Jig for forming hard carbon film over inner surface of guide bush using the jig

A hard carbon film is formed over an inner surface of a guide bush by fixing an auxiliary electrode support member for supporting an auxiliary electrode of a jig for forming a film in a center bore of the guide bush by an auxiliary electrode insulation member, disposing an auxiliary electrode in alignment with the axis of the center bore so as to face the inner surface, disposing legs, and a first electrode plate, a second electrode plate, and the insulation member which are fixed to the legs are placed on the bottom of a vacuum vessel placing the guide bush on the first electrode plate contacted electrically with a power source, while the projection of the auxiliary electrode support member projecting out of the auxiliary electrode insulation member is contacted electrically with the second electrode plate. The auxiliary electrode is grounded through the auxiliary electrode support member, the second electrode plate, the legs, and the vacuum vessel, a gas containing carbon is introduced into the vacuum vessel after evacuating the vacuum vessel, and a plasma is produced in the vacuum vessel by supplying electric power to the guide bush through the first electrode plate from the power source.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a jig for forming a film over the inner 
surface of a bore of a guide bush mounted on an automatic lathe to support 
a rodlike workpiece for rotation and axial sliding at a position near a 
cutting tool (cutter), and a method of forming a hard carbon film over the 
inner surface of the guide bush to be in sliding contact with the 
workpiece. 
2. Description of the Related Art 
Guide bushes mounted on the column of an automatic lathe to hold a rodlike 
workpiece for rotation at a position near a cutting tool are classified 
into rotary guide bushes and stationary guide bushes. A rotary guide bush 
rotates together with a workpiece and holds the workpiece for axial 
sliding. A stationary guide bush remains stationary and holds a workpiece 
for rotation and axial sliding. 
A guide bush of either type has a portion having a taper outer surface 
provided with slits to make the same portion elastic, a threaded portion 
to hold the guide bush on the column, and an inner surface for holding a 
workpiece. The inner surface always in sliding contact with a workpiece is 
liable to be worn and, particularly, the inner surface of a stationary 
guide bush is worn rapidly. 
Therefore, a guide bush proposed in JP-A No. 4-141303 has an inner surface 
to be in sliding contact with a workpiece which slides and rotates on the 
inner surface, provided with a superhard alloy or a ceramic material 
attached to the inner surface by brazing or the like. 
When the inner surface of a guide bush is attached with a superhard alloy 
or a ceramic material excellent in wear resistance and heat resistance the 
wear of the inner surface of the guide bush can be reduced to some extent. 
However, when the workpiece is subjected to heavy machining on an automatic 
lathe, in which the depth of cut is large and the cutting speed is high, 
the workpiece is damaged or seizing occurs due to decrease in the 
diametrical clearance between the guide bush and the workpiece even if the 
inner surface of the guide bush is attached with a superhard alloy or a 
ceramic material, because the superhard alloy and the ceramic material 
have a comparatively large coefficient of friction and a low thermal 
conductivity. Therefore, it has been difficult to increase the depth of 
cut and cutting speed. 
The stationary guide bush has advantages that a workpiece can be accurately 
machined in a high roundness because the workpiece can be held so that its 
axis may not run out, less noise is generated, and the automatic lathe may 
be of a simple, compact construction. 
However, the inner surface of the stationary guide bush is worn far more 
rapidly than that of the rotary guide bush and hence it is more difficult 
to increase depth of cut and cutting speed when the stationary guide bush 
is employed. 
In order to solve the problem, the inventors have proposed a guide bush 
which can drastically improve abrasion resistance of the inner surface of 
a guide bush to be in sliding contact with a workpiece without occurrence 
of damage to the workpiece and seizing, and increase a cutting amount and 
a machining speed by an automatic lathe. 
The hard carbon film is formed of a hydrogenated amorphous carbon closely 
resembling diamond in properties. Therefore, hydrogenated amorphous carbon 
is also called diamondlike carbon (DLC). 
The hard carbon film (DLC film) has a high hardness (not lower than Vickers 
3000 Hv), is excellent in wear resistance corrosion resistance, and has a 
small coefficient of friction (about 1/8 of a superhard alloy). 
There is a CVD method (Plasma Chemical Vapor Deposition Process) for 
forming a hard carbon film as a method of forming the aforementioned hard 
carbon film on the inner surface of the guide bush, in which, for example, 
a plasma is produced by evacuating the vessel to a vacuum of 
5.times.10.sup.-3 torr at which the film is formed in the atmosphere of a 
gas containing carbon by applying a DC voltage of -3 kV to the guide bush 
by a DC power source. 
However, since the hard carbon film is formed by decomposing the gas 
containing carbon mainly by the plasma produced around a region 
surrounding the guide bush in the plasma CVD method, the hard carbon film 
is formed uniformly on the outer surface of the guide bush, but the hard 
carbon film formed on the inner surface of the guide bush is inferior in 
adhesion and besides inferior in film quality such as hardness. 
This is because the plasma in the center bore generates an abnormal 
discharge called a hollow discharge since electrodes of the same potential 
face each other in the space of the center bore of the guide bush. The 
hard carbon film formed by this hollow discharge is a polymer-like film 
which is inferior in adhesion and rigidity, and is easily peeled off the 
inner surface of the guide bush. 
In the aforementioned method of forming a hard carbon film, a guide bush 11 
is applied with a DC voltage of -3 kV by a DC voltage power source 73 at a 
vacuum of 5.times.10.sup.-3 torr at which the film is formed. 
In such a state of a vacuum of 5.times.10.sup.-3 torr in the vacuum vessel, 
electric charges are liable to be concentrated in the space of the vacuum 
vessel, resulting in low impedance in the space. Therefore, an abnormal 
discharge, i.e., an arc discharge is liable to be caused at the moment 
when the plasma discharge starts. 
Further, adhesion of the film to the guide bush depends on the film quality 
formed at this initial stage of forming the film because the moment when 
the plasma discharge starts is also the initial stage of forming the hard 
carbon film. 
Accordingly, there arises a problem that the quality and adhesion of the 
hard carbon film is lowered and the film peels off the guide bush when the 
abnormal discharge, i.e., the arc discharge, is generated at the initial 
stage of the plasma discharge. 
The present invention is intended to solve such problems and to form a hard 
carbon film on the inner surface of a guide bush contacting a workpiece 
with excellency of quality and adhesion by the plasma CVD method. 
SUMMARY OF THE INVENTION 
In order to solve the above objects, the present invention provides a 
following jig for forming a film and a method of forming a hard carbon 
film over the inner surface of a guide bush. 
The present invention provides a jig for forming a film by supporting a 
guide bush in a vacuum vessel and conducting electricity through the guide 
bush when a hard carbon film is formed over the inner surface of the guide 
bush to be mounted on an automatic lathe and to be in sliding contact with 
a workpiece by a plasma CVD process. 
