On lathes — one of the most fundamental machining operations — the cutting tools that remove chips from the rotating workpiece to achieve the required form and dimensions are called turning tools (toolholders). Used on universal and CNC lathes, turning tools play a key role in many different operations such as roughing, finishing, grooving, threading and internal machining.
Structure and Types of Turning Tools
Turning tools generally consist of two main components: the toolholder body and the cutting inserts (carbide inserts or HSS tips) mounted at the tip.
1. External Turning Tools (External Toolholders)
- Roughing and Finishing Tools: Remove material from the outer surface of the workpiece to achieve the required diameter. They can cut by approaching longitudinally or from the face.
- Facing Tools: Remove material from the face perpendicular to the part axis to set the part length and produce a flat face.
2. Internal Turning Tools (Boring Bars)
- Used to machine the internal surfaces of pre-drilled or cored cast parts to achieve an accurate diameter and a smooth internal finish.
- Because their long, slender design makes them prone to vibration (chatter), a suitable bar diameter and cutting parameters must be selected.
3. Grooving and Parting Tools
- External and Internal Grooving Tools: Used to cut circlip, O-ring or locking grooves in the part.
- Parting Tools: Used with narrow, long-form inserts to separate (part off) the finished part from the bar stock.
4. Threading Tools
- Used with inserts of a special angle to cut threads of specific pitches and profiles (Metric, Whitworth etc.) on the outer diameter of the part or inside a bore.
Cutting Tool Materials
- HSS (High-Speed Steel) Turning Tools: Can be reground and reused repeatedly. Thanks to their high toughness, they are preferred on universal lathes and for interrupted cuts.
- Carbide Indexable Insert Toolholders: Offer high cutting speeds and long tool life on CNC lathes and in series production. A worn insert is easily indexed or replaced with a new one.
Correct Use and Technical Recommendations
- Centre Height Setting: The tip of the turning tool must be exactly level with the lathe spindle axis. Setting it too low or too high impairs the surface finish and causes the insert to break.
- Rigidity and Overhang: When clamping the toolholder in the tool post, the overhang should be kept as short as possible. Deflection and vibration both shorten tool life and reduce dimensional accuracy.
- Coolant: Coolant should be applied continuously to the cutting zone to reduce heat and aid chip evacuation