US2607174A - Method of grinding eyeglass lenses - Google Patents

Description

Aug. 19, 1952 R. LANlUs 2,607,174

METHOD OF GRINDING EYEGLASS LENSES Original Filed Aug. 23, 1946 5 Sheets-Sheet l Aug. 19, 1952 R. LANlUs METHOD OF GRINDING EYEGLASS LENSES 3 Sheets-Sheet 2 Original Filed Aug. 23, 1946 Mfg/LL Mm@ IN VEN TOR.

Aug. 19, 1952 R. LANlUs 2,607,174

METHOD oF GRINDING EYEGLAss LENsEs original Filed Aug. 25, 194e 5 sheets-sheet s Y @06722521 DCZgzJ/ @22526 Patented Aug. 19, 1952 METHOD or laRINDINd EYEGLAss LENsEs Ralph Lemus, cincinnati. ohio, assigner to Super-Cut, Inc., Chicago, Ill., a corporation of Illinois Continuation of application Serial No. 692,635, August Z3, 1946. This application' November f 25, 1949., Serial No. 129,350

1 Claim.

The presentinvention pertains to the art of grinding lenses` for eyeglasses.` Y

In grinding eyeglass lenses to a predetermined curvature it has heretofore been customary to employ or utilize a grinding apparatus comprising a vertically extending power driven spindle and a bowl-shaped receptacle having in the bottom thereof a central aperture through which the upper portion of the spindle extends, together with a castiron grinding tool which is mounted on Athe upper end of the spindle so as to rotatewith the spindle and has the top surface thereof provided with such a diopter curve that its contour is inconformity with the desired curvature i for the lens. The receptacle surrounds the tool and serves to retain beneath the tool a batch -of abrasive material in the form of a mixture of Water and loose abrasive particles such assilicon carbide particles or -'aluminum oxide grains. yIn vconnection with a lens grinding oper-ation thelens blank is applied to one side of a cast metal'holder by way of pitch or 'like material." Thereafter the blank is positioned -so that the exposed-surface thereof rests on the upper surface of the'cast metal grinding tool and downward pressure is exerted on the blank by way of a substantially horizontal lever which has one end thereof mounted for limited universal pivotal movement and its other end shaped to form a handle and carries on the central portion thereof a Adepending rod, the lower end of which is pointed and is adapted so to nt within a socket on the upper sideiof the cast metal holder as to permit the holder and lens to spin or revolve relatively to thetool during a grinding operation, After proper positioning of the blank and Vduring 'drive of the tool -by the spindle the operator scoops the abrasive material from the bottom of the receptacle vand deposits it onto the upper surface of the tool so that the tool together Vwith the material .effects the desired 'grinding of therbottom surface of the lens blank. Ordinarily the blank is subjected to four successive grinding operations. 'First of all the blank is rough ground by using in the grinding apparatus abrasive material, the abrasive particles of which have a mesh size between 45 and 80. After the rough grinding operation the blank is ground in a similar machine having the same type of grinding tool and abrasive material, the abrasive particles of which have a mesh.

size between r2o and 15o. VVThe second grinding operation vserves to reduce roughness in the form of deep scratches, grooves yand pits. `After the second grinding operation the blank is ground in `a third apparatus having-the same .type of a grinding tool and a batch of abrasive material, the abrasive particles of which have a mesh lsize between 220 and 280. The purpose of the third grinding operation is further to reduce roughness on the ground surface of the blank. At the conclusion of the third-grinding operation the blank is subjected to a so-called finish grind by grinding it in a fourth apparatus having the same type of :grinding tool and a batchy of abrasive material, the abrasive or ,grit particles of which have `a mesh size between 1000 and 1250. At the conclusion tof the finish grinding operation which serves completely to eliminate'roughness the ground surface of the blank is polished by placing it against :3, power driven felt pad that is treated orcoatedfwith rouge, cerium oxide or likeV materiaL In some instances at the conclusion of the aforementioned operations the other side of the blank is ground and polished in a similar manner in order to provide the desired curvature. The aforementioned method of grinding eyeglass lenses is subject to many objections. In the iirst place, grinding ofthe lens blank is extremely slow by reason of the fact that the grinding tools must by necessity be driven at a slow speed, such, for example, as 400 R. P. M. in order to prevent the loose abrasive material which is applied to them from being ung out of place by centrifugal force. Secondly, only a highly skilled operator is lcapable of carrying out the method because the operator must manipulate the lens blank with one hand and feed the loose abras-ive material with the other hand. Thirdly, the cast iron grinding tools which are employed in the .rough grinding operation and the subsequent grinding operations rapidly wear down and lose their proper curvature due to the .action of the abrasive material, and hence require frequent and costly reshaping or dressing. Fourthly, the blank is likely, especially in connection with rough grinding thereof, to crack or-have its edges chipped becauseof the vibration which is set up due to the large sized loose abrasive or grit `particles rolling Abetween the blank and the curved upper surface of the grinding tool.4 Fifthly, the various grinding oFFlcE x operations, due to the fact that loose or paste variety abrasive material is employed, are essentially untidy and laborious and often result in the operators hands being cut or injured. Sixthly, the cost incident to grinding the lens is high because the loose abrasive material must be frequently washed and cleaned and replaced or renewed due to becoming dull by reason of the accumulation of glass particles in it. Seventhly, the method ror technique does not readily lend itself to so-.called cylinder grinding, i. e., grinding the blank by holding it and the holder against spinning while at the same time rocking them back and forth radially with respect to the tool, because the operator can use but one hand to manipulate the blank and holder in view of the fact that Vthe other hand isvrequired to feed the loose abrasive material onto the upper surface of the tool for grinding purposes.