The jig for forming the film comprises 
a rodlike auxiliary electrode inserted into a center bore forming the inner 
surface of the guide bush, 
an auxiliary electrode support member made of a conductive material for 
supporting the auxiliary electrode along with the axis of the center bore 
so as to face the inner surface, 
an auxiliary electrode insulation member inserted into an stepped section 
which has an internal diameter larger than the diameter of the inner 
surface of the bore of the guide bush so as to fix the auxiliary electrode 
support member in the guide bush and to project the same in the opposite 
direction of the auxiliary electrode along the axis of the center bore 
thereof, 
a first electrode plate made of a conductive material on which the guide 
bush is mounted with its axis perpendicular while the end portion of the 
stepped section side is contacted therewith electrically, 
legs made of a conductive material to be put on the bottom of the vacuum 
vessel, 
a second electrode plate made of a conductive material which is integrated 
with the legs and is connected with the projection of the auxiliary 
electrode support member projected out of the auxiliary electrode 
insulation member, and 
an insulation member for insulating the first electrode plate from the 
second electrode plate and for fixing them to the legs. 
The jig for forming a film may be further provided with a guide bush 
receptor which comprises a conductive material for a larger contact area 
for the both that is mounted on the end face of the stepped section of a 
guide bush or on the first electrode plate. 
The jig for forming a film may be provided with an insertion member made of 
a cylindrical conductive material having an internal diameter equal to 
that of the inner surface of the center bore of the guide bush that is to 
be inserted between the inner surface of the stepped section of the center 
bore and the auxiliary electrode insulation member. 
The jig for forming the film may be constituted so that the auxiliary 
electrode insulation member comprises two porcelain insulators divided in 
the axial direction of the center bore of the guide bush, the auxiliary 
electrode support member being supported by the two porcelain insulators, 
and the auxiliary electrode supported by the auxiliary electrode support 
member being projected out of one of the porcelain insulators while a 
portion of the auxiliary electrode support member is projected out of the 
other porcelain insulator. 
Further, the jig for forming a film may be constituted so that the 
insulation member for insulating the first electrode plate from the second 
electrode plate and for fixing them to the legs comprises an insulation 
plate interposed between the first electrode plate and the second 
electrode plate and insulation members for covering the exposed portions 
of the first electrode plate and the second electrode plate respectively. 
The jig for forming the film may be provided with a dummy member comprising 
a conductive material having a cylindrical shape with an internal diameter 
substantially equal to that of the inner surface of the center bore of the 
guide bush and mounted on the end face of the guide bush boring at the 
inner surface. 
The jig for forming the film over a plurality of guide bushes may be 
constituted so that a plurality of auxiliary electrodes, auxiliary 
electrode support members and auxiliary electrode insulating members are 
provided for each of the guide bushes, and the first and second electrode 
plates, legs and insulating members are provided for a plurality of guide 
bushes in common. 
The method of forming a hard carbon film over the inner surface of a guide 
bush is carried out in the following manner employing the jig for forming 
the film. 
An auxiliary electrode support member for supporting the auxiliary 
electrode is fixed by the auxiliary electrode insulation member in the 
center bore of the guide bush in alignment with the axis of the center 
bore so as to face the inner surface. 
On the other hand, the legs, the second electrode plate, and the first 
electrode plate with the insulation member therebetween which are fixed to 
the legs are placed on the bottom of a vacuum vessel. 
The guide bush is placed on the first electrode plate with its expanded 
section downward and with the axis of the center bore perpendicular while 
the same is contacted electrically with the first electrode plate, and the 
first electrode plate is connected to a power source, while the projection 
of the auxiliary electrode support member projecting out of the auxiliary 
electrode insulation member is connected to the second electrode plate, 
and the auxiliary electrode is grounded through the auxiliary electrode 
support member, the second electrode plate, the legs, and the vacuum 
vessel. 
Next, a gas containing carbon is introduced through the gas inlet port 
after evacuating the vacuum vessel, and a plasma is produced by supplying 
electric power to the guide bush through the first electrode plate by the 
power source so as to form a hard carbon film of hydrogenated amorphous 
carbon over the inner surface of the guide bush. 
There is a method of forming a hard carbon film over the inner surface of a 
guide bush wherein a vacuum vessel provided with an anode and a filament 
therein is employed, and a plasma is produced by applying a DC voltage to 
the guide bush through the first electrode plate by the power source, a DC 
voltage to the anode, and an AC voltage to the filament, respectively. 
Or, a plasma can be produced in the vacuum vessel by applying radio 
frequency power to the guide bush through the first electrode plate by the 
power source. 
Further, a plasma can be produced in the vacuum vessel only by applying a 
DC voltage to the guide bush through the first electrode plate by the 
power source. 
Thus, an excellent hard carbon film can be formed over the inner surface of 
a guide bush by producing a stable plasma in the center bore since the 
guide bush is supported reliably with its axis of the center bore 
perpendicular in the vacuum vessel while the auxiliary electrode is 
disposed in the bore in alignment with the axis thereof while being easily 
grounded, thereby supplying electric power to the guide bush easily and 
stably. 
A guide bush receptor for a larger contact area for the guide bush and the 
first electrode plate is disposed between the guide bush and the first 
electrode plate, so that the plasma discharge can be stabler, thereby 
restricting dispersion of the thickness and quality of the hard carbon 
film. 
When the insertion member of the jig for forming the film is inserted into 
the stepped section of the bore of the guide bush so as to neighbor the 
inner surface, the clearance around the auxiliary electrode can be uniform 
with no steps in the depth of the inner surface of the guide bush formed 
with the hard carbon film, and the plasma formed around the auxiliary 
electrode can be uniform so that the hard carbon film can be formed in a 
uniform thickness and quality thereof. 
Also, by disposing the dummy member on the end face of the bore with its 
axis in alignment with the central axis thereof, the hard carbon film can 
be formed evenly on a region of inner surface of the bore. 
Further, by covering the exposed portions of the first and the second 
electrode plates respectively, so as to lengthen the time for forming the 
film to thicken the film thickness, an abnormal discharge, i.e., an arc 
discharge, is unlikely to be caused at the portions where the electrodes 
are exposed. 
The hard carbon film can be formed on inner surfaces of a plurality of 
guide bushes in a vacuum vessel by employing a plurality of the jigs for 
forming the film or the jig for forming the film on inner surfaces of a 
plurality of guide bushes. 
The above and other objects, features and advantages of the invention will 
be apparent from the following detailed description which is to be read in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will be described 
hereinafter with reference to the drawings. 
Description of Automatic Lathe Employing Guide Bush 
FIGS. 14 and 15 
The construction of an automatic lathe employing a guide bush for which the 
present invention is aiming will be briefly described first. 
FIG. 14 shows only a spindle and associated parts of a numerically 
controlled automatic lathe in a sectional view. The automatic lathe is 
provided with a stationary guide bush unit 37 that holds a guide bush 11 
fixedly to support a workpiece 51 (indicated by imaginary lines) rotatably 
on the inner surface 11b of the guide bush 11. 
