Size of a Milling Machine
The size of a milling machine is specified as follows
1. The size of the table (length and width)
2. The maximum lengths of longitudinal, cross and vertical travel of the table.
3. Number of spindle speeds, number of feeds
4. Spindle nose taper
5. Power required
6. Nett weight of the machine
7. The floor space required
8. Type of the machine
Fundamental Milling Processes
The various milling processes may be grouped under two headings:
- Peripheral milling
- Face milling
The machining is performed by the cutting edges on the periphery of the milling cutter. It is classified under two headings
- Up milling
- Down milling
In this method, the workpiece mounted on the table is fed against the direction of rotation of the milling cutter. The cutting force is minimum during the beginning of the cut and maximum at the end of cut. The thickness of chip is more at the end of the cut. As the cutting force is directed upwards, it tends to lift the workpiece from the fixtures. A difficulty is felt in pouring coolant on the cutting edge. Due to these reasons the quality of the surface obtained by this method is wavy. This processes being safer is commonly used and sometimes called conventional milling.
The workpiece mounted on the table is moved in the same direction as that of the rotation of the milling cutter. The cutting force is maximum at the beginning and minimum at the end of cut. The chip thickness is more at the beginning of the cut. The workpiece is not disturbed because of the bite of the cutter on the work. The coolant directly reaches to the cutting point. So the quality of surface finish obtained is high. Because of the backlash error between the feed screw of the table and the nut, vibration is setup on the workpiece.
Face Milling and End Milling
During face milling, the machining is performed by the peripheral cutting edges. The surface obtained by the processes is perpendicular to the axis of rotation of the cutter.
End milling is a process of the machining by milling cutters which have cutting edges both on the end face and on the periphery.