Milling, Turning and Drilling Time

Estimating machining time

At constant feed, cutting time is total feed travel divided by feed rate. For milling, use the actual tool centre path. For longitudinal turning, multiply feed per revolution by spindle speed to obtain axial feed rate. The same relation applies to drilling. At 100 mm per minute, a 20 mm hole depth plus 5 mm allowance takes 15 seconds. Four identical holes need one minute of cutting time.

Cutting time and cycle time

The drill point, breakthrough allowance and approach motion can change total feed travel. Obtain these distances from the operation plan. Loading, tool changes, rapid returns, peck retractions and dwell require additional time. The auxiliary input is the total for the entire job and is added only once. Calculate operations with different lengths or feed rates separately before adding their times.

Checking units and repetitions

Do not confuse feed rate with cutting speed. Time here depends on travel along the machining path per unit time. For turning and drilling, multiplying feed per revolution by spindle speed gives that rate. Feed per tooth is not an equivalent input.

For example, a milling path is 80 mm with 10 mm of additional feed travel at 180 mm/min. One pass takes (80+10)/180 = 0.5 minutes, or 30 seconds. Three identical passes give 1.5 minutes of cutting time. Adding 30 seconds of auxiliary time for the entire job gives 2 minutes total. Do not multiply auxiliary time by three again.

The allowance in this example is travelled at feed speed. Applying the same speed to a rapid approach distance may be inappropriate. Assess other motion types separately and enter their total auxiliary time. For unequal passes, separate operation calculations are easier to trace than an average path. Before using the result for capacity planning, confirm that loading and inspection times are actually included.