US2933965A - Method and apparatus providing an infinite range of radii for generating spherical segments and curved surfaces - Google Patents

Description

April 26, 1960 H G MURPHY 2,933,965

METHOD AND APPARATUS PROVIDING AN INFINITE RANGE OF RADII FOR GENERATING SPHERICAL SEGMENTS AND CURVED SURFACES Filed Oct. 8, 1957 4 Sheets-Sheet l /6 IN VENTOR $745010 6. MZ/QP/fl BY q /4M ATTORNEYS April 26, 1960 MURPHY H. G. 2,933,965 METHOD AND APPARATUS PROVIDING AN INFINITE RANGE OF RADII FOR GENERATING SPHERICAL SEGMENTS AND CURVED SURFACES Filed Oct. 8, 1957 4 Sheets-Sheet 2 25 W 35 Hillflll Z4 32 27 INVENTOR M42010 G. MUZP/I Y BY X0 A TTOR NEYS P" 1960 H. e. MURPHY METHOD AND APPARATUS PROVIDING AN INFINITE RANGE FOR GENERATING SPHERICAL SEGMENTS AND CURVED SU Filed Oct. 1957 INVENTOR #42010 G. MUG/ H) ATTORNEYS Apnl 26, 1960 H. cs. MURPHY 2,933,965

METHOD AND APPARATUS PROVIDING AN INFINITE RANGE OF RADII FOR GENERATING SPHERICAL SEGMENTS AND CURVED SURFACES Filed Oct. 1957 4 Sheets-Sheet 4 INVENTOR #42010 G. MflQPf/ ATTORNEYS United States Patent METHGD AND APPARATUS PROVIDING AN IN- FINITE RANGE OF RADII FOR GENERATING SPHERICAL SEGMENTS AND CUR D S FACES VE UR Harold G. Murphy, Peekskill, N.Y., assignor of one-third to Leon G. Hammerschlag, Philadelphia, Pa.

This invention relates to a method and apparatus which rovides an infinite range of radii for generating spherical segments and curved surfaces on a workpiece.

In the metal working art, one of the major technical problems has been that of generating or forming a true segmental spherical surface having a long radius of curvature. An example of such a surface is what is commonly called in the lens grinding trade a metal lap, and these are most commonly used in the optical arts for the production of opthalmic and precision lenses or the like. In the lapping process the glass body is ground to a shape conforming to that of the lap by moving it continuously in random directions across and against the lap as a grinding compound is applied. Therefore, there exists the problem not only of making the original lap at a reasonable cost, but in truing up the laps after they have worn beyond the point of minimum accuracy by the grinding compound. The need for truing the laps occurs in many small shops which do not have the resources to afford the expensive and complex machinery heretofore used in forming or truing the laps nor do they have the space for housing the cumbersome, largespread machinery.

In previously known methods and apparatus for forming or truing a lap, one of the most commonly used has been a radius bar fixture, wherein the radius of the bar has been equal to the radius of curvature of the desired spherical surface. In the curves of longer radii this has involved a very large and heavy device. The leverage through which the force applied at the point of the tool acts is so great that there is chattering of the tool on the work and only light cuts may be taken. In the way of example, a one-eighth diopter lens lap requires a radius bar of fourteen feet. Another method of cutting the laps has been by the use of electrically, hydraulically or pneumatically controlled tracer machinery, and this apparatus is complex, very costly and can only be handled by experts who have been especially trained for that purpose. This usually presents the problem of making the master pattern. Still another way of cutting the lap has been by use of the ball turning attachment. These attachments are very limited in range, because the diameter of the work is limited by the radius of the arm carrying the tool bit.

It may be pointed out that this problem is not restricted to the lens grinding field. The need for generation of a true spherical surface occurs in the tool and die industry and in the pattern making arts.

There has been a strong need, therefore, for a method and apparatus which is more simplified and less costly than that presently known, which is in a cost and size range that can be handled by the smaller shops, and which is within the capability of the average craftsman.

