US2932138A - Method and apparatus for manufacturing precision lenses - Google Patents

Description

April 12, 1960 E. E. FLUSKEY ETAL' 2,932,138

METHOD AND APPARATUS FOR MANUFACTURING PRECISION LENSES Filed Nov. 10, 1958 F IG.3J8. 3 %I It L FIG. 2. 2O

26 x 16 l -\i 24 Z2 30 an 12 FIG. 5. 5a

56 INVENTORS $331 31? LENS EDWARD E. FLU SKEY HUBERT U. BRUECKNER BY fa/ ATTORNEY METHOD AND APPARATUS FOR MANUFACTUR- llNG PRECISION LENSES Application November 10, 1953, Serial No. 772,942

1 Claim. (Cl. 51-209) v This invention relates to an improved means for grinding and polishing lenses to the extremely close tolerances required in optics and in the manufacture of precision instruments. More particularly it relates to novel lapping devices provided with a means for altering the curvature of the lapping surface to compensate for the unequal wear which is characteristic of known lapping devices and to restore the lapping surface to the precise size and configuration required for the production of the desired lens surface curvature.

In presently practiced methods of grinding and polishing lenses, one or more lenses is secured in a blocker by means of pitch or other adhesive material, as described for example in United States Patents 689,933 and 2,582,087.

When convex lenses are being ground or polished the single lens or blocker is mechanically rotated under a grinding or polishing lap which has been made to approximately the same radius of curvature as that desired on the finished lens or lenses. The lap is charged with an abrasive such as Carborundum, emery, precious stone dust or rouge, suitable for the type of glass employed, while the lap under pressure, is oscillated over the spherical surface of the lens or lenses being either ground or polished.

When concave lenses are being ground or polished, the process is identical to the method described above, with the exception that the lenses are placed over and above a suitably curved lap under pressure and oscillated over the surface of the lap, which is rotating at a suitable speed.

In the grinding or polishing operation the surface of the lens is altered in the desired fashion by the action of the abrasive. At the same time the surface of the lapping tool, even when made of such durable material as the cast iron known as Meehanite, is found to experience an undesirable change in shape due to the uneven wear inherent in the process. In the grinding or polishing of convex lens surfaces, wear of the lapping tool is greatest along the periphery of the tool face and least at the center of the lapping head. In shaping of lenses of concave shape the wear experienced is also greatest along the periphery of the lapping surface and in both instances this is inherent in the process and does not depend on the specific shapes or specific materials involved.

In precision optics, lenses are ground to Newtonian bands (1 light band is approximately 0.0000116 inch), and hence the accuracy of the contour of the lapping surface is of primary importance.

As grinding and polishing of lenses is presently practiced, skilled craftsmen known in the optical trade as lens grinders or lens polishers who from long years of training and experience have acquired an ability to correct or compensate for lap or tool wear must intermittently correct the lapping surface to maintain the precise accuracy of radius of curvature required in the finished lens.

States Patfi Ice] Since configuration of the lap is produced by precise and expensive processes it is necessary that the laps must be used to the fullest possible extent in order to permit the required economy of operation for competitive operation. Therefore, in practice, it is usually necessary to cut down any high spots which develop in use so as to restore the surface of the lap to the desired curvature, so that the lap may be reused.

The usual method of lap or tool correction is for the skilled technician to lap the surface requiring correction, by holding the same over a rotating cast iron block of a similar curvature and to laboriously lap with a suitable abrasive until the correction of curvature is obtained. Another method is to rotate the lap requiring correction, and to use a hand tool to cut away at the radius until the desired curvature is obtained. Since these corrections are pursued on a trial and error basis, by the skilled technician, they are very time consuming and require his absence from the lens grinding or polishing machine with a consequent loss of productive output.

In order to minimize this serious and repetitive production loss, we have invented a lap which has incorporated into the same, a means by which the lens grinder can make the minuscule corrections required without suffering the dual production losses entailed by his absence from his production machines and the laborious hand cutting or lapping previously required under prior art arrangements.

One object of the present invention is to provide a means whereby the contour of the lap may be restored to the precise curvature desired without recourse to the laborious cutting operations heretofore practiced.

Another object of the present invention is to provide a means whereby the extent to which the curvature of the lap is altered may be readily controlled by the lens grinder.

Still another object of the present invention is to provide a means whereby the curvature of the lapping surface may be either increased or decreased an amount directly related to a scale carried on the means for adjustment.

These and other objects will become more apparent from the following description and drawings in which:

Figure 1 is a view of the concave lap of Figure 2 as seen from the top;

Figure 2 is a front elevation, shown partly in section taken along line 22 of Figure 1;

Figure 3 is a view of the lap of Figure 2 as seen from the bottom;

Figures 4, 5 and 6 are similar views for a convex tool or lap, and

two flat portions 13 to facilitate the adjustment of the curvature of the lap as later described.

Body portion 14 is defined by a working face 16 possessing the curvature to be imparted to the lens or lenses to be ground and extending from a crown 18 at its center to a rim 20 at its periphery and by an opposite face 22 which comprises an arcuate portion extending from shank 12 to a circle of a maximum diameter 24 and terminating in a threaded peripheral band 26 between rim 20 and circle 24.