The primary object of this particular invention is to provide a method of grinding eyeglass lenses which eliminates the objections or defects of the method heretofore employed and is charac'- terized by the fact that it may be carried out much more expeditiously and with greater facility and at materially less cost and without cracking or chippingV the blanks. In general the improved method comprehends utilizing in the initial or so-called rough grinding operation a grinding tool with its upper or working curved surface in the form of diamond particles of a particular mesh size in a matrix, and rotating the tool at aspeed of no less than 1250 R. P. M. By utilizing such -a grinding tool the time incident to grinding the lens blank is materially reduced, and it is possible to eliminate the rst and second intermediate grinding operations. In addition, the tool Vholds its shape more or less inderlnitely and hence willgrind a great number of lens blanks to the desiredv curvature without the necessity of being dressed or renished. Another advantage in using a grinding tool, the upper or operative curved surface of which is in the form of diamond' particles in a matrix, resides in the fact that it is possible to drive the tool at a comparatively high speed and there is no loose abrasive material which must be handled by the operator. Still another advantage resides in the fact that since no loose abrasive material is necessary vibration of the blank being ground r is eliminated Vand hence there is substantially no likelihood of the blank becoming cracked or chipped. A further advantage resides in the fact that in connection with cylinder grinding of a lens blank the operator, because no handling of loose abrasive material is necessary, may use both hands and hence obtain more accurate grinding of the blank.

A further object of the invention is to provide an eyeglass lens grinding kmethod which is an important improvement in the art and eiiiciently and eiectively accomplishes its intended purpose while at 'the same time producing inherently new results.

Other objects of the invention and the various advantages and characteristics of the present eyeglass lens grinding method will be apparent from a consideration of the following detailed description. v

The invention consists in the method which is hereinafter more particularly set forth and deiined by the claim at the conclusion hereof.

In the drawings which accompany and form a part of this specification or disclosure and in which like numerals of reference denote corresponding parts throughout the several views:

Figure 1 is a perspective of an apparatus for use in carrying out the improved method of eyeglass lens grinding;

Figure 2 is a vertical longitudinal section of the apparatus;

Figure 3 is an enlarged vertical section of the spindle and grinding tool of the apparatus, showing a lens blank being spherically ground by permitting it to spin whilemoving it radially with respect to the tool;

Figure 4 is a perspective of the tool; and

Figure 5 is another enlarged vertical section of the spindle and grinding tool, illustrating a lens blank being provided with a cylindrical grind by holding it against rotation and rocking it back and forth bodily in a radial direction with respect to the tool.

The method constituting the invention involves grinding to a predetermined desired curvature an eyeglass lens blank 5 and is designed or adapted to be carried out in an apparatus like that which is shown in the drawings. In general such apparatus comprises a base structure` 6, a bowlshaped receptacle 1, a vertically extending spindle 8, a lap type grinding tool 9, and a pressure exerting lever I0. f

