in the bush-holder 2 by radially 
penetrating into the two sleeves 8 and 12 and partly in the radial 
positioning groove 22 provided in the block support BS. 
Two bearings, such as notably ball-bearings having a series of balls 26 and 
28, these latter being intended to support and rotatably guide the sheath 
4, are housed in a boring provided directly in the body 13 of the inner 
sleeve 12. The bearings 26 and 28 are retained firmly transversely and are 
axially positioned in relation to the longitudinal axis X1 by the radial 
thrust exerted by the body 13 on their outer ring, not numbered. The outer 
ring of the ball-bearing 26 bears axially against a shoulder (also not 
numbered) provided directly in the end or base 14. 
It will be noted that the block support BS, the bush-holder 2 (composed of 
the two outer 8 and inner 12 sleeves respectively and of the nut 18) as 
well as the outer rings of the ball-bearings 26 and 28 are firmly secured, 
especially in relation to the travelling headstock automatic lathe by 
fixing means (not shown). 
The sheath 4 has two substantially cylindrical sockets or coaxial tubular 
spindles 30 and 32 designated outer (30) and inner (32) respectively. The 
inner rings (not numbered) of the ball-bearings 26 and 28 respectively are 
directly engaged on one part of the outer socket 30, called the front with 
reference to the direction of forwards movement of the workpiece B, which 
is housed inside the bush-holder 2. The quill 4 which is thus caused to 
rotate by and in the bush-holder 2 is mechanically integral with the 
bush-holder 2 by means of the two ball-bearings 26 and 28. 
A spacer 34 which is interposed and which bears axially between the inner 
rings of said bearings, is engaged between the inner rings of said 
ball-bearings 26 and 28 and on the outer socket 30. It will also be noted 
that the inner ring of the ball-bearing 26 rests laterally on a shoulder 
which is formed by a radially projecting collar 36 provided on the outer 
socket 30. A notched nut 38 is screwed directly onto one free end E1 of 
the quill 4, as close as possible to the tool O and more particularly on a 
free threaded end of the outer tubular socket 30 having the same reference 
numeral. The screw 38 laterally and directly locks the inner ring of the 
ball-bearing 28 and axially retains the two bearings 26 and 28 as well as 
the spacer 34 therebetween on the outer socket 30. 
It will be noted here that the sheath 4, and notably the two outer 30 and 
inner 32 sockets or muffs respectively, the inner rings of the bearings 26 
and 28, the spacer 34 as well as the nut 38 are rotatably mobile on the 
one hand about the longitudinal axis of rotation X1 and, on the other 
hand, in relation to the bush-holder 2 as well as in relation to the block 
support BS. 
It should, however, be noted that the outer socket or muff 30, as well as 
all the elements 26, 28, 34 and 38 which bear from the outside thereon are 
firmly retained transversely in relation to the block support BS and in 
relation to the bush-holder 2. 
A partially oblong key groove 40 which opens on both sides in a radial 
direction, and notably opposite the inner socket or muff 32, is provided 
on the outer tubular socket 30, and notably on a part thereof which is 
termed the rear and which projects outside the bush-holder 2 in the 
opposite direction to the tool O. The key groove 40 also opens axially in 
a direction opposite the tool, facing a ring of a screw-nut VE system to 
be described hereinbelow. 
Housed inside the key groove 40 is a first locking pin 42 which is firmly 
retained inside the inner socket 32, notably by forced pressure, i.e. by 
driving. 
This locking pin 42 which projects radially from the inner socket 32 is 
adapted so as to be able to slide axially inside the groove 40 which 
freely guides the pin 42 transversely along the longitudinal axis X1 while 
ensuring the coupling in rotation of the two sockets 30 and 32 in relation 
to one another. It will thus be noted that the pin 42 and the groove 40 
form rotation securing means for rotation of the outer 30 and inner 32 
sockets together, while enabling them to freely slide transversely in 
relation to each other. In other words, the locking pin 42 and the 
radially opening groove 40 thus act as fastening or key means. 
Projecting radially inside the groove 40 is a nipple 44 provided at the 
free end of a rod forming a lever arm 46 which has a thread 48 near this 
nipple 44. 
