Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~ 13122
CLAMPING DEVICE FOR TOOL ~IOLDERS
The invention relates to a clarnping device for connecting basic holders or machine
spindles with tool holders or tools for m~chining, with partable staple-shaped
5 clamping elements which, with radially outwardly projecting clamping jaws, engage
behind clamping shoulders inside the machine spindle and the tool holder.
A clamping device of this type is disclosed in DE-C 39 04 259. The prior art device
has three clamping elements distributed at 120 over the periphery, which, with the
0 jaws located at one end, are permanently engaged with an inwardly projecting
shoulder of a basic holder. Positioned in the jaws on the tool holder side are radial
adjusting screws which can be operated through a corresponding radial bore from
outside the tool holder. The adjusting screws have a tapered tip which, when theadjusting screws are operated, comes into contact with the tapered tips of the two
other adjusting screws. The tips pressed against each other when the adjusting
screws are operated are intended to pivot the staple-shaped clamping elements
outwardly around the end Iying on the basic holder side and to engage the jaws on
the tool holder side with the latter's inwardly projecting shoulder.
20 There are various reasons for reservations about the suitability of this solution in
practice. The tapered tips are surely exposed to a high degree of abrasion. There is
a further disadvantage in that the tool holder has to be provided with a bore in the
vicinity of its taper, so that it is not possible to use just any tool holders. As a
glance at the drawing shows, a very large number of parts is required and hence
25 production, assembly and maintenance are costly. There is only a restricted axial
passage for coolant pipes.
The tool holder, whose mainly flatly tapered shank is self-lockingly clamped in the
machine spindle or in the basic holder, cannot be ejected when the tool holder is
30 loosened.
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Particularly where the tool holders or tools with hollow shanks specified under
DIN 69893 are concerned, it is also necessary, in addition to prior art mech~ni~m.c
for automatic clamping with machine spindles, to create clamping devices which
can also be operated m~ml~lly. In doing so, various requirements have to be met
to ensure reliable operation and to limit the cost of construction:
- The clamping force should be spread as uniformly as possible over several
clamping points distributed over the periphery of the inwardly projecting
shoulder or clarnping surface of the hollow shank of the tool holder. This is
lo the only way to ensure achieving the effect which can be attained via the
hollow shank of an inwards to outwards elastic distortion in the relatively thin-
walled taper to achieve a high degree of contact pressure on the inner taper of
the machine spindle or the basic holder. Furtherrnore, a uniform axial pulling
force results in a rigid clamp between the front face of the m~chine spindle or
the basic holder and the flange of the tool holder. Since it is practically
impossible to achieve the ideal case where the entire surface of the clamping
device rests against the entire encircling shoulder, a uniform distribution overseveral defined clamping surfaces should at least be achieved.
20 - The res ]lt~n~ force lines should be as short as possible, and the lateral forces
exerted on the machine spindle or the basic holder on the one hand, and on the
tool holder on the other hand, should be as low as possible.
- It ought to be possible to convey coolants at the centre of the machine spindle
through the clamping system to the tool holder and tool.
- In view of the flatly tapered hollow shank of the tool holder and the self-
locking which occurs on clamping, it ought to be possible to apply a high
ejection force.
As stated, these requirements are only partially met by the aforementioned prior art
clamping device, and only at a high construction cost.
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Even costlier is the clamping device described in EP-A-0 451 360. This also
provides for staple-shaped clamping elements which engage behind clamping
shoulders or clamping surfaces inside the basic holder or the machine spindle on-- the one hand, and the tool holder on the other hand, with the aid of jaws. Here,
too, the jaws on the basic holder side are captive whilst on the tool holder side,
they are engaged by pivoting the clamping elements. To effect this pivoting, there
is a tapered quill which has to be displaced in the axial direction. This displacement
is effected with the aid of a clamping nut screwed onto the quill, which has to be
rotated from the outside via a worm gear. This must be even costlier than the
o aforementioned embodiment according to DE-C 39 04 259.
The invention is based on the task of creating a clamping device of this generictype, which is simple, robust and does not require much m~inten~nce, thus
allowing economic use, and which, furthermore, does not entail eh~n~in~ or
modifying the standard toolholders as defined by DIN 69893.