A spindle stock 17 is mounted on the bed, not shown, of the numerically 
controlled automatic lathe for sliding movement in transverse directions, 
as viewed in the drawing. 
A spindle 19 is supported for rotation in bearings 21 on the spindle stock 
17, and a collet chuck 13 is mounted on the nose of the spindle 19. 
The collet chuck 13 is disposed in the center bore of a chucking sleeve 41. 
A taper outer surface 13a of the head thereof is in surface contact with a 
taper inner surface 41a of the chucking sleeve 41. 
A coil spring 25 formed by winding a spring band is inserted in an 
intermediate sleeve 29 at the back end of the collet chuck 13. The collet 
chuck 13 can be pushed out of the intermediate sleeve 29 by the action of 
the coil spring 25. 
The position of the front end of the collet chuck 13 is determined by a cap 
nut 27 fastened to the front end of the spindle 19 with screws and in 
contact with the front end of the collet chuck 13. The cap nut 27 
restrains the collet chuck 13 from being pushed out of the intermediate 
sleeve 29 by the force of the coil spring 25. 
A chuck operating mechanism 31 provided with chuck operating levers 33 is 
provided on the back end of the intermediate sleeve 29. The chuck 
operating levers 33 are operated to open or close the collet chuck 13 so 
that the collet chuck 13 releases or chucks the workpiece 51. 
When the chuck operating levers 33 of chuck operating mechanism 31 are 
turned so that the front ends thereof are moved away from each other, 
operating portions of the chuck operating levers 33 in contact with the 
intermediate sleeve 29 move to the left, as viewed in FIG. 14 to push the 
intermediate sleeve 29 to the left. Consequently, the chucking sleeve 41 
in contact with the left end of the intermediate sleeve 29 moves to the 
left. 
The collet chuck 13 is restrained from being pushed out of the spindle 19 
by the cap nut 27 fastened to the front end of the spindle 19 with screws. 
Therefore, when the chucking sleeve 41 is moved to the left, the taper 
inner surface 41a of the chucking sleeve 41 is pressed against the taper 
outer surface 13a of the slitted, coned head portion of the collet chuck 
13 and the taper inner surface 41a of the chucking sleeve 41 moves to the 
left along the taper outer surface 13a of the collet chuck 13. 
Consequently, collet chuck 13 is compressed and the inside diameter of the 
collet chuck 13 is reduced to grip the workpiece 51. 
When releasing the workpiece 51 from the collet chuck 13 by expanding the 
collet chuck 13 so that the inside diameter of the collet chuck 13 is 
increased, the chuck operating levers 33 are turned so that the front ends 
thereof are moved toward each other to remove the force acting to the left 
on the chucking sleeve 41. 
Then, the intermediate sleeve 29 and the chucking sleeve 41 are moved to 
the right as viewed in the drawing by the stored energy of the coil spring 
25. 
Consequently, the pressure applied to the taper outer surface 13a of the 
collet chuck 13 by the taper inner surface 41a of the chucking sleeve 41 
is removed to allow the collet chuck 13 to expand by its own resilience, 
so that the inside diameter of the collet chuck 13 increases to release 
the workpiece 51. 
Further, a column 35 is disposed in front of the spindle stock 17 and the 
guide bush unit 37 is placed on the column 35 with its center axis aligned 
with that of the spindle. 
The guide bush unit 37 is of a stationary type fixedly holding the guide 
bush 11 to support the workpiece 51 rotatably on the inner surface 11b of 
the guide bush 11. 
A bush sleeve 23 is fitted in the center bore of a holder 39 fixed to the 
column 35. A taper inner surface 23a is formed in the front portion of the 
bush sleeve 23. 
The guide bush 11 having a front portion provided with a taper outer 
surface 11a and slits 11c are fitted in the center bore of the bush sleeve 
23. 
The clearance between the inner surface of the guide bush 11 and the outer 
surface of the workpiece 51 can be adjusted by turning an adjusting nut 43 
screwed on the threaded portion of the guide bush 11 and contiguous with 
the back end of the guide bush unit 37. 
That is, when the adjusting nut 43 is turned clockwise, the guide bush 11 
moves to the right, as viewed in the drawing, relative to the bush sleeve 
23 and the taper outer surface 11a of the guide bush 11, similarly to the 
taper outer surface of the collet chuck 13, is compressed by the taper 
inner surface 23a of the bush sleeve 23 and the inside diameter of the 
slitted front portion of the guide bush 11 is reduced. 
A cutting tool (cutter) 45 is disposed further in front of the guide bush 
unit 37. The workpiece 51 is chucked by the collet chuck 13 mounted on the 
spindle 19 and supported by the guide bush unit 37. A portion of the 
workpiece 51 projecting from the guide bush unit 37 into a machining 
region is machined for predetermined machining by a combined motion of the 
cross feed motion of the cutting tool 45 and the longitudinal traverse 
motion of the spindle stock 17. 
A rotary guide bush unit that rotatably supports a guide bush gripping a 
workpiece will be described next with reference to FIG. 15, in which parts 
like or corresponding to those shown in FIG. 14 are designated by the same 
reference characters. 
Rotary guide bush units are classified into those holding a guide bush 11 
so as to rotate in synchronism with the collet chuck 13 and those holding 
a guide bush 11 so as to rotate in asynchronism with the collet chuck 13. 
A guide bush unit 37 shown in the drawing holds the guide bush 11 so as to 
rotate in synchronism with the collet chuck 13. 
The rotary guide bush unit 37 is driven by a drive rod 47 projecting from 
the cap nut 27 mounted on the spindle 19. A gear mechanism or a 
belt-and-pulley mechanism may be used instead of the drive rod 47 for 
driving the guide bush unit 37. 
The rotary guide bush unit 37 has a holder 39 fixed to a column 35. A bush 
sleeve 23 is inserted in the center bore of the holder 39 and is supported 
in bearings 21 on the holder 39, and the guide bush 11 is fitted in the 
center bore of the bush sleeve 23. 
The bush sleeve 23 and the guide bush 11 are similar in construction to 
those illustrated in FIG. 14, respectively. The clearance between the 
inner surface of the guide bush 11 and the outer surface of the workpiece 
51 can be adjusted by turning an adjusting nut 43 screwed on the threaded 
portion of the guide bush 11 which is contiguous with the back end of the 
guide bush unit 37. 
This automatic lathe shown in FIG. 15 is the same in construction as the 
automatic lathe illustrated in FIG. 14 except that this automatic lathe is 
provided with the rotary guide bush unit 37, and hence the further 
description thereof will be omitted. 
Description of Guide Bush 
FIGS. 12 and 13 
Guide bushes mounted on the automatic lathe and having an inner surface in 
sliding contact with a workpiece and formed with the hard carbon film 
according to the method of the present invention will be described next 
with reference to FIG. 12 and FIG. 13. 
FIG. 12 is a longitudinal sectional view of the guide bush, and FIG. 13 is 
a perspective view showing its exterior. 
