The first consideration which must be made when Hi-Helix end mills are to be used is selecting the correct one. This choice is based on two considerations: type of material to be cut and available rpms at the spindle.

When starting the end milling operation, the radial and axial depth of cut are usually predetermined according to the part configuration (see figure 1). The metal removal rate will be established by table feed rate. Table feed rate (ipm), is the product of the spindle speed (rpm), feed per tooth (ipt), and the number of flutes (T, teeth), the cutter has, (ipm = rpm x ipt x T).

Inherent to milling machines is that spindle speed is independent of table feed. Thus, the metal removal rate cannot be increased by increasing the rpms. An increase in rpms will, in contrast, decrease the feed per tooth and reduce the chip thickness. If an increase in the metal removal rate is required, the table feed must be increased. This may be achieved in various ways with different effects.

1. Decrease cutting speed (rpm) and maintain table feed. This will increase the chip thickness which directly relates to the feed per tooth and increases the metal removal rate.
2. Increase table feed (ipm) but maintain cutting speed (rpm). This also increases the chip thickness / feed per tooth.
3. Decrease the number of flutes ("T) maintaining cutting speed and table feed. By decreasing the number of flutes this, in turn, will increase the chip thickness and metal removal rate.