Apparatus for machining a polygon profile on a workpiece

In an apparatus for machining polygon profiles, comprising a workpiece spindle and a tool spindle (12) driven in synchronism therewith and carrying an eccentric tool (22), wherein the transmission ratio between the workpiece spindle and the tool spindle as well as the lateral distance therebetween are adjustable, the invention provides for additional adjustment of the eccentricity of the tool. This permits one and the same tool to be employed for pre-cutting various polygon profiles of any standard nominal size in a rational manner and with close approach to the final profile shape. The cutting speed is increased by providing a disk-shaped counterweight (21) with adjustable eccentricity located on the tool spindle adjacent the tool. A common adjustment means (18, 24 to 27) is effective to automatically adjust the eccentricity of the counterweight in correspondence to the respective eccentricity of the tool.

The invention relates to apparatus for machining a polygon profile on a 
workpiece. 
Already known is an apparatus of this type, wherein both the transmission 
ratio between the workpiece spindle and the tool spindle, and the distance 
between the axes of rotation of the workpiece and of the tool are 
variable, without there being provided any further adjustment possibility. 
This apparatus permits one and the same tool, for instance a disk cutter, 
to be employed for machining polygon profiles with varying numbers of 
edges and different diameters, but not for forming profiles with varying 
eccentricity. There is thus required a special tool for each eccentricity. 
If this known apparatus were thus to be employed for pre-cutting P3G 
profiles according to DIN 32 711 or P4C profiles according to DIN 32 712, 
a separate tool would be required for each nominal size associated with a 
specific degree of eccentricity. The rational pre-cutting of polygon 
profiles is therefore not possible with the known apparatus. 
Also known is an apparatus for turning polygon profiles wherein a tool 
carriage carrying a lathe tool is driven by a crank pin and a linkage to 
oscillate in synchronism with the rotation of the workpiece spindle (DE-PS 
133 283). This apparatus permits various elliptical shapes to be machined 
by adjusting the crank pin and a crank pin of the linkage accordingly. 
This known apparatus is therefore not either suitable for economically 
pre-cutting polygon profiles of varying shapes. Also, this apparatus is of 
rather complicated construction with a great number of driving and bearing 
elements, and the oscillating parts have a considerable mass, resulting in 
uneven running detracting from the precision of operation particularly at 
increased working speeds. It is the main object of the present invention 
to improve the apparatus defined in the introduction by simple means and 
to such effect that it may be employed for machining polygon profiles with 
varying numbers of edges and with varying nominal sizes without requiring 
the cutting tool to be changed. 
In accordance with the invention, this object is attained by providing for 
the adjustable, eccentric mounting of the machining tool relative to the 
tool spindle. 
In the apparatus according to the invention, a changeover to a polygon 
profile having a different degree of eccentricity does not require the 
cutting tool to be changed, in place of which the degree of eccentricity 
of the tool has merely to be adjusted in a quick and simple operation. 
Thanks to this characteristic feature in combination with the possibility 
to vary the transmission ratio between the workpiece spindle and the tool 
spindle as well as the distance between the axes thereof, the apparatus 
according to the invention is unique in permitting one and the same tool, 
for instance a cutter head with metal carbide inserts, to be employed for 
rationally precutting polygon profiles of any shape and size, particularly 
P3G and P4C profiles of any nominal size. In this context, the 
approximation to the ideal polygon shape is the closer, the greater the 
diameter of the tool, and as there is only one tool required, it may be 
selected to be of considerable size. 
A preferred embodiment of the invention permits the tool to be accurately 
balanced in a simple manner for each degree of eccentricity, so that it is 
possible to attain high rotary speeds and cutting speeds without excessive 
load on the apparatus, particularly on the mounting and drive arrangement 
of the tool spindle. In the case of a cutter head having a diameter of 
about 350 mm and carrying 32 metal carbide cutters, with the maximum 
degree of eccentricity being 8 mm, as generally considered sufficient for 
machining conventional polygon profiles, it is thus possible to attain 
operating speeds of 1,000 rpm without difficulty. 
