GB2066128A - Compensating centrifugal forces in a rotary rotary tool head - Google Patents

Abstract

A rotary tool head comprises a support member 1 which is to be secured to the spindle of a machine tool. The support member has at least one radially adjustable slider 4 which carries a tool 5. An adjusting rod 7 is displaceable coaxially with respect to the support member 1 and acts on at least one rack 8 with inclined teeth 8a which is axially movable in the support member 1. On the slider 4 a toothed bar 10 extends in the direction of slider movement and has teeth 10a in mesh with the rack teeth 8a and inclined at the same angle beta as the rack teeth 8a to the axis of rotation. An additional toothed bar 11 extends in the direction of slider movement and cooperates with an additional rack 15, e.g. via a pinion or pinions 12, which is axially movable in the support member 1 and is so biased by a prestressed spring assembly 16 that the spring assembly 16 applies to the slider 4 a force which is directed radially inwards towards the axis of rotation. This force opposes centrifugal force acting on the slider 4 and thereby reduces wear on the teeth of the rack 8 and the bar 10. The spring 16 act against the rod 7 or the support member 1. <IMAGE>

Description

SPECIFICATION Rotary tool head The invention relates to a rotary tool head. Turning heads are known comprising a support member which is to be secured to the spindle of a machine tool, having at least one radially extending guide for a radially adjustable slider carrying a tool, an adjusting rod which is movable coaxially wih respect to the support member and acts on at least one slantingly toothed rack which is axially movable in the support member, and a toothed bar which is arranged on the slider and extends in the direction of displacement thereof and whose slanting teeth mesh with those of the rack and are inclined at the same angle as the rack teeth with respect to the axis of rotation of the support member.

Known turning heads of this kind have one or generally two sliders which are at positions 1800 apart about the turning axis and are displaceable in opposite directions, and which each carry a tool. If the guides for the sliders are arranged in planes which extend perpendicularly to the axis of rotation of the support member, such turning heads are mainly suitable for producing flat end surfaces on workpieces. Such turning heads are then also referred to as facing heads. However, there are also turning heads in which the radially extending guide means are inclined for example at an angle of 600 with respect to the axis of rotation of the support member. Turning heads of this kind are frequently used for copying purposes.

Radial displacement of the sliders is effected, while the turning head is rotating, by means of the adjusting rod which is arranged coaxially in the support member and which acts on the abovementioned slantingly toothed racks. It has been found that, at the rotary speeds of 1200 r.p.m. which are generally used to date, a considerable amount of wear occurs at the racks and the toothed bars which cooperate with the racks. This is attributed to the fact that, besides the machining forces, considerable centrifugal forces act on the sliders, and such forces increase in proportion to outward displacement of the sliders. The sides of the teeth which bear the radially outwardly directed forces are subjected to a very severe degree of wear which results in a considerable reduction in the accuracy of adjustment of the sliders and thus the accuracy of working of the turning head.Indeed, the wear on the sides of the teeth results in play between the forward and backward movement of the rack and thus also between the radially inwardly or radially outwardly directed movement of the slider. This play results in inaccuracies in the radial adjustment of the sliders, which is a disadvantage in particular in copying turning operations as in such an operation the direction of movement of the sliders is reversed one or more times during the copying process.

The invention is based on the problem of providing a head wherein wear of the racks and toothed bars which are provided for displacement of the sliders is reduced or substantially eliminated, without detrimentally affecting the radial adjustment travel of the slider, while being of compact and simple construction.

According to the invention there is provided a rotary tool head as defined by claim 1 hereinafter.

The invention is based on the idea of applying to the slider a radially inwardly directed force which is produced by a spring assembly and which acts against centrifugal force. The return force of the spring assembly reduces the centrifugal forces so that the amount of wear which occurs at the toothed bars and racks which are provided for adjustment purposes is substantially reduced. This means that the working accuracy of the turning head is also maintained over a long period of time. In this connection, it is inevitable that each additional toothed bar and rack is subjected to a certain amount of wear, but this is of no importance as the accuracy of adjustment depends only on the accuracy of toothed bars and racks which provide for adjustment movement.As the spring assembly and the additional rack are arranged for axial displacement, the radial dimensions of the turning head are not increased by the additional components required. In particular also, such components are not moved radially outwardly by centrifugal force. As the centrifugal forces acting on the slider are substantially compensated, lower forces are required to produce radial adjustment of the slider and higher speeds of rotation can be achieved as toothed bars and racks which provide for the adjustment movement operate substantially without wear. Therefore, besides an increase in working accuracy, a head embodying the invention also has the advantage of higher working speed.

