US3680261A

US3680261A - Grinding machines

Info

Publication number: US3680261A
Application number: US54756A
Authority: US
Inventors: Maurice M Ward
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-07-14
Filing date: 1970-07-14
Publication date: 1972-08-01
Anticipated expiration: 1989-08-01

Abstract

A spiral grinding machine of the kind in which rotation of the workpiece spindle simultaneously with its axial translation is controlled by the movement of a block along a so-called ''''sine bar'''' settable at a chosen angle to the spindle axis, the machine incorporating control means for bringing about a continuous change in the rate of rotation of the spindle relative to the speed of its axial translation, so as to permit the grinding of spirals of constant helix angle on conically tapered workpieces.

Description

United States Patent Ward [ 51 Aug. 1,1972

[54] GRINDING MACHINES [72] Inventor: Maurice M. Ward, April Cottage,

Ringwood Rd., Ferndown, England [22] Filed: July 14, 1970 [2]] Appl. No.: 54,756

52 us. Cl. ..51/95 LH, 51/232 [51] Int. Cl. ..B24b 3/24 [58] Field of Search....5l/95 LH, 95 R, 232, BIG. 3]

[56] I References Cited UNITED STATES PATENTS 230,715 8/1880 Penney ..51/95 LH 2,212,855 8/1940 Chittenden ..51/95 LH 2,330,921 10/1943 Rickenmann ..51/95 LH X Murray ..51/95 LH X 2,597,648 5/1952 Lucas ..5l/95 LH X Primary Examiner-Lester M. Swingle Attorney-Bacon and Thomas [5 7] ABSTRACT A spiral grinding machine of the kind in which rotation of the workpiece spindle simultaneously with its axial translation is controlled by the movement of a block along a so-called sine bar settable at a chosen angle to the spindle axis, the machine incorporating control means for bringing about a continuous change in the rate of rotation of the spindle relative to the speed of its axial translation, so as to permit the grinding of spirals of constant helix angle on conically tapered workpieces.

5 Claims, 8 Drawing Figures PKTENTEDAus 1 I972 sum 2 BF 6 //v VEN T012 M/we/ce M W420 5 zim/dm ATTORNEYS PATENTEDaus 11912 3.680.261

sum 3 or 6 INVENTOI? MflUR/CE M. WARD A T TOR/V5 Y5 INVE TOR M/N/k/CE M WARD ,4 TTOPNE Y5 PATENTED H973 3.680.261

INVENTOR v MHZ/RICE M WARD ATTORNEYS GRINDING MACHINES This invention relates to grinding machines for grinding helical grooves in workpieces. The invention is particularly concerned with improvements in such machines of the kind in which a spindle for mounting the workpiece to be ground is itself mounted both for rotation about its axis (which will also be the workpiece axis in operation) and for rectilinear translational movement, both of such movements taking place simultaneously relative to a rotary grinding wheel in operation so as to grind a helical groove in the surface of the workpiece. Such machines include a so-called sine bar which is pivotally mounted so as .to be settable at a chosen angle to the direction of rectilinear translation of the spindle; a block or like follower member is mounted for movement along the sine bar and is pivotally connected to a cross-bar which is constrained to move only transversely relative to the said direction of translation of the spindle and is connected to the spindle by mechanism which, as the block moves along the sine bar simultaneously with translation of the spindle, converts the movement of the crossbar transversely to the spindle into rotation of the spindle, such conversion being effected for example by a cable drive or by a rack and pinion. The sine bar may take any of a number of forms; usually it comprises a cylindrical bar with the said block embracing the bar and slidable thereon, but any mechanical equivalent of such an arrangement may be employed instead, such as one or more elongate members defining an elongate track and the block or like follower being slidable in the track. Such a grinding machine is that referred to hereinafter as being of the kind described.

