Worked examples
Milling. A cut 10 mm wide and 5 mm deep at 600 mm/min removes 10 × 5 × 600 = 30,000 mm³/min, which is 30 cm³/min.
Turning. At 200 m/min, 0.2 mm/rev and a 2 mm depth: 200 × 0.2 × 2 = 80 cm³/min (the metric formula already folds in the factor 1000 from m to mm and the factor 1/1000 from mm³ to cm³).
What MRR tells you
- Roughing time: divide the volume to remove by the MRR. 400 cm³ of stock at 80 cm³/min takes five minutes of cutting.
- Comparing setups: a smaller step-over at a higher feed can match the MRR of a deeper cut while loading the tool differently – compare the numbers rather than guessing.
- Machine fit: the spindle power needed is roughly P = Q × kc / (60 000 × η) in kW with Q in cm³/min, kc in N/mm² and η the machine efficiency. Take kc for your material from the tool maker's data.
- Limits: MRR says nothing about surface finish, tool life or chatter. It is a measure of how fast you cut, not whether the cut is a good one.
Frequently asked questions
How do I calculate metal removal rate in milling?
MRR = ae × ap × vf: radial width of cut times axial depth times table feed. 10 mm × 5 mm × 600 mm/min = 30,000 mm³/min, or 30 cm³/min.
How do I calculate metal removal rate in turning?
MRR = vc × f × ap in cm³/min, with cutting speed in m/min and feed and depth in mm. At 200 m/min, 0.2 mm/rev and 2 mm: 80 cm³/min. Imperial: 12 × SFM × f × ap in in³/min.
How many cm³ is an in³?
Exactly 16.387064: 1 in³ = 16.387064 cm³, because one inch is exactly 2.54 cm.
Does MRR tell me the spindle power?
No – power also depends on the material's specific cutting force and the tool. Roughly, P in kW = MRR in cm³/min × kc in N/mm² ÷ (60 000 × efficiency); get kc from your tool supplier.
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.
- 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.
- Machining time – Cutting time from length, feed and spindle speed – turning with feed per revolution, milling with feed rate and number of passes.
- 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.