Chapters

This is a static copy of the chapter for search engines. The interactive version has animated figures, check questions, and buttons that load the example into the calculator.

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1. 01 What makes a shaft different

   A shaft is a rotating bar that carries torque from one place to another and, almost always, bending on the way.…

2. 02 Getting the loads right

   Nothing else in the calculation matters if the loads are wrong. For a shaft, the loads come from whatever is mounted on it, and each component has its…

3. 03 The rotating stress cycle

   This is the single most important fact about a rotating shaft. The bending moment can be perfectly steady and the material still sees a full tension–c…

4. 04 Notches: where shafts break

   Think of the stress as flowing along the shaft like a fluid. Wherever the flow has to squeeze past a change of section, the lines crowd together and t…

5. 05 Fatigue strength and the Marin factors

   Fatigue data comes from small, polished, perfectly loaded laboratory specimens. Your shaft is none of those things.…

6. 06 The design equations

   Now put it together. You have an alternating von Mises stress σ′ a , a steady one σ′ m , a fatigue strength S e and a tensile strength S ut .…

7. 07 Deflection, slope and critical speed

   Strength is often not what sizes a shaft. Gears that do not stay parallel wear out; bearings that are misaligned lose most of their life; a shaft that…

8. 08 Keys, fits and getting torque in

   The torque has to get from the hub into the shaft somehow. The parallel key is the most common answer, and it is worth knowing that you do not design …

9. 09 Designing a shaft, step by step

   Shaft design is iterative by nature: you cannot know the notch factors until you know the diameters, and you cannot know the diameters until you know …

10. 10 How the calculator works

    ShaftLab is a small finite-element and fatigue engine written from scratch in plain JavaScript.…