Known machines of this kind operate satisfactorily to grind a regular helical, i.e. one of substantially constant helix angle, in the surface of a cylindrical workpiece, as in such an operation the sine bar acts to maintain a constant relationship between the translation and the rotation of the spindle, and therefore of the workpiece, relative to the grinding wheel. However, satisfactory results have up to now been unobtainable when it is desired to grind a helical of constant angle in the surface of a tapered workpiece to form a tapered cutting tool, i.e. a workpiece of which the surface in which the helical is to be ground is conical. Examples of such tools are taper reamers, taper die sinking cutters, taps and taper gear hobs. The reason for this difficulty is that the conical nature of the surface in which the helical is to be ground results in the circumferential speed of movement of axially spaced points on such surface differing at a given rate of rotation. As a result, as grinding proceeds along the length of the workpiece the circumferential speed of movement of the workpiece surface past the grinding wheel constantly changes relative to the speed of translation of the workpiece so that the angle of the helical which is ground is not constant. The most notable disadvantage of this effect is that the rake of the cutting edge which is produced, by which is meant the angle between the two surfaces at whose intersection the cutting edge is defined, will vary along the length of the cutting edge, often to such an extent that the rake is positive (i.e. less than 90) at one end of the cutting edge and negative (i.e. greater than 90) at the other end. It is a primary object of the present invention to provide means whereby the above difficulty is obviated or at least substantially reduced.

Thus according to the invention there is provided a grinding machine of the kind described, having control means for automatically and continuously changing the rate of rotation of the said spindle during operation, relative to its speed of rectilinear translation.

With such a provision the constant relationship between the translational and rotary movements of the spindle which is a feature of known machines of the kind described, no longer exists, and the nature of the constant change in the rate of rotation of the spindle relative to its translation may be so selected that, for a workpiece of a given taper angle, the part of the conical surface which is in contact with the grinding wheel at any one time in operation will move at a circumferential speed which has a substantially constant rela tionship to the speed of translation of the workpiece. In other words, the nature of the continuous change in the rate of rotation of the spindle may be so selected that if the workpiece is translated at a substantially constant speed then the parts of its conical surface which successively contact the grinding wheel will also be moving at a substantially constant speed. This effect is the same as that which obtains in known machines when grinding a helix in a cylindrical surface, and a helix of substantially constant helix angle may therefore be ground in a conical surface by a machine according to the invention; more specifically, a cutting edge of substantially constant rake may be ground.

It may be remarked at this point that although it is convenient for the sake of clarity to refer to the effect on the rate of rotation of the spindle brought about when the spindle is translated at a substantially constant speed, the latter will not usually be the case in a manually operated machine. It will however be clear to those skilled in the art that, in machines of the kind described, changes in the speed of translation of the spindle do not affect the relationship between that speed and the spindles rate of rotation.

It will be appreciated that if the surface of the workpiece to be ground is purely conical then the nature of the change in the rate of rotation of the spindle, during axial translation thereof at a constant speed, will need to be a constant acceleration or deceleration. It is possible so to arrange a grinding machine in accordance with the invention as automatically to bring about a continuous change in the rate of rotation of the spindle (during axial translation thereof at a constant speed) of a more complex nature than a constant acceleration or deceleration, i.e. a continuously varying acceleration or deceleration, and this enables a helix of constant angle to be ground in at least some kinds of socalled formed workpieces, i.e. ones in which the shape of the surface to be ground is curved when seen in an axial cross-section of the workpiece. However, although it should be clearly understood that the present invention is applicable to this latter field, the ensuring description will be largely confined to arrangements for bringing about a constant acceleration or deceleration of the rate of rotation of the spindle for a constant speed of translation thereof, i.e. to arrangements suitable for ginding a helix of constant angle in a purely conical surface.

The preferred way in which a constant change in the rate of rotation of the spindle relative to its speed of translation is brought about in a machine according to the invention by providing a control element mounted for movement in concert with, and parallel to, the translation of the spindle, for continuously rotating the sine bar on its pivotal mounting during translation of the spindle; clearly such a continuous change in the angle of the sine bar to the direction of rectilinear translation of the spindle will bring about a continuous change in the rate of displacement of the cross-bar and a correspondingly continuous change in the rate of rotation of the spindle.

