Maximum chip thickness is the most important parameter for achieving a productive and reliable milling process.
Effective cutting will only take place when this is maintained at a value correctly matched to the milling cutter in use.
- A thin chip with a hex value that is too low is the most common cause of poor performance resulting in low productivity. This can negatively affect tool life and chip formation.
- A value that is too high will overload the cutting edge, which can lead to breakage.
Chip thinning allows for increased feed
Feed per tooth can be increased in the three following situations due to the chip thinning effect when:
1. Using straight edge cutters with lead angles larger than 0°.
2. Using round inserts or large radius inserts at smaller depths of cut, ap.
3. Peripheral milling at a small radial engagement, ae/De.
For straight edge inserts, chip thickness, hex, is equal to fz when lead angle is 0 degrees. As lead angle, ψr, increases, fz can be increased.
If the maximum chip thickness, hex, is .004 and the lead angle, ψr, is 45°, the feed recommendation, fz, is 1.4 x .004 = .0055 inch/tooth.
value varies depending on the cutter diameter and working engagement, the radial immersion of a cutter, ae
When this is smaller than 50%, maximum chip thickness is reduced relative to fz
Feed can be increased by the modification value in the table below depending on the ratio, ae
.787 inch (20 mm) – ae
= .079 inch (2 mm), ae
= .004 inch (0.1 mm), fz
= .007 inch/tooth (0.17 mm/tooth).