CNC Speeds and Feeds Calculator
Calculate cutting speed, spindle speed, feed rate, power, torque and material removal rate for milling, drilling and turning using established machining formulas.
- VcCutting speedm/min
- nSpindle speedrpm
- fzFeed per toothmm/tooth
- vfFeed ratemm/min
- ap / aeDepth of cutmm
- QMaterial removalcm³/min
n = (Vc × 1000) / (π × Dc)
01 / Operation
02 / Material
P — Steels — Structural and alloyed
03 / Tool and Cut Parameters
Cut Type
04 / Cutting Parameters
Suggested Values
In simple mode the values are derived automatically from the material, operation and cut type.
Primary Results
Spindle Speed
Feed Rate
Cutting Speed
MRR
Secondary Results
Moldence Engineering Score
Enter your parameters and calculate
Primary Results
Spindle Speed
Feed Rate
Cutting Speed
MRR
Secondary Results
Moldence Engineering Score
Enter your parameters and calculate
Engineering Disclaimer
This calculator produces theoretical starting values. Final cutting parameters must be validated against tool manufacturer catalogues, material hardness, tool holding rigidity, coolant conditions, machine power and trial cuts on the shop floor.
Calculation Formulas
Every result is produced with established engineering formulas based on ISO 3685, DIN 6580 and the ISO 513 material classification.
How is CNC spindle speed (RPM) calculated?
Spindle speed is how many revolutions the cutting tool makes per minute: n = (Vc × 1000) / (π × Dc), where Vc is cutting speed in m/min and Dc is the tool diameter in mm. The resulting RPM must be capped at the machine's maximum spindle speed.
What is cutting speed (Vc)?
Cutting speed is the linear speed of the cutting edge relative to the workpiece. Tool manufacturers publish it in m/min per material group, tool material and coating. A lower Vc extends tool life; a higher Vc raises productivity but builds heat.
What is feed rate (Vf)?
Feed rate is how fast the tool travels relative to the workpiece. For milling, Vf = fz × z × n; for turning and drilling, Vf = fn × n. It is expressed in mm/min and must be capped at the machine's maximum feed rate.
What is feed per tooth (fz)?
Feed per tooth is the distance each cutting edge removes in a single pass. Values that are too small cause rubbing instead of cutting — and work hardening in austenitic steels — while values that are too large can break the tool.
What is material removal rate (MRR)?
MRR is the volume of material removed per unit of time. For milling, MRR = ae × ap × Vf; for turning, MRR = Vc × ap × fn. A higher MRR shortens cycle time but demands more power and better heat management.
Why does cutting power matter?
Net cutting power (Pc) depends on specific cutting force (Kc) and material removal rate, and excludes drive losses. The power the machine must actually deliver is higher: Pm = Pc / η. Pm values beyond 70–80% of machine power lead to vibration and premature tool wear.
Why are these starting values rather than final ones?
Theoretical calculations ignore tool overhang, clamping rigidity, coolant effectiveness, hardness variation across the workpiece and machine dynamics. Real cutting parameters must be confirmed with trial cuts and compared against tool manufacturer catalogue data.
ENGINEERING NOTICE
This calculator produces theoretical starting values. Final cutting parameters must be validated against tool manufacturer catalogues, material hardness, tool holding rigidity, coolant conditions, machine power and trial cuts on the shop floor. Moldence accepts no liability for manufacturing decisions based on these values.
Frequently Asked Questions
Which operations does the calculator support?
Milling (end milling, profiling, roughing and finishing), drilling (blind and through holes, single or multiple) and turning (external and internal, roughing and finishing).
What is the difference between Simple and Advanced mode?
In simple mode the system suggests Vc, fz and fn automatically from the material, cutting tool and cut type. In advanced mode you enter those values yourself and can also define parameters such as Kc and machine efficiency.
What do the ISO material groups mean?
ISO 513 classifies workpiece materials for cutting tool selection: P for steels, M for stainless steels, K for cast irons, N for non-ferrous metals, S for titanium and superalloys, and H for hardened steels.
What should I do if the calculated power exceeds my machine capacity?
Reduce ap (axial depth of cut) or ae (radial width of cut), lower the cutting speed, or reduce feed per tooth. If power is still exceeded, the machine configuration may be unsuitable for this operation.
Why does radial chip thinning matter?
When the ae/D ratio falls below 0.5, the actual chip thickness at the cutting edge drops below the programmed fz. This shortens tool life and should be corrected by increasing the programmed fz.
Why is the L/D ratio critical?
L/D — tool overhang length divided by diameter — directly drives the tendency to vibrate. Above L/D > 3, ap and ae should be reduced; above L/D > 5 the operation carries a serious chatter risk.
How accurate is the surface roughness estimate?
Ra is derived from the theoretical formula Ra ≈ fn² / (18√3 × rε) ≈ fn² / (31.2 × rε) for turning. Actual Ra differs depending on vibration, workpiece material properties, tool wear and coolant conditions.
Can I enter these values straight into the machine?
Treat them as a theoretical starting point. Run a trial cut, observe chip colour and surface quality, compare against tool manufacturer catalogue values, and optimise the parameters step by step.
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The calculator provides theoretical starting values. In real production, Moldence engineers optimise these parameters against the actual material, tooling and machine conditions.