According to the invention, in a device of the aforementioned type this task is
solved by connecting 2 clamping elements with the aid of a parting element to a
clamping block whose outer diameter in the closed position is smaller than the
20 smallest inner diameter of both the machine spindle and the tool holder, and in that
the clamping elements each have two clamping surfaces on both sides which are
disposed such that the four clamping surfaces of the two clamping elements are
each distributed over the periphery of the clamping shoulders at angular distances
of approx. 90.
On both sides, the clamping elements each have two clamping surfaces which are
disposed such that the four clamping surfaces of the two clamping elements are
each distributed over the periphery at an angular distance of approx. 90. This
results in a very uniform and syrnmetrical distribution of the clamping force on the
30 clamping shoulders of the basic holder and the tool holder and, ~imlllt~neously~ a
symmetrical contact force distributed over the periphery between the inner taperand the outer taper and between the relevant front faces. This is particularly
important because this absorbs the radial stress on the clamping point caused byencircling bending forces.
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The unit desi~n~ted in this context as the clamping block, consisting of two
clamping elements and a parting element, can be mounted in its assembled state as
a unit into its intended position. Equally, it can easily be completely removed for
checking and m~inten~nce purposes. It is not necessary to assemble a large number
5 of relatively complicated parts with difficulty inside the basic holder or the machine
spindle. The flow of power takes place via the shortest path and almost without
any occurrence of lateral forces between the basic holder and the tool holder.
Modifications to the standard tool holder are not necessary.
o To simplify the following embodiments, reference will for the most part only be
made to the connection between a basic holder and a tool holder, although a
machine spindle can be provided in place of the basic holder, and a tool in place of
the tool holder.
15 In one pr~relled embodiment, the parting element is a di~ele,lLial screw which lies
inside the two sl~mping elements in oppositely coiled tapped holes. The advantage
of this solution is that the clamping elements are inevitably guided when they are
parted and drawn together. However, the parting element could also be a parting
screw which is screwed into one of the clamping elements and rests against the
20 other, or even a shank taper which is drawn between the clamping elements.
The parting element can be reached with a suitable tool through a radial bore in the
basic holder. The parting element is preferably connected via a detachable, non-rotating plug connection with a clamping journal which allows a plug-in tool to be
2s connected and which lies in the radial bore of the basic holder. Furthermore, a
second, oppositely positioned bore is preferably provided in the basic holder, in
which lies an ejecting journal from which proceeds a centering pin which engageswith play in a front face blind bore in the parting element. The clamping journal
and the ejecting journal lie in front face recesses on opposite sides of the standard
30 tool holder. Simultaneously, they serve as drivers for the tool holder.
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The parting element can also take the form of an eccentric cam. This results in the
significant advantage that the clamping elements can be fully parted by a rotation
of maximum 90, whilst with a di~e. en~ial screw or other parting screw several full
rotations may be necess~ry under certain circllm~t~nces. The use of an eccentric5 cam as the parting element is therefore particularly advantageous in those cases
where the tool has to be clamped in position in a restricted space or in positions
where access is difficult.
However, whilst a dirrerenLial screw can both part and draw together the clamping
o elements, if an eccentric carn is used the clamping elements can only be parted. The
clamping elements can, for example, be retracted with the aid of jaws which are
non-rotabably connected with the eccentric cam, which engage in pockets on the
inside of the clamping elements and which pull the clamping elements inwards.
Additionally, or alternatively, the use of a return spring could be considered.
The ejecting journal preferably has a non-circular or cam-shaped section and is
disposed in relation to the base of the associated recess in the tool holder in such a
way that the tool holder can be ejected from the basic holder with the aid of the
radial-outer portion of the flattened part by rotating the ejecting journal.
The clamping journal and the ejecting journal also have the additional function of
floatingly guiding the clamping block in the unclamped position in the vicinity of
the interface of the basic holder and the tool holder.
