US 3522680 A
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Description (OCR text may contain errors)
0 G. M. J. SAROFEEN 3,522,680
EXPANDED METAL FACING FOR A LENS ABRADING TOOL Filed March 23, 1967 FIG. 1. F1G.2.
' mmikvale le\"mml\z\l I I 22 21 20 M: m 9 23 15 F 14 I INVENTOR j GEORGE.M.J. SAROFEEN 15 16 3131! ATTORNEYS" United States Patent Oflice 3,522,680 Patented Aug. 4, 1970 EXPANDED METAL FACING FOR A LENS ABRADING TOOL George M. J. Sarofeen, P.O. Box 188,
Colonial Heights, Va. 23834 Filed Mar. 23, 1967, Ser. No. 625,366
Int. Cl. B24d 17/00 U.S. Cl. 51-358 1 Claim ABSTRACT OF THE DISCLOSURE A replaceable facing for a lens abrading tool fabricated from expanded metal sheeting and having a pressure sensitive adhesive on one side thereof with a removable non-adhesive layer on the adhesive material.
This invention relates to improvements in abrading apparatus and has particular reference to the provision of an improved lens abrading tool having a replaceable expanded metal surface portion.
In general, prescriptive curvatures are applied to ophthalmic lens blanks by rough grinding or generating the approximate desired curvature on a particular side thereof, fine grinding this side to a precise curvature and thereafter polishing the fine ground side to a high degree of optical perfection. The fine grinding or fining operation is commonly accomplished by placing the surface of the lens blank in contact with a cast iron surfacing tool having a surface curvature thereon which is precisely formed to the desired curvature to be reproduced and thereafter applying a slurry containing abrasive particles of a selected size to the tool surface while introducing a controlled pressure and oscillatory motion to either or both the tool and lens blank so as to cause the abrasive particles to abrade the surface of the blank. In this manner the surface eventually assumes the shape of the surface of the tool. The abrasive action of the slurry, during such an operation, causes the preformed surface of the tool to wear away. Eventually enough wear takes place to introduce errors of curvature to the tool surface and, consequently, to the surfaces of the lens blanks generated thereby. For this reason, it has been necessary to carefully gauge the curvature of the abrading surface of the tool before each fining operation. When an excessive amount of wear has taken place, the abrading surface is renewed by a well known, time-consuming and costly tool truing operation. On the average, the tool must be trued after each 3 or 4 grinding operations. Eventually the tool can no longer be trued and must be replaced.
It has been known to apply replaceable facings to abrading tools. For example in U.S. Pat. 2,886,923 21 facing of interwoven metallic wire strands is utilized. The interwoven strands are such as to permit the strands to shift laterally relative to each other. Such shifting often results in wide gaps between adjacent strands and bunching of strands which can introduce errors of curvature in the lens blank and even result in wearing of the tool surface.
To overcome this difliculty, the interwoven metallic wire strands are subjected to a process wherein a lacquer or shellac is applied at selected locations for adhering intersecting strands of the interwoven wire as shown for example in U.S. Pat. 3,225,495. Obviously, the additional treating process adds to the overall cost of operation. How ever, a more important disadvantage is that the lacquer or shellac bond react with the water and aluminum oxide slurry causing the bond to be destroyed and in effect, leaving an unbonded, interwoven mesh. Also, the bonding of the interwoven mesh restricts lateral shifting of the strands. While too much shifting? is a disadvantage some shifting of strands is desirable to allow forming of the facing over the curved tool surface.
The present invention, therefore, is intended to overcome the above-mentioned difiiculties and other limitations inherent in present-day lens surfacing techniques through the provision of novel replaceable facing for the abrading surface of a lens surfacing tool of the types which, when applied to the surface of the tool, will accurately assume the preformed shape of and become the effective abrading face of the tool Without being subject to loosening of its mesh pattern or bunching thereof or the deleterious effects of the abrading slurry.
Another object of the invention is to provide inexpensive detachable and disposable grinding face portions for a lens surfacing tool which may be simply and rapidly attached to or removed from the tool, simply shaped to the preformed surface of the tool and which will protect and preserve the preformed surface thereof during the abrading operations and thereby eliminate the heretofore age-old expensive and time-consuming tool truing operations.
Another object is to provide a protective disposable expanded metal facing for a lens grinding tool of the above character which, because of its give in either direction, will be substantialy self conforming to the surface shape of the tool when applied thereto and will more uniformly distribute the abrasive medium during the abrading operation.
Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings in which:
FIG. 1 is a top plan view of a lens surfacing tool embodying the invention;
FIG. 2 is a side elevational view of the tool shown in FIG. 1;
FIG. 3 is a perspective view of a sheet of grinding facing embodying the invention;
FIG. 4 is a fragmentary sectional view of 'one type of a grinding facing embodying the invention;
FIG. 5 is a diagrammatic fragmentary side view of a lens surfacing apparatus illustrating a particular use for a grinding tool of the type embodying the invention; and
FIG. 6 is a fragmentary sectional view similar to FIG. 4 illustrating an alternative type of facing and attachment means embodying the invention.