Thus in a preferred form of the invention the said control element is operative, during its said movement, to bring about continuous rotation of the sine bar on its pivotal mounting. The said control element may then comprise a secondary sine bar having a block mounted for movement therealong, which block forms the first part of a linkage interconnecting the secondary sine bar and the main sine bar. Such a secondary sine bar may, like the main sine bar, comprise a cylindrical bar having the said block embracing it and slidable thereon, or any suitable mechanical equivalent of such an arrangement. In an alternative arrangement the said control element comprises means defining a curved cam surface and the sine bar is biased to rotate on its pivotal mounting in an appropriate direction for an element of said linkage continuously to engage said cam surface. Preferably the secondary sine bar or the means defining said cam surface is mounted for selectable adjustment of its angle to the spindle axis, so that the rate of change of the rate of rotation of the spindle may be chosen depending on the degree of taper of a workpiece surface in which a helix is to be ground. For grinding a helix in workpiece surfaces of purely conical shape the secondary sine bar or cam surface will be straight; a curved secondary sine bar or cam surface may be employed, on the other hand, to grind a constant angle helix in some kinds of formed workpiece, by effecting a continuous change in the acceleration or deceleration of the rate of rotation of the spindle relative to its translatlon.

Where, in the above described forms of the invention, the said control element comprises means defining a track or cam surface in or against which a block or like follower is movable and the movement of which follower is transmitted to the main sine bar, the said track or cam surface may be of a more or less complex form to program the movement of the main sine bar during a series of successive operations; thus the track or cam surface could have a series of straight and/or curved portions arranged to bring about a series of different phases of movement of the main sine bar to grind a constant angle helix on successive differently shaped surface portions of a workpiece of complex shape.

In grinding machines according to the invention the support on which the main sine bar is pivotally mounted may itself be mounted from the base structure of the machine for positional adjustment parallel to the direction of rectilinear translation of the spindle-so as to permit adjustment of the position of the main sine bariin that sense in circumstances where the sine bar is set at such a large angle to the spindle axis that adequate translation of a workpiece relative to the grinding wheel cannot be obtained within the limitsof movement of the block or other follower along the main sine bar. Such an arrangement also facilitates positional adjustment of the main sine bar relative to a control element in grinding machines embodying the present invention.

In order that the invention may be more readily understood an embodiment of a grinding machine constructed in accordance with the invention will now be described by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a view of the grinding machine in front elevation;

FIG. 2 is a plan view of the machine;

FIG. 3 is a cross-section on the line III-III of FIG. 2;

FIG. 4 is a plan view of a mechanism for continuously rotating the sine bar of the machine on its pivotal mounting during operation, the sine bar itself being shown removed for the sake of clarity;

FIG. 5 is a cross-section on the line VV of FIG. 4; and

FIGS. 6 to 8 are three similar plan views of part of the machine, showing successive stages in the grinding of a helical groove in a tapered workpiece.

The grinding machine illustrated in the drawings is a machine of the kind described hereinbefore; the general arrangement of the machine will first be described with reference to FIGS. 1 and 2.

The machine includes a rigid base structure, generally indicated at l, carrying a mounting 2 for a driven grinding wheel 3 which is adjustable up and down by a vertical screw operated by a handle 4. The grinding wheel-3 is positioned above a table 5 which is mounted on the base structure 1 for rectilinear translational movement in a horizontal plane parallel to the horizontal dimension of FIGS. 1 and 2, the extent of translational movement of the table being delimited by adjustable stops 6. Translational movement of the table 5 is effected manually by a wheel 7 whose shaft 8 carries a pinion engaging a rack on the underside of the table. The drive to the table is disconnectable when desired by axial movement of the shaft 8 of the handle 7 to disconnect the pinion from the rack.- The table is also adjustable horizontally transversely of its length by means of a screw 9 operated by a handle 10.