25 According to another prerelled embodiment, in one ofthe clamping elements there
is at least one ejecting pin which runs through the second clamping element to the
opposite side, which, when the clamping block is screwed together, comes into
contact via one front face sloping surface with an opposite surface of the tool
holder and displaces the tool holder in the direction of ejection Said sloping
30 surface can be a conical tip of the ejecting pin, and the ejecting pin can engage via
the thread in the first clamping element and in this way be longit~l-lin~lly adjustable.
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As the opposite surface in this context, the base of one of the front face recesses in
the tool holder could be considered.
According to another p-efe-led embodiment, the front faces of the clamping
elements closest to the tool holder can be provided with sloping surfaces which, on
being drawn together, run up against the sloping surfaces of a connecting element,
possibly a coolant adapter, which displaces the tool holder in the direction of
ejection.
If an eccentric cam is used as the parting element, one of the cam surfaces of the
eccentric cam can run up against a sloping surface which is rigidly connected with
the machine spindle when the clamping jaws are loosened by rotating the eccentric
cam, so that the tool holder is ejected in this way.
S The interacting surfaces of at least one clamping shoulder and one pair of clamping
jaws are preferably at least partially sloped so that when the clamping elements are
radially parted, an axial pull is .cimlllt~neously exerted on the tool holder.
On the sides facing each other, the clamping elements can have at least one recess
which allows the passage of at least one coolant pipe through the interface between
the basic holder and the tool holder.
Entering in their radial direction into the radial bores of the basic holder which
accommodate the clamping journal and the eiecting iournal, there are stud bolts
which can be screwed into encircling grooves in the clamping journal and the
ejecting journal. In this way, the clamping journal and the ejecting journal can be
fixed in the axial direction, without being hindered in their rotation.
With respect to the state of the art, reference is also made to EP-B 0 172 850 and
WO 88/05358, which, in a comparable context, disclose the use of di~ele,lLial
screws for parting clamping elements. However, said publications relate to
solutions which overall are not comparable with the problem posed in this instance,
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and which overall do not meet the stated requirements.
Other features and advantages of the invention result from the sub-claims.
5 Preferred examples of embo~ nentc of the invention will be described in more
detail below with reference to the enclosed drawings, in which
Fig. 1 shows a partial cross-section of a basic holder with
tool holder and clamping device in the clamped state;
Fig. 2 is a partial cross-section from the left in Fig. 1 and
shows the clamping device in the clamped position;
Fig. 3 is equivalent to Fig. 2, but shows the closed position
of the clamping block;
Fig. 4 is a part section along the line 4-4 in Fig. 1;
Fig. 5 is equivalent to Fig. 1, but shows a different
embodiment of the ejecting device;
Fig. 6 is equivalent to Fig. 2, but shows a front elevation of
the embodiment of Fig. 5;
Fig. 7 is a part section along the line 7-7 in Fig. 5;
Fig. 8 shows another embodiment of an ejecting device;
Figs. 9a, b and c depict various cross-sections of the clamping
shoulders;
Fig. 10 shows another embodiment of the invention with an
2 1 ~ 2
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eccentric cam as the parting element;
Fig. 11 is a section along the line 11 - 11 in Fig. 10;
Fig. 12 is an enlarged top plan view of an eccentric cam;
Fig. 13 shows the clamping device of Fig. 10 in the parted
position;
o Fig. 14 is a section along the line 14-14 in Fig. 13;
Fig. 15 is a top plan view of the eccentric cam in the parted
position.
Figs. 1 to 3 will be considered first. Fig. 1 shows to the left a basic holder 10, in
place of which, as mentioned, there could be a machine spindle, and to the right a
tool holder 12. The basic holder 10 has an inner taper 14, which corresponds with
an outer taper 16 in the tool holder 12. The outer taper of the tool holder borders
on a hollow shank, inside which a clamping shoulder 18, which is inclined at less
than 30G, projects according to the aforementioned DIN 69893 standard.
Inside the basic holder 10 there is also a hollow space not design~ted in further
detail, in which an inwardly projecting clamping shoulder 20 is located. In the
example shown, the clamping shoulder 20 is sloped at less than 30 in the opposite
direction to the clamping shoulder 18 of the tool holder.
