Centerless grinders are used for mass production of generally cylindrical components which require a ground finish. Their main advantage is that it is not necessary to mount and dismount each workpart between centres, and thus less overall time is taken for each grinding operation.

However in a centerless grinder, the workpart is not rigidly held, and thus the grinding of radial faces is difficult if not impossible because the axial grinding loads cannot be effectively opposed.

A typical centerless grinder comprises a machine bed, a control wheel rotatable on the bed about a horizontal axis, a carriage having a grinding wheel rotatable thereon about an axis generally parallel to the axis of the control wheel and at the same height above the bed, and a workpart support arranged between the control wheel and grinding wheel at a height which will support a workpart in the plane defined by the wheel axes.

The upper part of the workpart support is angled towards the control wheel so as to maintain a workpart at the desired height and in contact with the control wheel.

Grinding is carried out by moving the grinding wheel against the workpart, the control wheel providing the necessary reaction force for grinding diameters.

Automated loading and unloading of workparts is usually provided.

Both the grinding wheel and control wheel require dressing from time to time, and for this purpose a diamond tipped dresser is provided to dress a respective wheel on the non-working side in the plane of the wheel axes.

Grinding on the working side is not usually possible because of the automatic loading and unloading mechanism.

Both the grinding wheel and control wheel may be profiled to suit a stepped workpart, and this enables several diameters to be ground at once.

The axes of the control wheel and grinding wheel may diverge slightly in order to maintain the axial position of the workpart, and the outer face of each wheel is dressed accordingly in the known manner.

As mentioned above, it is not generally possible to grind a radial face with a centerless grinder, and accordingly where ground diameters and radial faces are required it is conventional to mount the workpart on a between-centres grinder for the entire grinding operation.

This is time consuming, difficult to automate, and increases the chances of scrapping workparts due to machining errors.

It has been proposed to grind a diameter and a radial face at the same time by feeding the grinding wheel at an angle. However it has been found that the maximum feed angle is small (about 5°) and accordingly the depth of material which can be removed from the radial face is also

small in relation to the depth removed from the diameter.

Very careful positioning of the workpart is required in order to grind the radial face effectively, and to prevent the workpart jumping out of the grinding gap.

What is required is a centerless grinder which can grind one or more radial faces independently of diameters in a safe and controlled manner.

According to the invention there is provided a centerless grinder comprising a machine bed, a control wheel rotatable on the bed about a first horizontal axis, a carriage mounted on the bed for horizontal movement parallel to and perpendiciirar to said axis, the carriage having a grinding wheel rotatable thereon about a second horizontal axis in a plane containing said first horizontal axis, and an upstanding workrest between the control wheel and grinding wheel, wherein the grinding wheel is mounted for arcuate movement on said carriage so as to permit the direction of said second axis to be varied within said plane, and clamp means is provided to maintain a workpart in contact with the workrest and control wheel.

Such an arrangement permits the rotation axes of the control and grinding wheel to be set at a significant angle, <BR> <BR> <BR> <BR> e. g. 30°, and thereby to permit radial faces to be ground by movement of the carriage with respect to the machine bed, the clamp means maintaining the workpart in position. In a preferred embodiment the clamp means is a roller or pad acting vertically on the workrest. The clamp

force of the clamping means is preferably adjustable. In use the axis of rotation of a clamp roller is preferably vertically above the axis of rotation of a workpart.

In a preferred embodiment the grinding wheel is mounted on a pivot member having a pivot axis between said horizontal axes. The pivot member may be pivotable between adjustable end stops on either side of a line perpendicular to said first axis in said plane. The pivot member may be moved between end stops by an actuator, or may be under control of a stepper motor or the like so as to give computer control of position.

The position of said clamping means and of said first horizontal axis may be adjustable, for example for initial setting purposes.

The grinder may further include a dresser mounted to one side of the control wheel and having dressing tips substantially at the pivot angle of said pivot member.

Alternatively the grinder may include a dresser on a pivot mounting so as to pivot in said plane through an angle substantially equivalent to the pivot angle of said pivot member. Thus a single dresser can be provided to dress the grinding wheel at the appropriate angle with respect to the first axis.

In general the invention provides an apparatus and method for grinding radial faces and diameters on a centerless grinder. Radial faces at one or both ends of a diameter can be ground independently of the diameter.

Other aspects of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompanying drawings in which: Fig. 1 is a schematic plan view of a prior art centerless grinder; Fig. 2 is a schematic section on line 2-2 of Fig. 1; Figs. 3 and 4 correspond to Figs. 1 and 2 and show a centerless grinder according to the present invention; Figs. 5 and 6 are partial sectional views showing the grinder of Fig. 3 in alternative grinding positions; and Fig. 7 is a partial section showing the grinding gap and corresponding to Figs. 5 and 6.

Fig. 1 illustrates a machine bed 11 having a carriage 12 mounted thereon for movement about mutually perpendicular axes represented by arrows 13. A control wheel 14 is mounted for rotation on the bed about a fixed axis 16. A grinding wheel 17 is mounted on the carriage 12 for rotation about a parallel axis 18. A workpart support 19 is fixed relative to the bed 11 and has an angled upper face to support a workpart 20 on the centreline of the axes 16,18.

As illustrated the workpart support is angled to urge the SUBSTITUTE SHEET (RULE 26)

workpart against the control wheel 14 in order to stabilize its position.

The control wheel 14 and grinding wheel 17 are driven conventionally by electric motors. A fixed diamond tipped dresser 21 is shown at the rear face of the grinding wheel.

In operation the carriage 12 is traversed to dress the grinding wheel 17 on the dresser 21 between workpart grinding cycles. A pivotable dresser (not shown) is provided to swing down for dressing of the control wheel.

