GB2264246A

GB2264246A - Grinding machine for cutting blades.

Info

Publication number: GB2264246A
Application number: GB9203094A
Authority: GB
Inventors: Stephen Geoffrey Bernhard
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-02-13
Filing date: 1992-02-13
Publication date: 1993-08-25
Anticipated expiration: 2012-02-13
Also published as: GB2264246B; GB9203094D0

Abstract

A grinding machine (10) for grinding cutting blades comprises a blade support assembly (54, 56) and a grinding wheel (20) assembly which in use is attached to a pair of support rails (17, 18), the operative grinding position lying between the rails (17, 18) when projected onto a plane passing through both rails. The grinding position preferably lies substantially centrally of the rails when projected onto the plane along a direction which is normal to the plane. A drive motor (24) is operative to engage a drive means (30) and thereby cause the grinding wheel assembly to traverse reciprocally along the support rails (17, 18). The drive means (30) is attached at opposite ends to the grinding machine and at least one of the ends has a vibration damping means (34) disposed between the one end and the grinding machine. <IMAGE>

Description

IMPROVEMENTS IN GRINDING MACHINES The invention relates to grinding machines used for grinding cutting blades such as helical rotary blades and flat bed knives of lawn mowers.

Grinding machines are known to comprise a grinding wheel and a blade support which is used to present the cutting face of a blade at a suitable orientation with respect to the grinding wheel. The grinding wheel is rotated by a motor and engages the blade cutting face usually by moving the grinding wheel in a direction normal to the face. The blade cutting face is ground by traversing the grinding wheel longitudinally of the blade and along the face.

Movement of the wheel can be effected manually or automatically. In the latter case, it is known, for example, to have a continuous drive chain fixed to a grind wheel assembly and passing over sprockets suitably mounted to the grinding machine. Repeated grinding operations can be carried out automatically by causing the drive chain to move first in one direction and then in the other direction. However, a known problem of the prior art is that when the direction of movement of the grinding wheel assembly is reversed the large change in momentum causes the grinding machine to move violently thereby potentially offsetting the calibrated orientation of the blade with respect to the grinding wheel.

A known grinding machine is described in British Patent 6194Ol(Reynolds). That patent discloses a grinding wheel assembly mounted on two parallel support rails and a blade support assembly similarly mounted on two parallel support rails. The operative position of the grinding operation, that is where the grinding wheel and blade cutting surface meet, is located above a plane passing through all four support rails. The operative position is also at a point between the respective pairs of support rails. The point may be defined as that point in the aforementioned plane projected down from the operative position along a direction normal to the plane.The spaced arrangement of the pairs of support rails means that relatively little movement of either the guiding wheel assembly or the blade support assembly at the support rails can cause a larger moment (and hence movement) at the operative grinding position. This construction of a grinding machine gives rise to potential problems of misalignment of the blade cutting surface and grinding wheel the alignment of which is usually accurately calibrated to give a desired relief angle to the blade cutting edge along its entire length.

The invention seeks to avoid or at least mitigate these and other problems of the prior art. Accordingly, in one apsect of the invention, there is provided a grinding machine for grinding cutting blades, which grinding machine comprises a blade support assembly and a grinding wheel assembly which in use is attached to a pair of support rails which rails also define a plane passing through each rail, wherein the operative grinding position lies between the rails when projected onto the plane along a direction which is normal to the plane.

Beneficially this aspect of the invention enables greater stability of the relative orientation of the grinding wheel and blade cutting edge when in use.

A preferred feature of this aspect of the invention provides that the operative grinding position lies substantially centrally of the rails when projected onto the plane along a direction which is normal to the plane.

A further aspect of the invention provides a grinding machine for grinding cutting blades, which grinding machine comprises a blade support assembly, a grinding wheel assembly, a pair of support rails, a drive means and a drive motor, wherein the drive means is attachable to the grinding wheel assembly and the drive motor is operative to engage the drive rail and to cause the grinding wheel assembly to traverse reciprocally along the support rails, and wherein the drive means is attached at opposite ends to the grinding machine and at least one of the ends has a vibration damping means disposed between the one end and the grinding machine.