A preferred further aspect of the invention permits the change over to a 
different polygon profile to be carried out in a particularly rapid and 
simple manner, as the adjustment of the tool eccentricity automatically 
results in a corresponding adjustment of the counterweight, so that the 
latter does not have to be adjusted separately. 
Set forth are a number of advantageous further aspects of the invention 
contributing to a simple construction of the common adjustment provisions 
for the tool and counterweight, and to an accurate fixation of the tool 
and counterweight relative to one another. 
Finally, the aspect of the invention contributes to a particularly smooth 
low-wear running of the apparatus, as the two toothed belts are effective 
to dampen any remaining unbalance.

The apparatus shown in FIGS. 1 to 4 substantially consists of a 
conventional turning lathe comprising a base frame 1, a workpiece spindle 
2 carrying a chuck 3, a tailstock 4, a screw spindle 5, a support carriage 
6 mounted for sliding movement parallel to the axis of rotation of the 
workpiece spindle 2, and a tool carriage 7 mounted on carriage 6 for 
movement transversely of the axis of rotation of workpiece spindle 2. 
Workpiece spindle 2 is driven by a motor 8, and is itself drivingly 
connected to screw spindle 5 through a variable reduction gear arrangement 
9. 
Rotatably mounted at the rear of the turning lathe in parallel relationship 
to workpiece spindle 2 is a splined shaft 10 drivingly connected to 
workpiece spindle 2 through a variable transmission gear arrangement 11. 
The transmission ratio between the workpiece spindle and the splined shaft 
may for instance be selected at 1:3 and 1:4 for pre-cutting the standard 
polygon profiles P3G and P4C, respectively. Rotatably mounted on tool 
carriage 7 of support 6 in the region between splined shaft 10 and the 
axis of rotation of workpiece spindle 2 is a tool spindle 12 extending 
parallel to workpiece spindle 2 and splined shaft 10, respectively. Tool 
spindle 12 is driven from splined shaft 10 at a transmission ratio of 1:1 
by means of a pair of endless toothed belts 13. The two belts 13 
interconnect a total number of four sheaves or gears, the first of which 
is mounted for axial displacement on splined shaft 10, while the last one 
is fixedly mounted on the righthand end of tool spindle 12. The two 
intermediate sheaves are non-rotatably connected to one another and 
mounted on a shaft carried by a pair of levers 14. One of the two levers 
14 is pivotally mounted on splined shaft 10, while the other lever 14 is 
pivotally mounted on tool spindle 12. The thus formed articulated toothed 
belt transmission gear arrangement ensures that tool spindle 10 is 
accurately driven with the speed of splined shaft 10 in any position of 
support 6 and its tool carriage 7. A guide fork 15 or the like ensures 
that the sheave mounted on splined shaft 10 always follows the movements 
of support 6. 
The lefthand end portion of tool spindle 12 is formed with a radial flange 
16 with a concentric stub shaft 17 projecting therefrom and having a screw 
thread formed at its end. Rotatably mounted on stub shaft 17 is an 
eccentric sleeve 18 having two eccentric portions 19 and 20, the 
eccentricity "e" of which with respect to the axis of the tool spindle is 
4 mm in each case, the two eccentric portions 19, 20 being offset by 
180.degree. relative to one another. The righthand eccentric portion 20 
adjacent flange 16 carries a counterweight 21 in the form of a circular 
disk rotatably mounted thereon with its inner bore. This inner bore is 
offset by the distance "e" relative to the center axis of the 
counterweight, so that the latter is aligned in concentric relationship to 
the tool spindle axis, as in FIGS. 2 and 3, or is offset relative thereto 
by the distance "2e", depending on the angular position of eccentric 
portion 20 and counterweight 21 relative to one another. In the present 
case, counterweight 21 is thus adjustable to a maximum eccentricity of 8 
mm, as in FIG. 4. The other eccentric portion 19 of excenter sleeve 18 
carries a tool 22 in the form of a cutter head provided with thirty-two 
metal carbide cutters and having a diameter of for instance 350 mm. An 
inner bore of the cutter head for rotatably mounting it on eccentric 
portion 19 is again offset by the distance "e" relative to the center axis 
of the cutter head, so that the latter may be aligned in concentric 
relationship to the tool spindle axis, as in FIGS. 2 and 3, or may be 
offset relative thereto by the maximum distance "2e", depending on its 
angular position relative to eccentric portion 19. In the present case, 
the eccentricity of tool 22 is adjustable between "Zero" and 8 mm. A nut 
23 threaded onto the screw thread of stub shaft 17 serves to axially 
compress tool 22 and counterweight 21 between itself and flange 16 of tool 
spindle 12. At the same time, excenter sleeve 18 is locked in position 
thereby, so that no additional clamping element is required for this 
purpose. 