A head 11 is mounted on a supporting structure 12 rigidly secured to the table 5, the head housing a spindle 13 which is adapted to mount a workpiece via a chuck 14 secured to the spindle and protruding from the end of the head 11. The head will move with the table 5 when translational movement of the latter is effected by the wheel 7, and the axis of the workpiece mounting spindle 13 is aligned with the direction of movement of the table. It will thus be seen that lengthwise translational movement of the table brings about similar movement of the workpiece in the chuck 14, relative to the grinding tool 3, in a directional parallel to the axis of the workpiece.

The spindle 13 is mounted for rotation in the head 1 1 and is drivable in rotation by a cross-bar 15 which extends across the table 5 beneath the head 1 1 and is constrained to move only at right angles to the axis of the spindle 13, being mounted in a slideway in the head support 12. Transmission of drive from the cross-bar 15 to the spindle 13 is via a rack 50 on the cross-bar which engages a pinion 51 on the spindle. Thus a workpiece mounted in the chuck 14 is rotatable about its axis relative to the grinding tool 3, and such rotation can occur simultaneously with the translational movement of the workpiece paralel to its axis.

A so-called sine bar 16, in this case a cylindrical bar, is mounted with its axis horizontal and in the same plane as the axis of the cross-bar 15. The sine bar is pivotally mounted from the base structure of the machine on a V-section cradle 17 and a support block 18 which is mounted in bearings 19 for rotation about a vertical axis; a calibrated dial 20 is provided on the block 18 and is settable relative to a pointer 21 (FIG. 2). A block 22 is mounted to embrace the sine bar 16 for sliding movement therealong and is pivotally connected to the cross-bar by a lockable ball joint 23. In FIGS. 1 and 2 the sine bar 16 is shown with its axis parallel to that of the spindle 13 so that, upon translational movement of the table 5, sliding movement of the block 22 along the sine bar will not bring about any axial movement of the cross-bar 15 to rotate the spindle 13. It will be appreciated, however, that with the sine bar set with its axis at any angle displaced from parallelism with the axis of the spindle l3, translational movement of the table and consequent movement of the block 22 along the sine bar will bring about axial movement of the cross-bar 15 to rotate the spindle 13; such rotation of the spindle 13 will have a fixed relationship with the translational movement of the spindle along its axis so long as the sine bar remains stationary during the axial translationof the spindle 13.

So as to enable a helix of constant helix angle to be ground on the conical surface of a tapered workpiece, the machine incorporates control means for automatically and continuously changing the rate of rotation of the spindle 13 during operation, relative to its speed of axial translation. In this particular embodiment of the invention, such control means is arranged to bring about continuous rotation of the sine bar 16 on its pivotal mounting during axial translation of the spindle.

The control means comprises a control element in the form of a secondary sine bar 24 mounted from the table 5 so as, in operation, to move with and parallel to the axial translation of the spindle 13. The secondary sine bar is pivotally mounted at one end 25 on a block 26 for rotational about a vertical axis, and at the other end is furnished with a vertical pin slidably received in an arcuate slot 27 formed in a sector plate 28. Both the block 26 and the sector plate 28 are slidably and lockably mounted in a slot 29 in a bar 30 secured to the table 5, the slot 29 extending parallel to the axis of the spindle 13.

A block 31 embraces the secondary sine bar 24 for sliding movement therealong and a bar 32, constituting the first element of a linkage between the secondary sine bar 24 and the main sine bar 16, is pivotally connected to the block 31 for rotation about a vertical axis. The bar 32 is slidably associated with a bar 33 constituting a second element of the said linkage and is adjustable along and lockable relative thereto, and the bar 33 is connected to the underside of a block 34 which itself is secured in a slidably adjustable and lockable manner to the underside of an arm 35 mounted from the block 18 which mounts the main sine bar 16. The bar 33 is rotatable relative to the block 34 for setting, but is held rigid with the block during operation. The arm 35 extends radially with respect to the pivotal axis of the main sine bar 16 so that longitudinal displacement of the linkage formed by the

bars

32 and 33 will bring about rotation of the block 18 and thus rotation of the main sine bar 16 about its pivotal axis.

