End Mills- In selection and use of end mills, precautions should be observed for best results. A milling machine with ample power should be used. Select an end mill of proper design and mount it with the least possible overhang. The end mill must be sharp, and must run as concentric as possible. Scored, battered, or worn end mill shanks, holder/adaptor holes or shanks, as well as a worn or misaligned machine spindles each can contribute to a lack of concentricity. Non-concentric set-ups lead to premature wear, rough surface finish and excessive oversize cutting action.

Emphasize rigidity of the individual job set up. The best aligned spindle-holder-end mill combination is ineffective if the set up if too light, work insecurely clamped, or improperly supported. Fig. 10 shows various end mill applications.

To determine selection of either a two-flute or a multiple-flute end mill, several basics must be considered:

1, Type of cut
2, Chip space required
3, production rate desired
4, Surface finish required

Two-flute end mills have a greater chip handling capacity than multiple-flute end mills. Two-flute end mills are center cutting. Multiple-flute end mills are available in both center cutting and non-center cutting. An end mill must be center cutting in order to plunge cut.

When two-flute end mills and multiple-flute end mills are run at the same feed rate (inches per minute), multiple-flute end mills may produce finer finished and longer tool life than two-flute end mills, owing to a lighter chip load per tooth. Too light a chip load can cause excessive wear.

Higher production rates may be achieved with multiple-flute end mills because feed per tooth is in direct proportion to the number of flutes, enablingan increase in feed rate.

Roughing end mills can be used in a wide variety of materials and will generally remove more material in less time than conventional heavy duty end mills. Roughing end mills permit the use of heavier feed rates, which will increase production rate and may extend tool life.

A common problem associated with slotting, using end mills, is the leaning slot. Non-perpendicular sides of the slot being milled are attributed to a combination of worn spindle, an end will with excessive projection from the spindle, ro excessive chip load.

The major cause of this condition is deflection of the end mill due to the cutting forces. The resulting slot is tipped so that its sides are not parallel to the machine spindle axis and its location is displaced laterally from the intended position. This condition can be minimized by reducting chip load, using shorter-fluted end mills with short overall lengths, or using end mills with straight or low helix angle flutes.

CLIMB OR CONVERTIONAL MILLING