As the centrifugal force acting on a slider increases with adjustment of the slider in a radially outward direction, it is advantageous for the opposing return force of the spring assembly also to increase upon adjustment of the slider in a radially outward direction. There are two possible ways of achieving this.

The first way provides that the prestressed spring assembly is supported against a member (e.g. a flange plate) which is rigidly connected to the support member so that the force which is directed radially inwards towards the axis of rotation increases with adustment of the slider radially outwards. In this arrangement, the return force of the spring assembly does not remain constant, but, upon displacement of the slider outwards, the spring assembly is compressed by corresponding displacement of the rack towards the member which is rigidly connected to the support member. This causes the return force of the spring assembly and thus the radially inwardly directed force acting on the slider, to be increased.

Two pinions can be used between the toothed bar and the additional rack, the diameter of a second pinion being greater than that of a first pinion so that the force which is directed radially inwards towards the axis of rotation increases with displacement of the slider radially outwards. In this case also, the spring assembly is compressed upon displacement of the slider in a radially outward direction.

These two possible designs may possibly also be combined, in order to provide for optimum compensation of the centrifugal force.

The invention will now be described in more detail, solely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of one half of a copying turning head embodying the invention, Figure 2 is a longitudinal sectional view at a line Il-Il in Figure 1 of part of the turning head, Figure 3 is a cross-sectional view at a line Ill-Ill in Figure 1 of part of the turning head, and Figure 4 is a longitudinal sectional view of part of a second embodiment of the invention.

In Figure 1 there is shown a cylindrical support member 1 of a copying turning head, which may consist of a plurality of parts but which for simplicity and clarity is shown as a one-piece member. At its rear, the support member 1 has a flange plate 1a with a centering recess 2 which fits on to the spindle of a turning or special-purpose machine (not shown). The support member 1 can be secured to the spindle by means of the flange plate 1 a.

At the front of the support member 1, there are two guides 3 which are at positions displaced relative to each other through 1800 about the axis of rotation A-A of the support member 1. Only one guide 3 is shown in Figure 1. The guides 3 extend radially and are inclined at an angle a of 600 with respect to the axis of rotation A-A of the support member 1, which coincides with the spindle axis. In each of the guides 3 there is a slider 4 which is adjustable in the direction V and carries a tool 5 with an interchangeable cutting plate 6.

An adjusting rod 7 is so arranged in the support member 1 as to be displaceable in the axial direction B, and is coaxial and concentric with respect to the support member 1. The adjusting rod 7 carries a flange 7a at its front end. For each slider 4 there is fixedly connected to the flange 7a a rack 8 which is axially movable in a guide bush 9. The rack 8 has slanting or inclined teeth 8a on both sides thereof, the teeth 8a being on both sides inclined at the same angle ss of 600 with respect to the axis A-A. Provided on the slider 4 are two toothed bars 10, the slanting or inclined teeth 1 0a of which engage the inclined teeth 8a and are inclined at the angle P with respect to the axis of rotation A-A, like the teeth 8a.During rotation of the support member 1, when the adjusting rod 7 is moved in the axial direction B, the slider 4 is adjusted in the direction V by the same amount by the action of the rack 8 and the toothed bars 10. If the adjusting rod 7 is moved rearwardly, i.e. towards the right in Figure 1,with respect to the support member 1,the slider 4 is adjusted radially outwardly, and vice-versa. The greater the radial distance of the centre of gravity of the slider 4 from the axis of rotation A-A, the greater are the centrifugal forces acting on the slider 4.