In operation, when the table 5 is moved longitudinally by rotation of the handle 7 to effect axial translation of the spindle 13, the secondary sine bar 24 moves with the table and parallel to the axis of the spindle 13. During such movement of the secondary sine bar the block 31 is constrained to slide along it and, the secondary sine bar being set at an angle to the direction of its movement, the block 31 will be displaced transversely to the direction of movement of the secondary sine bar. This movement of the block 31 is transmitted via the

linkage

32, 33 and the arm 35 to the block 18 so as to rotate the main sine bar 16 simultaneously with the axial translation of the spindle and the workpiece mounted thereby.

The result of this continuous rotation of the main sine bar simultaneously with axial translation of the spindle is to bring about a continuous change in the rate of displacement of the cross-bar 15 at right angles to the spindle axis and thus a corresponding continuous change in the rate of rotation of the spindle, relative to its axial translation. It is, in fact, found that the continuous change in the rate of displacement of the cross-bar 15 is a substantially constant acceleration or deceleration, depending of course on the direction of the axial translation of the spindle 13. The magnitude of such acceleration or deceleration depends on the angle at which the secondary si'ne bar 24 is set with regard to the axis of the spindle 13; the greater such angle the greater will be the acceleration or deceleration produced. Thus the angle of the secondary sine bar can be set in dependence on the taper angle of the conical surface of a workpiece on which a constant angle helix is to be ground. This setting may be calculated as follows:

Considering a part-conical workpiece having a diameter D at its smaller end and a diameter D at its larger end, the angle of rotation for the workpiece over its conical length being a .1 1 xrrof360 The main sine bar 16 must be set initially to the angle required to give the workpiece the desired helix angle at its smaller end D,. If the desired angle is 20, for example, the main sine bar 16 setting angle is 30 (this figure is applicable to a particular machine, but other models of machine using the sine bar system for grinding spirals may differ from this depending on the drive ratio between the cross-bar and the spindle. The corresponding main sine bar setting for the larger end diameter D2 to give a helix angle of 20 is, for this machine, 8 15 minutes. Therefore, over the length of the workpiece the main sine bar 16 has to change its angle from 30 to 8 15 minutes. This is achieved by setting the secondary sine bar 24 and a adjusting the

linkage elements

26,27,32,33,34 and 35 to cause this change in. angle, the rate of change being governed by the total angular movement a over the conical length of the workpiece.

. The movement of the various elements of the machine during the grinding of a constant angle helix on the conical surface of a tapered workpiece 36 may be seen from FIGS. 6 to 8, which show three successive stages in the grinding of such a helix. During this grinding process the table 5, and thus the workpiece 36, is

moved in the direction of the arrow A in FIG. 6. The

secondary sine bar 24 has been set at an angle to the direction of movement of the table calculated in the manner set out above, and the operation begins with the block 31 approximately half way along the secondary sine bar. As grinding proceeds, the secondary sine bar moves to the left as seen in FIGS. 6 to 8 with the result that the block 31 slides to the right on the sine bar and consequently moves away from the table 5. As a result the arm 35 is rotated clockwise and such rotation is transmitted to the main sine bar 16 so that the angle which the latter makes with the axis of the spindle l3 gradually decreases. Consequently, the rate of displacement of the cross-bar 15 inwardly towards the table gradually decreases, and thus so does the rate of rotation of the spindle 13. As a result, the circumferential speed of the point on the surface on the workpiece 36 that is engaged by the grinding wheel 3 at successive times in the grinding operation remains constant instead of increasing as would be the case if the spindle 13 were to be rotated at a constant rate.