The threaded rod 46 is screwed into a tapped part 50 of a collar 52 by a 
sliding adjustment on the rear part of the outer socket 30 which projects 
to the outside of the bush-holder 2 and in which the groove 40 is directly 
recessed. The collar 52 thus directly overlaps the key groove 40. 
Retention of the rod 46 in relation to the outer socket 30 as well as 
thereon is ensured solely by the abutment of the thread 48 of the rod 46 
on the outer circumference of the socket 30. 
It should be noted that the nipple 44 ensures the linkage and mechanical 
connection as far as rotation is concerned between the rod 46 and the 
outer socket 30. 
At the other end of the rod 46 there is provided a recess 54 (FIG. 2) 
within which is housed a first end of a resilient member composed of a 
helicoidal traction spring 56, the second end (not shown) of which is 
firmly retained by conventional attachment means to a fixed support (not 
shown). 
A joint 60 capable of pivoting about a second longitudinal axis X2 of 
rotation, parallel to the first X1 and comprising part of external 
actuating means AME which are shown here in very diagrammatic form by a 
screw jack formed of a piston 62 sliding inside a cylinder 64 firmly 
retained by the support means, (not shown) is provided in the vicinity of 
the traction spring 56 and at the end closest to the rod 46. The actuating 
means AME make it possible to actuate positively, that is at will up to a 
desired position, the rotation of the sheath 4 towards at least two 
positions of opening (PO) and closing (PF) respectively of the clamping 
means 6 and also make it possible to retain the said sheath in these two 
positions, which are shown in broken lines in FIG. 2. To achieve this, the 
actuating means AME have a conventional control circuit (not shown) of the 
pneumatic and/or electronic type capable of transversely guiding the 
piston 62. Controlled opening of the clamping means 6 makes it possible to 
extract a workpiece, and notably a discard at the end of machining, 
whereas the controlled closure permits the feeding of workpieces to be 
machined by immobilizing the workpiece, which in this case acts as a 
abutment. 
It will be understood from the following description that the rod 46 and 
the traction spring 56 constitute the resilient return means of the sheath 
4, these return means having the general designation R. 
The return means R are capable of resiliently resetting any displacement in 
rotation of the sheath 4 effected in one direction of rotation, termed 
opening (shown in FIG. 2 by the arrow DRO). These resilient return means R 
thus have a permanent tendency to bring the sheath 4 back in a direction 
DRF termed closure, opposite to the direction of opening DRO. It will be 
understood from the following explanation that the directions of rotation 
DRO and DRF correspond respectively to the directions of opening and 
closing of the clamping means 6 which are housed inside the sheath or 
quill 4. 
The guide bush 1 of the invention also has a screw-nut system VE arranged 
on one free end E2 (FIG. 1) of the sheath 4. This extremity, which is 
opposite the free extremity E1, projects outside the bush-holder 2 in a 
direction opposite the tool O-tool holder P assembly. 
The screw-nut system VE has a ballscrew the screw V of which is directly 
disposed on the outer circumference of the inner socket 32, near its free 
end E2 and on its rear part by the means of a suitable hemispherical 
recess. 
The screw-nut assembly VE, the screw V of which is thus disposed directly 
on the sheath 4, also has a nut E which is disposed in a ring 66 firmly 
mounted in relation to the bush-holder 2 and mounted directly thereon by 
means of two headed screws 68 and 70, these latter being screwed into 
tappings provided inside the end 14 of the inner sleeve 12. 
Spacers 72 (only one of which has been partly shown in FIG. 1) composed of 
tubular rings are engaged around each of the screws 68 and 70 and are 
laterally interposed between the ring forming the nut 66 and the end 14 of 
the inner sleeve 12. 
It should also be noted that the screws 68 and 70 associated respectively 
with the spacers 72 form angular displacement stops for the rod 46. 
The clamping means 6, which are shaped in order to receive and rotatably 
guide a supported section SP of the workpiece to be machined B, is housed 
inside the sheath 4, and in particular in the inner socket 32. 