It is an object of this invention to provide apparatus which in its preferred form is in the nature of an attachment to a standard metal cutting lathe, but which may also be applied to other metal workingmachine tools which have a rotatable spindle for holding a workpiece, such as milling machines and boring mills.

it is a further object of the device to provide an inexpensive and simple method and apparatus capable of use in a small shop for generating a spherical segment of any selected plus or minus radius ranging from slightly above zero to infinity, and which method and apparatus does not require any unusual degree of skill, and is within the capability of the average trained machinist.

Still another object of the invention is to provide a method and apparatus wherein the surface generated may be a positive spherical segment, a piano surface or a negative spherical segment.

Still another object of the invention is to provide apparatus of simple and inexpensive construction which has a range in one machine that is equivalent to that which formerly had to be provided by several different machines, and which can accomplish the work of the radius bar, ball turning attachments and tracing devices which are now in common use for generating spherical segments and curved surfaces.

Still another object of the invention is to provide a. method and apparatus capable of generating accurate spherical segments without tool chatter marks and of such quality that handwork is not required for the finished surface.

A further object of the invention is to provide a method and apparatus which is not limited solely to cutting spherical segments but which may also be used to cut internal and external radii, such as bearing races and the like.

A further object of the invention is to provide an apparatus which is capable of rapid and ready adjustment for turning a surface of any selected radius.

Another object is to provide apparatus which is, of rigid construction which is capable of operation in a confined area and which operates close to the headstock of the lathe machine tool, the cutting tool overhang being at a minimum, thus minimizing the nuisance of tool chatter.

Still another object of the invention is to provide a method and apparatus which with minor changes can be adapted to grinding or metal spinning operations. For example, a grinding quill can be used instead of a tool bit, laps and dies can be ground to a mirror finish, glass lens blanks can be rough ground with a diamond abrasive wheel, and fiat metal sheets can be spun into segmentospherical shells.

With the above and other objects in view, as will be presently apparent, the invention consists in general of certain novel details of construction and combinations of parts hereinafter fully described, illustrated in the accompanying drawings and particularly claimed.

In the accompanying drawings like characters of reference indicate like parts in the several views, and:

Fig. l is a fragmentary front elevational view of a metal working lathe with the attachment of the invention in place on the lathe bed and in position to be adjusted for a cut of selected radius of curvature, the surface to be generated being shown by dotted lines;

Fig. 2 is a fragmentary top plan view of the attachment as applied to a metal working lathe;

Fig. 3 is a cross-sectional view of the attachment taken on the line 3-3 of Fig. 2;

Fig. 4 is a fragmentary view of the attachment taken in the direction of the arrow 4 in Fig. 3;

Fig. 5 is a cross-sectional view taken on the line 5-5 of Fig. 3;

Fig. 6 is a cross-sectional view taken on the line 6-6 of Fig. 3;

s 3 r Fig; 7'. is a fragmentary elevational view taken in the direction of. the arrows 7 in Fig. 3;

Fig. 8 is a schematic view illustrating themethod involved in the present application and showing the path of the tool relative to the plane of rotation of the workpiece during a cutting operation; i

Fig. 9 is a modification of the attachment of the present invention wherein an electric motor is applied for causing movement of the tool bit in its desired path over the work; and

inthe direction of the arrows It] in Fig. 9. The present invention involves both a novel method and a novel and preferred. apparatus for carrying out the method. Since difierent forms of apparatus might be developed and used in applying the method, the method will first be described in detail and the preferred form of apparatus will then be separately and more fully disclosed.

The method can best be disclosed by reference to the schematic diagram shown in Fig. 8 of the drawings.

a he. line A-l.;A represents the axis of rotation of a work a '10 Fig. 10 is a further view of the same modification taken piece C. *It is essential that the plane. of this workpiece be normal to the axis ATTA and that the axis be fixed. Gl st ingtool D'is then made to, revolve about an axis BB, and if this tool were revolved in a full circular path of 360, this path would-be represented by the broken line'E, In carrying out/the method, it is neces-- spherical surface will be generated on the face of the W ZkP PQ- J By placing the axis of rotation BB so. that it intersects the axis of rotation A-,-,-A of the workpiece behind the workpiece, as shown in Fig. 8, a positive or convex E I 9 ma b s ns a 0 he other h if the i 's of rotation BB of the tool is made to intersect the axis of rotation in front of the workpiece, a negative or concave surface will be generated.

