U.S. patent number 3,640,356 [Application Number 04/884,396] was granted by the patent office on 1972-02-08 for diamond bit.
This patent grant is currently assigned to Shell Oil Company. Invention is credited to Robijn Feenstra.
United States Patent |
3,640,356 |
Feenstra |
February 8, 1972 |
DIAMOND BIT
Abstract
A diamond bit, the diamonds in the sidewall thereof being set in
a blunt position in a direction radial to the central axis of the
bit as well as in a cutting position in a direction tangential to a
helical line passing through the cutting tip of the diamond and
having a central axis coinciding with the central axis of the
bit.
Inventors: |
Feenstra; Robijn (Rijswijk,
NL) |
Assignee: |
Shell Oil Company (New York,
NY)
|
Family
ID: |
10173275 |
Appl.
No.: |
04/884,396 |
Filed: |
December 12, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Apr 30, 1969 [GB] |
|
|
22,061/69 |
|
Current U.S.
Class: |
175/434;
125/39 |
Current CPC
Class: |
E21B
10/46 (20130101) |
Current International
Class: |
E21B
10/46 (20060101); E21b 009/36 () |
Field of
Search: |
;175/329,330 ;76/108
;125/39 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Purser; Ernest R.
Claims
I claim:
1. A diamond bit for drilling a hole in a subsurface formation,
said diamond bit having a central axis and comprising:
a bit body;
means carried by the bit body for connecting the bit body to a
tubular drill string;
diamonds set in the bottom part of the bit body to cut the bottom
of the hole when used therein;
sidewall diamonds set in the sidewall of the bit body to cut the
sidewall of the hole, each of said sidewall diamonds being
positioned at a cutting diameter on the bit body and being set in a
blunt position in a direction radial to the central axis of the
diamond bit as well as in a cutting position in a direction
tangential to a helical line passing through the cutting tip of
that sidewall diamond and having a central axis coinciding with the
central axis of the diamond bit, this tangential direction being
taken at the cutting tip of the sidewall diamond.
2. The diamond bit of claim 1 wherein the diamond bit comprises
additional diamonds set in the upper part of the sidewall of the
bit body which additional diamonds touch a conical plane having a
central axis coinciding with the central axis of the diamond bit,
this conical plane being arranged with the apex thereof in a
direction opposite to the direction in which the bit is axially
loaded during operation, said additional diamonds being positioned
at cutting diameters no greater than the largest cutting diameter
of said first-mentioned sidewall diamonds set in the sidewall of
the bit body.
3. The diamond bit of claim 1, wherein at least some of the
sidewall diamonds set in the sidewall of the bit body touch a
conical plane having the central axis thereof coinciding with the
central axis of the diamond bit, this conical plane being arranged
with the apex thereof in the direction in which the bit is axially
loaded during operation.
4. The diamond bit of claim 3, wherein the apex angle of the
conical plane is between 0.degree. 10' and 20.degree..
5. The diamond bit of claim 1, wherein at least some of the
sidewall diamonds set in the sidewall of the bit body touch a
rotational symmetrical plane which is concave with respect to the
central axis of the diamond bit, which has a central axis
coinciding with the central axis of the diamond bit, and which can
be arranged tangentially to a group of conical surfaces having the
central axis thereof coinciding with the central axis of the
diamond bit and the apices thereof in the direction in which the
bit is axially loaded during operation.
6. The diamond bit of claim 5, wherein the group of conical
surfaces to which the rotational symmetrical plane can be
tangentially arranged consists of cones which have apex angles
between 0.degree. 10' and 20.degree..
7. The diamond bit of claim 3 wherein at least some additional
sidewall diamonds set in the sidewall of the bit body touch a
cylindrical plane intersecting the conical plane and having a
central axis coinciding with the central axis of the diamond bit,
said additional diamonds being positioned at cutting diameters
equal to the largest cutting diameter of all other diamonds
arranged in the sidewall of the bit body.
8. The diamond bit of claim 5 wherein at least some additional
sidewall diamonds arranged in the sidewall of the bit body touch a
cylindrical plane intersecting the rotational symmetrical plane and
having a central axis coinciding with the central axis of the
diamond bit, said additional diamonds being positioned at cutting
diameters equal to the largest cutting diameter of all other
diamonds arranged in the sidewall of the bit body.
