Turning insert grade
The insert grade is primarily selected according to:
- Component material (ISO P, M, K, N, S, H)
- Type of method (finishing, medium, roughing)
- Machining conditions (good, average, difficult)
The insert geometry and insert grade complement each other. For example, the toughness of a grade can compensate for lack of strength in an insert geometry.
Turning insert shape
The insert shape should be selected relative to the entering angle accessibility required for the tool. The largest possible nose angle should be selected to provide insert strength and reliability. However, this has to be balanced against the variation of cuts that need to be performed.
A large nose angle is strong, but requires more machine power and has a higher tendency for vibration.
A small nose angle is weaker and has a small cutting edge engagement, both of which can make it more sensitive to the effects of heat.
Cutting edge strength
(Large nose angle)
- Stronger cutting edge
- Higher feed rates
- Increased cutting force
- Increased vibration
Less vibration tendency
(Small nose angle)
- Increased accessibility
- Decreased vibration
- Decreased cutting force
- Weaker cutting edge
Turning insert size
Select insert size depending on the application demands and the space for the cutting tool in the application.
With a larger insert size, the stability is better. For heavy machining, the insert size is normally above IC 25 mm (1 inch).
When finishing, in many cases the size can be reduced.
How to choose insert size
- Determine the largest depth of cut, ap
- Determine the necessary cutting length, LE, while also considering the entering (lead) angle of the tool holder, the depth of cut, ap and the machine specification
- Based on the necessary LE and ap, the correct cutting edge length, L and IC for the insert can be selected
Turning insert nose radius
The nose radius, RE, is a key factor in turning operations. Inserts are available in several sizes of nose radius. The selection depends on depth of cut and feed, and influences the surface finish, chip breaking and insert strength.
| Small nose radius|| Large nose radius|
- Ideal for small cutting depth
- Reduces vibration
- Weak cutting edge
- Generally better chip breaking
- High feed rates
- Large depths of cut
- Strong edge security
- Increased radial forces
Depth of cut and cutting forces
The relationship between nose radius and depth of cut affects vibration tendencies. The radial forces that push the insert away from the cutting surface become more axial as the depth of cut increases.
It is preferable to have more axial forces than radial. High radial forces can have a negative effect on the cutting action, which can lead to vibration and bad surface finish.
As a general rule of thumb, choose a nose radius that is equal to or smaller than the depth of cut.