Inside the hollow space formed by the basic holder 10 and the tool holder 12 there
are, at the top and the bottom in Figs. 1 to 3, two clamping elements 22, 24, which
are connected via a di~le,lLial screw 26 to a partable clamping block. The thread
of the di~elt;ll~ial screw 26 engages via oppositely coiled thread portions 28,30
with corresponding tapped holes (not deei~n~ted) in the clamping elements 22, 24.
Rotating the difrelellLial screw 26 therefore allows the clamping elements 22,24 to
be parted or brought together. The clamping elements 22,24 are prevented from
2~3122
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- rotating and mi~ligning themselves by the fact that they abut to the left against an
encircling shoulder (not design~ted) inside the basic holder, or are located in the
- immediate vicinity thereo
In the front elevation of Figs. 2 and 3, the clamping elements 22,24 have an
ess~nti~lly rect~n~ r profile and with their two outer corners form four jaws
32,34,36,38, which are shown more precisely in Fig. 1. As Fig. 1 shows, the
clamping elements 22,24 are staple-shaped, so that they not only have the jaws
32,34,36,38 to be seen in Fig. 2, but also four corresponding jaws at the axially
0 opposed end, of which jaws 40 and 42 can be seen in Fig. 1. The jaws 32 to 42
form four clamping surfaces on each axial side, which, corresponding with the
inclination of the clamping shoulders 18,20, are also inclined at less than 30. It can
be seen that by radially parting the clamping elements 22,24, the tool holder 12 is
axially drawn into the basic holder 10 and is subsequently also radially parted.
To rotate the di~rellLial screw 26 and thus to part or draw together the clamping
elements 22,24, a clamping journal 44 is provided, which lies in a radial bore 46 in
the basic holder 10. The clamping journal 44 also runs through a front face recess
in the left edge of the tool holder 12, which is prescribed by the aforementioned
standard. In this way the clamping journal siml.lt~neously exercises a driver
function for the tool holder 12 when the basic holder 10 is rotated. At the radial-
inner end of the overall cylindrical clamping journal 44, a hexagon spigot 50
projects inwardly into a corresponding recess (not dçsign~ted) in the bottom front
face of the di~erell~ial screw 26. A di~e~ , non-circular cross-section can
naturally also be used instead of the hexagonal cross-section. On its radial-outer
front face the clamping journal also has a hexagon socket 52 which allows an
appropriate tool for rotating the clamping journal 44 to be connected. As shown in
Fig. 2, the section of the clamping journal 44 which lies in the basic holder 10 is
provided with an encircling groove 54, in which engages a stud bolt 56 which is
screwed into the wall of the basic holder 10 perpendicular to the axis of the
clamping journal 44. Interacting with the groove 54, the stud bolt 56 fixes the
clamping journal 44 in the axial direction, but allows it to rotate.
21~3122
~o
On the side diametrically opposed to the clamping journal 44 there is another radial
bore 58 in the wall of the basic holder, in which lies an eiecting journal 60 which is
the equivalent of the clamping journal 44. Projecting radially inwards from the
inner end of the ejecting journal 60 there is a centering pin 62, which engages with
5 play in a front face bore 64 in the dirreren~ial screw 26 at the upper end thereof in
Fig. 1. With the aid of the hexagon spigot 50 of the clamping journal 44 and thecentering pin 62 of the ejecting journal 60, the clamping block consisting of the
two clamping elements 22,24 and the di~lenLial screw 26 is held floatingly in the
unclamped state (Fig. 3) inside the hollow space ofthe basic holder 10 and the tool
o holder 12. As Fig. 2 shows, the ejecting journal 60 is also fixed in the axialdirection by a stud bolt 66. Furthermore, the eiecting journal 60 also lies in a front
face recess 68 in the tool holder 12 and thus also serves as a driver for the latter
when the basic holder is rotated.
5 A further function of the ejecting journal 60 lies in that its section 70 which lies in
said recess 68, shown in Fig. 4 in cross-section, is non-circular and has a flattened
side 72 which lies opposite the base of the recess 68. When the ejecting journal 60
is rotated, pressure towards the right in Fig. 1, i.e. in the direction of ejection, is
thus exerted on the tool holder 12. For the purpose of effecting this rotation, the
20 ejecting journal 60 is also fitted on its outer front face with a hexagon socket 74.