9. The diamond bit of claim 1 wherein said sidewall diamonds set in
a blunt position in a direction radial to the central axis of the
diamond bit have at least one substantially flat plane and wherein
said sidewall diamonds are set in said bit body with a
substantially flat plane of the sidewall diamond in the plane of
the sidewall of the bit body.
10. The diamond bit of claim 1 wherein said sidewall diamonds set
in a blunt position in a direction radial to the central axis of
the diamond bit have at least one substantially flat plane and
wherein said sidewall diamonds are set such that there is a line of
contact between the sidewall diamond and the plane of the sidewall
at the trailing part of a flat plane of the sidewall diamond with
respect to the direction of motion of the sidewall diamond in
operation of the diamond bit and such that the leading part of said
flat plane of the sidewall diamond is within the bit body.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to diamond bits, and more particularly to
diamond bits such as can be used in well drilling.
2. Summary of the Invention
Diamond bits are used in particular for drilling holes through rock
material of poor drillability, which is often required when
drilling subsurface formations for the purpose of prospecting for
and/or recovering oil or other valuable products.
These bits are of the rotary type and the diamonds thereof exert a
scraping action on the rock through which a hole is being drilled,
the bit being loaded in an axial direction and being rotated around
its central axis.
Bits of this type are especially useful for drilling through deep,
abrasive, hard formations, since under these operating conditions
they have a longer life than any other type of rotary rock bit,
such as a roller bit. Consequently, a diamond bit has to be
replaced less frequently than a bit of another type. The higher
material and manufacturing costs of a diamond bit as compared with
other types of bits are easily compensated by the advantages
obtained as a result of the reduction in time required to replace
the worn bits during drilling operations.
The object of the invention is to provide a diamond bit which is
less liable to be damaged by lateral vibrations during drilling
than known diamond bits.
A further object is to provide a diamond that which is less liable
to wobbling than known diamond bits.
Still a further object of the invention is to provide a diamond bit
in which the diamonds are less liable to be crushed or burned than
in known diamond bits.
These objects are achieved by designing the bit in such a manner
that no oversize-hole cutting will occur when the bit is operated
in the formation. Oversize-hole cutting causes the diamonds on the
bottom part of the bit or the face of the bit (that is the part of
the bit cutting the bottom of the hole) to cut zigzag tracks and to
cross each other's tracks, thus giving rise to shock loads on the
diamonds. Another consequence of oversize-hole cutting is that the
bit on being rotated in the hole is subject to wobbling, whereby
the diamonds arranged in the face of the bit become overloaded.
Still a further consequence of oversize-hole cutting is that the
flow of drilling fluid over the surface of the bit and along the
diamonds is no longer exclusively controlled by the waterways
arranged in the outer wall of the bit body, so that diamonds which
are insufficiently cooled owing to the disturbance of the required
drilling fluid distribution over the surface of the diamond bit
will be burned out.
Design of a diamond bit such that oversize-hole cutting is obviated
will prevent lateral vibration, as well as wobbling of the diamond
bit during operation, and will further ensure the required
distribution of cooling and washing fluid along the cutting tips of
the diamonds. It will be appreciated that the lifetime of such a
bit is appreciably longer than that of bits which cut an
oversize-hole when used in a subsurface formation.
The diamond bit according to the invention comprises a bit body and
means for connecting the body to a tubular string, the body
carrying diamonds for cutting a hole in a formation in which the
bit is operated by rotation around the central axis thereof. The
bit further comprises diamonds arranged in the sidewall of the bit
body for cutting the sidewall of the hole, each of these diamonds
being set in a blunt position in a direction radial to the central
axis of the diamond bit, as well as being set in a cutting position
in a direction tangential to a helical line passing through the
cutting tip of the diamond and having a central axis coinciding
with the central axis of the diamond bit, this tangential direction
being taken at the cutting tip of the relevant diamond.
The diamonds arranged in the sidewall of the bit body may touch a
conical plane having the central axis thereof coinciding with the
central axis of the diamond bit, the conical plane being arranged
with the apex thereof in the direction in which the bit is axially
loaded during operation. The apex angle of this conical plane may
be between 0.degree.10' and 20.degree..
