CALCULATORS / SHAFTS, COUPLINGS AND ROTATING ASSEMBLIES

Press-fit torque from interface pressure calculator

Frictional torque from supplied interface pressure; pressure is not solved.

shafts-press-fit.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

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

Scenario	normalN	capacityN*m
	15708	23.5619
	12566.4	18.8496

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.

torque target23.56 N*m✓ passes

BASELINE INPUTS

pressure10 MPadiameter20 mmlength25 mmfriction0.15

CALCULATED

normal15708 N

capacity23.562 N*m

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Shaft-hub interference fit
# Scope: Frictional torque from supplied interface pressure; pressure is not solved.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

pressure = 10 MPa
diameter = 20 mm
length = 25 mm
friction = 0.15

normal := pressure*pi*diameter*length [N]
capacity := friction*normal*diameter/2 [N*m]

check torque target: capacity >= 20 N*m

scenario alternative: pressure = 8 MPa

Calculated from your source · not saved

Baseline · Baseline

torque target23.56 N*m ✓ passes

alternative · alternative

torque target18.85 N*m × fails

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.

normal: normal = pressure*pi*diameter*length [N]
capacity: capacity = friction*normal*diameter/2 [N*m]

Original worked example

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

Given

pressure: 10 MPa
diameter: 20 mm
length: 25 mm
friction: 0.15

Calculated

normal: 15708 N
capacity: 23.5619 N*m

Assumptions and limits

Frictional torque from supplied interface pressure; pressure is not solved.

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: Shaft-hub interference fit. Inputs: diameters; interference; material properties. Outputs: contact pressure; transmitted torque estimate. Model scope: Elastic shaft models and specified supports. 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: diameters, interference, material properties
Outputs: contact pressure, transmitted torque estimate
Modes: calculate, compare, sweep
Drawing: Shaft load diagram

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