Metric mechanical and electronic travel indicators can also be used. The mechanical dial travel indicator (Figure C-48) uses a roller that contacts a moving part of the machine tool. Travel of the machine component is indicated on the dial. This type of travel indicator discriminates to .01 mm. Wheel. Mechanical dial travel indicators are used in many applications such as reading the travel of a milling machine saddle and table (Figure C-49).
The digital electronic readout or DRO (Figure C-50) uses a sensor attached to the machine tool. Machine tool component travel is indicated on an electronic digital display. The equipment can be switched to read travel in inch or metric dimensions.
Metric conversion devices can be fitted to existing machine tools for a moderate expense. Many new machine tools, especially those built abroad, have dual system capability built into them.