Turning feeds, speeds and time calculator

Ideal turning RPM and axial feed at constant surface speed.

cnc-turning.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	speedrpm	feedmm/s
	1061.03	1.76839
	1326.29	2.21049

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

spindle speed budget1061.03 rpm✓ passes

BASELINE INPUTS

diameter30 mmcuttingSpeed100 m/minfeedPerRevolution0.1 mm

CALCULATED

speed1061 rpm

feed1.7684 mm/s

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Turning feeds, speeds and time
# Scope: Ideal turning RPM and axial feed at constant surface speed.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

diameter = 30 mm
cuttingSpeed = 100 m/min
feedPerRevolution = 0.1 mm

speed := 2*cuttingSpeed/diameter [rpm]
feed := cuttingSpeed*feedPerRevolution/(pi*diameter) [mm/s]

check spindle speed budget: speed <= 2000 rpm

scenario alternative: diameter = 24 mm

Calculated from your source · not saved

Baseline · Baseline

spindle speed budget1061.03 rpm ✓ passes

alternative · alternative

spindle speed budget1326.29 rpm ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

speed: speed = 2*cuttingSpeed/diameter [rpm]
feed: feed = cuttingSpeed*feedPerRevolution/(pi*diameter) [mm/s]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

diameter: 30 mm
cutting speed: 100 m/min
feed per revolution: 0.1 mm

Calculated

speed: 1061.03 rpm
feed: 1.76839 mm/s

Assumptions and limits

Ideal turning RPM and axial feed at constant surface speed.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Turning feeds, speeds and time. Inputs: stock diameter; length; depth; feed; cutting speed. Outputs: RPM; removal; nominal time. Model scope: Tool, stock and machine-specific cutting data. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: stock diameter, length, depth, feed, cutting speed
Outputs: RPM, removal, nominal time
Modes: calculate, compare, sweep
Drawing: Tool engagement and material-removal preview

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS