1. CHAPTER 6 REFERENCE PLANE DPT 312 METROLOGY ROSHALIZA HAMIDON

2. OVERVIEW  Every linear measurement start at reference point and end at measured point  When we needed an additional reference, we called it a reference surface or plane

3. Flatness and perpendicularity  Flatness, the levelness of a surface, is the degree to which the reference plane corresponds to the theoretically perfect plane  These surface are often called datum plane  In Whitworth time (1903-1887), three plate method is used for generating flatness  Next to flatness, the most important reference is perpendicularity or right angle

4. Modern reference plane  Granite surface plate Provide superior reference surfaces Granite surface plates can be produced to flatness that we measure in millionth of an inch at comparatively low prices when compared with cast iron and steel reference surface Characteristics  Do not rust or corrode  Absorb so little moisture  Great thermal stability

5. Care and Maintenance  Keep the surface clean and free from buildup of dust, dirt, grease etc.  Do not use granite surface plate as workbench or lunch table  Surface plate should be checked regularly for wear  Surface plate should be calibrated on an established timetable, depending on the frequency of use

6. Care and Maintenance (cont’) Following these rules will extend the life of surface plate