The present invention relates to the working-spindle of the headstock
of a lathe or milling machine and, more specifically, to the coupling of the spindle
shaft and the hollow rotor of the headstock drive motor, according to the preamble
of claim 1.
Lathe headstock working-spindles are known in which the motor stator
is incorporated into an outer frame on the machine, and the spindle shaft is supported
by bearings as on the machine tool described in EP-743511-A1. The bearings supporting
the working-spindle shaft at both ends are subject to wear and need to be replaced.
In the spindles whose shaft is shrunk directly in to the drive rotor
hollow, with their axis perfectly aligned, and their front nose for attaching the
chuck is of larger diameter than the bearings, the latter can only be removed for
replacement from the shaft rear end. Thus, the spindle must first be detached
from the rotor, with the aid of a hydraulic pump then, once the bearings are replaced,
the shaft must once more be shrunk on the rotor with the cooperation of a heating
furnace. The need for this special equipment or tooling involves taking them to
the lathe site and costly replacement operations.
DE-4122545 describes a solution for the easy removal of the bearings
from the front end of the spindle without the need to detach the rotor spindle
shaft. This solution makes spindle construction expensive, since it is formed in
two parts, one of them the detachable spindle front flange which enables the bearings
to slide to the front of the lathe.
Patent Abstract of Japan vol. 016, no. 141 (M-132)- & JP 04002438
A, discloses a cooling structure for machine tool spindle driving motor, comprising
a motor stator, a rotor with an intermediate sleeve in alignement with the axis
of the rotor, a hollow shaft of the spindle directly connected to the rotor sleeve
for driving the spindle in its rotation, a set of front bearing supporting the
spindle shaft, and the hollow shaft has a portion of thickened wall attached to
the intermediate rotor sleeve, and cooling means for conducting a coolant inside
the hollow spindle shaft.
DISCLOSURE OF THE INVENTION
The object of the invention is a coupling for the shaft of the spindle
of the headstock of a lathe or milling machine to the hollow rotor of the headstock
drive motor, as defined in claim 1. With a coupling according to the invention,
the front bearings are replaced following detachment of the spindle but without
the need of the help of equipment or tooling either for detachment or for subsequent
shrinking on to the rotor, all the operations being done manually using standard
DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a lengthwise cross-section of the headstock spindle,
with the motor, according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In the embodiment of the invention of the coupling into the lathe
headstock 1 shown in Figure 1, the shaft 2a of the spindle 2 is coupled
with the rotor 3, and the stator 4 of the motor is incorporated into the lathe
frame 5. The motor 3,4 is of AC voltage type and water-cooled from the inlet 13,
has a hollow rotor 3 to drive lathe and milling machine headstocks, of a high
rigidity because of the fitting of the motor components between the main spindle
bearings 6,7. The headstock of the workpiece is fitted to the frontal nose 2b of
the spindle, and the spindle shaft 2a, which is also hollow, is driven by
the spindle 2 having their respetive axis correctly aligned in order to ensure
a balanced rotation.
The shaft 2a is supported at each end with a set of bearings
6,7, the front bearings 6 are shielded by the front motor cover 14 and enclosed
behind the frontal nose 2b of the spindle between the cover 14 and the rotor 3,
while the frontal nose 2b closes the cover 14 frontally. The rear bearings 7 are
shielded by the rear motor cover 15 and are easily removable by hand from the
rear end of the shaft 2a for replacement. On the other hand, the front bearings
6 are housed between the frontal nose 2b of the spindle and the motor 3,4, and
so must be removed by first detaching the spindle 2 of the rotor 3, and then extracting
it from the machine in order to take out the bearings 6 by sliding them to the
rear end of the shaft 2a. Once the bearings 6, 7 have been replaced, the
shaft 2a is once more attached to the rotor 3, completely aligned. In order to
achieve such detachement of the spindle 2 from the rotor 3 without the help of
assembly and dismantling equipment, the shaft 2a of the spindle is coupled
to the rotor 3 by means of the coaxial sleeve 8, which pressure fits the rotor
3 by means of hot shrinking.
The inside diameter of the coupling sleeve 8 and the diameter of
the spindle shaft 2 are adjusted to ensure a minimum play 11 enabling them to be
fitted without the aid of equipment. The coupling sleeve 8 is attached to the spindle
shaft 2a, to be driven in rotation by means of a set of drive bolts 9 and
pins 10 distributed on the front circular crown wheel of the coupling sleeve 8,
for which the front end wall 8a is thickened and juxtaposed to the thickened
wall part 2c of the shaft 2. The set of bolts 9 and pins 10 fit in holes
12 opened from the frontal nose 2b of the spindle for ease of access.
The wall of the sleeve 8 is of a given thickness, limited by the
inside diameter of the rotor 3, but thick enough to prevent deformation during
compression by the rotor 3 following shrinking, and by the resistance to the torsion
stress due to the traction of the spindle 2.