CTR K

Power Screw — validation & limitations

What this calculator checks and the method behind each result, the independent reference cases its engine is tested against, and what it does not check. Use it to decide how far you can rely on a result.

Open the Power Screw

What it calculates

Standard / method: Shigley §8-2 · ASME B1.5 / DIN 103 thread forms

Method: Shigley's Mechanical Engineering Design (Budynas & Nisbett, 11th ed., §8-2) — power-screw raise/lower torque, thread efficiency, self-locking, bearing pressure and root stresses. Thread GEOMETRY: ASME B1.5 (Acme, α = 14.5°) · DIN 103 / ISO 2901 (metric trapezoidal Tr, α = 15°) · ANSI B1.9 (buttress, 7°/45°). Those are dimensional standards and contain no torque or efficiency model.

  • Raise and lower torque with collar friction — Shigley §8-2, for Acme (ASME B1.5, α = 14.5°), metric trapezoidal (DIN 103 / ISO 2901, α = 15°), square (α = 0°) and buttress (ANSI B1.9, α = 7°) thread forms
  • Mechanical efficiency and self-locking / overhauling check (λ vs arctan μ′)
  • Efficiency map — η vs lead angle and vs friction coefficient across five μ values
  • Mechanical advantage analysis — ideal and actual MA, handle force, back-drive torque
  • Thread strength and wear life — shear-stripping stress, contact pressure and Archard wear criterion
  • Von Mises combined stress — the worse of the thread root (first-thread share 0.38, Shigley §8-2 method) and the screw core at the minor diameter

Standards this tool applies

  • ASME B1.5 — Shigley §8-2 power-screw analysis on basic ASME B1.5 Acme geometry (no thread classes or tolerances) — raise/lower torque, efficiency, self-locking, Von Mises root stress, nut contact pressure and Archard wear life, for Acme, metric trapezoidal, square and buttress thread forms.

Validation evidence — independent reference cases (0)

Each case runs the tool's engine on a worked example whose values come from a published source or a hand derivation from the cited equations, and an automated regression test asserts the engine against those values within the stated tolerance. "Conservative" means the engine is known to sit on the safe side of the reference and the test asserts that side. Sources are cited; their text is not reproduced.

No independent reference case is registered for this tool yet. Its engine is covered by the regression suite, but no published worked example has been reproduced end to end.

Limitations

Not checked by this tool

  • Column buckling of the screw under its own thrust — Check the root diameter as a column with /buckling (Euler / Johnson)
  • Fatigue and thread-root notch factors under cyclic load — The von Mises stress is static; check cyclic duty with /fatigue using a thread notch factor
  • Shock and dynamic loads — Static load only; multiply the load by your dynamic factor
  • Whirling (critical speed) of a long rotating screw — Not computed; use the same end-fixity method as /ballscrews with the root diameter
  • Temperature effect on friction and heat build-up in the nut — Friction is constant; check the nut maker's pressure-velocity and duty-cycle limits
  • Thread-form manufacturing tolerances — Nominal geometry; recheck stripping and contact pressure with the tolerance-class minimum dimensions

Results are engineering calculations for qualified users — see the disclaimer. Other tools: all validation pages · standards reference · symbols glossary.