The same general practices of machine tool maintenance, fixturing and rigidity of tool setup recommended for turning apply equally well for milling. Short tool extensions and properly adjusted machine tools are essential to good performance.

To avoid chipping, several techniques can be employed. Milling a short distance at the exit side of the part before starting the cut is very effective in avoiding breakout, just as chamfering the end of a cylinder is for turning. Lowering feed-rates will lessen chipping upon exit, but directly affects productivity. Tool rotation can be used to lessen exit edge chipping for flat surfaces by using climb milling rather than conventional milling passes. Elimination of “up” milling rotation for contour milling will generally adversely affect tool life and is not recommended.

The advent of high-speed milling centers with CNC controls creates the best circumstances for use of diamond-coated end mills. Multiple fluted-coated end mills allow maximum use of the higher spindle speeds without sacrifice to wear, while unattended profiling can be used to maximize productivity results.

Always use square end mills with a small radius. Diamond tools are very brittle and sharp corners will break upon entry into a cut. A 0.010-0.015″ corner will greatly strengthen the tool, providing extra durability.

Always use cutters with the most flutes possible for the machining conditions. Roughing at high feedrates usually dictates using only two flutes. Economics dictate use of four flutes because the cost for a diamond-coated end mill is the same, regardless of flute count. Improved surface finish always results from multiple flutes.

Starting conditions for milling vary considerably for graphite, but generally 2,000 spm and 0.004 inches per flute per revolution is a conservative starting point.