Parting and grooving formulas and definitions
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In this section you find parting and grooving formulas and definitions for how to calculate cutting speed, feed rate or other parameters that affect the machining in your turning centre, lathe tool or multi-task machine.
Cutting speed, vc
The workpiece rotates at a certain number of revolutions per minute. This provides a specific cutting speed vc (or surface speed) measured in m/min (feet/min) at the cutting edge. Normally, cutting speed is set as a constant value, which leads to variations in rpm as the machined diameter changes.
Feed rate,fn
The tool movement in direction X and Z is called feed rate (fn), or fnx/fnz. When feeding towards centre (fnx), the rotations per minute (rpm) will increase until it reaches the rpm limit of the machine spindle. When this limitation is passed, the cutting speed (vc) will decrease until it reaches 0 m/min at the component centre.
Chip control
The feed has a great influence on chip formation, chip breaking, and thickness, and also influences how chips form in the insert geometry. In sideways turning or profiling (fnz), the depth of cut (ap) will also influence chip formation.
Feed (fn) and depth of cut (ap) have the largest affect on productivity.
| Symbol | Designation/definition | Unit, metric (imperial) |
|---|---|---|
| ap | Cutting depth | mm (inch) |
| vc | Cutting speed | m/min (feet/min) |
| fn | Feed rate | mm/rev (inch/rev) |
| fnx | Radial cutting feed | mm/rev (inch/rev) |
| fnz | Axial cutting feed | mm/rev (inch/rev) |
| n | Spindle speed | rpm |
| OH | Overhang recommended | mm (inch) |
| CDX | Cutting depth maximum | mm (inch) |
| H | Shank height | mm (inch) |
| WB | Blade thickness | mm (inch) |
| δ | Deflection | mm (inch) |
How to calculate cutting speed for parting off
Cutting speed,
vc (m/min)
Cutting speed,
vc (feet/min)
Overhang and deflection, OH and δ
Formula for tool deflection
Overhang and deflection when parting off
Overhang and deflection when side turning