The clamping means 6, which are shown in greater detail in FIGS. 4 and 5, 
are composed of a bearing 79 having an assembly of rollers 80 freely 
rotatably mounted directly in contact (by rolling friction) on the outer 
circumference of the supported section SP of the workpiece to be machined 
B. The rollers 80 are radially retained by being enclosed in a cage 82. 
The cage 82 as well as the rollers 80 are housed and retained from outside 
in a radial direction by means of an outer ring 84 which is composed of 
three sectors (only one of which 85 has been given a reference) separated 
by spacer slits 86. The sectors 85 and the ring 84 have an outer shape of 
the double frustroconical type, termed biconical. 
The biconical ring 84 also has three longitudinal grooves 88 which are 
respectively provided on the outside of the segments 85 and which open on 
the one hand axially on both sides on the ring 84 and on the other hand 
radially only towards the outside, opposite the socket 32 (FIG. 1). The 
grooves 88 are oriented with respect to the axis of rotation X1 and they 
are staggered by 120.degree. in respect of one another. The outer 
frustroconical circumference termed the rear of the ring 84 is shaped so 
as to engage inside the free end E1 of the inner socket 32 and more 
particularly inside a seating 89 of corresponding frustroconical shape. It 
will be noted that this rear frustroconical circumference is the only one 
which is functional, only the front circumference permitting release. 
Disposed upstream of the roller bearing 79 (still in relation to the 
direction of forwards transverse movement ATB of the workpiece to be 
machined B, FIG. 1) are sensor means 90 composed, as more clearly visible 
in FIGS. 6 and 7, of three segments (only one of which 91 has a reference 
numeral) of outer frustroconical shape adapted to be housed inside the 
terminal seating 89. 
The three segments 91 which form the sensor means 90 constitute a 
cylindrical boring 92 of variable diameter, this boring being in contact 
with permanent friction (sliding friction) against the workpiece to be 
machined B, and in particular against one section thereof termed the 
controlled section SC. The sensor means 90 are capable of detecting every 
negative and/or positive dimensional variation of the workpiece B and they 
are able at any instant to detect every variation in the diameter of the 
workpiece B of the controlled section SC when this workpiece is driven by 
a rotating movement. These sensor means 90 notably form detection means of 
said dimensional variations. 
It will be noted that the controlled section SC is advantageously arranged 
on the workpiece B directly in front of the supported section SP in 
relation to the direction of transverse forwards movement ATB of the 
workpiece B, that is that it is arranged upstream of this supported 
section SP. 
It will be noted that the three segments 91 which form the sensor means 90 
each have one groove 94, these latter having the same configuration as 
that of the grooves 88. 
It should be noted that the grooves 88 and 94 respectively of the bearing 
79 and of the sensor means 90 are adapted to receive respectively the 
second and third rotation blocking pins 96 and 98 which project radially 
and which are firmly held, notably by forced pressure of the driven type 
inside the socket 32. 
It will thus be understood that the sensor means 90 as well as the bearing 
79 together form the clamping means 6 which are of the friction clamping 
type. The sensor means form the entry of the clamping means 6 which 
explains why the boring 92 is bevelled at the rear in the direction of the 
end E2 of the sheath 4, the extremity by which the workpiece B is 
introduced. 
These sensor means 90 and the bearing 79 rotate together with on the one 
hand the tubular socket 32 by the means of the assemblies pins 
96,98-grooves 88,94 which form wedge-shaped connections and on the other 
hand with the outer tubular socket 30 by means of the pin 42 and the 
groove 40. The sensor means 90 and the bearing 79 which form the friction 
clamping means 6 are thus rotatably integral with the sheath 4. 
Nevertheless these elements 90 and 76 can slide freely by axial 
displacement along the axis X1 in relation to the sheath 4 and notably in 
relation to the inner tubular socket 32. 
Housed inside the tubular socket 32 is another resilient member composed of 
a helicoidal compression spring 100 disposed directly and coaxially inside 
a cylindrical boring 33 provided in the inner socket 32, as a continuation 
of the frustroconical seating 89 and contiguous thereto. 
It will be noted that the helicoidal compression spring 100 rests laterally 
by its two ends, and is thus placed under tension, on the one hand against 
the sensor means 90 and, on the other hand, against an adjusting wedge 102 
which is housed in the boring 33 and which is axially maintained therein 
by a shaped shoulder on a collar 104 provided at the end E2 of the sheath 
4 and more particularly at the corresponding free end of the socket 32. 