In another embodiment, the diamonds arranged in the sidewall of the
bit body may touch a rotational symmetrical plane which is concave
with respect to the central axis of the diamond bit and has a
central axis coinciding with the central axis of the diamond bit,
which plane has tangential cones which are arranged with the apices
thereof in the direction in which the bit is axially loaded during
operation and have apex angles with a value between 0.degree. 10'
and 20.degree..
Some of the diamonds arranged in the sidewall of the bit body may
touch a cylindrical plane having a central axis coinciding with the
central axis of the diamond bit. These latter diamonds have a
cutting diameter which is equal to the largest cutting diameter of
the other diamonds arranged in the sidewall, and lie-- in the
operative position of the bit wherein the central axis thereof is
vertically arranged--above the other diamonds arranged in the
sidewall.
The sidewall of the bit body may comprise further diamonds, which
touch a conical plane having a central axis coinciding with the
central axis of the diamond bit and being arranged with the apex
thereof in a direction opposite to the direction in which the bit
is axially loaded during operation, these diamonds being arranged
in a position lying-- in the operative position of the bit wherein
the central axis is vertically arranged--above the plane passing
through the upper diamonds which are arranged in the sidewall of
the body to cut the sidewall of the hole.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a side view of a diamond bit according to the
invention;
FIG. 2 is a longitudinal cross section of the bit shown in FIG. 1
taken in the direction of the arrows 2--2;
FIG. 3 is a horizontal section of the bit shown in FIG. 1 taken in
the direction of the arrows 3--3;
FIG. 4 shows an enlargement of the diamond which is located at the
intersection of section 2--2 and section 3--3 in FIG. 1;
FIG. 5 shows a longitudinal cross section through the diamond shown
in FIG. 4 in the direction of the arrows 5--5;
FIG. 6 shows a horizontal cross section through the diamond shown
in FIG. 4 in the direction of the arrows 6--6; and
FIG. 7 represents an alternative of detail A in FIG. 2 on a larger
scale than FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred embodiment of the invention shown by way of example in
FIGS. 1--3 of the drawing comprises a bit body 1 formed by a
wear-resistant material, in which body diamonds 2 are set. These
diamonds are grouped alongside waterways 3 via which drilling
liquid is passed to cool the diamonds 2 and keep them clean from
drilling flour and cuttings. The liquid further cools the bit body
1 and carries away the rock cut by the diamonds 2. The bit body 1
may consist of tungsten carbide grains which are sintered together
and to the steel shank 4 in a known manner such as that of
Feenstra, U.S. Pat. No. 3,453,719. The diamonds 2 are set in the
bit body 1 and the waterways 3 are formed in the mass of tungsten
carbide particles before the sintering process is carried out.
Since these techniques are known, they are not described here in
detail.
The steel shank 4 comprises a coupling 5 provided with connecting
means such as screw thread 6 suitable for connecting the diamond
bit to a drill collar string (not shown) or other tubular string.
If desired, the steel shank 4 may be connected directly to the
shaft of a hydraulic turbine or an electric motor suitable for
being operated in a borehole. The shank 4 is further provided with
a central channel 7 for passing drilling liquid from the interior
of the tubular string connected to the screw thread 6 of the
coupling 5, to the waterways 3 arranged in the surface of the bit
body 1.
The center part of the bit body 1 has a conically shaped
introversion 8 (FIG. 2) and a channel 9 is provided connecting the
channel 7 in the shank 4 with the apex of the conically shaped
introversion 8. Since the channel 9 is not concentrically arranged
with respect to the central axis of the bit body 1, no core will be
formed from the formation when the bit according to the invention
is being operated in a subsurface formation.
The waterways 3 run from the channel 9 over the curved "face" 10 of
the bit body 1 and over the sidewall 11 (also indicated by "gauge"
side).
The exact position of the diamonds in the sidewall 11 will now be
described with reference to the FIGS. 4, 5 and 6, which show a
diamond corresponding to that in FIG. 1, which is located at the
intersection of the sectional planes 2--2 and 3--3.
FIG. 4 is an enlargement of this diamond in the position shown in
FIG. 1, and FIGS. 5 and 6 are cross sections thereof, respectively,
along sectional planes 5--5 and 6--6 in FIG. 4.