Referring to the drawings, a guide bush 11 is shown in a free state in 
which a front end portion is open. The guide bush 11 is shaped 
substantially like a cylinder with a center bore 11j in the axial 
direction thereof and a head portion having a taper outer surface 11a at 
one longitudinal end thereof, and a threaded portion 11f in the other 
longitudinal end thereof. 
Further, the center bore 11j of the guide bush forms an inner surface 11b 
that holds a workpiece 51, inside the head portion having the taper outer 
surface 11a, and forms a stepped section 11g having the internal diameter 
greater than that of the inner surface 11b, in the region of the center 
bore other than the inner surface 11b. 
Three slits 11c are formed at angular intervals of 120.degree. so as to 
extend through the head portion having the taper outer surface 11a and an 
elastic bendable portion 11d. 
The clearance between the inner surface 11b and the workpiece 51 indicated 
by imaginary lines in FIG. 12 can be adjusted by pressing the taper outer 
surface 11a of the guide bush 11 by the taper inner surface of the bush 
sleeve, so that the elastic bendable portion 11d is bent. 
Further, the guide bush 11 has a fitting portion 11e between the elastic 
bendable portion 11d and the threaded portion 11f. When the guide bush 11 
is fitted in the center bore of the bush sleeve 23 shown in FIGS. 14 and 
15, the fitting portion 11e fits the center bore closely to set the guide 
bush 11 with its axis in alignment with the center axis of the spindle. 
The guide bush 11 is made of alloy tool steel (SKS). When forming the guide 
bush 11, a workpiece of carbon tool steel is machined in predetermined 
external and internal shapes, and the machined workpiece is subjected to 
quenching and annealing. 
Preferably, a superhard lining 12 having a thickness of 2 mm to 5 mm is 
attached to the inner surface 11b of the guide bush 11 as shown in FIG. 12 
by brazing. 
The superhard lining is composed of, for example, 85% to 90% of tungsten 
(W), 5% to 7% of carbon (C), and 3% to 10% of cobalt (Co) as binder. 
However, when the head portion having the taper outer surface 11a is 
compressed, a clearance in the range of 5 to 10 .mu.m is formed between 
the inner surface 11b and the workpiece 51 in the radial direction thereof 
to allow the workpiece 51 to slide relative to the guide bush 11, which 
abrades the inner surface 11b. 
Further, when the guide bush 11 is used on a stationary guide bush unit, 
the workpiece 51 supported on the guide bush 11 rotates at a high surface 
speed relative to the inner surface 11b and, when an excessively high 
pressure is applied to the inner surface 11b by the workpiece 51, seizing 
may occur. 
Therefore, the inner surface 11b of the guide bush 11 is coated with a hard 
carbon film (DLC film) 15 of a thickness in the range of 1 to 5 .mu.m. 
The hard carbon film is very similar in properties to diamond as described 
above; the hard carbon has a high mechanical strength, a small coefficient 
of friction, a satisfactory self-lubricity, and excellent corrosion 
resistance. 
Therefore, the hard carbon film 15 covering the inner surface 11b enhances 
the wear resistance of the guide bush remarkably, the guide bush 11 
withstands an extended period of use and heavy machining, the wear of the 
inner surface 11b in contact with the workpiece 51 is reduced, the 
possibility of exerting abrasive damage to the workpiece 51 is reduced, 
and seizing between the guide bush 11 and the workpiece 51 can be avoided. 
Although the hard carbon film can be formed directly over the inner surface 
of the base material (SKS) for the guide bush 11 or over the inner surface 
of the superhard lining 12, it may be formed by way of a thin intermediate 
layer (not illustrated) for enhancing adhesion to the inner surface 11b. 
An element of group IVb in the periodic table of elements, such as silicon 
(Si) or germanium (Ge), a compound containing silicon or germanium, or a 
compound containing carbon, such as a silicon carbide (SiC) or titanium 
carbide (TiC) may be used as the intermediate layer. A compound of 
titanium (Ti), tungsten (W), molybdenum (Mo) or tantalum (Ta) and silicon 
(Si) may be applicable for the intermediate layer. 
The intermediate layer may be a two-layer film consisting of a lower layer 
of titanium (Ti) or chromium (Cr), and an upper layer of silicon (Si) or 
germanium (Ge). 
The titanium or chromium comprising the lower layer of the intermediate 
layer which works for enhancing adhesion to the base material of the guide 
bush 11 or the superhard lining 12, and silicon or germanium of the upper 
layer which works for forming covalent bond, which bonds the hard carbon 
film 15 firmly. 
The thickness of the intermediate layer is to be approximately 0.5 .mu.m. 
However, in the case where intermediate layer comprises two layers, the 
thickness of the upper and lower layers is to be respectively 
approximately 0.5 .mu.m. 
The intermediate layer may be formed by a sputtering process, an ion 
plating process, a chemical vapor deposition (CVD) process or a metal 
spraying process. 
When the superhard lining 12 is made of silicon carbide (SiC), the 
intermediate layer may be omitted, because silicon carbide is a compound 
of silicon and carbon included in group IVb of the periodic table of 
elements and silicon carbide and the hard carbon film 15 formed on the 
superhard lining 12 make covalent bond which secure high adhesion. 
The hard carbon film is formed directly over the inner surface 11b of the 
guide bush 11 or by way of the intermediate layer by employing the jig for 
forming the film in a vacuum vessel in the CVD method, details of which 
will be described later. 
Jig for Forming Film According to Present Invention 
FIGS. 1 and 2 
A best embodiment of a jig for forming the film according to the present 
invention will be described next with reference to FIG. 1 and FIG. 2. FIG. 
1 is a sectional view showing a state in which a jig for forming a film is 
employed in its best embodiment according to the present invention, and 
FIG. 2 is a sectional view showing only members mounted on the guide bush. 
The guide bush 11 shown in FIG. 1 and FIG. 2 shows an example thereof in 
which the inner surface 11b is formed without the superhard lining 12 
shown in FIG. 1. However, this can be applied to a guide bush formed with 
the inner surface 11b with the superhard lining provided. 
The jig 80 for forming the film comprises a member mounted on the guide 
bush 11 and a member secured fixedly on the bottom of the vacuum vessel. 
The members mounted on the guide bush 11 comprise a rodlike auxiliary 
electrode 71, an auxiliary electrode support member 72, first and second 
porcelain insulators 81, 82, i.e., auxiliary electrode insulation members, 
an insertion member 83, a guide bush receptor 84, and a dummy member 53. 
The auxiliary electrode 71 is fit into a large diameter portion 72a of the 
auxiliary electrode support member 72 to be supported there, and is 
inserted into a center bore 11j forming the inner surface 11b of the guide 
bush 11. The auxiliary electrode 71 is made of a metal such as stainless 
steel and is formed in a rodlike shape. 
The first porcelain insulator 81 and the second porcelain insulator 82 as 
the auxiliary electrode insulation members are divided in the axial 
direction of the center bore 11j of the guide bush 11, and the both are 
fitted in the stepped section 11g. The first porcelain insulator 81 and 
the second porcelain insulator 82 are respectively made of ceramic 
insulation material. 