Beneficially this aspect of the invention reduces the vibration effect when the direction of motion of the grinding wheel assembly is reversed. Thus it is possible to minimise the adverse effect of the large vibrations which occur when the grinding wheel assembly reverses direction and hence maintain a more accurate grinding operation.

A preferred feature of this aspect of the invention provides that both ends of the drive rail comprise vibration damping means. The vibration damping means may be a resilient means such as a coil or other spring for example. The drive means can comprise a chain.

Another aspect of the invention provides a grinding machine for grinding cutting blades, which grinding machine comprises a blade support assembly, a grinding wheel assembly, and a pair of support rails to which the grinding wheel assembly is movably attachable, wherein the grinding wheel assembly comprises a grinding wheel which abuts a blade during a grinding operation and which grinding wheel is positioned between the support rails during said grinding operation.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIGURE 1 shows a schematic perspective view of a grinding machine according to the invention; FIGURE 2 shows a schematic plan view of the grinding machine shown in Figure 1; FIGURE 3 shows a schematic front elevational view of a drive wheel and chain of the first embodiment of the invention; and FIGURE 4 shows a schematic elevation view of the drive chain coupling to a side wall of a grinding machine according to the invention.

Referring to Figure 1 there is shown a grinding machine 10 according to the invention which comprises a blade support assembly 12 and grinding wheel assembly 14. The grinding wheel assembly 14 comprises a traversing plate 16 having an adjustable plate 28 onto which is mounted two bearings 26, a drive shaft 22 journalled in the bearings 26, and a cup shaped grinding wheel 20 attached to one end of the drive shaft 22. Traversing plate 16 is mounted by means of rollers (not shown) to support rails 17 and 18. First support rail 17 has a circular cross-section whilst second support rail 18 has a flat upper surface and is rectangular in cross-section.The rollers bearing on each support rail can provide stability to traversing plate 16 since rectangular support rail can be gripped from above and below thereby reducing vertical movement at that end whilst the cylindrical support rail can be gripped substantially horizontally thereby reducing horizontal movement at that support rail, while both sets of rollers allow longitudinal movement. In operation the grinding wheel assembly mounted on traversing plate 16 traverses from one longitudinal end of support rails 17 and 18 to the other end and can reverse its direction of movement. It is possible to provide a predetermined reversing and/or stopping position at desired positions to suit the grinding operation in hand.

The traversing operation is effected by a drive motor housed inside motor housing 24 which is attached to the underside of traversing plate 16. Grinding machine 10 comprises a drive means 30 which may be a chain or grooved rack for example. The drive means 30 is connected to grinding machine side walls 4 and 5 by end attachments 32.

Referring to Figures 3 and 4 it can be seen that drive means 30 is a chain which at one end comprises a vibration damping means 34 which in this example is a coiled spring.

Coiled spring 34 is attached to a hooked bolt 32 which is connected to side wall 5. The vibration damping means 34 should provide sufficient rigidity to enable the traversing plate to pull against the chain and thereby move along supporting rails 17 and 18 but should also provide sufficient damping so that when the grinding wheel assembly 14 reverses its traversing direction the change in momentum is substantially absorbed by the vibration damping means and not transferred to the grinding machine as a whole in a sudden movement. The drive motor 31 may comprise a sprocket 40 as shown in Figure 3 and a biased arm 42. In operation the direction of rotation of sprocket 40 may be clockwise or anti-clockwise and in order to effect movement of the grinding wheel assembly 14, biased arm 42 causes drive means 30 and sprocket 40 to engage.

Grinding wheel 20 is driven by means of a second motor housed inside motor housing 24. The grinding wheel is mounted on adjustable plate 28 which is hinged at one side on a spindle 29 and can be raised and lowered about this hinge. Additionally, the grinding wheel 20 can be moved in a transverse direction of the grinding machine 10 using adjustment means 23.