Finally, Figs. 2 and 3 show that on the facing sides on both sides of the diLre~e~lLial
screw 26, the two clamping elements 22,24 have corresponding, semi-circular
recesses 76,78,80,82 which complement each other to form a circular hollow space25 when the clamping elements 22,24 are drawn together. These hollow spaces with a
circular cross-section serve to accommodate coolant pipes 84,86 which connect a
coolant adapter 88 and a coolant distributor 90 which are part of a coolant system,
not shown separately, for cooling the tools.
Figs. 5 to 7 are ess~n~i~lly equivalent to Figs. 1, 2 and 4 and will therefore only be
explained with regard to the differences.
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These differences relate to the ejecting system for ejecting the tool holder 12 out of
- the basic holder 10.
According to Figs. S and 6, screwed adjustably into the upper clamping element 22
- 5 there are two ejecting pins 92,94 which run through the lower clamping element 24
as shown in Figs. 5 and 6 in corresponding bores (not deci~n~ted~. The threaded
engagement with the upper clamping elements 22 permits longi~ltlin~l adjustm~nt
The bottom ends of the ejecting pins 92,94 are truncatedly sloped, as can be seen
in Fig. 6.
It is obvious that when the clamping elements 22,24 are screwed together with the
aid of the differential screw 26, the clamping pins 92,94 protrude downwards outof the bottom clamping element 24. In doing so, as Fig. 7 shows, they come into
contact, directly bordering on the periphery of the lower clamping journal 44 in the
two corners ofthe front face recess 48 ofthe tool holder 12, with the edges ofthe
recess. As a result of the sloping surfaces of the trllnc~ted ends of the ejecting pins
92,94, an axial pressure is exerted on the tool holder, which leads to it being
ejected. When this ejection procedure takes place, the entire clamping block cannot
yield upwardly as in Figs. 1 and 2 since the top portion of the upper clamping
element rests against the clamping shoulders.
Fig. 8 is a partial representation relating to Fig. 1, and is limited to showing the
two closed clamping elements 22,24 and the coolant distributor 90. The coolant
distributor 90 has, in the longitu~in~l central axis of the basic holder and the tool
holder, on the side closest to the clamping elements, a tnlnc~ted connecting
element 91 which is associated with corresponding recesses (not decign~ted) on the
opposite surfaces of the clamping elements 22,24, which, when the clamping
elements are drawn together, complement themselves to form a truncated recess.
When the clamping elements 22,24 are drawn together, the corresponding sloping
surfaces cause pressure to be exerted on the coolant distributor 90, which as
shown in Fig. 1, borders closely against the inner surface of the tool holder, in the
direction in which the tool holder is ejected.
Figs. 9a,b and c show vanous cross-sections of the clamping shoulder 20 of the
basic holder. The representation shown in Fig. 9c corresponds with that in Figs. 1
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and 4. In Fig. 1, a completely radial clamping shoulder is shown in connection with
a correspondingly shaped clamping surface on the clamping elements. Fig. 9b is acombination of the two possibilities and shows a partially sloped, partially radially
- shaped clamping shoulder.
s
When assembling a tool holder the two clamping surfaces 22,24 are first screwed
shut on the block with the aid of the di~~ ial screw. In this state they can be
introduced inside the basic holder or the machine spindle. With the aid of the
clamping journal 44 and the ejecting journal 60, they are then floatingly f~xed in
0 position. The clamping device can now be operated. In this direction they allow a
tool holder to be inserted into the basic holder. The tool holder merely has to be
rotated until the clamping journal 44 and the ejecting journal 60 engage in the
corresponding front face recesses 48 and 68 of the tool holder. If the clamping
journal 44 is now rotated, the two clamping elements move apart in step in the
1S radial direction until the jaws come into contact with the clamping shoulders 18,20
of the tool holder and the basic holder or the machine spindle. By contimling the
clamping operation the tool holder is drawn axially inwards into the basic holder.