The first porcelain insulator 81 and the second porcelain insulator 82 are 
provided with a throughhole for insertion of the auxiliary electrode 71 
and the auxiliary electrode support member 72 for supporting the auxiliary 
electrode 71 by fitting therein, and further the second porcelain 
insulator 82 is provided with a projection 82a projecting out of the guide 
bush 11. The auxiliary electrode 71 is supported by the auxiliary 
electrode support member 72 so as to be disposed in the center of the 
center bore 11j of the guide bush 11. 
The first porcelain insulator 81 is provided with a small diameter bore 
portion 81a through which the auxiliary electrode 71 is inserted with a 
clearance of 0.01 mm to 0.05 mm thereabout and a large diameter bore 
portion 81b for positioning the large diameter portion 72a of the 
auxiliary electrode support member 72. That is, the first porcelain 
insulator 81 is provided with a stepped bore portion. 
Meanwhile, the second porcelain insulator 82 is provided with a stepped 
bore portion 82b for positioning the large diameter portion 72a and a 
small diameter portion 72b of the auxiliary electrode support member 72. 
The large diameter portion 72a of the auxiliary electrode support member 72 
is clamped between the two porcelain insulators 81 and 82 so that the 
small diameter portion 72b of the auxiliary electrode support member 72 is 
projected out of the second porcelain insulator 82. 
The insertion member 83 comprises a conductive material having a 
cylindrical shape with a diameter equal to that of the inner surface 11b 
of the center bore 11j of the guide bush 11, the external shape of which 
fits the internal shape near the inner surface 11b of the center bore 11j 
of the guide bush 11. The insertion member 83 is inserted in the vicinity 
of the inner surface 11b of the stepped section 11g of the center bore 11j 
of the guide bush 11 and is held by the first porcelain insulator 81 at 
the lower end thereof. 
Further, a guide bush receptor 84 provided with an internal thread is 
screwed on an external thread of the threaded portion 11f provided at the 
end portion of the stepped section side 11g of the guide bush 11. The 
guide bush receptor 84 is made of a metal such as stainless steel and 
serves to provide a large contact area to the guide bush 11 and a first 
electrode plate 85, described later, and to prevent the first porcelain 
insulator 81 and the second porcelain insulator 82 from being dropped off 
the center bore 11j of the guide bush 11. 
The dummy member 53 comprises a conductive material having a cylindrical 
shape with a diameter substantially equal to that of the inner surface 11b 
of the center bore 11j of the guide bush 11 and is placed on an end face 
11h of the bore of the guide bush, where it is fixed thereon easily 
detachable with an adhesive. 
FIG. 2 shows a state in which the insertion member 83, the guide bush 
receptor 84, and the dummy member 53 are mounted on the guide bush 11 
although they are not essential. 
On the other hand, the members placed fixedly on the bottom of the vacuum 
vessel are the first electrode plate 85 to be connected electrically to 
the guide bush 11, the legs 100 placed on the bottom of the vacuum vessel, 
a second electrode plate 86 to be connected electrically to the auxiliary 
electrode support member 72, and the insulation member for insulating the 
first electrode plate 85 and the second electrode plate 86 and for fixing 
them to the legs 100. The first electrode plate 85, the second electrode 
plate 86, and the legs 100 are respectively made of a conductive material 
such as stainless steel. 
The insulation member comprises a first insulation member 87 for covering 
the exposed portion of the first electrode plate 85, a second insulation 
member 89 for covering the exposed portion of the second electrode plate 
86, and a third insulation member 88 interposed between the first 
electrode plate 85 and the second electrode plate 86. These may of an 
insulation material, i.e., ceramics such as aluminum or zirconia or a 
fluorocarbon resin such as Teflon (a registered trademark). 
The first insulation member 87 is provided with an opening 87a which fits 
the external dimension of the guide bush receptor 84. The first electrode 
plate 85 is formed with a hole 85a for insertion of the projection 82a of 
the second porcelain insulator 82, while the second electrode plate 86 is 
provided with a center hole 86a for insertion of the small diameter 
portion 72b of the auxiliary electrode support member 72 projected out of 
the projection 82a. 
The third insulation member 88 is also provided with a hole for piercing 
through the small diameter portion 72b of the auxiliary electrode support 
member 72. The second insulation member 89 for placing the third 
insulation member 88 thereon is provided with a recess 89a, in which the 
second electrode plate 86 is fitted so as to hold the surfaces tightly. 
When the jig 80 for forming a film is used, the insertion member 83 and the 
first porcelain insulator 81 and the second porcelain insulator 82 for 
supporting the auxiliary electrode and the auxiliary electrode support 
member 72 are inserted into the center bore 11j of the guide bush 11 as 
shown in FIG. 2, and thereafter the guide bush receptor 84 is screwed on 
the threaded portion 11f to be fixed there, and the dummy member is placed 
and fixed on the end face 11h of inner surface 11b of the guide bush 11. 
The guide bush receptor 84 is fit in the opening 87a of the first 
insulation member 87 by holding the guide bush 11, and the guide bush 11 
is placed on the first electrode plate 85 with its axis perpendicular in a 
manner such that the bottom of the guide bush receptor 84 contacts the 
upper surface of the first electrode plate 85 as shown in FIG. 1. 
At this time, since the guide bush receptor 84 is provided, the area where 
the guide bush 11 contacts the first electrode plate 85 becomes large. 
Accordingly, by connecting the power source 73 to the first electrode 
plate 85, a negative DC voltage can be applied to the guide bush 11 
stably. 
Also, at this time, the projection 82a of the second porcelain insulator 82 
is fitted into the hole 85a of the first electrode plate 85. The small 
diameter portion 72b of the auxiliary electrode support member 72 projects 
downward out of the second porcelain insulator 82 and pierces through the 
third insulation member 88 to be fitted in the center hole 86a of the 
second electrode plate 86. 
Therefore, the auxiliary electrode 71 is grounded through the auxiliary 
electrode support member 72, the second electrode plate 86, the legs 100 
and a vacuum vessel, not illustrated. 
By holding the auxiliary electrode support member 72 for supporting the 
auxiliary electrode 71 in the stepped section 11g of the guide bush 11 by 
way of the first porcelain insulator 81 and the second porcelain insulator 
82, the auxiliary electrode 71 can be disposed accurately in the center of 
the center bore 11j of the guide bush 11. 
In case the auxiliary electrode 71 is deviated from the axis of the center 
bore 11j of the guide bush 11, the plasma discharge between the auxiliary 
electrode 71 and the inner surface 11b of the guide bush 11 is unbalanced 
causing dispersion of the thickness and quality of the hard carbon film. 
