Basic Milling Operations

Cutting Speed and Feed Rate
Determining the cutting speeds and feed rates are heavily dependent on the following 8 factors:
1) Type of material to be machined
2) Nature of the heat treatment
3) Rigidity of the setup
4) Physical strength of the cutter
5) Cutting tool material
6) Power available at the spindle
7) Type of finish desired
8) Cutting fluid to be used

Cutting Speeds
The cutting speed of a milling cutter is expressed in surface per minute (sfpm) or meters per minute (mpm) and is the distance that a point on the periphery of a cutter travels in 1 minute at a particular rotational speed. The formula of cutting speed is as shown below:
Cutting Speed, CS= (Diameter (D) ×∏×rpm) ÷12
Where the diameter is in inches
Feed Rates
Several conditions must be considered when choosing the proper feed rate for a milling operation. Two major factors are the number of teeth of the cutter and its strength. The formula to determine feed rate is as shown below:
Feed Rate=chip load × number of teeth × rpm

Types of Milling Operations

Plain Milling
Plain milling is the process of milling a surface that is parallel to the axis of the cutter and basically flat. It is done on plain or universal horizontal milling machines with cutters of varying widths that have teeth only on the periphery.

Side Milling
A cutter that has teeth on the periphery and on one or both sides is used for side milling operation. There are several types of side milling. Straddle Milling and Gang Milling are some example of side milling operations.

Straddle Milling
Two-sided milling cutters are used. The cutters are half-side or plain-side milling cutters and have straight or helical teeth. Stagger-tooth side milling cutters can also be used. The cutters cut on the inner sides only or on the inner sides and the periphery.


Gang Milling
Three or more cutters are mounted on the arbour and several horizontal, vertical and angular surfaces are machined in one pass.

Face Milling
This operation can be done on both vertical and horizontal milling machine. The purpose of face milling is that it produces a flat surface that is perpendicular to the spindle on which the cutters are mounted. The cutters are of varying diameters and complexity.

Contour Milling
Contour milling operations are milling operations done on workpieces with an irregular shape such as connecting rods and pistons.

End Milling
End milling is probably the most versatile milling operations. Many types of end mills can be used on both the vertical and the horizontal milling machines. End mills are available in sizes ranging from 1/32 to 6 inches and are in almost any shape needed.