When this happens clamping pressure builds up on the front face of the basic
holder and the tool holder, and sim~llt~neously~ increasing radial pressure which
20 builds up over the clamping surfaces and clamping shoulders, causes the relatively
thin-walled taper of the tool holder to widen and press against the inner taper of
the basic holder. Once a given torque is att~ined the clamping process ends and a
tight connection is formed between the basic holder or machine spindle and the
tool holder.
2s
The reverse procedure results in loosening. However, since the inner taper of the
basic holder and the outer taper of the tool holder are relatively flat, self-locking
occurs so that a separation does not automatically take place. Various alternative
ejecting devices for the purpose of ejecting have therefore been described above,
30 and the manner in which they operate can be inferred from the pre~ious
description.
Figs. 10 to 15 relate to another embodiment of the clamping device of the
invention, which differs from the embodiment of Figs. 1 to 6 above all in that the
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parting element is not a differential screw, but an eccentric cam. The eccentric cam
- can be rotated in the manner already described, yet only requires an angle of
rotation of maximum 90. Otherwise, the main difference in the construction withrespect to the embodiment described above lies onIy in the fact that the axis of the
eccentric cam runs between the two clamping elements, whilst with the differential
screw, it runs vertically through the two clamping elements.
Because of the numerous conformities with the first embodiment the individual
parts in Figs. 10 to 15 bear reference numerals which correspond with those of the
0 first embodiment but have merely been increased by 100. A further description is
therefore largely unnecessary. Parts not present in the first embodiment and which
relate to the eccentric cam are desi,en~ted by reference numerals starting from 200.
Figs. 10 and 11 show clamping elements 122,124 in the closed position. An
eccentric cam 200 which is shown in Fig. 12 on its own and slightly enlarged, but
in the position of Fig. 10, has an elongated shape with two parallel edges 202,204
and two cam surfaces 206,208. The gap between the straight edges 202,204 is
much smaller than the gap between the cam surfaces 206,208. As shown in Figs.
10 to 12, the eccentric cam 202 lies flatly, ie. with the top and bottom edges
202,204 between the clamping elements 122,124 so that the latter can be displaced
inwards, thereby releasing the tool holder. The clamping elements will not of
course move inwards, ie. towards the axis of rotation of the arrangement, of their
own accord since they can be held self-lockingly against the clamping shoulders
118,120 and the bottom clamping element at least will remain in the bottom
2s position due to gravity. Therefore, to draw them together, there may be springs,
rubber bands or suchlike, whose pulling force may not under certain circumct~nces
be sufficient to overcome the self-locking forces on the clamping shoulders.
Therefore, according to the invention, jaw discs 210,212 are non-rotatably secured
to the axis of rotation of the eccentric carn on both the front faces thereof. The jaw
discs have two oppositely positioned radially projecting jaws 214,216 which, when
the eccentric cam is rotated in the unclamping direction, ie. approximately anti-
clockwise in Fig. 10, engage in pockets 218,220 on the
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radial-inner side of the clamping elements 122,124. A portion of the pockets
- 218,220 is undercut and in this manner they forrn shoulders 222,224 against which
the jaws 214,216 abut on anti-clockwise rotation in Fig. 10, so that the clamping
- elements are driven inwards.
From Fig. 12 it can be seen that the two carn surfaces 206,208 slope very flatly so
that when the cam surfaces interact with the insides of the clamping elem~nt~ 122,
124, self-locking occurs.
o Figs. 13 and 15 are equivalent to Figs. 10 to 12, but show the clamping device in
the clamped position. In this case the eccentric cam 200 is positioned vertically in
Figs. 13 and 15. The jaws 214,216 point upwards and downwards. The clamping
elements 122,124 engage in the manner already described behind the clamping
shoulders 118,120 of the basic holder and the tool holder.
To eject the tool holder 112 where an eccentric cam 200 is used as the parting
element, there can be a sloping surface 226 (Fig. lS) which is rigidly connectedwith the tool holder 112, which the carn surface runs up against when the eccentric
cam is loosened, so that the tool holder is ejected. As shown in Fig. 15, the sloping
surface is contrived at the end of a pin 228 which is screwed into the coolant
distributor 190.
