GlossaryKind of term: Manufacturing termCutting time (main time)
What is cutting time?
Cutting time is the part of the cycle in which the tool moves at feed and removes material; one turning pass at fixed rpm takes t = L / (f × n).
Older process-planning texts call it main time. The short approach and overrun at feed are included, even though no material is removed during them. Rapids, tool changes, loading and unloading fall outside it: they are non-cutting time. In longitudinal turning at constant spindle speed, t = L × i / (f × n), with path length L in mm including approach and overrun, number of passes i, feed f in mm/rev and spindle speed n in rpm; the result is in minutes. In milling t = L / vf, with vf = fz × z × n in mm/min. Example: 120 mm at f 0.2 mm/rev and 1,000 rpm gives 0.6 min per pass.
What does cutting time depend on?
The formula assumes constant spindle speed. With constant surface speed, as in facing or along a profile with changing diameter, n changes with diameter, so you calculate per diameter range or take the time from CAM simulation. The maximum spindle speed caps n, so at small diameters the cutting speed falls below the value chosen. In milling, path length depends on strategy: the same pocket gives a different path with trochoidal milling than with offset clearing. The formulas use programmed feed; on the machine, feed override can make the actual time shorter or longer, and acceleration and deceleration on short moves add to it.
How does cutting time work in practice?
Cutting time can be worked out from the drawing and the cutting data, which often makes it the starting point of a time estimate. On its own it gives too short a cycle time, because non-cutting time comes on top. On a large, simple part cutting time is often the bulk; on a small part with many tools the non-cutting time can be larger. Adding non-cutting time as a flat percentage of cutting time is an estimating convention, and no single percentage fits every type of work.
What is cutting time often confused with?
Cutting time is not machining time: machining time also counts the rapids and tool changes between cuts. Nor is it cycle time, which, depending on the convention, also counts loading, clamping and unloading.
Frequently asked questions
What is the cutting time formula for turning?
t = L × i / (f × n): path length with approach and overrun, times passes, divided by feed times spindle speed. With L in mm, f in mm/rev and n in rpm it gives minutes; at constant surface speed, work per diameter range.
How do you calculate cutting time in milling?
Divide the total cutting path by the table feed vf = fz × z × n. Without CAM you estimate path length from the volume, the width of cut and the number of layers; with CAM it comes from the toolpath.
Is cutting time part of cycle time?
Yes, as one part of it. Cycle time is cutting time plus non-cutting time, such as tool changes, rapids, loading and unloading. Which share is larger depends on the part and the number of tools.