The base structure 6 is horizontally elongated and comprises a horizontal t'op Wall I I and a continuous dependingV side wall I2. The top wall I I defines with the side wall I2 an open bottom compartment I3 and has at one end thereof an integral upstanding annular flange I4. The receptacle 'I rests on, and is shaped conformably to, a seat I5 on the upper margin of the flange I4 and has a circular aperture I6 in the central portion of its bottoinwall. The portion ofthe bottom wall that define sthe aperture I6 is shaped to form an upwardly extending tubular neck I'I. The spindle 8^ has the central portion thereof journalled in anti-friction bearings on` the top wall I I of the base structure 6 and is arranged so that the lower end thereof projects into 'the compartment I3 and itsupper end projects upwards through the neck I1. Drive of the spindle, is ef,- fected by way of an electric motorl I8 and a belt and pulley connection I9. The motorv I8 is mounted on the end of the top wall II that is opposite the upstanding flange Il and is arranged so that the armature shaft thereof extends vertically. The belt and pulley connection I9 is located in the compartment I3 and includes a pulley (not shown) on the lower end of the armature shaft of the motor I8, a pulley 20 on the lower end of the spindle, and a belt 2| around the two pulleys.` Preferably the electric motor I8 is a constant speed motor and serves in connection with the belt and pulley connection I9 to drive the spindle 8 ata speed no less than 1250 R. P. M. In practice it has been found that so far as the improved method is concerned the desired results are obtained when the spindle is driven at a speed between v1250 and 6000 R. P. M. If thespindle is driven at a speed less than 1250 R. P. M. the time incident to carrying out a lens blank grinding operation is too slow for economical purposes. The upper end of the spindle 8 is tapered to a small extent as shown in Figure 3.

The grinding tool 9 constitutes the medium for grinding the lens blank 5 to the desired curvature and is in the form of a wheel. It consists of a circular or disc-like body 22 and a hub 23. The body and hub arepreferably formed integrally with one another. Brass, bronze or any other suitable. metal' is used to for-m .the tool a andthe latter is preferably inthe forni of a casting. The body 22 extends horizontally when the grinding tool is in its normal or operative posi' tion and has the upper' surface thereof provided with such a dio-pter curve that' its contour corresponds to, or is the complement of, the .curvature that is desired to beformed in the lensblank in connection with spherical grinding thereof. If the lens blank is to be ground in a concave fashion the upper surface of the body .22 has a convex diopter curve, as shown-in the drawings. If the lens blank is to be ground so as to have a convex surf-ace the upper or working surface of the tool body 22 is `made so that it has a concave diopter curve. The upper surface of the body 22 of the grinding tool is covered with diamond particles which are embedded in a matrix. Ihe latter may be made of any suitable material and servesto bond the diamond particles rigidly or fixedly to the upper surface of the vtool body 2.2. In practice it has been found that optimum results are obtained when' the diamondparticles .are 'of-mesh sizey from approximately 60 to 120.

If the :diamond particles are too coarse as the result of being lower than approximately 60 .mesh they either .so'chip the blank as to render the blank useless or cut too deeplyfinto the lens blank and make it necessary for the operator to perform an intermediate grinding operation .on the blank with a different wheel of rthe same diopter curve but with liner diamonds. On the other hand, if the diamondl particles are too fincas the result of the mesh size thereof vbeing in excess of approximately 120 the time necessary to elfect a lens blank grinding operation is prolonged to the point where the method or technique is impractical or has no advantage over the heretofore employed eyeglass lens blank grinding method which utilizes a cast iron lap as the grinding tool or instrumentality. As shown in Figure 4, the diamond particles .extend throughout the entire area of the upper surface of the toolbody and are uniformly distributed throughout the matrix. The hub 23 of the grinding tool!) is connected to, and depends from, the central portion of the circular body 22. It embodies a central socket 24 which is shaped and adapted to receive the upper end of the spindle 8. As shown in Figure .3, the socket 24 is upwardly tapered in conformity with vthe upper end of the spindle in order that there is a press or drive lit between the tool and the spindle when the tool is in its operative position. When it is desired to replace the tool with another grinding tool having a differently contoured Working surface the tool is removed merely by forcing it upwards out of engagement with the upper end ofv the spindle 8. vAs shown in Figure 4 of the drawings the upper end of the socket 24 is open at the center of the disc-like body 22 and the diamond particles are in the form of an annular band, the width of which is approximately equal to the size of the lens blank 5. The width of the 4aiorfvementioned band is the distance between the inner and outer marginsor edges of the band. As clearly illustrated, the band consisting of diamond particles and .the latters matrix is essentially solid or continuous. Y