Therefore, by setting the external shape of the first porcelain insulator 
81 and the second porcelain insulator 82 so as to fit the internal 
dimension of the stepped section 11g of the guide bush 11, and further by 
controlling the position of the auxiliary electrode 71 by the bore 
portions 81a, 81b and 82b of the porcelain insulators 81 and 82, the 
auxiliary electrode 71 can be accurately disposed in the center of the 
center bore 11j of the guide bush 11. Consequently, no dispersion of 
thickness and quality of the hard carbon film formed on the inner surface 
11b is caused. 
Further, since the projection 82a of the second porcelain insulator 82 
projecting out of the guide bush 11 fits in the hole 85a of the first 
electrode plate 85 as described before, the guide bush 11 and the 
auxiliary electrode 71 can be separated and insulated perfectly from each 
other by the projection 82a. 
When the dummy member 53 is used, the tip of the auxiliary electrode 71 
should be within the upper end face of the dummy member 53 in a range of 1 
mm to 2 mm as shown in the figure, and when it is not used, it should be 
within the upper end face 11h of the guide bush 11 in a range of 1 mm to 2 
mm. 
When the jig 80 for forming a film is used, an abnormal discharge such as 
an arc discharge is not caused at the first electrode plate 85 even when 
the time for processing the film is lengthened in order to form a thick 
carbon film since the exposed surface of the first electrode plate 85 is 
covered with the first insulation member 87. 
In this embodiment, since the guide bush receptor 84 is provided and the 
guide bush 11 is placed on the first electrode plate 85 so that the bottom 
surface thereof contacts the upper surface of the first electrode plate 
85, the guide bush 11 can be stabilized and have an increased area for 
conducting electricity, but the guide bush receptor 84 can be omitted and 
the guide bush 11 may be directly placed on the first electrode plate 85. 
Next, embodiments for the method of forming a hard carbon film on the inner 
surface 11b of the guide bush 11 by employing the jig 80 for forming a 
film or the jig 80' for forming a film for a plurality of guide bushes 
will be described with reference to FIG. 3 to FIG. 11. 
First Preferred Embodiment 
FIG. 3 
FIG. 3 is a sectional view of an apparatus employed in the method of 
forming a hard carbon film over the inner surface of a guide bush in the 
first embodiment according to the present invention. 
In the first embodiment, the guide bush 11 is disposed in the vacuum vessel 
61 provided with a gas inlet port 63 and an evacuation port 65 by using 
the jig 80 for forming the film described before as shown in FIG. 3. The 
description thereof will be omitted since the guide bush 11 relates to 
each member of the jig 80 for forming the film as shown in detail in FIG. 
1. 
The vacuum vessel 61 is grounded, and the first electrode 85 is connected 
to the negative side of a DC power source 73. The vacuum vessel 61 is 
provided with an anode 79 and a filament 90 at its upper inner portion 
thereof and the anode 79 is connected to an anode power source 75 while 
the filament 90 is connected to a filament power source 77. 
The vacuum vessel 61 is evacuated to a vacuum of less than 
3.times.10.sup.-5 torr through the evacuation port 65 by an evacuation 
means, not illustrated. 
Thereafter, benzene (C.sub.6 H.sub.6) as a gas containing carbon is 
supplied through the gas inlet port 63 into the vacuum vessel 61 so that 
the pressure in the vacuum vessel 61 is adjusted to a vacuum of 
5.times.10.sup.-3 torr. 
Subsequently, a DC voltage of -3 kV is applied to the guide bush 11 by the 
DC power source 73 through the first electrode plate 85, further a DC 
voltage of +50V is applied to the anode 79 by the anode power source 75, 
and further an AC voltage of 10V is applied to the filament 90 by the 
filament power source 77 so that a current of 30A flows. 
Then, a plasma is produced around the guide bush 11 in the vacuum vessel 61 
so that a hard carbon film of hydrogenated amorphous carbon is formed over 
the surface of the guide bush including the inner surface by the plasma 
CVD process. 
In this case, since the auxiliary electrode 71 is disposed in the center of 
the center bore of the guide bush 11, the same potentials do not face each 
other in the inner region of the center bore, so that hollow cathode 
discharge, i.e., an abnormal discharge, does not occur and the adhesion of 
the hard carbon film formed on the inner surface 11b of the guide bush 11 
is improved. Further, the hard carbon film can be formed in a uniform 
thickness from the open end through the depth thereof since the potential 
characteristic are uniform with respect to the longitudinal direction of 
the center bore of the guide bush 11. 
The dummy member 53 is employed in this embodiment and in the following 
respective embodiments, the effect of which will be described here. 
In the method of forming a hard carbon film shown in the drawing, a plasma 
is produced both around the inner surface of the guide bush 11 and in a 
region surrounding the guide bush. When the dummy member 53 is not used, 
electric charges are liable to be concentrated on the end face of the 
guide bush 11 and the potential of a portion of the guide bush 11 around 
the end face tends to become higher than that of the inner surface of the 
guide bush 11, leading to the so-called edge effect. Here, the intensity 
of the plasma in the vicinity of the end face of the guide bush 11 is 
greater than that in other portions thereof and is unstable. Further, a 
portion of the guide bush 11 around the end face is subject to the 
influence of both the plasma produced in a region surrounding the guide 
bush 11 and that produced inside the guide bush 11. 
When a hard carbon film is formed under such conditions, the adhesion and 
quality of the hard carbon film differ slightly between at a portion in a 
range of several mm away from the end face of the guide bush 11 and at 
other portions thereof. When the hard carbon film is formed by disposing 
the dummy member 53 on the end face of the guide bush 11, the portion 
where the adhesion and the quality of the film are different is not formed 
on the inner surface of the guide bush 11 but is formed on the inner 
surface of the dummy member 53. As a result, the portion where the 
adhesion and the quality of the film are different is not formed at all on 
the inner surface of the guide bush 11. 
According to the present embodiment, the exposed region of the first 
electrode plate 85 is covered with the first insulation member 87. 
Therefore, arc discharge is not generated at the first electrode plate 85 
even when the time for forming the film is lengthened, so that increments 
of the film thickness of the hard carbon film formed on the inner surface 
11b of the guide bush 11 can be achieved since a plasma discharge for a 
long period of time is possible, and durability of guide bushes can be 
extended and reliability in a long term use can be enhanced. Further, 
reproducibility of the quality and thickness of the hard carbon film 
formed on the inner surface 11b of the guide bush 11 is improved. 
Further, the insertion member 83 is inserted in the vicinity of the inner 
surface 11b of the guide bush 11 in this embodiment. The insertion member 
83 has an internal diameter substantially equal to that of the inner 
surface 11b of the center bore 11j of the guide bush 11. Accordingly, no 
steps are formed in the vicinity of the inner surface 11b of the guide 
bush 11. 
Namely, the clearance between the inner surface 11b of the guide bush 11 on 
which the hard carbon film is formed and the vicinity thereof and the 
auxiliary electrode 71 is uniform so that the plasma discharge is stable 
around the auxiliary electrode 71. Accordingly, the quality and thickness 
of the hard carbon film formed over the inner surface of the guide bush 
can be improved. 
