DEVELOPMENT OF A CAD/CAM PROGRAM FOR SELECTION OF FITS AND TOLERANCES WITH AN APPLICATION TO LIMIT GAUGES

Abstract

In the present work a compute package has been developed to select fits and tolerances, to be used for the design of limit gauges, and to generate a part program for execution on a CNC vertical milling machine.

This package contains three main parts:

The first part contains the logic and information as summari.zed in ISO standards for fits and tolerances. It can be used as a guide for fits and tolerances selection in general.

In the second part plain and threaded limit gauges have been designed as examples using the information and data developeU in the first part.

The third part contains the logic for generating a CNC part program from 2-D drawing created using Auto-CAD (microcomputer­ based CAD system). The tool path is extracted and a file created to contain a complete set of data and instructions for the purpose of manufacturing a part on a STARMILL training vertical milling machine controlled by a personal computer.

The package has been developed using AutoLISP (an implementation of the LISP programming language) and runs through AutoCAD. It can run on an IBM PC or IBM compatible.

The developed package has many advantages. It was designed as menu driven programs to be flexible and easy for use. It makes it easier for ttie designer to select the appropriate fits and tolerances according to the particular engineering application.• It. fills the gap of most CAD systems in specifying