The lever i0 of the grinding apparatus overlies the bowl-shaped receptacle l and normally extends substantially horizontally. One end of the lever is shaped to form a handle 25 andthe other end of the lever is connected to the upper end of a standard 26 by a sleeve 2l and a bifurcated pivot element 28 in order that the lever is per- 6 v-mitted :to'swing laterally ,.fandlup and downf and also rotate aboutits axis. .A-'rod 29:.extends through, Vand nts slidablyin,V `vavertical hole in the vrcentral portion .of the iever.v lrll'and'is releasably and adjustabl-y .secured in pmoebywaywof; a knob equipped set screw-30. Thelowerendof the rod is pointed and adaptedin connectionv withia lens grinding .operation to bearaagainst a holder 3|V for the lens .blank 15. Such -holder the form of a rectangular block oil-cast ironand has on the central portion of its3upperfsurface a,

socket 32 for receiving vthe pointed lower .end of the rod 29. The socket is so dimensioned or proportioned that when the `pointedlower end .of-the rod is Adisposed in it during aso-called .spherical lens grinding operation thegholderytogether. with the vlens blank isffree toffspin: relatively-to .the grindingtool 9.-

' ff Y .In addition to the parte y'.heretmore-ir1entioned the grinding apparatusfcomprises ,a tube 33.@for supplying aliquidcoolant to the upper or working curved surface. of thev disc-likejbodypf the grinding tool. One vend yof .the, tube connected to any suitable source ofpycoolantand the other end of the tube is positionedover the .grinding tool body .22, .as shown in IFigure 2..5A drain 34 formed in the bottom ivall .of .the bowl-.shaped receptacle 1 in. order.. to permit thejcoolant to .drain from the .receptaoleafterit hasbeen Adischarged over the diamond particles rconstituting vthe working .surface of the tool body..

of Cincinnati, Ohio. Water. may also be utilized as the coolant, provided that itis treated with an agent for renderingit non-rusting.

When it is .desired to grind the lens .y blank 5 the blank is mountedonthe Aunder side'of -the holder 3l, .pitch .or othersuitabl'e material being employed to hold the'blankin'bon'ded or connected relation with the holder. y'After proper mounting of the lens blank ,5 with respect t0 the holder V3| the blankvis placed'on-thelworking or abrasive upper surface vof the body 2 2 of the tool. Thereafter the pointed lower -end of the rod 29 is located or positioned fin' the .socket 32 in lthe upper .side or face ofthe blank holder andfthe apparatus is set into operation by startingthe electric motor I8. During drive .of .the tool at a speed no less than 1250..R.-P. M.` the operator moves the lever l0 .back andQf'o-rthf in a sidewise direction in order tofca'us'ethe blank.to `move substantially radially withfiiespect Ito the. tool body 22. During such movementftheblank and holder spin and the band -ofl diamond particles constituting the working. upper surface of the tool body grinds the bottom surface of the blank. During the grinding operation the coolant is kfed onto the working surface of thebody of the tool lby Way of thetube 33,-and downwardV pressure is .applied to the blank-byjway of the lever l0. In lconnection with initial rough grinding of. the

blank it is contemplated that the operatorvwill ,exert on the end of the lever l a heavy downward pressure of approximately to 15 pounds. After the lens blank has been rough ground to the predetermined or desired extent the downward pressure on the end of the lever is reduced to approximately one pound. When the blank is subjected to such light downwardpressure for a limited period of time the diamond particles constituting the upper or Working surface of the body of the grinding tool effect a smooth grinding'of the blank and thus eliminate any deep scratches or furrowsin the surface of the lens blank that is being ground. By reducing the downward pressure 'on the .blank during the end of the rough grinding operation intermediate grinding operations are unnecessary. After the aforementioned rough grinding operation the ground surface of the blank has' the diopter (spherical) curve of the tool through all meridians. Such surface is then provided with a finish grind and is subsequently polished in any conventional or Well known manner. 'In practice it has been found that when the grinding tool is rotatedfat a speed of about 3500 R. P. M., the diamond particles have a mesh size of approximately' 60 to 120 and are'closelyv distributed throughout the matrix', as shown in Figure 4, and the downward pressure on the end of the lever I0 is approximately l5 pounds the blank is ground away at a rate of approximately 3 millimeters in l5 seconds. It has also been found that by materially reducing the` pressure on the blank after rough grinding to the desired extent the ground surface of the blank is sufficiently smooth and free from deep grooves and scratches to permit it to be finish ground Without intermediate grinding operations.