In the illustrated machine, the block 18 on which the main sine bar 16 is supported is rotatably mounted on a substantially L-shaped bracket 37. A block 38 on which the block 18 is directly mounted is slidably supported on top of the upright member 39 of the L- shaped bracket 37, for movement at right angles to the movement of thev table 5 and thus at right angles to the axis of the spindle 13. A screw drive 40 (FIG. 3) is provided for adjusting the block 38, and thus the block 18 and the main sine bar 16 mounted thereon, inwardly and outwardly relative to the table, the screw being rotatably mounted in a block 41 secured to the member 38 and being turnable by a handle 42 furnished with a calibrated dial 4-3.This adjustability of the main sine bar towards and away from the table 5 permits controlled displacement of the cross-bar to rotate the spindle 13 without any axial translation of the spindle occurring. This facility is useful in effecting radial infeed of a workpiece when desired, i.e. rotation of the workpiece about its axis without axial translation thereof, and may be employed in the up flute grinding of milling cutters, hobs and the like as already mentioned herein. Suitable limit stops and a locking device (not illustrated) are preferably associated with the drive screw 40, for delimiting the range of movement of the block 38 and locking it in any position when desired.

The support bracket 37 on which the main sine bar 16 is mounted is slidably mounted on a front face of the base structure 1 of the machine so as to be movable in the same direction as the table. A screw 44 rotatably mounted in a bracket 45 secured to the said base structure engages in a threaded bore 46 in the foot member 47 of the L-shaped bracket 37 for driving the bracket along its sliding mounting relative to the base structure. This facility is useful in permitting adjustment of the position of the sine bar 16 when the latter is set at such a large angle to the spindle axis that adequate travel of a workpiece cannot be attained within the limits of movement of the block 22 on the sine bar 16. Furthermore, such adjustment of the position of the sine bar 16 in the direction of movement of the table, when the sine bar is set at a relatively small angle, brings about radial infeed of a workpiece mounted on the spindle 13. In addition, this facility is useful in effecting fine adjustment of the position of the main sine bar relative to the control means for bringing about the continuous change in the rate of rotation of the spindle in accordance with the present invention.

It will thus be seen that the invention provides grinding machines of the kind described, embodying efficient and reliable means for permitting the grinding of a constant angle helix in the conical surface of a tapered workpiece, and in particular for grinding a cutting edge with a substantially constant rake. It may also be noted that a machine embodying the present invention may alternatively be employed to grind a helix of constantly varying helix angle in the surface of a cylindrical workpiece, or indeed in the surface of a tapered workpiece, either of which operations may be desired in some circumstances.

Iclaim:

1. A grinding machine for grinding helical grooves in workpieces, comprising a base, a workpiece carrying spindle mounted on said base for simultaneous axial rotation and rectilinear translation relative to a grinding wheel, a sine bar pivotally mounted on a pivotal mounting so as to be settable at a chosen angle to the direction of rectilinear translation of the spindle, a follower member mounted for movement along the sine bar, a cross-bar pivotally connected to said follower member and constrained to move only transversely relative to the said direction of translation of the spindle, connecting means between the cross-bar into rotation of the spindle, and control means for automatically and continuously changing the rate of axial rotation of the said spindle relative its speed of rectilinear translation during operation, said control means including a control element mounted for movement in concert with, and parallel to, the said rectilinear translation of the spindle and being operative, during its said movement, to bring about continuous rotation of the sine bar on its pivotal mounting.

2. A grinding machine as claimed in claim 1, wherein the pivotal mounting upon which the said sine bar is pivotally mounted is itself mounted from the base for positional adjustment thereon parallel to the direction of rectilinear translation of the said spindle.

3. A grinding machine as claimed in claim 1, including a linkage interconnecting the said control element and the sine bar.

4. A grinding machine as claimed in claim 3, wherein the said control element comprises a secondary sine bar and the said linkage includes a follower member mounted for movement along said secondary sine bar.

5. A grinding machine as claimed in claim 4, wherein the said secondary sine bar is mounted for selectable adjustment of its angle to the spindle axis.

223 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,680,261 Dated August 1, 1972 Inventor(x) MAURICE M. WARD It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F- In column 4 (claim 1) line 46, should read: -i

-dle, connecting means between the cross-bar and the spindle for converting movement of the crossbar into rota- Signed and sealed this 6th day of February 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSGHALK Attesting Officer Commissioner of Patents