Referring more particularly to the drawings in which like reference characters represent like parts throughout the several views thereof, the device embodying the invention comprises a lens surfacing tool 10 having a body portion 11 formed of cast iron. or any other suitable shape-retaining material having a curved surface 12 on one side thereof shaped substantially to the curvature desired to be formed on one side of a lens blank and a wire mesh facing 13 detachably secured thereto.
The exposed surface of the facing 13 serves as the abrading surface of the composite surfacing tool 10. This, of course, differs from the conventional surfacing tool which performs the lens abrading operations directly upon the curved preformed surface 12 of the tool the action of which unavoidably causes a wearing away of the tool surface and, after continued use, introduces errors of curvature and other deformities in the resultant finished surfaces of the lens blanks being abraded thereby.
In an attempt to avoid the well-known time-consuming and costly surface truing operations common to the trade, metal sheet-like replaceable coverings or facings of interwoven construction or the like have been used to protect the abrading surface of the tools. In practice it has been found that the interwoven strands are subject to severe lateral displacement and when the strands are bonded to overcome this displacement, they are not readily conformable to the various degrees of curvature required in the trade, particularly when constructed of a thickness and/or durability sufficient to withstand at least one abrading operation. In this case, the problem of conformability has, of course, led to the production of inferior lens surfaces caused primarily by bunching or separation of strands or stretched areas in the wire mesh covering, which unavoidably occur while attempting to fit the foil to the abrading tool.
With this in mind, I have found that expanded metals overcome all previously known disadvantages of wire mesh facings 13, particularly the interwoven type. An expanded metal facing can readily be formed to the smooth curved surface of the abrading tool because of its expandibility and compressibility in any direction so that the overall facing 13 precisel conforms to the shape of the surface to which it is applied.
A soft copper expanded metal mesh of approximately 25 strands per inch with a wire size of approximately .007 inch has proven, for all pracitical purposes, to produce the most satisfactory results both from a standpoint of durability and conformability. There are no synthetic bonds and the diamond shaped grillwork may be die punched from flattened sheets. However, other combinations of wire sizes, mesh structures or types of wire such as bronze, nickel, steel etc. may be used. For example, the perforations may be hexagon shape. Die punched hole patterns and slits can also advantageously be used. The important characteristic of the material is that it is capable of yielding or expanding in all directions.
Since the wear, normally incurred upon the abrading surface of the conventional cast iron surfacing tool, will, in the case of the present invention, take place upon the abrading surface of the facing 13, it is essential that said facing be of a readily replaceable and disposable type which may be simply, efficiently and quickly attached to or removed from the surface of tool 10. In this respect, the metal facing 13 has proven to be of a durability sufficient to outlive the wearing effect of at least one lens surfacing operation while accurately producing the resultant surface of a lens blank being abraded thereon. Although a single facing 13 may be repetitively used, to avoid the possibility of introducing distortion to the resultant lens surfaces being formed, it is most practical to replace the facing after each surfacing operation.
With regard to the matter of attaching the facing 13 to the surface of tool 10, this may be accomplished in the manner shown or described in US. Pat. 2,886,923. Preferably however, one side of the facing 13 is provided with a pressure sensitive adhesive by which the facing is adhered to the surface of the abrading tool.
FIGS. 3 and 4 best illustrate one preferred form in which an expanded metal facing 13, initially in sheet-like form, is provided on one side thereof with a thin layer 14 of any one of many commercially available adhesives. The outer side of the adhesive layer is preferably provided with a removable protective latex or other suitable treated layer 15 of paper, cloth or the like. The layer 15 is removed or stripped just prior to securing the facing to the tool. Layer 15 may be formed on the adhesive layer at the time the composite sheet of facing is fabricated and facilitates handling and storing as it covers the adhesive material.
In such a construction, the facing 13 is applied to the tool surface by removing the backing 15 and pressing the facing onto the tool with the adhesive layer 14 against the formed surface 12. In pressing the facing 13 against surface 12, the expanded metal facing will accurately assume the preformed shape of the surface due to its flexibility which causes it to give or yield in all directions.
The composite unit may be fabricated in large sheetlike form, to be cut to the approximate contour shape of the surface of the tool as shown in FIGS. 1 and 2, prior to being attached thereto. By so doing, a saving in material is accomplished since no overlapping of the sides of the body portion 11 of the tool is necessary.
It should be readily apparent that although the curved surface of the surfacing tool 10 is illustrated as being convex, the facing 13 may be made to conform to and be applied to concave tool surfaces, and other types of implements are adapted for use in conjunction with the yieldable facing material.
