Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to chucks for holding a workpiece
in a machine such as a lathe.
A variety of chucks or gripping devices are known in the
machine and tool industry for holding a workpiece or a tool
bit. Many of these chucks have movable or sliding jaws which
can be moved radially inwardly or outwardly in order to hold
or grip the end of a workpiece or a tool bit. These jaws are
sometimes moved by means of a special tool or key that is
turned manually.
One common form of chuck used with a lathe is called a
scroll chuck which can be of the self-centering type.
Although the number of jaws in chucks of this type can vary,
in many cases these chucks are equipped with three or four
jaws that can be moved radially inwardly or outwardly by means
of an annular scroll member that is turned about a central
axis in order to manoeuvre the jaws. Scroll chucks have
several advantages including versatility and ease of use. One
form of improved scroll chuck is that disclosed in and
illustrated in applicant's own United States patent No.
5,141,239 which issued August 25, 1992, the disclosure of
which is incorporated herein by reference. With this improved
scroll chuck the possibility of one or more of the jaws of the
chuck becoming accidentally disengaged is substantially
reduced.
United States patent No. 4,630,836 issued December 23,
1986 to Hilti Aktiengesellschaft describes a chuck suitable
for use in a drill such as a hammer drill, which chuck has
clamping jaws to secure a tool. These jaws each have a convex
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surface transverse to the chuck axis. The more radially
inward portion of the convex surface has a V-shaped notch
extending in the axial direction of the chuck and this notch
forms a pair of spaced edges which are said to grip the
surface of the tool so that it can be reliably rotated. In the
illustrated version of this chuck, there are three clamping
jaws.
The present invention provides an improved chuck for
holding a workpiece in a machine wherein the jaw devices are
provided with an unique improved profile that provides better
gripping or holding power, whether the workpiece be round or
square in cross-section.
The present invention also provides a chuck for holding
a workpiece which has improved jaw devices that can be readily
manufactured without undue difficulty and that are easy to use
when working with a machine such as a lathe.
According to one aspect of the invention, a chuck for
holding a workpiece in a machine such as a lathe includes a
jaw holder having a front side facing in the direction of the
workpiece, radially extending slots in this front side, and
means for attaching the holder to the machine for turning
about a central chuck axis. Two or more jaw devices are
detachably mounted in these slots of the holder and are
radially movable therein. Each jaw device has an inner
workpiece engaging surface that forms a profile when it is
viewed from the front of the jaw device in the direction of
the central chuck axis. This profile comprises a central
concave arc and two similar convex curves located at opposite
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ends of the concave arc. There are also means for moving the
jaw devices radially inwardly or outwardly.
In one preferred embodiment, the chuck is a scroll chuck
having a scroll member rotatably mounted on the holder, which
member has a spiral-shaped rib formed on the front surface
thereof. This rib extends along recesses formed on the jaw
devices.
According to another aspect of the invention, a chuck for
holding a workpiece in a machine such as a lathe includes a
jaw holder having a front side facing in the direction of the
workpiece and a mechanism for mounting the holder in or to the
machine for turning about a central chuck axis. A number of
jaw devices are mounted for radial movement inwardly or
outwardly in the holder. Each of these devices has a
workpiece engaging surface that faces radially inwardly
towards the central chuck axis and that forms a profile when
it is viewed from the front of the chuck in the direction of
the central chuck axis. The profile comprises a central
concave arc and two convex curves located at opposite ends of
this arc. There are also means for mounting the jaw devices
for radially movement in the holder.
Further features and advantages will become apparent from
the following detail description taken in conjunction with the
accompanying drawings.