I tion.

A plurality ofslits 30 extend radially inwardly from the threaded band to a point on the inner working surface intermediate of the crown 18 and the peripheral rim 20. Slits 30 are cut through the body portion 14 so as to extend from the working surface 16 to the opposite surface 22 of the body. In the embodiment shown, these slots were formed by drilling eight holes in the lap distributed symmetrically about a central axis and then sawing the slits 30 outwardly to the threaded periphery. A greater or lesser number of slits may be employed depending on the amount of flexibility it is desired to add to the natural resilience of the cast iron tool.

A compensating ring 32 having an annular shape is threaded onto the threaded portion of the lap body. One surface of the ring 32, carries a scale 34, which is adapted to cooperate with an indexing means 36 on the lap body. An arrow is shown in Figure 1 for this purpose. For even finer adjustment, a Vernier could be substituted for the arrow 36. Other indexing means may be employed or the scale and pointer may be interchanged, if desired without departing from the intended scope of the inven- Two flats 38 are provided to receive a wrench or spanner, when adjusting the lap.

In Figures 4-6 corresponding portions of the convex lap shown have been given identifying primed numerals,

corresponding to the unprimed numerals for Figures l-3.

In Figure 7 there is shown in greatly exaggerated form and for purposes of illustration, the progressive wear experienced by a lap in actual service. As noted above the wear inherently increases progressively from a minimum at the crown to a maximum along the periphery of the lap.

Our novel lap is manufactured by casting a suitable shape and finishing it to the desired contour in the usual manner. Thereafter a thread is out along the rim, and radial slits are sawed in the lap body as shown. The device is assembled after complementary threads have been cut in the ring 32.

By means of the structure described above it is possible for the lens grinder to alter the radius of curvature of the working face of the lap by minute amounts in a precise and determinable manner and the following explanation illustrates one specific combination found suitable for achieving the desired result.

One typical lap formed in accordance with our invention had the following dimensions:

Radius of curvature-0.8950 Number of slots8 Threads-40 threads per inch Angle of thread-1 The major outside diameter of lap 10, ringportion 26, was threaded40 threads perone inch being selected only for purposes of illustration. The thread was cut on a one degree taper in relation to its horizontal axis. Compensating ring 32' was also provided with a similar pitch thread, at the same common angle. To adjust the lap for size, it was placed in a fixture adapted to receive shank 12 and the two flat portions thereof, which prevented rotational movement of the shank and body portions.

The compensating ring was then rotated by means of a wrench or spanner laid across flats 38, to either diminish or increase the radius of curvature, according to the direction of rotation.

Arrow 36 and scale 34 permit the operator to gage the amount of expansion or contraction of the lap.

It will be readily appreciated that the amount ofv di-. ametral contraction or expansion is one-half of the prod net of the pitch (expressed in inches) multiplied by the tangent of the angleof taper.

With a linear pitch of 0.025 inch with an angle of 1' (taper), the product of the two factors is 001745 X0025 or 0.00043625 inch. The diametral movement is twice this or 0.0008725 inch.

The amount of change in diameter of the lap for each graduation on scale 34, depends on the number of gradnations. If one hundred and twenty graduations are provided, each corresponds to 3 degrees of are. With a rotation of 3, the diameter. of the lap is changed 0.0008725" divided by or 0.00000727 inch which is a little more than half of a Newtonian band.

As a practical matter, the choice of pitch and angle is dictated by the size of the lap or tool and it should be evident that other combinations of thread and taper could be used without departing from the scope of the present invention.

While we have described a preferred form of device for precisely adjusting the contour of a resilient lap produced in accordance with our invention, it will be apparent that other means such as expanding Wedges, eccentrics, cams and other diverse forms could be employed to achieve the desired result and such means are intended to be comprehended as within the scope of our invention.

We are aware of prior art efiorts to adjust the radius of curvature of a lap by means located along the central axis of the lap, but such adjustments are not uniform for a uniform amount of rotation and are not adapted to the'precision obtainable with the circumferential adjusting means constituting the present invention.

Having now described our invention in accordance with the patent statutes, we claim:

An adjustable lap for manufacturing precision lenses which may be adjusted to compensate for wear without the necessity of lapping or remachining to restore said lap to its original size or magnitude of curvature, said lap consisting of a shank portion extending between a terminal portion adapted to be received in a chuck on a driving mechanism and joined at its other extremity to a generally cup-shaped body portion integral therewith comprising a working face and another face, the working face extending arcuately from the central axis of the lap to. a circular rim constituting the lip portion of said cup; the other face having an arcuate configuration corresponding generally to the configuration of the working face and extending from the junction of the shank portion and the cup-shaped body portion toward the lip portion of said body; a plurality of slots extending through the body portion of said lap radially disposed about the central axis of said lap; time pitch tapered threads bridging the surface of said lap between the lip of the body portion and the maximum diameter portion of the other surface of said lap; a compensating ring bearing fine pitch threads mating with the said tapered threads on said lap; a scale and index means located each on one of said compensating ring and said lap body, where by the amount of relative movement between said body and said ring may be precisely controlled and the adjustment in the curvature of said working face may be precisely effected in terms of said graduations to compensate for wear.

References Cited in the file of this patent France May 12,

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