This adjusting wedge 102 as well as the collar 104 each have a bevel making 
it possible to introduce the workpiece to be machined B into the sheath 4. 
The wedge 102 can be chosen or machined in a thickness as a function of the 
force which it is desired to apply axially to the clamping means 6. 
It will also be noted that this force is transmitted to the bearing 79 of 
the clamping means 6 by the intermediary of the sensor means 90 which abut 
laterally against the cage 82 and against the segments 85 of the ring 84. 
The bearing 79 rests by means of the rollers 80 in axial contact against a 
stop composed of a small cup 106 housed directly inside the outer socket 
30 and retained therein by a band 108 formed at the free extremity E1 of 
the socket 30. 
In operation, the guide bush of the invention functions as follows. 
It is firstly proposed to describe the automatic mode of operation where 
the actuating means AME are rendered inoperable for example by an open 
connection of their pneumatic circuit, not shown. 
When a workpiece or stock bar B, which is rotated by the rotating movement 
RB and which is being machined by the tool O or which has just been 
introduced in the quill 4 by the input end E1 has a controlled section SC 
of an outer diameter substantially larger (positive variations in 
dimensional tolerances) than that of the boring 92 of the sensor means 90 
or of the supported section SP of the workpiece B, mechanical jamming 
immediately occurs due to the friction between the sensor means 90 and the 
workpiece B because of the adjustment which becomes tightened between this 
controlled section SC and the sensor means 90. 
This jamming immediately rotates the sensor means 90 which are much more 
sensitive than the bearing 79 to any dimensional variation in the 
workpiece because of their frictional contact therewith, said friction 
being of the sliding friction type. 
The sensor means 90 being mechanically secured at least in rotation to the 
quill 4, as explained hereinabove, the two sockets 30 and 32 are driven in 
subsequent manner in rotation about the longitudinal axis of rotation X1, 
causing immediate angular displacement of the entire sheath 4 (and of the 
rod 46) in the direction of rotation shown by the arrow DRO. 
Since the socket 30 is connected to the screw-nut system VE which notably 
presents a thread to the left, rotation of the sheath 4 automatically 
induces only a concomitant translatory displacement of the inner tubular 
socket 32 in the direction of translatory displacement shown by the arrow 
DTO in FIG. 1. 
Since the inner socket 32 moves towards the rear in FIG. 1, the 
frustroconical seating 89 tends to leave its contact (tangential 
separation and sliding) with the sensor means 90 and with the bearing 79 
constituting the clamping means 6. 
This separation is ensured by the action of the helicoidal compression 
spring 100 which drives back and separates the sensor means 90 as well as 
the bearing 79 axially from the socket 32 and above all from the terminal 
seating 89. Because of this it will be noted that the helicoidal 
compression spring 100 forms a first resilient member capable of axially 
displacing the clamping means 6 in relation to the sheath 4 to release it 
radially. 
It can also be seen that (1) the translatory displacement of the inner 
socket 32 away from the sensor means 90 and the bearing 79, and that (2) 
the screw-nut system VE in association with the first resilient member 100 
constitute opening means of the clamping means 6 which are directly 
sensitive to the positive dimensional variations of the workpiece to be 
machined B, the helicoidal spring 100 or first resilient member being 
directly actuated by the translatory displacement of the sheath 4 and in 
particular by the transverse displacement of the socket 30. 
Moreover, if in the opposite case the controlled section SC of the 
workpiece to be machined B has an outer diameter smaller than that of the 
supported section SP of this same workpiece B (negative variations of 
dimensional tolerances) play is created between the outer circumference of 
the controlled section SC and the boring 92 of the sensor means 90, which 
permits the return means R (which have, incidentally been previously 
displaced) from bringing the sheath back, in the direction of rotation 
shown by the arrow DRF in FIG. 2, into a direction of rotation termed 
direction of closing. 
It will be noted that this direction of closing is opposite to the 
direction of rotation of the workpiece B shown in FIG. 2 by the arrow RB. 
Because the rod 46 of the return means is mechanically subjected in 
rotation to the quill 4 by the outer socket 30, due to the screw-nut 
system VE which forms movement transformation means, the return of the rod 
46 causes transverse displacement of the quill 4 and notably of the inner 
socket 32, along a direction of displacement shown by the arrow DTF (FIG. 