In order to compensate for such centrifugal forces and in order to reduce the wear at the rack 8 and the toothed bars 10, a mechanism is provided which includes an additional toothed bar 11 arranged on the slider 4 and extending in the direction of movement V thereof. The additional toothed bar 1 is preferably arranged on the rear side 4a of the slider 4, which is remote from the tool 5, 6, as shown. It meshes with a pinion 12 which is rotatable about a spindle 13 which extends perpendicularly to the direction of movement V and parallel to the rear side 4a. The spindle 13 is arranged in a mounting bush 14 which is rigidly mounted in the support member 1.

The teeth 12a of the pinion 12 also mesh with the teeth 1 5a of an additional rack 15 which is movable in the mounting bush 14 axially, that is to say, parallel to the axis of rotation A-A of the support member 1. The additional rack 15 bears against an adjusting screw 17, which is axially screwable in the flange 7a, through a spring assembly 16 comprising a plurality of plate springs 16a. The prestressing of the spring assembly 16 can be set by means of the adjusting screw 17.

The spring assembly 16 applies to the rack 15 a force which is directed axially forwards, i.e. towards the left in direction Din Figure 1, and causes the pinion 12 to rotate in the clockwise direction, in direction C. Since the pinion 12 also meshes with the additional toothed bar 11, a force P directed radially inwards towards the axis of rotation A-A is exerted on the slider 4. Figure 1 shows the slider 4 in its most radially outward position. When the adjusting rod 7 is moved forwards, i.e. towards the left in Figure 1, the slider 4 is moved radially inwards by means of the rack 8 and the toothed bars 10, i.e. upwards in Figure 1. When this occurs, the pinion 12 rotates in the direction indicated by arrow C, whereby the additional rack 15 is moved forwards in direction D.

As at the same time the flange 7a also moves forwards over the same distance, the prestressing of the spring assembly 16 remains constant. Therefore, the spring assembly 16, the additional rack 15, the pinion 12 and the toothed bar 11 apply to the slider 4 a radially inwardly directed force P which is constant over the adjustment travel thereof and which opposes the centrifugal force.So that the same sides of the teeth in the rack 8 and the toothed bars 10 shall always bear against each other and thus to avoid play between the sides of the teeth, it is advantageous for the prestressing force of the spring assembly 16 to be such that, even when the slider 4 is moved inwards to its most radially inward position, there is still a residual centrifugal force predominating which, although it increases continuously in an outward direction, does not change its direction and cause any markings on the turned surface of the work. In this arrangement, although the centrifugal forces are not completely compensated, they are at least reduced. The wear on the toothed bars 10 and the rack 8 is thus substantially reduced and the accuracy of adjustment is maintained over a longer period of operation. Although the teeth on the additional toothed bar 11, the pinion 12 and the additional rack 15 are subject to wear, this wear does not affect the accuracy of adjustment of the tool.

Although in the illustrated embodiment there is a transmission ratio of 1:1 between the additional toothed bar 11 and the additional rack 15, other transmission ratios can be established by nonrotatably connecting to the pinion 12 a second pinion having larger diameter and mounted on the same spindle, the first pinion 12 then meshing with the toothed bar 11 only and the larger second pinion meshing with the rack 15. Because of the different transmission ratio, the whole arrangement can then be better adapted to the spring characteristic of the spring assembly 16 to provide more accurate compensation for centrifugal forces. If, in this arrangement, the slider 4 is moved outwards by the rack 8 and the toothed bar 10, the flange 7a is displaced to the same extent towards the right Figure 1.As however there is a different transmission ratio between the first and the second pinion, the larger second pinion causes the rack 15 to be moved towards the right by a greater amount than the flange 7a. This causes an increase in the prestressing of the spring assembly 16 which then opposes the higher centrifugal forces when the slider 4 is displaced in an outward direction. In this way it is possible to provide almost complete compensation for the centrifugal forces, and to prevent them from acting on the toothed bars 10 and the rack 8. Wear at these points is thus substantially eliminated and the accuracy of adjustment is maintained over an even longer period of operation.

