Method and apparatus for engraving characters

Abstract

A method and apparatus for engraving characters by the use of numerically controlled machine tools. The characters are engraved by moving a first machine tool about the outline of the desired character. Where the character has inside corners, a second numerically controlled machine tool is moved about the outline at the inside corner at a plurality of depths to reduce the radius of the curvature at the inside corner.

What is claimed as the invention is: 
     
       1. A method of engraving inside corners of embossed characters with a numerically controlled machine tool device comprising the steps of: providing a rotatably mounted cutting tool having a tapered cutting portion;   rotating said cutting tool;   .Iadd.moving said cutting tool to an apex of an inside corner; .Iaddend.   positioning .[.the.]. .Iadd.a .Iaddend.tip of said cutting tool at a plurality of successive depths with respect to .[.the.]. .Iadd.a .Iaddend.land of said character .Iadd.at the apex of the inside corner.Iaddend.;   moving said cutting tool with respect to the land of said character about .[.the.]. .Iadd.a .Iaddend.desired outline of said character .Iadd.at the apex of the inside corner .Iaddend.so that .[.the.]. .Iadd.an .Iaddend.axis of said tool .Iadd.is moved vertically and horizontally .Iaddend.at each of said depths .Iadd.so that the tool .Iaddend.is spaced from .[.the.]. .Iadd.a desired .Iaddend.borderline of said character a distance equal to .[.the.]. .Iadd.a .Iaddend.radius of said tool in .[.the.]. .Iadd.a .Iaddend.plane of said land of said character;   whereby the radius on said inside corner is reduced to the radius of said tool in the plane of said land of said character when said tip of said tool is at a depth with respect to the land of said character which is the smallest of said successive depths.   
     
     
       2. A numerically controlled device for engraving; said device comprising a pair of rotatable cutting tools mounted closely together, said cutting tools each having a tapered cutting portion, a support member for an engravable member and control means for moving said support means with respect to said cutting tools, said control means causing said cutting tools to follow a desired pattern with respect to said engravable member, the first of said cutting tools having a larger diameter and being moved by said control means for removing large areas of excess material about said desired pattern, said second cutting tool and said engravable member being moved with respect to each other by said control means to remove the excess material at inside corners of said pattern not accessible by said first cutting tool, said cutting tools being positioned by said control means so that .[.the.]. .Iadd.an .Iaddend.axis of each cutting tool is spaced from .[.the.]. .Iadd.an .Iaddend.outline of said pattern in accordance with .[.the.]. .Iadd.a .Iaddend.radius of the cutting tool in the plane of the top surface of the engravable member, said second cutting tool being positioned at a plurality of depths so that the radius at the inside corners of said pattern can be reduced to the radius of said second cutting tool adjacent its tip. 
     
     
       3. The invention of claim 1 and further including the step of placing said cutting tool at .[.the.]. .Iadd.said .Iaddend.apex of said inside corner at the largest depth of said tool with respect to the land of the character and moving said cutting tool both vertically and horizontally towards the apex of .[.the.]. .Iadd.a .Iaddend.desired character so that .[.the.]. .Iadd.an .Iaddend.inside corner of the character is smoothed. 
     
     
       4. A method of engraving embossed characters with a numerically controlled machine tool comprising the steps of: providing a first rotatably mounted cutting tool having a tapered cutting portion;   rotating said first cutting tool;   positioning said cutting tool at a first predetermined depth with respect to .[.the.]. .Iadd.a .Iaddend.top surface of said character equal to .[.the.]. .Iadd.a .Iaddend.depth of said character;   moving said cutting tool with respect to said character about .[.the.]. .Iadd.a .Iaddend.desired outline of said character so that .[.the.]. .Iadd.an .Iaddend.axis of said tool is spaced from .[.the.]. .Iadd.a .Iaddend.borderline of said character by a distance equal to .[.the.]. .Iadd.a .Iaddend.radius of said tool in .[.the.]. .Iadd.a .Iaddend.plane of the top surface of said character;   providing a second rotatably mounted cutting tool .Iadd.mounted adjacent said first cutting tool and .Iaddend.having a tapered cutting portion with a smaller radius than said first cutting tool;   .Iadd.moving said second tool with respect to said character so that said character is disposed below said second cutting tool; .Iaddend.   positioning said second cutting tool at a second predetermined depth intermediate of said first predetermined depth; and   moving said second cutting tool with respect to said character about the desired outline of said character wherein excess material outside said desired outline remains so that the axis of said second tool is spaced from said borderline of said character by a distance equal to the radius of said tool at the top surface of said character.   
     
     
       5. The invention of claim 4 wherein said second cutting tool is positioned at a plurality of successive depths between said second predetermined depth and said first predetermined depth and said second cutting tool is moved at each of said depths about the desired outline of said character with said axis of said second tool being spaced from said borderline of said character by a distance equal to the radius of said cutting tool in the plane of said top surface of said character at each of said depths. 
     
     
       6. .[.The invention of claim 5 and further including the step of.]. .Iadd.A method of engraving embossed characters with a numerically controlled machine tool comprising the steps of: providing a first rotatably mounted cutting tool having a tapered cutting portion;   rotating said first cutting tool;   positioning said cutting tool at a first predetermined depth with respect to a top surface of said character equal to a depth of said character;   moving said cutting tool with respect to said character about a desired outline of said character so that an axis of said tool is spaced from a borderline of said character by a distance equal to a radius of said tool in a plane of the top surface of said character;   providing a second rotatably mounted cutting tool having a tapered cutting portion with a smaller radius than said first cutting tool;   rotating said second cutting tool;   positioning said second cutting tool at a second predetermined depth intermediate of said first predetermined depth;   moving said second cutting tool with respect to said character about the desired outline of said character wherein excess material outside said desired outline remains so that the axis of said second tool is spaced from said borderline of said character by a distance equal to the radius of said tool at the top surface of said character, said second cutting tool being positioned at a plurality of successive depths between said second predetermined depth and said first predetermined depth and said second cutting tool being moved at each of said depths about the desired outline of said character with said axis of said second tool being spaced from said borderline of said character by a distance equal to the radius of said cutting tool in the plane of said top surface of said character at each of said depths; and .Iaddend.   positioning said second cutting tool at .[.the.]. .Iadd.a .Iaddend.center of any excess material remaining and simultaneously moving said cutting tool upwardly and towards the desired borderline of said character so that additional excess material may be removed.   
     
     
       7. The invention of claim 2 wherein said device includes a plurality of said pairs of cutting tools, said support member extending adjacent each of said pairs of said cutting tools so that a plurality of engravable members may be engraved simultaneously. 
     
     
       8. The invention of claim 7 wherein said support members include a plurality of indexing devices and said engravable members comprise wheels having a plurality of engravable platforms about .[.the.]. .Iadd.a .Iaddend.periphery thereof, said indexing devices adapted to rotate said wheels, said indexing devices being caused to rotate by said control means after a character has been engraved in each of said wheels.