1). 
As a consequence hereof, the conical seating 89 returns or has the tendency 
to return to press against the sensor means as well as against the bearing 
79, which generates radial displacement of the clamping means 6 towards 
the workpiece B and notably towards the supported section SP or at least 
that which increases the pressure of tightening thereon. 
It will thus be seen that, by being connected to a traction spring 56, the 
rod 46, which forms one arm of the lever solid with the quill 4, 
constitutes return means R but also, in association with the inner socket 
32, closing means of the clamping means 6. It will be noted that the 
angular displacements of the rod 46 can be limited between the two stops 
composed of the spacers 72 and the screws 68 and 70. In this case the rod 
46 and the return means R of the bush of the invention occupy their 
position, termed the working position, which has the reference PT and 
which is shown in solid lines in FIG. 2. 
It will also be noted that the return means R which are composed of the 
resilient member, termed the second resilient member, formed by the spring 
56 connected to the quill 4, are capable of inducing rotating movement of 
this sheath and its concomitant translatory displacement to radially urge 
the clamping means 6 in its radial direction of closure, that is to say 
towards the workpiece B. 
It will moreover be noted that on the functional level, the closing means 
of the clamping means, which are composed of the return means R as well as 
more precisely of the conical terminal seating 89 of the inner socket 32 
and by the corresponding frustroconical regions of the bearing 79, are 
directly sensitive to negative dimensional variations of the workpiece B. 
It may also be noted that the sensor means 90 form guiding means of the 
opening means and of the closing means, permitting the almost 
instantaneous and automatic adjustment of these latter on the workpiece B. 
It will be understood from the foregoing that the quill 4 presents an 
oscillating rotating movement about the working position (PT) in permanent 
search of equilibrium between an opening action and a closing action of 
the clamping means 6 in relation to the workpiece B. 
Adjustment means have therefore been provided guided by an oscillating 
rotating movement of the quill, said movement being sensitive to the 
variations in dimensional tolerance of the workpiece B. It will also be 
noted that on the functional level, the adjustment means of the invention 
are mechanically controlled by the workpiece itself. 
These adjustment means which are capable of controlling the opening and 
closing means of the bush to compensate for positive and negative 
variations in dimensional tolerance of the workpiece are capable of 
instantaneously actuating the opening and closing means of the clamping 
means 6, directly in response to the variations in dimensional tolerances 
of the workpiece to be machined, to supply pressure of the clamping means 
on the workpiece B which is substantially constant. 
It will be noted that the functional characteristics of the guide bush of 
the invention thus operate as a result of the arrangement of the movement 
transformation members formed by the screw-nut system VE which is 
associated with the quill 4 and which is adapted to transform the 
oscillating rotating movement of the quill 4 in a concomitant forwards or 
backwards translatory displacement thereof, along the arrows DTO or DTF 
respectively, this translatory displacement being capable of directly 
actuating the opening and closing means of the clamping means 6. 
The controlled operation mode is similar to the mode of operation 
previously described. The controlled operation mode does, however, differ 
in the control of the opening and closing means, which occurs in a 
positive manner due to the action of the control means AME and notably of 
the screw jack 62,64. The sensor means 90 are thus in a state of rest, 
this mode of operation being capable of being put into operation 
regardless of the state of movement of the workpiece, i.e. when it is both 
in the dynamic or static state. The rod 46 always actuates closure of the 
clamping means 6 due to the kinemat:,cs and to the actuation of the 
previously described elements under the effect of the spring 56 which may 
be assisted by the control means AME. 
In addition, the rod 46 can control the opening of the clamping means 6 by 
the rotation and subsequent displacement of the quill or sheath 4, as 
explained hereinabove, this time solely under the effect of the actuating 
means AME which become priorities in relation to the detection and guiding 
means formed inter alia by the sensor means 90. 
Finally, it should be noted that in an embodiment that is not shown, the 
clamping means 6 can be composed solely of segments, such as the segments 
91 of FIG. 6, covering the two sections controlled SC and supported SP 
respectively, without having roller bearings. 
Clamping means of this type are thus entirely friction-based clamping means 
in which the bearing simultaneously forms the sensor means.