In the drawings,
Figure 1 is a side view of scroll chuck constructed in
accordance with the invention mounted on a lathe, only a
portion of which is shown;
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Figure 2 is a front view of the scroll chuck provided
with the improvement of the invention;
Figure 3 is a front view of the jaw holder from which the
four jaws that are shown in Figure 2 have been removed for
purposes of illustration;
Figure 4 is a perspective view showing the rear side of
the jaw holder of Figure 3;
Figure 5 is a side elevation of a single jaw device
constructed in accordance with the invention;
Figure 6 is another view of the jaw device of Figure 5
taken from the left hand side of Figure 5;
Figure 7 is a schematic illustration showing the frontal
profile of known chuck jaws showing the manner in which these
jaws grip a workpiece having a square cross-section;
Figure 8 is a schematic view similar to Figure 7 but
showing how the four jaws of a chuck constructed in accordance
with the invention grip a workpiece having a square cross-
section;
Figure 9 is a schematic illustration showing how the jaws
of the present chuck engage a tubular or round workpiece
having a diameter corresponding to the nominal diameter of the
chuck;
Figure 10 is a schematic illustration similar to Figure
9 but showing how the same jaws of the chuck engage a
workpiece having a circular cross-section with a diameter of
intermediate length; and
Figure 11 is a schematic illustration similar to those of
Figure 9 and 10 but showing the chuck jaws of the invention
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gripping a workpiece having a round cross-section with the
maximum diameter that can be held by the chuck.
As shown in Figure 1, a scroll chuck 10 constructed in
accordance with the invention is mounted on a rotatable shaft
of a lathe 12. Only a portion of the lathe housing 14 is
shown in Figure 1. The lathe shaft extends outwardly from the
centre of the bearing support 16. The lathe itself is of the
usual construction and forms no part of the present invention.
The projecting end of the shaft of the lathe can be threaded
for attachment to the scroll chuck 10.
The illustrated scroll chuck 10 includes a jaw holder 18
having a front side 20 facing in the direction of the
workpiece 22. The illustrated holder has four radially
extending slots 26 to 29 but it will be understood that the
holder of the present chuck can have as few as two and as many
as six or more slots depending upon the number of jaws or jaw
devices in the scroll chuck. The slots extend to a circular
central opening 30. The holder includes means for attaching
the holder to the lathe for turning about a central chuck
axis. The illustrated attaching means comprises a sleeve
section 32 which is internally threaded at 34 for attachment
to the shaft of the lathe. A small threaded opening 36 can be
provided for a set screw to secure the chuck in place.
A scroll member 38 of known construction is rotatably
mounted on the sleeve section 32. This member has a spiral-
shaped rib 40, portions of which can be seen through the
radial slots of the holder in Figure 3. This rib is formed on
a front surface of the scroll member 38 and it engages the jaw
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devices so that rotation of the scroll member about the
central chuck axis causes the jaw devices to move radially
inwardly or outwardly.
In the lllustrated scroll chuck there are four jaw
devices 45 to 48. Except for the novel profile of workpiece
engaging surfaces 49, the jaw devices-can be constructed in a
known manner and are very similar to one another. The
construction of these jaw devices will be described with
references to Figures 2, 5 and 6, the latter two figures
illustrating~the jaw identified by reference 48. Each device
is detachably mounted in its respective slot and is radially
movable therein. Preferably each jaw device comprises a first
jaw member 50 which is the portion which is seen in Figure 2.
The first jaw member is located forwardly of the jaw holder
18. As shown, each jaw device has two substantially radially
extending sidewalls 52 and 54. It also has an arc-shaped
outer sidewall 56 which extends between the two sidewalls 52
and 54. The first jaw member has a forwardly extending flange
58 which is used to grip the workpiece. This flange has an
outer surface at 59 located opposite the workpiece engaging
surface 49, which outer surface forms a convex circular arc.
The workpiece engaging surface 49 is formed on this flange 58
and this surface faces radially inwardly towards the central
chuck axis indicated at A in Figure 2.
There is also a second jaw member 60 which is detachably
connected to the first jaw member by means of two screws 62
and 64. These screws extend into suitable threaded holes
formed in the second jaw member. This second jaw member is
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located in the respective slot of the jaw holder and is
slidable therein. The radially extending sides of the second
jaw member are formed with grooves 66. In these jaws are
positioned two edge flanges 68 and 70 that extend along each
slot of the ~aw holder and that retain the jaw member 60 in
this slot. There are formed on the bottom or rear surface of
each jaw member 60 several slightly curved recesses 72. The
aforementioned rib 40 on the scroll member extends along these
recesses so that rotation of the rib about the central axis
forces the jaw devices either inwardly or outwardly. As
explained in the present applicant's U.S. patent No.
5,141,239, the scroll chuck is preferably provided with jaw
retention means which can include pin member 80. As this jaw
retention means forms no part of the present invention, a
detailed description thereof is deemed unnecessary in the
present application.