Although in the embodiment shown in Figures 1 to 3 the spring assembly 16 acts on the adjusting rod 7 through the flange 7a, it may instead act on the flange plate 1 'a of the support member, as shown in Figure 4. In this arrangement, the flange 7'a has a through bore 18 of suitably large diameter for the additional rack 15 and the spring assembly 16 to pass therethrough. The adjusting screw 17 is adjustably screwable in the flange plate 1 'a as shown. This arrangement has the advantage that the force exerted by the spring assembly 16 and centrifugal force do not act on the adjusting rod 7 and therefore do not have to be overcome by the means actuating the adjusting rod 7.In addition, when the slider 4 is displaced outwardly, the rack 15 is moved towards the right and thus compresses the spring assembly 16, so that even with the transmission of 1:1 between the rack 15 and the bar 11 there is an increase in the return force of the spring assembly 16 and consequently also in the radially inwardly directed force acting on the slider 4. Thus, an increasing centrifugal force is opposed by an increasing return force which substantially compensates for the centrifugal force.

Instead of transmitting force by means of a pinion, it is possible to omit the pinion and provide direct transmission of force from the additional rack on which the force of the spring assembly acts, to one or more toothed bars which are arranged on the slider. The additional rack must then have slanting or inclined teeth, similarly to the rack 8. The toothed bars which mesh with this rack have extension portions in to which the slantingly toothed additional rack engages. Similarly to the rack 8, the additional rack is also provided with slanting or inclined teeth on both sides. The rack 8 and the additional rack must of course be arranged at such a spacing from each other that the additional rack never engages that region of the toothed bars which the rack 8 engages.

The embodiment described hereinbefore with reference to the drawings is a copying turning head having two oppositely movable sliders, the guide means of which are inclined at an angle of 600 with respect to the axis of rotation A-A. However, the invention may also be used with the same advantages in so-called facing head in which the slider guide means are arranged in a plane which extends perpendicularly to the axis of rotation. The invention can equally be used in turning heads in which there is only one slider. In each case, the speed of rotation of the turning head can also be substantially increased, due to substantial compensation for centrifugal forces. The turning head according to the invention has, to date achieved a speed of 2000 r.p.m. without any wear worth mentioning occurring at the toothed bars and racks which provide for adjustment movement.

Claims (8)

1. A rotary tool head comprising a support member to be secured to the spindle of a machine tool, having at least one radially extending guide for a radially adjustable slider for carrying a tool, an adjusting rod which is movable coaxially with respect to the support member and which acts on at least one rack which is axially movable in the support member and has inclined teeth, a toothed bar which is arranged on the slider and which extends in the direction of displacement thereof and whose teeth mesh with those of the rack and are inclined at the same angle as the rack teeth with respect to the axis of rotation of the support member, wherein an additional toothed bar which extends in the direction of movement of the slider is arranged on the slider and cooperates with an additional rack which is axially movable in the support member and which through a prestressed spring assembly is so braced against the support member or the adjusting rod or a member rigidly connected thereto that the spring assembly applies to the slider a force which is directed radially inwards towards the axis of rotation.

2. A rotary tool head according to claim 1, wherein the additional toothed bar is arranged on the rear side of the slider, which is remote from the tool when present, and meshes with a pinion which is rotatable about an axis extending perpendicularly to the direction of movement and parallel to the rear side, and the pinion engages the additional rack directly or by way of a second pinion which is non-rotatably connected to the pinion.

3. A rotary tool head according to claim 1 or claim 2, wherein the prestressed spring assembly bears against a member which is rigidly connected to the support member so that the force which is directed radially inwardly towards the axis or rotation increases with displacement of the slider radially outwardly.

4. A rotary tool head according to claim 2, wherein the diameter of the second pinion is greater than that of the first pinion so that the force which is directed radially inwardly towards the axis of rotation increases with displacement of the slider radially outwardly.

5. A rotary tool head according to claim 1, wherein the prestressing of the spring assembly is adjustable by means of an axially screwable adjusting screw against which the spring assembly bears.

6. A rotary tool head according to claim 1, wherein the spring assembly comprises a plurality of plate springs.

7. A rotary tool head according to claim 1 or claim 3, wherein the additional rack also has inclined teeth and meshes with an extension of the first said toothed bar, which extension forms the additional toothed bar.

8. A rotary tool head according to claim 1 and substantially as described hereinbefore with reference to Figures 1, 2 and 3 or to Figure 4 of the accompanying drawings.