US 3919811 A
A grinding wheel having two sections of different hardness and a periphery with two grinding tracks sloping inwardly towards one another and a groove therebetween for engaging, centering and grinding the periphery of an eyeglass lens forming a facet on said lens located at or near to the front curvature of said lens.
Description (OCR text may contain errors)
United States Patent [191 Hedelin 1 GRINDING WHEEL FOR FORMING A FACET ()N THE PERIPHERY OF AN EYEGLASS LENS  Inventor: Lars Hedelin, Skarnasvagen 5, 182
63 Djursholm, Sweden  Filed: Apr. 25, 1974  Appl. No.: 463,997
 Foreign Application Priority Data Apr. 25, 1973 Sweden 7305793  US. Cl. 51/204; 51/207; 51/284  Int. Cl. B24B 9/14; B24D 7/18  Field of Search 51/204, 206 R, 101 LG,
 References Cited UNITED STATES PATENTS Stern 51/284 X 1 Nov. 18, 1975 Raphael 51/284 Barnett 51/284 Primary E.\'uminerDonald 0. Kelly Attorney, Agent, or Firm-Ulle C. Linton ABSTRACT A grinding wheel having two sections of different hardness and a "periphery with two grinding tracks sloping inwardly towards one another and a groove therebetween for engaging, centering and grinding the periphery of an eyeglass lens forming a facet on said lens located at or near to the front curvature of said lens.
3 Claims, 7 Drawing Figures US. Patent Nov. 18,1975 Sheet 1 of2 US. Patent Nov. l8, 1975 Sheet20f2 3,919,811
GRINDING WHEEL FOR FORMING A FACET ON THEPERIIHERY OF AN EYEGLASS- LENS This invention refers to a method for grinding around the periphery of an eyeglass lens a facet which axially-is located at or near to the front curvatureofuthe lens and a grinding wheel construction for carrying-out the method. 1
The methods hitherto known to obtain such facets are mechanical and involye complicated manual opera tions especially when very curved lenses are to be provided, with such facets. I
The main object of the invention thus resides in ob: taining a fully automatical niethodenabling the opera tor to grind a facet which follows the front curvature of the lens independent of the thickness of the lens and the curvature thereof.
To obtain these and other objects the invention is carried out in accordance with the claims.
In the drawing a preferred embodiment of the invention is illustrated by means of schematical views.
FIG. 1 is a section through a lens and an active part of two grinding wheels for grinding the facet, at an early stage of grinding.
FIG. 2 is a similar section but illustrating the end stage of the grinding operation FIG. 3 is a similar section showing the grinding wheels and the finished lens separated FIG. 4 is a view similar to that of FIGS: 1 3 but illustrating the grinding of a so called mini -facet, in an initial locating stage of grinding FIG. 5 shows the parts in a second locating stage and FIG. 6 shows the parts in the final locating stage FIG. 7 shows in its upper part a minifacet-grinded lens and in its lower part the composite grinding wheel for carrying out the grinding operation.
According to the invention the axial localisation of the facet is carried out automatically in that the lens is continuously guided relative to the grinding wheel as sembly comprising two grinding sections in the axial di rection thereof as a consequence of different grinding capacities of the grinding wheel parts which generate the different facet surfaces. Said difference in grinding ability is obtained by a careful matching of the amount of grinding particles such as diamond powder and the binding medium between the two grinding wheel sections.
In FIGS. 1 3 inclusive, a facet grinding of a lens is schematically illustrated. According to this embodiment of the invention the grinding wheel assembly comprises two coaxial grinding wheels 1, 2, which are arranged in a face to face relationship upon the same driving shaft. Each grinding wheel has a sloping grinding surface 3, 4 for generating the facet surfaces 5, 6 of the lens 7. The grinding wheel 1 is made up in such a way that it will have a lower grinding wheel 1 is made up in such a way that it will have a lower grinding capacity than the grinding wheel 2. To this end said wheel I has a relative grain density of approximately 115 150 71 whereas the wheel 2 has a grain density of approximately 70 7c. The grinding grains may consist of a mixture of diamond grains and grains of carbide or oxide types. When a high percentage of another mate rial than diamond, for example carbide grains is chosen the relative hardness of the bonding in the grinding track should also be higher. Best suited as bonding media are metal alloys with a base consisting of FE,
. wheels or both l ens and grinding wheels easily movable in an axial direction the facet point 8 will be axially located in deipendance of the, relation between the amount of glass 9* that the left grinding track 3 has ground awayand'the amount 10 which th'eright grinding track 4 has ground away during the same time. The facet surface 5 will by this arrangement constantly be narrower than the facet surface 6 so that the point 8 of the facet will be located closer to the front curvature ll of the lens tharito the inner, rear curvature 12.