The diamond 12 shown in FIG. 4 is approximately cube-shaped and
located with a flat plane thereof in the surface of the sidewall 11
(FIGS. 5 and 6). This means that the diamond is set in a blunt
position in a direction radial to the central axis (not shown) of
the diamond bit. Thus, the diamond cannot exert any cutting action
as a result of load being exerted on the diamond 12 in a direction
not coinciding with this central axis.
It can further be seen that in the position shown in FIG. 4, the
lower plane of the diamond 12 makes an angle B with the horizontal
line 13. This angle B may be in the order of 0.degree. to
30.degree., and if desired even be negative. Consequently, on
movement of the diamond 12 in the direction of arrow 14 (being the
movement of rotation of the diamond bit) the tip 15 of the diamond
12 is in a cutting position when load is exerted thereon in a
direction axial to the central axis of the bit. It will be
appreciated that the diamond 12 set in the sidewall 11 of the bit
body 1 is thus in a cutting position in a direction tangential to a
helical line passing through the cutting tip 15 of the diamond 11
and having an axis coinciding with the central axis of the diamond
bit, this tangential direction being taken at the cutting tip 15 of
the diamond 12. It will be appreciated that if the angle B is
negative, the corner 15A of the diamond 12 will act as a cutting
tip. It will further be appreciated that what has been described
with reference to the diamond 12 shown in FIGS. 4-6, also applies
to all the other diamonds 2 set in the sidewall 11 of the bit body
1, which diamonds will--when the diamond bit is operated in a
subsurface formation--cut the wall of the hole which is then being
drilled by the bit.
The angle between the surface of the sidewall 11 and the central
axis of the diamond bit is indicated by C in FIG. 5. Since in the
embodiment shown in FIGS. 1-6 of the drawing, the sidewall 11 of
the diamond bit is conical, the apex angle of the cone on which the
sidewall 11 is located is twice the value of the angle C. This
value preferably may be between 0.degree. 5' and 10.degree.. It
will be appreciated that the value of angle B increases with
increasing values of the angle C.
The relationship between the cutting diameters of the diamonds of
the diamond bit will now be described.
The expression "cutting diameter" of a diamond is understood to
mean the diameter of a circle in a plane perpendicular to the
central axis of the diamond bit in which the relevant diamond is
located and along which circle the cutting tip of the diamond
travels during rotation of the bit around its central axis.
When the bit shown in FIGS. 1-3 is operated in a subsurface
formation, the diamonds set in the bottom portion 10 of the bit
body 1 will cut the bottom of a hole, whereas the diamonds set in
the sidewall 11 will cut the sidewall of this hole. It will be
clear that the hole which is being drilled by the diamonds set in
the bottom part 10 of the diamond bit will be enlarged in diameter
by the action of the diamonds set in the sidewall 11. The sidewall
11 being of conical shape, this enlargement takes place gradually
since the diamonds placed at higher levels of the sidewall show an
increase in the cutting diameter thereof.
Since the diamonds set in the sidewall 11 of the bit are set in a
blunt position in a direction radial to the central axis of the
diamond bit a hole results from the operation of the bit in a
subsurface formation, wherein all the diamonds arranged in the
sidewall 11 are in contact with the wall of the hole. The
horizontal components of loads exerted by the drill string and the
drill collar string on the bit in directions other than the central
axis of the bit will be taken up in the contact plane between the
sidewall 11 and the wall of the hole without any cutting action
occurring in direction radial with respect to the central axis of
the diamond bit. Thus, the contact between the diamonds in the
sidewall 11 and the wall of the hole will be maintained in all
circumstances without oversize-hole cutting being caused
thereby.
The advantages are threefold. In the first place, the diamonds of
the bottom part 10 of the bit remain in their own track and cannot
cut zigzag tracks and cross each other's tracks, which would occur
if the hole was oversize and would result in shock loads being
exerted on the diamonds. Secondly, the fluid flow across the
surface of the bit remains controlled exclusively by the waterways
3, because the bit profile fits the hole profile in the absence of
oversize cutting. Consequently, each diamond will be adequately
cooled and there will be no burning of the diamonds such as often
occurs when an oversize hole is being drilled. Thirdly, the
stabilization of the string is better than in an oversized hole, as
a result of which wobbling of the bit is reduced and the life of
the diamonds is prolonged.