Second Preferred Embodiment 
FIG. 4 
FIG. 4 is a sectional view of an apparatus employed in the second 
embodiment of the method of forming a hard carbon film over the inner 
surface of a guide bush. 
In FIG. 4, parts like or corresponding to those shown in FIG. 3 are 
designated by the same reference characters and the description thereof 
will be omitted since the guide bush 11 relates to each member of the jig 
80 for forming the film similarly as in FIG. 1. 
The vacuum vessel 61 employed in the second embodiment is not provided with 
any anode 79 nor any filament 90 as shown in FIG. 1. 
The guide bush 11 is disposed in the vacuum vessel 61 by using the jig 80 
for forming the film similarly to the first embodiment described before. 
The vacuum vessel 61 is evacuated to a vacuum of 3.times.10.sup.-5 torr by 
an evacuation means, not illustrated, and thereafter methane gas 
(CH.sub.4) as a gas containing carbon is supplied from the gas inlet port 
63 into the vacuum vessel 61 so that the pressure in the vacuum vessel 61 
is adjusted to a vacuum of 0.1 torr. 
A plasma is produced in the vacuum vessel 61 by applying radio frequency 
power from a radio frequency power source 69 of 13.56 MHz in oscillation 
frequency through a matching circuit 67. 
In the second preferred embodiment also, since the auxiliary electrode 71 
is disposed in the center bore of the guide bush 11, a uniform plasma is 
produced around the outer surface and in the center bore of the guide bush 
so that a hard carbon film can be formed in a uniform thickness over the 
inner surface 11b. The operation and effect other than that are the same 
as in the first embodiment described before. 
Third Preferred Embodiment 
FIG. 5 
FIG. 5 is a sectional view of an apparatus for illustrating a method of 
forming a hard carbon film over the inner surface of a guide bush in the 
third embodiment according to the present invention. 
In FIG. 5, parts like or corresponding to those shown in FIG. 3 are 
designated by the same reference characters and the description thereof 
will be omitted since the guide bush 11 relates to each member of the jig 
80 for forming the film similarly as in FIG. 1. 
The hard carbon film forming method in the third embodiment is different 
from the first embodiment shown in FIG. 3 in that the anode 79 and the 
filament 90 are not provided in the vacuum vessel 61, the vacuum vessel 61 
is evacuated to a vacuum of less than 3.times.10.sup.-5 torr and 
thereafter methane gas (CH.sub.4) as a gas containing carbon is supplied 
from the gas inlet port 63 into the vacuum vessel 61 adjusting the vacuum 
to 0.1 torr, and a DC voltage of -600 V is applied from the DC power 
source 74 to the first electrode plate 85 to be connected to the guide 
bush 11 so that a plasma is produced in the vacuum vessel 61. 
In the third preferred embodiment also, a hard carbon film can be formed in 
a uniform thickness over the inner surface 11b of the guide bush 11. The 
operation and effect other than that are the same as in the embodiments 
described before. 
Fourth Preferred Embodiment 
FIG. 6 
Embodiments for forming a hard carbon film simultaneously over the inner 
surface of a guide bush employing a plurality of jigs 80 for forming the 
film will be described next with reference to FIG. 6 to FIG. 8. 
The fourth embodiment shown in FIG. 6 is carried out by the same plasma 
production method described in the first embodiment with reference FIG. 3. 
The method in the fourth embodiment is the same as the first embodiment 
shown in FIG. 3 except in that a plurality of (two in the drawing) guide 
bushes 11, 11 are provided with the jigs 80, 80 for forming the film in 
one vacuum vessel 61, and each of the first electrode plates 85, 85 of the 
jigs 80, 80 for forming the film is supplied with a DC voltage of -3 kV by 
respective independent DC power source 73. 
Thus, the respective guide bushes 11, 11 are supplied with a negative DC 
voltage by independent DC power sources 73, 73, and independency of the 
plasma discharge can be enhanced, thereby preventing interference between 
the plasma discharges, and stabilizing the plasma discharge in the center 
bore of the respective guide bushes 11. Consequently the hard carbon film 
formed over the inner surfaces 11b of the respective guide bushes 11 is 
formed without dispersion of film thickness and the quality thereof can be 
improved. 
According to the embodiment, the hard carbon film can be formed 
simultaneously over the respective inner surfaces 11b of a plurality of 
the guide bushes 11 uniformly with excellent quality. The operation and 
effect other than that are the same as in the first embodiment described 
before. 
Although an example in which the hard carbon film is formed simultaneously 
over the inner surfaces 11b of two guide bushes 11 is shown here, the hard 
carbon film can be formed simultaneously over the inner surfaces 11b of 
three or more guide bushes 11. 
Fifth Preferred Embodiment 
FIG. 7 
The fifth embodiment shown in FIG. 7 is carried out by the same plasma 
production method described in the second embodiment with reference to 
FIG. 4. This method in the fifth embodiment is the same as the second 
embodiment shown in FIG. 4 except in that a plurality of (two in the 
drawing) guide bushes 11, 11 are disposed in one vacuum vessel 61 by using 
the jigs 80, 80 for forming the film, and each of the first electrode 
plates 85, 85 of the jigs 80, 80 for forming the film is supplied with a 
radio frequency power of 13.56 MHz in oscillation frequency through a 
matching circuit 67, 67 by respective independent radio power source 69. 
In this embodiment also, since the respective guide bushes 11, 11 are 
supplied with a radio frequency power by respective independent radio 
frequency power source 69, independency of the plasma discharge can be 
enhanced, thereby preventing interference between the plasma discharges, 
stabilizing the plasma discharge in the center bore of the respective 
guide bushes 11, and consequently an effect equal to the fourth embodiment 
described above can be obtained. 
In this embodiment also, the hard carbon film can be formed simultaneously 
over the respective inner surfaces 11b of a plurality of guide bushes 11 
uniformly with excellent quality. The operation and effect other than that 
are the same as in the second embodiment described before. 
Sixth Preferred Embodiment 
FIG. 8 
The sixth embodiment shown in FIG. 8 is carried out by the same plasma 
production method described in the third embodiment with reference to FIG. 
5. The method in the sixth embodiment is the same as the third embodiment 
shown in FIG. 5 except in that a plurality of (two in the drawing) guide 
bushes 11, 11 are disposed in one vacuum vessel 61 by using the jigs 80, 
80 for forming the film, and each of the first electrode plates 85, 85 of 
the jigs 80, 80 for forming the film supplied with a voltage of -600V by 
respective independent negative DC power source 74. 
In this embodiment also, since the respective guide bushes 11, 11 are 
supplied with a positive DC voltage by respectively independent positive 
DC power sources 74, 74, independency of the plasma discharge can be 
enhanced, thereby preventing interference between the plasma discharges, 
and stabilizing the plasma discharge in the center bores of the guide 
bushes 11, and consequently an effect equal to the fourth embodiment 
described above can be obtained. 
