Max chip thickness

​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 h_ex 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, a_p.
3. Peripheral milling at a small radial engagement, a_e/D_e.

 

 

 

For straight edge inserts, chip thickness, h_ex, is equal to f_z when lead angle is 0 degrees. As lead angle, ψ_r, increases, f_z can be increased.

Example:
If the maximum chip thickness, h_ex, is .004 and the lead angle, ψ_r, is 45°, the feed recommendation, f_z, is 1.4 x .004 = .0055 inch/tooth.​

 

 

 

• Best performance is achieved when the lead angle, ψ_r, remains over 30° when using round insert cutters or ball nose end mills at limited depths of cut. This means that the depth of cut should not exceed 25% x insert diameter, iC.
• For larger depths of cut, it is better to use square inserts with a constant ψ_r of 45°.
• The chip thickness, h_ex, varies with round inserts, and depends on the lead
  angle. With low a_p/iC ratios, the feed can be increased considerably in order to raise the chip thickness to a desired level.
• Round inserts have a higher maximum chip thickness capability than straight edge solutions, due to the stronger insert shape and longer cutting length.
 

Example: CoroMill 300 insert geometry E-PL

 

 

 

​The h_ex value varies depending on the cutter diameter and working engagement, the radial immersion of a cutter, a_e/D_c.

When this is smaller than 50%, maximum chip thickness is reduced relative to f_z.

Feed can be increased by the modification value in the table below depending on the ratio, a_e/D_c.

Example:
D_c .787 inch (20 mm) – a_e = .079 inch (2 mm), a_e/D_c = 10%
h_ex = .004 inch (0.1 mm), f_z = .007 inch/tooth (0.17 mm/tooth).