Machine for machining spiral cutting edges on cutting tools

#The invention concerns a machine of the type for machining a spiral cutting edge on a workpiece having an elongate shank with an at least partially rounded head by relatively moving the workpiece and a rotating machining tool, to produce a machined tool from the workpiece. The machine comprises a support unit having first and second supports mounted for sliding movement relative to one another in a horizontal plane and rotation together about a vertical axis; a headstock carried by the first support, the headstock having a spindle for carrying the workpiece to be machined, and being positionable so that the axis of the spindle intersects said vertical axis; and a device mounted on the second support for helicoidally driving the headstock spindle.

#A known machine of this type, described in applicant's U.S. Pat. No. 3,851,563, comprises a carriage carrying a transverse slide on which is mounted a longitudinal slide by means of a support which is rotatable and inclinable on the transverse slide. The device for helicoidally driving the headstock spindle is fixed on the inclinable part of the support and includes a cursor moving along a stationary guide whose angular inclination can be set from 0.degree. to 90.degree. relative to the longitudinal slide. To machine a hemispherical end of a workpiece, the support of the longitudinal slide is inclined by an angle equal to the slope of a spiral to be cut on the cylindrical part of the workpiece, the centre of the sphere is brought onto the vertical axis of rotation, and then, after having brought the rotating machining tool (e.g. a grinding wheel) to the operating position, the support is turned by 90.degree. about the vertical axis. This rotation produces a grinding along a circular arc, i.e. in a plane. Then the device for helicoidally driving the headstock spindle is started, and the ground circular arc is extended by a spiral, with a progressive unbroken joint between the two parts of the machined cutting edge. This machine, which provided a progress over the prior machines since it enabled a continuous machining capable of automation, nevertheless involves some drawbacks. Firstly, the mass that must be held inclined at a very precise inclination is great, and this requires a costly structure. Secondly, although the joint between the extremity of the circular arc (which in projection is rectilinear) and the spiral cutting edge is unbroken, this joint is in the form of an indefinite curve over a relatively short distance. Finally, on its rounded end, the machined tool (for example a spiral cutter) has a non-spiral cutting edge coplanar with the tool axis, and this may adversely effect the machining characteristics of the end of the tool.

#An aim of the invention is to obviate these drawbacks.

#The accompanying drawings show, schematically and by way of example, an embodiment of the invention.

#FIG. 1 is a schematic elevational view of the machine with some parts removed;

#FIG. 2 is a cross-section along line II--II of FIG. 3, with a detail shown in cross-section along line II'--II';

#The machine shown in FIG. 1 comprises the components of applicant's previous machines, well known to persons skilled in the art, and not shown in detail, including a longitudinal slide 1a mounted for sliding in a direction, perpendicular to the plane of FIG. 1, on a piece 1b fixed to or as shown integral with the frame of the machine; a transverse slide 1c, also directly mounted on the frame, under the slide 1a, passing through piece 1b and slidable in a direction parallel to the plane of FIG. 1; and, on slide 1c a column carrying a grinding wheel carrier, as schematically indicated by broken line 1c', a grinding wheel carrier (3) of the indicated type being fully described in U.S. Pat. No. 3,851,563. Only the axis 18 of this carrier is shown, carrying a grinding wheel 19 in a position for grinding a workpiece 20 to form a hemispherically-ended, helicoidally-toothed milling cutter. The two slides 1a, 1c enable the positions of the grinding wheel 19 and of the workpiece 20 to be set relative to one another, in a manner corresponding to the relative setting of grinding wheel 15 and workpiece 8 in the patent, although the exact details of the present machine are not identical with these of the patent. On the longitudinal slide 1a are mounted the principal components of the grinding machine, including a first support in the form of a table 2 having a longitudinal groove 3 of T-section for securing a headstock 4 including a rotary workpiece-supporting spindle 5 whose axis is perpendicular to the plane of FIG. 1. The headstock can for example be identical to headstock 7 described in U.S. Pat. No. 3,851,563. Table 2 is slidably mounted on a second support 6 by the intermediary of a well-known type of slide 7/8 with needle bearings 6a, FIG. 2. The support 6 has a box-like lateral part 9 in which are machined two T-section grooves 10 and 11 for securing a device 12 for helicoidally driving the spindle 5 of headstock 4. Details of this device are not shown, as a device of this kind is described in U.S. Pat. No. 3,851,563 at 51,104 etc. Of course, other known devices of the same type (sometimes called "sine bars") could be used. The box-like lateral part 9 is connected by vertical ribs 13 to a horizontal plate 22 forming part of the second support 6 and which accordingly can be made very rigid while it is relatively light, also set FIG. 2.

#In addition to its longitudinal movement along groove 3, the headstock 4 can also be slightly moved transversely to the table 2 by means of two knurled nuts 63 and 64, to be described presently.

#The support unit formed by the table 2 which can also be called a ("first support") and the aforementioned second support 6 is mounted on a third support comprising a vertical shaft or column 14 and, a plate 15 pivoted about a horizontal shaft 16. This shaft is mounted on a base 17 removably fixed on the longitudinal slide 1a. The vertical shaft 14 is also fixedly mounted and rigidly held on base 17.