In this embodiment also, the hard carbon film can be formed simultaneously 
over the respective inner surfaces 11b of a plurality of guide bushes 11 
uniformly with excellent quality. The operation and effect other than that 
are the same as in the third embodiment described before. 
Jig for Forming Film for Plurality of Guide Bushes 
FIGS. 9, 10, 11 
The jig 80' for forming a film employed for forming a carbon film 
simultaneously over a plurality of guide buses which is shown in FIGS. 9 
to 11 is provided with a plurality of rodlike auxiliary electrodes 71, 71 
to be inserted into the center bores forming the inner surfaces 11b of a 
plurality of the guide bushes 11, 11, a plurality of auxiliary electrodes 
support members 72, 72 for supporting the respective auxiliary electrodes 
71, 71 and a plurality of porcelain insulators (auxiliary electrode 
insulation members) 81, 81, 82, 82 for fixing the respective auxiliary 
electrode support members 72, 72 inserted into the expanded section of the 
center bores of the respective guide bushes 11, 11. They are also provided 
with a plurality of guide bush receptors 84, 84, a plurality of insertion 
members 83, 83 to be inserted into the plurality of the guide bushes 11, 
11, and a plurality of dummy members 53, 53 to be mounted on the end faces 
of the respective guide bushes 11, 11, all of which are the same as the 
respective members of the jig 80 for forming the film described before. 
Not only two of these members but also the number of them corresponding to 
the number of guide bushes 11 which can be disposed simultaneously are 
provided on the jig. 
Further, the jig 80' is provided with a common first electrode plate 85' 
made of a conductive material to be contacted electrically on which a 
plurality of the guide bushes 11, 11 are mounted with their axes 
perpendicular, common legs 100 made of a conductive material to be put on 
the bottom of the vacuum vessel 61, a common second electrode plate 86' 
made of a conductive material for insertion of the small diameter portions 
of the auxiliary electrode support members 72, 72 which are integrated 
with the legs 100, and common insulation members 87', 88', 89' fixed to 
the legs 100' for insulation between the first electrode plate 85' and the 
second electrode plate 86'. 
The first insulation member 87' is provided with a plurality of holes for 
the plurality of the guide bushes receptors 84, 84 to be fitted therein. 
Seventh Preferred Embodiment 
FIG. 9 
An embodiment for forming a hard carbon film over the inner surface 
employing a plurality of jigs 80' for forming a film simultaneously over a 
plurality of guide bushes will be described next FIG. 9 is a sectional 
view of an apparatus for illustration of the seventh embodiment according 
to the present invention for forming the hard carbon film over the inner 
surface of a guide bush. In FIG. 9, parts like or corresponding to those 
shown in FIG. 6 are designated by the same reference characters and 
description thereof will be omitted. 
The method in the seventh embodiment is the same as the fourth embodiment 
shown in FIG. 6 except in that a plurality of guide bushes 11, 11 are 
disposed in the vacuum vessel 61 by using the jig 80' for forming the 
film, and the respective guide bushes 11, 11 are supplied with a voltage 
of -3 kV through a common first electrode plate 85' by a common DC power 
source 73. 
Accordingly, although the operation and effect are almost the same as those 
of the fourth embodiment, the hard carbon film can be formed 
simultaneously and uniformly over the respective inner surfaces of a 
multiplicity of guide bushes at a lower cost and with greater efficiency 
since the members secured in the vacuum vessel 61 are commonly used for 
the plurality of the guide bushes 11, and the DC power source 73 for 
applying a DC voltage of -3 kV to the respective guide bushes is also 
commonly used for the respective guide bushes 11. 
Eighth Preferred Embodiment 
FIG. 10 
FIG. 10 is a sectional view of an apparatus for illustration of the eighth 
embodiment of the method of forming the hard carbon film over the inner 
surface of the guide bush according to the present invention. In FIG. 10, 
parts like or corresponding to those shown in FIG. 7 are designated by the 
same reference characters and description thereof will be omitted. 
The method in the eighth embodiment is the same as the fifth embodiment 
shown in FIG. 7 except in that a plurality of guide bushes 11, 11 are 
disposed in the vacuum vessel 61 by using the jig 80' for forming the 
film, and the respective guide bushes 11, 11 are supplied with radio 
frequency power through a common matching circuit 67, and the first 
electrode plate 85' is supplied by a common radio frequency power source 
69. 
Accordingly, although the operation and effect other than that are the same 
as in the fifth embodiment described before, the members of the jig for 
forming the film which are secured in the vacuum vessel 61 are common to a 
plurality of the guide bushes 11, and the radio frequency power source 73 
for applying radio frequency power to the respective guide bushes and the 
matching circuit 67 are also common to the respective guide bushes 11, so 
that the hard carbon film can be formed simultaneously over the respective 
inner surfaces of the guide bushes at a lower cost and with greater 
efficiency. 
Method According to Ninth Embodiment 
FIG. 11 
FIG. 11 is a sectional view of an apparatus for illustration of the ninth 
embodiment for forming the hard carbon film over the inner surface of the 
guide bush according to the present invention. In FIG. 11, parts like or 
corresponding to those shown in FIG. 8 are designated by the same 
reference characters and description thereof will be omitted. 
The ninth embodiment is the same as the sixth embodiment shown in FIG. 8 
except in that a plurality of guide bushes 11, 11 are disposed in the 
vacuum vessel 61 by using the jigs 80' for forming the film, and the 
respective guide bushes 11, 11 are applied with a DC voltage of -600V 
through a common first electrode plate 85' by a common DC power source 74. 
Accordingly, although the operation and effect other than that are almost 
the same as in the sixth embodiment described before, the members of the 
jig for forming the film which are secured in the vacuum vessel 61 are 
common to a plurality of the guide bushes 11 and the DC power source 74 
for applying a DC voltage of -600V to the respective guide bushes 11 is 
also common to the respective guide bushes 11, so that the hard carbon 
film can be formed simultaneously over the respective inner surfaces of 
the guide bushes at a lower cost and more efficiently. 
Supplementary Explanation 
In the method of forming the hard carbon film according to the present 
invention described with reference to FIG. 3 to FIG. 11, although an 
example in which methane gas or benzene gas as a gas containing carbon is 
used, a gas containing carbon other than methane, such as ethylene or a 
vapor of a liquid containing carbon such as hexane may also be used. 
Further, argon (Ar) gas, nitrogen (N.sub.2) gas, helium (He) gas or 
hydrogen (H.sub.2) gas may be added to the methane, ethylene or hexane 
gasses containing carbon. 
Thus, addition of argon gas or nitrogen gas to the gas containing carbon 
controls the speed of forming the film. Thereby, the hard carbon film can 
be minute, and further, any part of the hard carbon film with poor 
adhesion and quality can be removed by sputtering using nitrogen or argon, 
thereby improving the quality of the film. Further, when hydrogen is added 
to the gas containing carbon, any dangling bonds of the carbon can be 
filled with the hydrogen, which is effective for improving the quality of 
the hard carbon film.