Referring more particularly to FIG. 5, the tool 10 is generally secured to a tool-supporting arm 16 or the like of a conventional lens surfacing machine 17 by a clamp 18. A lens blank 19 having been previously properly attached to a holder 20, is positioned upon the expanded metal facing 13 of the tool 10. An oscillating motion is then imparted in a well known manner to arm 16 while the attached lens blank 19, through suitable alignment retaining means 21 and crank spindle 22, simultaneously describes a path of movement relative to that of the tool 10. The combined movement between the lens blank 19 and facing 13 then produces a scrubbing action on the surface of the blank. An abrasive slurry 23 is applied to the facing 13 between the facing and lens blank. Due to the scrubbing action the surface of the blank is abraded to a point where it assumes precisely the shape of the abrading face of the facing 13.
Referring to FIG. 6 an alternative type of facing is illustrated which utilizes an interwoven wire mesh 24. As previously described one of the difficulties experienced with interwoven mesh is the separation of the strands which is not completely avoided when selected areas are bonded due to deleterious effects of the abrading slurry on the lacquer bonds. 1 have found that by completely covering both sides of the screen with a thin plastic coating which seals all of the openings, the added strength necessary to withstand a single lens surfacing operation is provided.
To this end, the facing 13 has applied to both surfaces in a well known manner thin heat-softenable plastic coatings 25 and 26 the composite unit may be pressed between a pair of dies to force the coating between the strands and form a homogeneous structure which upon cooling will harden and hold the windings together. During the abrading operation, the thin coating 25 adjacent the lens blank is rapidly worn down and the exposed surface of the mesh 24 becomes the abrading surface while the plastic layer serves to maintain the strands intact and prevent unravelling or bunching. It should be apparent, that an expanded metal facing could also be utilized in this embodiment and the usual adhesive could be applied. In the alternative, the facing could be attached by means of a spring-type clamp (not shown) or other suitable clamping means used in connection with the abrading tool.
With the present invention, the surface 12 of the abrading tool 10 is provided at the factory with curvatures of radii so controlled as to compensate for the thickness of the facing 13 to be subsequently applied thereto whereby the radii of curvatures at the abrading surface of the facing 13, when applied to the tool, would be precisely that of the resultant surface desired on the lens blank. The body portions 11 of the abrading tools 10 are either molded directly to the desired shapes through the use of sintered metals or plastics or tooled in the usual manner at the factory.
Subsequent to an abrading operation, a polishing pad is attached to the abrading surface of the conventional surfacing tool and to finish the previously abraded lens blank surface by a polishing operation which is conducted in a manner similar to that of the abrading operation, with the exception of applying a polishing medium to the tool and lens blank rather than an abrasive slurry. In such cases, however, when the face of the tool was directly used in abrading and was provided with the true curve to be reproduced on the blank the thickness of the polishing pad in many instances caused a noticeable change in the resultant radius of curvature of the polished surface formed thereby and also errors of curvature.
The present invention avoids the above-mentioned difiiculties and permits the use of more recently introduced superior types of plastic polishing pads throughout the various ranges of curvatures known to the trade since the abrading facing 13 can be controlled to be of a thickness substantially equal to that of a polishing pad which would subsequently replace the facing during a polishing operation. Moreover, nor errors in curvature due to wear during a previous abrading operation can possibly exist since such wear would be incurred only upon the disposable expanded metal facing 13.
It will be apparent that many modifications will suggest themselves to those skilled in the art as to the details of construction and arrangement of parts shown and described without departing from the scope of the invention as expressed in the accompanying claims. Therefore, it is to be understood that all material set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
1. A lens surfacing tool comprising a body portion having one side shaped to fit within a supporting part of a surfacing machine with which said tool is to be used and its opposed side provided with a surface curvature substantially in conformity with the curvature desired of a 25 surface of a lens to be formed by said tool, a die perforated metal facing overlying and detachably secured to said opposed side of the tool in intimate fitted relation with the surface curvature thereof, said facing perforations being defined by the residual metal of the sheeting so as to be yieldable in all directions to cause the overall facing to conform to the surface curvature of said opposed side of the tool when forced thereagainst whereby said facing when in position of use on said surfacing tool will provide an exposed abrading surface thereon in conformity with the curvature of the surface of the tool to which it is applied and the texture of said exposed abrading surface resulting from the yielded condition of said residual metal.
References Cited UNITED STATES PATENTS 2,281,635 5/1942 Strauss 161-113 2,313,293 2/1943 Weiss 1611 13 XR 2,511,816 6/1950 Shaw 161-113 2,886,923 5/1959 France 51-383 3,144,737 8/ 1964 Faas 51-395 HAROLD D. WHITEHEAD, Primary Examiner US. Cl. X.lR.
2 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,522, 30 Dated Auglst 4, 1970 Inventor(s) George M. J. Sarofeen It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
In the references cited, column 6, "2,313,293" should be 1 2,3l2,293--.
SIENED Aidu $2 EALELR m'qg (SEAL) A VIII-LIME E BOHUYLE? JR g duflewhml fiomissioner of Patents Attesting Office