The present application discloses a preferred and novel apparatus for carrying out the method involved and this apparatus is designed to be attached to a stand h d metal working lathe or other suitable machine tool. Therefer ence numeral 10. indicates; the ways of astand and and known lathe. The 'lathe is provided with a headstock 11 and anyknown chuck 12 for holding a workpiece W. This workpiece is usually preworked to provide it with a chuck-holding spindle, which later is used to-hold the lap. in the lapping machine. A feed carriage 13 slides along the. ways and is controlled and moved by thehand-crank 14. A crossfeed carriage moveson ways onthe feed carriage 13 and is controlled by thehand-crank 16. The crossfeed carriage '15 is providedwith bolt holes 17, as shown in Fig. 3. Up to sthis points all the construction described is standard and 'well known in the. art.

The. attachment of the present invention is provided with a base plate 18, which has formed therein an annular T-slot 19 with'thenarrowneck of'thev slot opening upwardly. This base p1ate-18 is fixed to the crossfeed carriage by T-bolts 21 which are inserted through apertures 22 in the base plate. below the T-slo ts. The base plate is furtherprovided with an upwardlydirected; integrally formed boss 24 which }supports a ring-shaped element that is formed into a ring gear 25 by the cutting-Lof gear-teeth inthe peripheral edge thereof. This G to the point H, or alternately from H to G,.a

plate 18, and the base an upstanding annular asserts.

ring gear 25 is keyed to the boss 24' or is integrally formed therewith, as desired. a

A frame bracket 23 is rotatably mounted on the base plate is preferably provided with flange 26 which cooperates with a corner groove 28 in the circular base 27, so that the base plate 18 and circular base 27 will remainin accurate alignment during relative rotation. The circular base 27 is provided with a large bore 29 for receiving the ring gear 25and a smaller intersecting counterbore 30 for receiving a p1nion 31 which meshes with the ring gear 25. The pinion 31 is mounted on a stub shaft 32 which extends through'the upper wall of the circular base, and a knurled knob 33 is fixed to the stub shaft.

At least three bolts 34 extend through apertures 35 in' the circular -baseand the heads of these bolts engage the annular T-slots 19 in the base plate 18. The base plate 18 is preferably provided with a scale 36 and the circular base 27 with an arrow or indicating mark 37. When the. attachment is in use this provides an indication of the angle of inclination 'of the tool bit axis to the axis of rotation of the work, which angle controls the radius of curvature of the spherical segment generated; a

A gear housing 38 is mounted upon and secured to the frame bracket 23. by means of the screws 39. Each of the screws projects'through a segmental arcuate slot 49, formed in the frame bracket23. The gear housing 38 has formed thereon an eccentric boss 41 which is rotatable in a circular opening 42 formed in theframe bracket 23. An indicating scale 43 is placed on the eccentric boss 41, with the 0 of the scale being positionecl at the point of smallest radius of the eccentric boss. Rotation of the gear housing about its eccentric boss 41 will raise or lower the shaft 49, as will later be described, and tightening of the screws 39 will then hold the gear housing 38 in adjusted position. a

. The gear housing 38 isprovided with a cover 45 which is countersunk in a groove 46 in the outer edge of the housing, the cover being fastened by screws 47. A tool bar platen 48 is mounted, on the gear housing 38 and this platen is provided with a shaft 49 which is journalled for rotation in apertures 50 and 50 in the cover 45 and eccentric boss 41, respectively. The inner end of the shaft 49 is threaded and is provided with locknuts 51. These locknuts permit the shaft to be set tightly enough to prevent play, but with just enough clearance for rotation; V

The gear housing 38 is further provided with a bore 52 which receives a worm wheel 53 which is keyed to the shaft 49. The said housing is provided with a transverse bore 54 in which is journalled the shaft 55, and

' an intersecting 'vertical opening 57 which houses a worm 56 which is pinned or keyed to the shaft 55. The shaft 55 is provided with anextension 58 and a finger bar 59 by means of which the shaft may be manually rotated.