It will further be appreciated that the form of the sidewall 11 of
the drill bit is not restricted to a conical plane as described
with reference to FIGS. 1-6. With equally favorable results, this
sidewall may be formed by a rotational symmetrical plane obtained
by rotating a slightly curved line around the central axis of the
bit. This sidewall must have a positive curvature, and the diameter
of the bit body in cross sections perpendicular to the central axis
of the bit has to increase in an upward direction. To prevent heavy
axial loads on the diamonds in the sidewall, the projection of this
sidewall on the bottom of the hole should be relatively small. This
means that the apex angles of the cones which can be arranged
tangentially to this sidewall should be small, preferably in the
order of 0.degree. 10' - 20.degree.. These cones are arranged with
the apices thereof in the direction wherein the bit is axially
loaded.
If a hole has been undercut by a previous bit, those diamonds of a
new bit which have the largest cutting diameter will be excessively
loaded when this new bit is run into the hole. Some of these
diamonds may be crushed or broken out and to prevent undercutting
of the hole by this new bit it is advisable to have some more
diamonds with a cutting diameter equal to this largest cutting
diameter located above the diamonds in the sidewall of the bit.
Although a single diamond above each row of diamonds arranged along
a waterway may be sufficient for the purpose, more than one
diamond, for example, four or five, may be applied. These diamonds
are arranged in the sidewall of the bit and touch a cylindrical
plane having a central axis coinciding with the central axis of the
bit. Like the diamonds arranged in the sidewall of the bit for
cutting the wall of the hole when the bit is being operated, each
diamond arranged in the cylindrical part of the sidewall and having
a cutting diameter which is equal to the largest cutting diameter
of the other diamonds arranged in this sidewall is set in a blunt
position in a direction radial to the central axis of the diamond
bit, and is set in a cutting position in a direction tangential to
a helical line passing through the cutting tip of the diamond and
having an axis coinciding with the central axis of the diamond bit,
this tangential direction being taken at the cutting tip of the
relevant diamond.
Retrieval of the bit from the hole may be made easier by providing
the upper part of the bit body with a conically shaped part, which
part may be provided with diamonds touching the conical surface.
These diamonds may be set sharp and/or blunt.
The three above-mentioned features will now be described with
reference to an embodiment which shows all these features. It will,
however, be clear that these three features need not be applied
together. FIG. 7 of the drawing shows part of a sidewall of a bit,
which part can be considered as an alternative of detail A of the
cross section of the bit shown in FIG. 2, but on a larger scale.
The cross section shown in FIG. 7 is taken over a row of diamonds
instead of over a waterway as is the case in FIG. 2.
The shank 20 shown in FIG. 7 carries a bit body 21 made of
wear-resistant material and carrying diamonds touching the outer
surface thereof. This surface is divided into four zones 22, 23, 24
and 25.
Zone 22 is the lower or bottom part of the bit body carrying
diamonds 26 which are set so as to cut the bottom of the hole when
the bit is operated in a subsurface formation.
Zone 23 is that part of the sidewall which carries diamonds 27 each
of which is set blunt in a radial direction, and sharp in a
direction tangential to a helical line passing through the cutting
tip of the diamond and having an axis coinciding with the central
axis of the bit. All the details given with reference to the
diamond 12 in FIGS. 4-6 also apply to these diamonds, except,
however, that the diamonds 27 do not touch a conical plane, but a
rotational symmetrical plane 28, which is concave with respect to
the central axis of the diamond bit and has a central axis
coinciding with the central axis of the diamond bit. This plane 28
further has cones (not shown) touching the plane, which cones are
arranged with the apices thereof in the direction in which the bit
is axially loaded during operation, and which cones preferably have
apex angles with a value between 0.degree. 10' and 20.degree..
Zone 24 is that part of the sidewall which carries diamonds 29,
each of which is equal to the uppermost diamond 27' in cutting
diameter as well as in setting. Diamond 27' is the uppermost
diamond of a row of diamonds 27 located in zone 23 and touching the
rotational symmetrical plane 28. The diamonds 29 touch a
cylindrical part of the sidewall and are arranged to take over the
function of the diamond 27' should this diamond fail. This prevents
the hole from being undercut if the diamond 27' and the
corresponding diamonds in other rows are burnt or broken out.
