In turning operations, the difference between a perfect part and a scrapped workpiece often lies in the geometry of the cutting tool. Whether you are using a solid high-speed steel (HSS) bit or a modern indexable tool with carbide inserts, knowing the anatomy of your tool is essential for troubleshooting and optimization.
Each part of the tool serves a specific mechanical purpose in the metalworking process.
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1. The Shank: The Foundation of Stability
The shank is the main body of the tool that is clamped into the toolpost.
- Function: It must be rigid enough to withstand the immense cutting forces without bending or vibrating.
- Maintenance: Ensure the shank is clean and free of burrs to maintain a precise center height relative to the workpiece.
2. The Face (Rake Face): Where the Magic Happens
The face is the top surface of the tool over which the swarf (chips) flows.
- Rake Angle: The slope of this face is called the rake angle. A positive rake angle reduces cutting force and heat but makes the edge sharper and more fragile.
- Chip Control: In modern carbide inserts, the face often features a complex chipbreaker geometry to curl and break chips into manageable “6” or “C” shapes.
3. The Flank and Clearance Angles
The flank is the surface of the tool that faces the workpiece during the cut.
- Clearance (Relief) Angle: To prevent the tool from rubbing against the finished surface of the workpiece, the flank must be ground at a clearance angle.
- Impact: Insufficient clearance causes friction, leading to chatter and poor surface finishes.
4. The Cutting Edge and Nose Radius
The cutting edge is the line that actually performs the shearing of the metal.
- Nose Radius: This is the rounded tip at the intersection of the side and end cutting edges. A larger nose radius improves the surface finish and increases tool strength but can increase the risk of vibration in thin workpieces.
- Side Cutting Edge Angle: This determines how the tool enters the cut, influencing the thickness of the chip.
5. The Base and Heel
The base is the bottom surface of the shank, while the heel is the curved portion at the bottom of the tool head.
- Alignment: The base must be perfectly flat. If the base is uneven, the tool will tilt, changing the effective cutting angles and compromising the engineering tolerances.
Next we give a guidance for the choice of bigger rake angle and smaller rake angle for you:
| Value Selection | Situations |
| Small rake angle | 1. When machining brittle and hard materials 2. When roughing and interrupted cutting |
| Big rake angle | 1. When machining plastic and soft materials 2. When finishing |
A. Effects of clearance angle
The main function of the clearance angle in machining is to reduce the friction between the tool flank and the machined surface. When the rake angle is fixed, the increase of the relief angle can increase the sharpness of the cutting edge, the cutting force is reduced, and the friction is reduced, so the machined surface quality is high; however, the excessive relief angle reduces the strength of the cutting edge, poor heat dissipation, and wear The amount is large, so the tool life is reduced.
The principle of rear angle selection is: in the case of less severe friction, choose a smaller rear angle.
Here we give a guidance for the choice of bigger clearance angle and smaller clearance angle for you:
| Value Selection | Situations |
| Small clearance angle | 1. In order to increase nose strength when roughing 2. When roughing and interrupted cutting |
| Big clearance angle | 1. In order to reduce friction when finishing 2. When machining materials easy to be hardened |
B. Effects of inclined angle
The positive or negative edge inclination determines the direction of chip discharge, and also affects the strength and impact resistance of the tool tip.
As shown in the figure a. below, when the edge inclination angle is negative, that is, the tool tip is at the lowest point relative to the bottom plane of the turning tool, and the chips flow to the machined surface of the workpiece.
Reducing the main declination angle can improve the strength of the tool, the heat dissipation condition is good, and the roughness of the machined surface is small. This is because when the entering angle is small, the cutting width is long, so the force per unit cutting edge length is small. At the same time, reducing the entering angle can improve the life of the tool.
Usually, when turning slender shafts and stepped shafts, choose a 90° entering angle; when turning on the outer circle, end face and chamfering, choose a 45° entering angle.
Increase the main declination angle, the radial component force is reduced, the cutting is smooth, the cutting thickness is increased, and the chip breaking performance is good.
Below we have a guidance for the choice of bigger approach angle and smaller approach angle for you:
| Value Selection | Situation |
| Small approach angle | For those materials with high intensity, high hardness and hardened layer on the surface |
| Big approach angle | When rigidity of the machine is not enough |
The secondary declination angle is the main angle that affects the surface roughness, and its size also affects the tool strength. Too small secondary declination will increase the friction between the back of the secondary and the machined surface, causing vibration.
The selection principle of the secondary declination angle is that a smaller secondary declination angle should be selected under the conditions of rough machining or without affecting friction and vibration; a larger secondary declination angle can be selected during finishing.
E. Nose radius
The radius of the tool nose arc has a great influence on the strength of the tool nose and the roughness of the machined surface.
The radius of the tool nose arc is large, the strength of the cutting edge increases, and the wear of the front and flank surfaces of the tool can be reduced to some extent. However, when the radius of the tool nose arc is too large, the radial cutting force increases, and vibration is easily generated, which affects the machining accuracy and the surface roughness of the workpiece.
Below we can see the difference between a bigger nose radius and a smaller nose radius:
| Value Selection | Situation |
| Small nose radius | Finishing at small cutting depth Machining parts such as slender shaft When the rigidity of the machine is not enough |
| Big nose radius | When roughing/When machining hard materials(intermittent cutting) When the rigidity of the machine is good |
Take TNMG1604 CNC turning insert as an example: when you need to finish at smaller cutting depth, you may choose TNMG160404, and you may use TNMG160408 or TNMG160412 when for roughing.
If you’re new to CNC turning and don’t know much about the components of a turning tool, choosing the right type of tool to use with your lathe can be problematic. However, instead of worrying about how much you have to know, hire the services of professionals in this field. At UKO, we have engineers and R&D teams with many years of CNC machining experience who understand the different types of lathe cutting tools and their applications. By choosing us, you gain years of experience and an attitude towards quality delivery. Please contact us. We are always at your service!