A cutting blade 50, such as a bed knife for a lawn mower, which is to be ground by the grinding machine 10 is shown in the schematic plan elevation of Figure 2. The cutting blade 50 is mounted on adjustable brackets 54 and 56 which are adjustably attached to mounting blocks 55 and 57 respectively. Mounting blocks 55 and 57 are slidably attached to support beam 52. This beam 52 is hingably attached to grinding machine end walls 4 and 5 at bearings 60 and 64 respectively. Bearing 60 comprises a graded joint which enables accurate adjustment of the orientation of beam 52, and therefore of an attached cutting blade 50, with respect to grinding wheel 20. To effect rotation of beam 52 there is provided a handle 62.Of course, whilst the description given here refers to mounting a bed knife to grinding machine 10 any similar substantially linear blade such as those of ice skates could be mounted to a grinding machine with relatively minor adjustment to the blade support assembly 12. Similarly, it is envisaged that grinding machine 10 according to the invention may be adapted to operate on cylindrical cutters having helical rotary blades.

Thus, in operation the blade surface or edge to be ground is mounted between brackets 54 and 56 and suitably oriented with respect to the grinding surface of grinding wheel 20.

Grinding wheel 20 is then brought into contact with the cutting surface.

The grinding wheel is rotated by the motor as previously described and traversed along the face of the cutting blade. It can be seen from Figure 2 that the operative cutting position (ie point of contact between blade and grinding wheel) at any one given time is at a point which when projected onto a plane passing through support rails 17 and 18 along a direction normal to that plane, lies between the support rails 17 and 18. In this embodiment, as shown in Figure 2 the operative position is substantially centrally located between the support rails 17 and 18 in the plane which passes through the rails. The invention provides a longer traversing plate 16 which extends between the displaced support rails 17 and 18 compared with known grinding machine. This provides greater stability to the relative orientation of grinding wheel 20 with respect to cutting blade 50 since in known grinding machines the operative grinding position lies outside the support rails 17 and 18 when projected onto the plane as previously described. Thus, undesired nontranslational movement of traversing plate 16, or movement in directions not longitudinally of the grinding machine 10, can have less effect on the relative orientation of the grinding wheel 20 with respect to cutting blade 50 in a grinding machine according to the invention compared with the known art.

Claims

1. A grinding machine for grinding cutting blades, which grinding machine comprises a blade support assembly and a grinding wheel assembly which in use is attached to a pair of support rails which rails also define a plane passing through each rail, wherein the operative grinding position lies between the rails when projected onto the plane along a direction which is normal to the plane.

2. A grinding machine as claimed in claim 1 wherein the operative grinding position lies substantially centrally of the rails when projected onto the plane along a direction which is normal to the plane.

3. A grinding machine as claimed in claims 1 or 2 wherein one of the support rails has a circular cross-section in the transverse plane of the grinding machine and the other support rail has a substantially flat upper surface.

4. A grinding machine for grinding cutting blades, which grinding machine comprises a blade support assembly, a grinding wheel assembly, a pair of support rails to which the grinding wheel assembly is movably attachable, a drive means and a drive motor, wherein the drive means is attachable to the grinding wheel assembly and the drive motor is operative to engage the drive means and thereby to cause the grinding wheel assembly to traverse reciprocally along the support rails, and wherein the drive means is attached at opposite ends to the grinding machine and at least one of the ends has a vibration damping means disposed between the one end and the grinding machine.

5. A grinding machine as claimed in claim 4 wherein both ends of the drive means comprise vibration damping means.

6 A grinding machine as claimed in claim 4 or 5 wherein the vibration damping means is a resilient means.

7. A grinding machine as claimed in claim 6 wherein the damping means comprises a coil spring.

8. A grinding machine as claimed in any one of claims 4 to 7 wherein the drive means comprises a chain.

9. A grinding machine for grinding cutting blades, which grinding machine comprises a blade support assembly, a grinding wheel assembly, and a pair of support rails to which the grinding wheel assembly is movably attachable, wherein the grinding wheel assembly comprises a grinding wheel which abuts a blade during a grinding operation and which grinding wheel is positioned between the support rails during said grinding operation.

10. A grinding machine substantially as described herein with reference to or as illustrated in the accompanying drawings.