For positive transmission of the torque from tool spindle 12 to tool 22, 
the end face of the latter facing towards counterweight 21 is formed with 
a radial slot 24 for engagement with a first crank bolt 25 attached to 
counterweight 21. Offset by 180.degree. relative to first crank bolt 25, a 
second crank bolt 26 is attached to the opposite end face of counterweight 
21 for engagement with a radial slot 27 formed in flange 16. The crank 
slot arrangements formed by slot 24 and first bolt 25 and second bolt 26 
and slot 27, respectively, are effective to positively connect tool 22 to 
tool spindle 16 in any angular position of eccentric sleeve 18 relative 
thereto. 
The two crank slot arrangements 24, 25 and 26, 27, respectively, are 
further effective to form a constraint guidance of tool 22 and 
counterweight 21 relative to one another and relative to tool spindle 12, 
so that on rotation of eccentric sleeve 18 for increasing the eccentricity 
of tool 22, the eccentricity of counterweight 21 is likewise increased in 
the opposite direction. Similarly, reduction of the eccentricity of tool 
22 results in a corresponding reduction of the eccentricity of 
counterweight 21. While the outer diameter of counterweight 21 is smaller 
than that of tool 22, its axial width is correspondingly greater than that 
of the tool, so that the two elements are of substantially identical mass. 
This is necessary because the two eccentric portions 19 and 20 are of 
equal size. It is also possible, however, to select eccentric portions of 
different sizes, in which case the mass of counterweight 21 has to be 
modified accordingly. It should be mentioned, that in the embodiment 
described and shown, perfect equilibration, although in any case provided 
in the maximum eccentricity position "2e" (FIG. 4), is not fully achieved 
in the intermediate positions between the "0" eccentricity position (FIG. 
3) and the maximum eccentricity position "2e". It has been found, however, 
that the resulting unbalance is of no importance in practical operation. 
By suitably designing the adjustment means for eccentric sleeve 18, or the 
guide means for tool 22 and counterweight 21, it is of course also 
possible to achieve perfect equilibration in any position. 
If the eccentricity of tool 22 is to by varied, nut 23 is released, and 
eccentric sleeve 18 is rotated relative to stub shaft 17. This may be 
carried out in a simple manner by means of a suitable tool engaging 
recesses 28 formed in the end face of eccentric sleeve 18. Rotation of 
sleeve 18 automatically results in a corresponding adjustment also of 
counterweight 21 for equilibration of the assembly. To complete the 
adjustment, nut 23 is retightened, whereupon the apparatus is ready for 
operation. 
The above described apparatus is ideally suited for precutting P3G and P4C 
polygon profiles of any standard nominal size, for instance on a long 
shaft 29 clamped between the chuck and the tailstock 4. The feed movement 
of the support 6 required for this operation is automatically brought 
about by screw spindle 5. Thanks to the large diameter of tool 22 made 
possible by the automatic equilibration, the desired final profile shape 
can be approached very closely, so that only a minimum amount of material 
has to be left remaining for the final shaping on a polygon grinding 
machine. The conversion to the desired basic profile shape, i.e. a 
triangular or quadrangular shape, is carried out by suitably adjusting 
transmission gear 11, adjustment to the desired basic profile diameter by 
suitable adjustment of tool carrier 7, adjustment to the eccentricity 
associated with the basic diameter is carried out by adjusting eccentric 
sleeve 18, and the required feed movement is adjusted by correspondingly 
adjusting reduction gear 9. It is thus not required to exchange any parts 
or to employ different cutting tools.