Shaft Design Calculator
Screen a solid shaft diameter using combined bending and torsion, user-selected shock factors and allowable shear stress.
Use the Shaft Design Calculator
Screen a solid shaft diameter using combined bending and torsion, user-selected shock factors and allowable shear stress.
Calculations happen locally in your browser. ToolLott does not send these inputs to a server for this tool.
Preliminary engineering screening only. It does not replace project-specific design, applicable codes/standards, manufacturer data, transient/fatigue studies, geotechnical or site assessment, professional review or independent verification.
How to use it
Replace the worked-example values with actual project data. Review the intermediate quantities and visible assumptions before using the result elsewhere.
How the Shaft Design Calculator works
Screen a solid shaft diameter using combined bending and torsion, user-selected shock factors and allowable shear stress. The methodology below exposes the production equation, a QA-verified worked example and the boundary between this screen and detailed design.
Calculation breakdown
ToolLott will explain the current inputs and displayed result here.
Equivalent-torque solid-shaft screening
The production engine evaluates Te = sqrt((Kb M)^2 + (Kt T)^2); d = [16 Te/(pi tau)]^(1/3). It begins by convert bending moment and torque from N.m to N.mm., then combine them with entered shock/fatigue factors into equivalent torque., and finally solve the solid circular shaft torsion relation for diameter. This keeps the calculation auditable instead of hiding design assumptions behind a single number.
Te = sqrt((Kb M)^2 + (Kt T)^2); d = [16 Te/(pi tau)]^(1/3)ToolLott evaluates the relationship using the entered units and full numeric precision before display rounding.
| Symbol / input | Meaning | Unit |
|---|---|---|
torque | Torque (N.m) | user input |
bendingMoment | Bending moment (N.m) | user input |
allowableShear | Allowable shear stress (MPa) | user input |
bendingFactor | Bending factor Kb | user input |
torsionFactor | Torsion factor Kt | user input |
Step-by-step method
- Convert bending moment and torque from N.m to N.mm.
- Combine them with entered shock/fatigue factors into equivalent torque.
- Solve the solid circular shaft torsion relation for diameter.
Worked example
Mia, a project engineer, has a shaft transmitting about 190 N·m plus a known bending load and needs a preliminary diameter comparison before detailed fatigue design.
Example inputs
- Torque (N.m): 190
- Bending moment (N.m): 300
- Allowable shear stress (MPa): 60
- Bending factor Kb: 1.5
- Torsion factor Kt: 1.2
Calculation / processing
Equivalent torque term = sqrt((1.5 x 300)^2 + (1.2 x 190)^2) = 504.46 N.m.Use allowable shear = 60 MPa in d = [16Te/(pi tau)]^(1/3).Preliminary diameter = 34.99 mm.
Use the result as a screening or quantity-planning value and compare it with the project criteria, manufacturer data and applicable engineering requirements before making a design or procurement decision.
Assumptions
- The entered values are representative of the condition being screened and use the units shown on the page.
- The equation models only the stated relationship; omitted system effects are not silently estimated.
Limitations
- This page is not engineering certification and does not replace applicable standards, design loads, manufacturer data, site investigation or competent professional review.
- Results can change materially when real geometry, losses, transients, material properties, duty cycles, safety factors or regulatory criteria differ from the simplified inputs.
Common questions
Is this a final engineering design?
No. It is a transparent screening calculation using the entered assumptions and the stated equation.
Why does the page show assumptions and limitations?
Engineering formulas are only valid within their modelling assumptions; exposing them helps users decide what additional design checks are required.
Should I use the rounded displayed value in later design work?
Use suitable calculation precision and the governing project/standard requirements rather than relying on display rounding alone.
Methodology sources
Related ToolLott tools
A realistic way Mia could use this tool
Mia is a project engineer.
Mia has a shaft transmitting about 190 N·m plus a known bending load and needs a preliminary diameter comparison before detailed fatigue design.
For the worked run, Mia enters torque = 190; bending moment = 300; allowable shear = 60; bending factor = 1.5; torsion factor = 1.2. With those exact values, the page produces Preliminary solid-shaft diameter: 34.99 mm; every input remains visible so the result can be traced back to the scenario data.
The practical output is Preliminary solid-shaft diameter: 34.99 mm. That gives Mia a concrete basis to a preliminary diameter comparison before detailed fatigue design. The page also keeps this limitation explicit: Preliminary screening/planning calculation only.
Fictional scenario using realistic example data. For Ready tools, the worked result is tied to the tested example shown in the tool. Replace the figures with your own inputs and independently verify important professional, financial, legal, health or safety decisions.
What this calculator is for
Use it to screen a solid shaft diameter using combined bending and torsion, user-selected shock factors and allowable shear stress.
It sits within ToolLott’s Mechanical collection, where you can also calculate bearing life, belt length, gear ratio, power transmission, shaft checks, thermal expansion and torque.