It is also possible to use jaw devices that comprise a
single member or piece only rather than two separate members.
Such unitary jaw devices are known per se in the chuck art.
The workpiece engaging surface 49 forms a profile when it
is viewed from the front of the jaw device in the direction of
the central chuck axis A, this profile being shown in Figures
2 and 8 to 11. The profile comprises a central concave arc 90
and two similar convex curves 92 and 94 located at opposite
ends of the concave arc 90. The advantages of this curved
profile for the workpiece engaging surface of the jaw can be
seen from Figures 7 to 11 of the drawings. Figure 7
illustrates the profile of the workpiece engaging flanges of
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- a prior art chuck, such as the one shown in applicant's own
United States patent No. 5,141,239. In this prior art chuck,
the flanges 100 are in the form of circular arcs with each
flange having a concave inner surface 102. This inner surface
5terminates in sharp angle corners at 103 and 104. With these
traditional style jaws therefor, the workpiece 106 which has
a square profile is engaged on each of its four sides by only
the corners 103 and 104 of each device. The holding power for
such a chuck in this situation is quite low and even
10relatively small digs into the workpiece can knock it loose.
Figure 8 illustrates how a chuck 10 constructed in
accordance with the invention is able to provide improved
gripping of the workpiece 110 which has a square cross-
section. With the chuck of the invention, each of the jaw
15devices 45 to 48 engages its respective side of the workpiece
along the opposite end portions of the flange 58, that is, in
the region of the convex curves 92 and 94. Because of the use
of these convex curves a relatively large surface area of the
jaw device engages the side of the workpiece and this results
20in high holding power and excellent security.
The profile of the workpiece engaging surfaces in the
chuck of the invention provides much better holding power for
round workpieces as well as the aforementioned square
workpieces and this advantage is illustrated in Figure 9 to
11.
In Figure 9, the four flanges 58 of the jaw devices
engage a min;mum diameter round workpiece 112. In this
position, the jaw devices are at their radially innermost
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position and the workpiece engaging surfaces 49 contact the
exterior of the workpiece closely for a substantial
circumferential distance on all four sides. At this so called
"nominal diameter" jaw devices constructed in accordance with
the invention grip as well as the traditional jaw design, that
is the design shown in Figure 7.
With a somewhat larger or intermediate diameter workpiece
such as the workpiece 114 shown in Figure 10, the workpiece
engaging surfaces 49 of the jaw devices are still able to grip
the workpiece with a relatively large surface area and thus
the jaw devices are capable of providing good holding power.
This is not the case with the traditional jaw design which,
with this diameter workpiece, would have a much smaller
contact area between the jaws and the sides of the workpiece.
This is because only the end edges 103 and 104 of each jaw
device engage a side of the workpiece.
With a maximum diameter workpiece such as the workpiece
116 shown in Figure 11, the curved workpiece engaging surfaces
49 still provide a good grip as there is a relatively large
surface area of each jaw device engaging the side of the
workpiece. Again, if the previously known jaw design shown in
Figure 7 were used, these jaws would grip the sides of the
workpiece only with their corners, resulting in poor holding
power compared to that of the jaw devices of the invention.
In order to provide even better holding power with a
chuck constructed in accordance with the invention, each
workpiece engaging surface can be serrated as illustrated in
Figures 5 and 6. In other words, the workpiece engaging
r 21 26 3 72
surface is formed with a series of side-by-side teeth 120,
which teeth extend along the inside of each flange 58 in
planes perpendicular to the central chuck axis.
As indicated, Figure 9 illustrates the jaw device 45 to
48 when they are moved to an innermost position where adjacent
ends of adjacent jaw devices contact one another. Preferably,
in this innermost position, the central concave arcs 90 are
circular arcs of the same circle centered on the central chuck
axis. In this way, excellent gripping power is provided by
the chuck at;its nominal diameter.
It will be apparent to one skilled in the art that
various modifications and changes could be made to the
illustrated and described chuck without departing from the
spirit and scope of this invention. For example, instead of
a scroll chuck, the curved jaw of the invention can be used in
cam operated chucks or other types of chucks where the jaws
can be either independently or synchronously operated. The
invention can also be employed in collet chucks. Accordingly,
all such modifications and changes as fall within the scope of
the appended claims are intended to be part of this invention.
