Shaft Key Calculator

When to use this CAD/mechanical design tool

• Use when checking gear, pulley, sprocket, or hub key length.
• Use before detailed shaft design.
• Use when comparing torque-transfer assumptions.

How to use

1. Enter one mechanical-design case using typed dimensions, counts, RPM values, tolerances, or drafting selections.
2. Click the exact action button for the selected tool; default values, typing, URL-prefilled values, and worked examples do not generate results automatically.
3. Review the output cards, warnings, assumptions, visual summary, copy text, and downloads before using the result in CAD, drawing, supplier, or inspection workflow.
4. Verify final values against applicable standards, supplier catalogs, validated CAD documentation, manufacturing limits, inspection practice, and qualified engineering review.

Input guide

Shaft diameter and torque

Used to estimate tangential force at shaft radius.

Key width, height, and length

Rectangular key dimensions used for shear and bearing area.

Allowable stresses

User-selected shear and bearing limits for preliminary length comparison.

Notation

Output interpretation

• Required length is the larger of shear and bearing requirements.
• Stress utilization above one indicates the entered key length is not adequate under selected assumptions.
• Final key and keyway dimensions must follow standards and material data.

Supported CAD/mechanical design use cases

• rectangular keys
• static torque-transfer planning
• metric and inch conventions

Unsupported patterns

• splines
• Woodruff keys
• fatigue
• fretting
• fit and keyway tolerance selection
• hub cracking

How to interpret the output

• Bearing stress can govern short keys.
• High utilization calls for longer key, larger key, stronger material, or different torque-transfer method.
• Hub length can limit available key length.

CAD and mechanical-design guidance

• Use standard key sizes where possible.
• Check shaft stress separately.
• Review fatigue, hub material, fits, retaining methods, and assembly practice.

Worked examples

Assumptions

• Inputs are typed planning values and are not extracted from CAD files, supplier catalogs, drawings, PLM, CAM, ERP, or inspection systems.
• Metric calculations use millimetres unless the output explicitly states another unit; inch calculations use inches unless the output explicitly states another unit.
• The result is a preliminary calculator or drafting helper and not a certified standards database, CAD kernel, inspection report, or supplier approval.
• Rectangular key with uniform load distribution is assumed.
• Metric stress is N/mm^2 and inch stress is psi.

Practical guidance

• Use Shaft Design Calculator for shaft stress.
• Use Pulley Ratio or Gear Dimensions tools to connect torque-transfer context.

Common mistakes

• Using shaft radius instead of diameter incorrectly in F = 2T/d.
• Forgetting metric N m to N mm conversion.
• Ignoring bearing stress on the key side.

Limitations

• No fatigue, shock, keyway stress concentration, fit, hub strength, spline, Woodruff key, retaining-ring, or material-certification check is included.
• ScholarTool CAD and mechanical-design calculators provide general engineering calculation and planning support. They do not replace supplier requirements, certified standards, CAD software documentation, manufacturing review, inspection standards, or professional engineering judgement.
• The tool does not open, upload, parse, repair, or validate CAD files, drawings, STEP, STL, DXF, DWG, CAM, or CNC data.
• The tool does not perform strength certification, fatigue validation, finite-element analysis, supplier catalog selection, standards compliance certification, or inspection programming.

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