The grinding wheel can alternatively be dressed on a dresser 22 mounted at the front, to one side of the control wheel, if space permits. Grinding cycles are carried out by moving the carriage 12 towards and away from the control wheel 14, the plunge depth of the grinding wheel being adjusted according to the actual diameters of the wheels after dressing. CNC control is usually provided for such machines. Manual adjustment of the position of the control wheel may be provided for initial setting purposes.

Figs. 3 and 4 illustrate the principal features of the present invention as applied to a generic prior art centerless grinder. Common parts carry the same reference numerals as were used in the description of Figs. 1 and 2.

The grinding wheel 17 is mounted on a support 31 which is pivotable on the carriage 12 through an angular range, represented by arrow 32, about an axis 33. A clamp roller 34 mounted in any suitable manner applies a downward load on the workpart 20.

As illustrated by the arrows showing the direction of rotation, the control wheel 14 rotates anti-clockwise, and drives the workpart 20 which rotates clockwise. In turn the workpart drives the clamp roller 34 anti-clockwise. The clamp roller itself is in contact with neither the control wheel 14 nor the grinding wheel 17. Typically the clamp roller is the same diameter as the workpart, though for smaller diameters (less than 8mm) a graphite lubricated friction pad may suffice and for large diameters (greater than 12mm) a clamp roller smaller than the workpart may be sufficient.

In its simplest form the support 31 is pivotable between fixed end stops by any suitable actuator, the range of movement being about 60°. As will be apparent the normal carriage movement permitted along axes 13 permits the grinding wheel to approach the workpart in any desired direction permitted by the support 31.

Two diamond tipped dressers 35,36 are provided to one side of the control wheel and pointing one each side of the normal perpendicular approach direction of the grinding wheel 17. As an alternative to the fixed dressers 35,36, a single dresser pivotable through a fixed angle between end stops may suffice.

Figs. 5-7 illustrate the invention in greater detail.

A cylindrical workpart 41 has multiple diameters which must be ground to size-this kind of workpart is typically ground in a centerless grinder using stepped grinding and

control wheels 17,14. The respective profiles of the wheels 17,14 are trued by occasional dressing in the manner noted above.

The workpart 41 includes radial faces 42 (Fig. 5) and 43 (Fig. 6) which require grinding to size.

In use the clamp roller 34 applies a downward force to the workpart 41 so as to maintain engagement with the control wheel 14 by virtue of the angled upper face of the workpart support 19. In this way axial forces on the workpart can be resisted.

The support 31 is set to pivot through an angle which will grind a suitable amount of material from the radial faces 42,43 of the workpart 41; as illustrated the pivot angle is about 15° each side of the normal perpendicular approach direction. The actual angle is not critical, as will become apparent.

The grinding wheel 17 is dressed to the appropriate profile on the angled dressers 35,36 using the normal traversing movement of the carriage 13, dresser 35 dealing with the profile portion marked A, and dresser 36 dealing with the profile portion marked B. The control wheel 14 is dressed in the usual manner. As will be appreciated from Figs. 5 and 6, the grinding wheel 17 is dressed so as to define pairs of frusto-conical surfaces with the surfaces of each pair being disposed at right angles to each other. In the embodiment shown, a first pair 50 comprises two surfaces 52,54, a second pair 56 comprises surfaces 58,60, a third

pair 62 comprises surfaces 64,66 and a fourth pair 68 comprises surfaces 70,72. Since the grinding wheel 17 is dressed after the pivot angle is set, the actual angle is itself not important; a rough setting 1° may be appropriate to ensure minimal material removal during the first dressing operation.

The pivot axis 33 is set so that the difference in grinding position for sections A and B of the grinding wheel is minimal.

In use a typical grinding cycle will comprise the following steps.

The workpart 41 will have at least one diameter ground by conventional perpendicular approach of the grinding wheel 17 without application of the clamp roller 34. This first (reference) ground diameter must be one which is supported by the control wheel and workrest. During this operation the grinding wheel 17 will be positioned at one or other angular end stop. This first step ensures that one or more location diameters are made truly round, but it may not be necessary in every case.

Next the grinding wheel is marginally retracted, by e. g. 0.05mm, and the clamp roller 34 applied. Any suitable method of clamp roller application is possible, for example hydraulic, pneumatic or spring; the clamping force may be adjustable, and is typically set at the minimum necessary for effective grinding.

The grinding wheel 17 is then traversed on the

carriage 13 to grind the faces on one side of the component 41 (Fig. 5) either to absolute position, or by removing a set amount using touch (acoustic) sensing. These faces are supported by the control wheel 14.

As shown in Fig. 5, the surfaces 58,64,70 of the grinding wheel 17 grind circumferential surfaces 76,78,80 on the workpart 41 while the surfaces 60,66,72 are disposed radially so as to grind the radial surface 43 and further radial surfaces 82,84.

Subsequently the grinding wheel is withdrawn and pivoted to the second end stop.

In Fig. 6 the surface 52 of the grinding wheel 17 is parallel with the axis of the workpart 41 so as to grind a circumferential surface 74 on the workpart while the surface 54 is disposed radially so as to grind the radial surface 42.

In each case the clamp roller 34 prevents axial grinding forces from forcing the workpart out of the grinding position.

It may be desirable to tip the machine bed at an angle, for example less than 10° to the horizontal, to improve coolant distribution during the grinding process.

The pivot axis of the grinding wheel could alternatively be on the opposite side of the axis of rotation of the grinding wheel, as will be apparent from a geometrical consideration.

In practice it may be sufficient to permit the grinding wheel to pivot through 10° or less on either side of a mid position.