In most cases the face t surfaces form therebetween an angle of When lenses thicker'than 3mm are to be provided with facets a special facet design, named mini-facet is used. In such mini-facets the width of the facet is limited to three mm and the rest of the lens is ground cylindrical. To obtain facets of this kind the arrangement according to FIGS. 4 7 is used. As appears from FIG. 4 the left hand grinding wheel 13 has a surface 14 which is inclined relative to the horizontal reference plane in the drawing about l.5 -2 the lower portion being located to the right in the drawing. The facet grinding surface of wheel 13 is designated 15. The right hand grinding wheel 16 has also a surface 17 which is inclined 1.5- 2 relative to the horizontal reference plane the lower portion being located at the left in the drawing. The facet grinding surface of wheel 16 is designated 18. Furthermore the surface 14 of the left hand grinding wheel has a diameter which is somewhat bigger (preferably 0.4 0.5 mm) than that of the surface 17 of the right hand grinding wheel. By these measurements it is insured that the facet on such a lens will not be located at the middle of the lens or near to its rear side but just at the front curvature 19 as requested.
If the lens first contacts the grinding surface 14 of the grinding wheel 13 as illustrated in FIG. 4 the inclination of said surface brings the lens to be displaced to the right and owing to the bigger diameter of said grinding surface the grinding surface 17 is initially out of contact with the lens.
If however the lens according to FIG. 5 initially comes into contact with the surface 17 of the right hand grinding wheel 16 said lens is displaced towards the left owing to the inclination of said surface 17.
In both cases the lens will consequently take the correct position as shown in FIG. 6 and the balance between the ground off amounts of glass insures that the facet will have its correct position entirely independent of the variations in lens thickness from one point to another.
In FIG. 7 the ground off amounts 20 and 21 of each grinding wheel are illustrated and the shape of the ground lens as well as of the grinding wheel assembly is also illustrated.
The grinding of a mini-facet has heretofore been a cumbersome work only possible to be carried out by I specialists but according to this invention the work is carried out fully automatical without any intervening action whatsoever from the operator during the grinding operation. Lenses of varying dippter strength and having thicknesses from approximately 1 mm up to for instance 12 mm may be automatically grinded. The axial guiding of the lens relative to the grinding wheels in a dynamically balanced grinding operation is therefore of utmost importance. The grinding wheel assem bly may consist of one single wheel with two grinding 3 tracks or two separate grinding wheels.
1. A grinding'wheel for grinding around the periphery of a relatively thick eyeglass lens a facet which is axially located at or near to the front curvature of the lens comprising two grinding tracks for grinding the facet, one of said tracks having a higher grinding capacity than the other track, said lens and said grinding track being mounted floatingly in axial direction relative to each other said grinding tracks being situated on the periphery of at least one grinding wheel. said grinding wheel being profiled to generate at least one of the facet surfaces and that said wheel has a first slightly sloping peripheral conical surface which continues to a second sloping surface, said wheel having a groove between said sloping surfaces. said first sloping surface 4. being capable of guiding the lens into said groove for forming the facet.
2. A grinding wheel construction according to claim 1 wherein the diameter of said first slightly sloping surface, of said wheel having the less grinding capacity somewhat exceeding the diameter of the corresponding part of the other sloping surface of said grinding wheel.
3. A grinding wheel construction according to claim 1 wherein said grinding wheel is composed of two grinding wheel sections, one wheel section has a grain density of l 15 to 150% and the other grinding wheel section, has a grain density of 25-70% and a hardness of its bonding material about lO-SO7c higher than that for the first-mentioned grinding wheel section.