Rotation of the shaft 55 will cause rotation of the worm 56,:the worm gear 53,-and the platen 48 about the axis of its shaft 49. a 1

The platen 48 is provided with a transverse groove 60 which receives a heavy tool bar 61. This toolbar is' held in adjusted position in its groove 60 by means of the straps 62 which are fixed to the platen 48 by means of the screws; 63.v The tool bar is provided with a hooked endv 64, which has; a transverse bore 65 formed therein.- A pin 66 slides within the bore 65 and the head of the pin is provided, with. a'through opening 67,

which is slightly-larger in diameter than the thickness 'of a toolbit 68;which, is positioned therein. 'The upper end of the pin 66 is threaded and.v provided with a nut 69 and Washer 70. Tightening of the nut 69 will cause the tool bit 68to be drawn tightly against the under surface 'of the hooked end 64 of the tool bar 61, and

it will be firmly held in adjusted position.

' In the, modifications shownv in Figs. 9 and 10, it is ass 3,965

shown that it is possible to drive the shaft 55 and worm {56 by means of a motor M which is mounted on the gear housing 38 by means of a bracket 71. Since the shaft 55 must revolve slowly, the shaft 55 is provided with a large gear 72 and the motor M is provided with a small gear 73. Suitable power lines and switch means, not shown, will be provided for the motor.

If the attachment is used on a variable speed lathe, the power for rotating the shaft 55 could be supplied by a universal joint take-01f from the lathe cross-slide power feed. This would provide maximum accuracy and surface finish.

In order to provide a seal between the platen 48 and the gear housing 38, a wiper ring or sleeve 74 may be provided to cover the joint, as best shown in Fig. 3.

The operation of the apparatus described is as follows:

The workpiece W is mounted in the chuck or spindle 12 and securely tightened. The bolts 34 of the frame bracket 23 are then loosened, and the frame bracket 23 is rotated to the desired setting on the scale 36 by turning the knob 33. As the pinion 31 is turned by the knob, the fact that it meshes with the gear ring 25 causes the frame bracket to be rotated. The effect of the rotation of the frame bracket 23 is to vary the angle of inclination of the axis of rotation of the tool, namely the shaft 49, to the axis of rotation of the workpiece W. It is this angle of inclination which determines the radius of curvature of the spherical segment generated. With reference to the schematic showing of Fig. 8, if the angle of inclination of the axis B-B to the axis AA is very small, the radius of curvature will be very large. As the angle of inclination is moved closer to 90, the radius of curvature of the generated surface will become progressively smaller. Therefore, when the desired angle of the axis of rotation of the tool has been attained, the bolts 34 are tightened securely.

It is important that the axis of rotation of the shaft 49 intersect the axis of rotation of the workpiece W, which is the centerline of the lathe. This is accomplished by loosening the screws 39 and rotating the gear housing 38 about its eccentric boss 41. This will raise or lower the shaft 49 by a measured amount and until the desired intersection of axis is obtained. The screws 39 are then tightened to fix the housing 38 and shaft 49 in adjusted position.

These adjustments having been made, the crossfeed carriage 15 is then moved by the hand-crank 16 until the tool bit point as it rotates about the shaft 49 moves through the axial center of the workpiece.

The final adjustment having been completed, the lathe is ready for the cutting operation. The cut is normally taken from the outside diameter toward the center of the workpiece. The tool bit it brought into contact with the work by moving the feed carriage 13 with the hand-crank 14. The shaft 55 is then rotated counterclockwise until the tool bit 68 is outside of the maximum .diameter of the workpiece. The depth of the cut is controlled by the amount the feed carriage 13 is moved toward the work, and when this has been set, the shaft 55 is turned clockwise by the finger bar 59 to move the ,tool bit 68 against the Work. The tool bit first comes into contact with the outside diameter of the work and :this rotation of the shaft 55 is continued until the tool lbit passes through the dead center thereof. Additional cuts are made by moving the feed carriage 13 an increment toward the work, and the swing of the tool bit by the shaft 55 is repeated. If necessary, and if the work is inaccurate upon testing, adjustments may be made in the basic settings. The cuts are then repeated until work cleans up and a suitable surface finish is achieved.

