Worked examples
Turning. A 100 mm cut at 0.2 mm/rev and 1,000 RPM: feed rate = 0.2 × 1,000 = 200 mm/min, so t = 100 / 200 = 0.5 min (30 s) per pass. Three roughing passes take 1.5 minutes.
Milling. A 300 mm path run three times at 600 mm/min: 300 × 3 / 600 = 1.5 min.
What the number leaves out
- Non-cutting time: rapid moves, tool changes, clamping, measuring and chip clearing often exceed the cutting time on small batches.
- Approach and overrun: add a few millimetres at each end to L, or the estimate is optimistic.
- Acceleration: on short moves the machine never reaches the programmed feed, so the real time is longer than L divided by the feed.
- To plan a job, add the time per part for all passes and operations, then add set-up time divided by the batch size. For the volume side of the same question see the metal removal rate calculator.
Frequently asked questions
How do I calculate machining time for turning?
t = L / (f × RPM): the length of cut divided by the feed rate, where feed rate is feed per revolution times spindle speed. 100 mm at 0.2 mm/rev and 1,000 RPM takes 0.5 minutes.
How do I calculate machining time for milling?
t = path length × passes / feed rate. A 300 mm path run three times at 600 mm/min takes 1.5 minutes.
Does this include set-up and tool changes?
No. It is the time the tool is in the cut. Rapid moves, tool changes, clamping and measuring come on top and can exceed the cutting time on small batches.
Why is the real time longer than the calculation?
Approach and overrun add length, and on short moves the machine accelerates and decelerates without ever reaching the programmed feed.
More free machinist calculators
- Inch to mm – Convert inches to millimetres and back, fractions like 1 3/8 included. Exact factor 25.4, with a chart of every 1/64 inch.
- RPM and feed – Calculate spindle RPM from surface speed and diameter, surface speed from RPM, and feed rate from chip load – metric and imperial, with formulas.
- Taper – Taper ratio, half angle and taper per foot from the large and small diameter and the length, or the small diameter from the angle.
- Bolt circle – X and Y coordinates of evenly spaced holes on a bolt circle, with the hole spacing, start angle and centre offset. Copy the table into your program.
- Sine bar – Gauge block height for a sine bar angle, or the angle from a known stack, for 5 in, 10 in, 100 mm, 200 mm or any other bar length.
- Metal removal rate – Metal removal rate in cm³/min or in³/min from depth, width and feed – milling and turning, metric and imperial, with the formulas.
- Drill point depth – Length of a drill's point cone from diameter and point angle, and the total depth needed for a full-diameter hole to depth.
- Right triangle – Hypotenuse and angles from two legs, or the legs from the hypotenuse and an angle – for chamfers, dovetails, tapers and hole positions.
- Decimal to fraction – Turn a decimal inch or a millimetre value into the nearest fraction – 8ths to 128ths – with the error in millimetres.
- Degrees to DMS – Convert decimal degrees to degrees, minutes and seconds and back, with the angle in radians.
- SFM to m/min – Convert surface feet per minute to metres per minute and back, and inches per minute to mm per minute, with the exact factors.
- TPI to pitch – Convert a thread pitch in millimetres to threads per inch (TPI) and back, for matching metric and inch threads.
- Cpk calculator – Paste measurements from Excel, enter USL and LSL and get Cp, Cpk, Pp and Ppk. Says plainly when 25 values are too few for an index.
- Tolerance stack-up – Add up the tolerances of a chain of parts: closing gap, worst case and statistical RSS for up to eight dimensions. Free, in your browser.
- Fit clearance – Enter hole and shaft limits and get minimum and maximum clearance and the kind of fit – clearance, transition or interference.
- Chip thinning – Feed per tooth to program when the radial width of cut is below half the cutter diameter, so the real chip thickness stays right.
- Ball-nose stepover – Scallop height left by a ball-nose cutter from the stepover, or the stepover for a wanted scallop height, on a flat surface.
- Surface finish – Theoretical Rt and estimated Ra of a turned surface from the feed per revolution and the tool nose radius.
- Torque and power – Torque from power and speed in newton-metres or pound-feet, and power from torque and speed. The formulas with worked examples.
- Spur gear – Pitch and outside diameter, centre distance, ratio and circular pitch of a pair of external spur gears from the module and the tooth numbers.
Making parts for a customer who wants paperwork?
Automotive and aerospace customers ask for proof that the parts match the drawing. See first article inspection (FAI), PPAP explained and the true position calculator.