Basics of Turning (Depth of Cut | Feed | Feed Rate | Nose Radius, Nose Angle, Approach Angle)

In this video, we take a closer look at turning. Depending on the generated surface and the direction of feed, that is, whether the turning is performed parallel or perpendicular to the axis of rotation of the workpiece, a distinction is made between longitudinal turning and facing, as well as thread cutting. Furthermore, a distinction can be made between external turning and internal turning.
Depending on the feed direction, the cutting edge has a main cutting edge and a secondary cutting edge. The main cutting edge performs the primary cutting action. Accordingly, there is also a main flank face and a secondary flank face.
The rake angle describes the inclination of the rake face in the axial direction of the turned part. However, it can also incline downward or upward in the radial direction. This angle is referred to as the inclination angle. With a negative inclination angle, the material is not cut at the very tip of the cutting edges, but rather further outward. As a result, the cutting corner is subjected to less stress, and the risk of edge breakage is reduced.
Negative inclination angles, however, are disadvantageous during finishing because the chip is guided by the inclination of the rake face toward the machined surface, which can cause damage. Therefore, a positive inclination angle is recommended for finishing. A positive rake angle can also be beneficial when machining materials that tend to adhere or weld.
The nose angle is formed by the main cutting edge and the secondary cutting edge. The larger the nose angle, the greater the stability of the cutting edge and the lower the risk of edge breakage. In addition, the increased surface area improves heat dissipation and reduces the thermal load on the cutting edge, resulting in a longer tool life.
The corner where the rake face and the flank faces meet is called the cutting edge corner. The cutting edge corner is not sharp but rounded to improve the stability of the cutting edge. The corresponding radius is referred to as the nose radius or cutting edge radius. Large nose radii result in stable cutting edges and allow for high feed rates and large depths of cut, as required in roughing operations. In addition, the large radius improves heat dissipation.
Due to the larger contact area at the rounding with large nose radii, high radial forces can occur, which may lead to vibrations. This then deteriorates surface finish, shape accuracy, and dimensional accuracy. In such cases, a smaller nose radius should be chosen for finishing. Nose radii should be selected to be smaller than the depth of cut in order to achieve a high surface quality. Additionally, the feed rate during roughing should be less than half of the nose radius. For finishing, the feed rate should not exceed one third of the nose radius.
The angle formed during turning between the main cutting edge and the workpiece surface to be produced is called the approach angle kappa. The approach angle affects chip breaking, the forces involved, and consequently the tendency to vibrate. The smaller the approach angle, the longer the cutting edge engaged in the cut, and the better the cutting forces are distributed. Approach angles of 90 degrees or more are required when producing right-angled shoulders.
The approach angle also influences the forces acting on the cutting tool and the workpiece. By decomposing the forces, it can be seen that the normal force of the cutting edge can be divided into an axial component (feed force) and a radial component (passive force). The radial passive force tends to push the workpiece away and causes vibrations. However, the passive force can be significantly reduced by selecting larger approach angles.
Chip breaker steps are grooves incorporated behind the cutting edge of the tool, located directly on the rake face. The chips formed are deflected by these geometries so that they break at regular intervals. In this way, long continuous chips are avoided, and short-breaking chips are produced. Chip breaker steps can have very different geometries.

00:00 Turning
00:21 Turning Processes (Longitudinal Turning)
01:11 Design of a Lathe
01:44 Longitudinal Turning
02:25 Geometry of Turning Tools with Indexable Inserts
03:24 Clearance Angle, Wedge Angle, and Rake Angle
03:53 Inclination Angle
04:59 Effect of the Inclination Angle on Chip Formation
06:42 Nose Angle epsilon
07:17 Nose Radius
08:31 Approach Angle
09:42 Passive Force and Feed Force
11:34 Corner radius, approach angle, and depth of cut
12:07 Wear
13:43 Facing (Face Turning)
14:27 Thread Turning
15:55 Flank Clearance Angle
16:24 Full-profile, partial-profile, and multi-tooth inserts
17:57 Grooving turning
18:32 Parting off
18:42 Profile Turning
09:01 Left, right, and neutral tool holders
19:57 Internal Turning Tools (Boring Bars)
20:26 Form, application, and standardization of indexable inserts (ISO 1832)
23:09 Chipbreaker step