It will thus be seen that the method and apparatus disclosed provides in one operation and one piece of apparatus a range of radius of curvature which is substantially infinite. The surface generated may range from the smallest radius that is practical relative to the size of the tool parts to a radius that is infinite, since if the adjustments are such that the axis of rotation of the tool bit is parallel to the axis of rotation of the workpiece, a plano surface will be cut.

While there are herein shown and described the preferred embodiments of the method and apparatus, it is to be understood that minor changes may be made therein without departure from the spirit and scope of the invention as claimed. It will be evident that if adjustments in the settings were made, a curved surface other than a spherical segment could be generated on the work.

What is claimed is:

1. A machine tool comprising a work holding spindle, a set of ways, said spindle being parallel to said ways, a tool feed carriage on said ways, a crossfeed carriage on said feed carriage disposed in a plane parallel to said ways, a base, means for fixedly attaching said base to said crossfeed carriage, a frame bracket rotatably mounted on said base about an axis perpendicular to a plane parallel to said ways, means for fixing said frame bracket in adjusted rotated position about said axis, a shaft journalled for rotation in said frame bracket and positioned substantially parallel to said ways, means to rotate said shaft, a tool holding means secured to the outer end of said shaft and extending transversely thereof, and a cutting tool secured to one end of said tool holding means.

2. A machine tool comprising a work holding spindle, a set of ways, said spindle being parallel to said ways, a tool feed carriage on said ways, a crossfeed carriage on said feed carriage disposed in a plane parallel to said ways, a base, means for fixedly attaching said base to said crossfeed carriage, a frame bracket rotatably mounted on said base about an axis perpendicular to a plane parallel to said ways, means for fixing said frame bracket in adjusted rotated position about said axis, a bearing housing secured to said frame bracket, a shaft journaled for rotation in said bearing housing and positioned substantially parallel to said ways, means to raise and lower said bearing housing and to fix said housing in a selected adjusted position, means to rotate said shaft, 2. tool holding means secured to the outer end of said shaft and extending transversely thereof, and a cutting tool secured to one end of said tool holding means.

3. A structure as set forth in claim 1, wherein the means to raise and lower said bearing housing includes an eccentric boss extending from said housing into a circular opening in said frame bracket, and said means to fix said housing in a selected adjusted position includes a plurality of bolts secured to said housing, each of said bolts extending through an arcuate slot in said frame bracket.

4. A machine tool comprising a work holding spindle, a set of ways, said spindle being parallel to said ways, a tool feed carriage on said ways, a crossfeed carriage on said feed carriage disposed in a plane parallel to said ways, a base, means for fixedly attaching said base to said crossfeed carriage, a frame bracket rotatably mounted on said base about an axis perpendicular to a plane parallel to said ways, means for fixing said frame bracket in adjusted rotated position about said axis, a shaft journaled for rotation in said frame bracket and positioned substantially parallel to said ways, means to rotate said shaft, a platen at the outer end of said shaft, a tool bar positioned against said platen and extending transversely thereof, means to clamp said tool bar to said platen, and a cutting tool secured to one end of said tool bar.

5. The method of generating a segmental true spherical surface on a workpiece with a cutting tool, wherein the radius of curvature of said surface may be selected from a range starting from above zero and ending below infinity, comprising the steps of rotating said workpiece about a fixed axis in a plane normal to said axis and moving a cutting tool against the workpiece about an mmu h the .sa axis pr ma OI P OTH R F RENCE Rcfex'en'ces cued the file of thls Patent lubl c t n Am ican M hinist, o um 7, N9- :21;

UNITE TAT P ENT November 23, .1922 (p.813). Q r 745,431 0m 13 .1, 1903 7 1,663,192 Compton Mar. 20, 19278

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