A large number of all eyeglass lenses that are ground require so-called cylindrical correction, which means that a lens must be provided with a predetermined curvature through one of its meridians and another predetermined, stronger or weaker, curvature through another meridian. In connection with the grinding operation, the operator by holding the lens blank stationary and applying downward pressure to one marginal part or another may'either induce or eliminate any desired amount of prism. It is also contemplated that when it is desired to impart cylindrical correction to alens after spherical grinding thereof, the operator will grasp the blank holder in such manner as to prevent it from spinning or rotating, and then rock the blank back and forth on the workingsurface of the rotating tool along one of the meridians of the blank for imparting the desired predetermined cylindrical curve thereto.` The hereinbefore described methlod of imparting cylindricalV correction to a lens is at least 5 to 6 times faster: and far more accurate than the method heretofore used in the commercial production of anl eyeglass lens, and since the operator is ablemore accurately to control the optical center'of the lens being ground, the time required to finish such'lens on a. nish'cylindrical machine is' reduced by 50%, thereby effecting outstanding economical results. In' connection with ycylindrical grinding the blank is rocked radially with respect to the rotating tool, as shown in Figure 5 and it is first subjected to heavy downward pressure and then light pressure as in the case of spherical grinding.V If the band of diamond particles Von the grinding tool is convex as shown in Figures 4 and 5 cylindrical correctionv along one meridian after spherical.

grinding of the lens blank is, of course, eected by rocking the blank bodily back and forth in an arc, the radius of Which is greater than 'the curvature radius of the upper surface of the grinding tool, it being obvious that if the blank is rocked back and forth in an arc, the radius of which is the same as the curvature radius of the upper surface of the tool, no cylindrical correction of the blank could be obtained and the blank would have only the spherical grind which it had originally.

The herein described method of grinding an eyeglass lens blank by Way of a grinding tool, the working surface of which is formed for the most part of diamond particles may be carried out in an extremely short length of time and by a semiskilled operator. It eliminates the necessity of subjecting the blank to intermediate grinding operations after the initial or original grinding operation, and eliminates cracking or chipping of the blank. The latter is directly attributable to the fact that by grinding with fixed diamond particles on the grinding tool the blank is not subjected to vibration, such as is encountered when loose abrasive is employed in connection with a cast iron grinding tool. By utilizing as the grinding medium for a lens blank fixed diamond particles that are bonded or xedly attached to the bodyof the tool, the tool holds its shape for a longr period of time and will grind a large number of lens blanks without the necessity of dressing or refinishing it. The subject method lends itself to cylinder grinding because the operator may use both hands in radially rocking the blank by reason of the fact that it is not necessary to apply with one hand loose abrasive material to the grinding tool.

This application is a continuation of United Statespatent application Serial No. 692,635, filed by me on August 23, 1946 and now abandoned.

The invention is not to be understood as restricted to the precise details set forth since these may be modified within the scope of the appended claim Without departing from the spirit and scope of the invention.

I claim:

That improvement in grinding a glass eyeglass lens blank so that it has on one surface thereof a predetermined diopter curve, which comprises rotating about its axis, and at a speed of between 1250 and 6000 R. P. M. a comparatively Wide, lap type, disc-like grinding tool having a small sized, concentric, circular grinding area contoured to possess said predetermined diopter curve and in the form of a xed annular band Which is substantially the same in Width as the blank and consists of a metallic matrix together with diamond particles only having a mesh size from 60 to and so closely distributed throughout the matrix that when the tool is driven at said speed and said one surface of the blank is rst pressed against the grinding area under a comparatively heavy pressure of approximately 5 to 15 pounds and then under a materially less pressure of approximately 1 pound said grinding area operates initially to grind away said one surface of the blank at an extremely rapid rate and then conditions said one surface of the blank so that it is sufciently smooth and free from deep grooves and scratches to permit it to be directly finish ground, delivering a liquid coolant onto the grinding area, during rotation of the grinding tool at said speed and while the coolant is being delivered grinding the blank' by first manually pressing said one surface of the blank against the grinding area under said comparatively heavy pressure and until said one surface has acquired the diopter curve of the tool and then manually pressing said one surface of the blank against the grinding area under said materially less pressure and for a sufficient length of time to condition it for nish grinding, and after so grinding said one surface of the blank finish grinding said one surface preparatory to polishing.

RALPH LANIUS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Pryor Feb. 12, 1918 Number OTHER REFERENCES The Optical Shop and Counter by A. H. Johnson, published by the Professional Press Inc., Chicago, Illinois, 1934.

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