Zone 25 is the upper part of the sidewall, which part carries
diamonds 30. It will be clear that this part of the sidewall does
not cut the wall of the hole when the drilling bit is in operation,
but will guide the bit when the latter is being lifted from the
hole. The diamonds 30 are set sharp and prevent wearing out of the
zone 25 during retrieval of the bit from the hole. Moreover, the
bit can be cut free in an upward direction by rotation during
retrieval of the bit from the hole.
It will be appreciated that the invention is not limited to the
examples described above with reference to the drawing, but that
various modifications may be introduced in these examples.
Some of these modifications are mentioned below.
The invention is not limited to bits having a bottom part or lower
part 10 and a conical introversion 8 shaped as shown in FIG. 2. Any
other form of bottom part or introversion thereof may be applied
which is suitable for the purpose.
Furthermore, the invention is neither limited to the number and
distribution of the diamonds over the surface of the bits as shown
in FIGS. 1-3 and 7, nor to the number and shape of the waterways 3,
nor the distribution of these waterways over the surface of the
bits as shown in FIGS. 1-3 and 7.
The apex angle of the conical surface which is touched by the
diamonds arranged in the sidewall 11 of the bit shown in FIGS. 1-3
preferably may be between 0.degree. 10' and 20.degree.. This
sidewall 11 may further be extended in an upward direction by a
zone 24 as shown in FIG. 7 and/or a zone 25 as is also shown in
FIG. 7.
The application of the inventive diamond-studded sidewall which
prevents oversize cutting of a borehole is further not restricted
to diamond bits having a drilling liquid supply 9 as shown in FIG.
2. If desired, any other suitable supply of drilling liquid may be
used. Furthermore, the invention is not restricted to bits which do
not leave a core in the center of the hole, but may also be used
with core bits, or bits leaving a core of small diameter which is
subsequently broken by the action of the bit and the fragments of
which are removed via a side opening in the bit.
As shown in FIGS. 4, 5 and 6, the blunt position of a diamond with
respect to loads exerted in a direction radial and perpendicular to
the central axis of the diamond bit is obtained by placing a
substantially flat plane of the diamond in the plane of the
sidewall. However, this blunt position may also be obtained by
placing the diamond in a "dragging" position which means that the
point of contact between the diamond and the conical plane is the
trailing part of the diamond when viewed in the direction of
movement of the diamond along the wall of the borehole. This means
that the direction of rotation of the diamond bit unit has to be
taken into account when placing the diamonds. This direction can be
derived from the type of screw thread used. Normally, the bit, the
drill collars and the drill pipes are right-hand threaded, which
means that the diamond bit unit is rotated clockwise when looking
into the hole (arrow 14 in FIG. 4). The angle R in FIG. 6 indicates
the angle between the diamond plane and the conical plane, through
which the diamond can be "dragged" along the wall of the borehole
without cutting in a radial direction. The corner 15A of the
diamond 12 then acts as cutting tip in a direction tangential to a
helical line having a central axis coinciding with the central axis
of the bit. This line passes through the tip 15A and the tangential
direction is taken at the tip 15A.
Although the diamonds shown in the drawing to which the above
examples refer are all approximately cube-shaped, it will be
appreciated that differently shaped diamonds may also be used,
provided that they are set in such a position that they cut in a
direction tangential to a helical line passing through the cutting
tip of the diamond and having an axis coinciding with the central
axis of the diamond bit unit, this tangential direction being taken
at the cutting tip of the relevant diamond, and that they are blunt
in a direction radial to the central axis of the diamond bit.
A diamond bit having the diamonds in the sidewall thereof set in
accordance with the present invention may be used with advantage in
the diamond bit unit described and claimed in copending application
No. 839,541, filed July 7, 1969 and now U.S. Pat. No.
3,534,294.
If desired, the diamond bit according to the invention may be used
in combination with stabilizers and/or reamers of known design.
These known stabilizers may for example be of rubber or hard-faced
steel and are carried by the drill string at some distance above
the diamond bit according to the invention. They will dampen the
oscillating movements of the drill string. The known reamers, if
applied, are also located above the diamond bit according to the
invention. Since these known reamers have the characteristic
feature of being able to cut in directions radial to the central
axis of the reamer, the hole is cut to a diameter greater that the
outer diameter of the reamer, which has the advantage that the
diamond bit (and the reamer) can be lifted very easily from the
hole, or run in.
* * * * *