Screw Jack / Power Screw Torque Calculator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Mechanical, Civil & Structural Engineering — Statics/Dynamics, Strength of Materials, Machine Design, Civil, HVAC, Vibration

Tranche

tranche-4

Evidence ID

t4-190

Ledger rows

1

No ledger note is attached.

Review findings

The specification is not honest as written for its stated square/ACME capability: the thread angle input is unused, T_lower is claimed but not formulated, and efficiency is thread-only unless collar and other losses are added. Leave honest_label empty is inappropriate; it should state the supported thread geometry, the angle convention, and that torque/efficiency exclude collar friction.

Formula and scope findings

• T_raise is the standard square-thread raising-torque formula when F is axial load, dm is mean pitch diameter, l is lead, and μ is the thread friction coefficient; it is not directly valid for ACME/V-threads without replacing μ by an effective friction coefficient, commonly μ_eff=μ sec(α), where α is the thread half-angle.
• The specification claims T_lower but provides no lowering-torque formula. For a square thread, the standard thread-only formula is T_lower=(F dm/2)[(μπdm-l)/(πdm+μl)].
• The thread angle input is unused and its meaning is ambiguous: thread included angle versus half-angle. For ACME/V-threads, the angle changes the effective friction coefficient and therefore raising torque, lowering torque, efficiency, and self-locking.
• The self-locking condition μ>tan(λ) is valid for a square thread, with tan(λ)=l/(πdm), but for an angled thread it should use the effective friction coefficient and the specification does not state whether equality is treated as self-locking.
• The efficiency formula e=Fl/(2πT) is the screw-thread mechanical efficiency for raising torque only and excludes collar/bearing friction, gearbox losses, and other losses. It is not a complete screw-jack efficiency unless those exclusions are honestly stated.

Unit assumptions

• F is an axial force in N, dm and l are lengths in the same unit, and torque is returned in force-length units; using N and m returns N·m.
• l is lead, not pitch. For a single-start screw they are equal; for a multi-start screw, lead equals pitch multiplied by the number of starts.
• μ is dimensionless thread friction coefficient; it must be nonnegative.
• The test calculations using the supplied formula treat the thread as square-thread geometry, so thread angle is set to 0° unless specifically illustrating the ACME ambiguity.
• The helix angle is λ=atan(l/(πdm)).
• Efficiency is dimensionless and is normally reported as a fraction or multiplied by 100 for percent.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The raising-torque denominator vanishes when pi dm=mu l, producing an undefined result. The calculator must reject that input rather than return a finite torque. The thread-angle input also has an unresolved convention because it is supplied but absent from the stated formulas.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "F_N": 10000,
    "dm_m": 0.05,
    "l_m": 0.0157079633,
    "mu": 0.2,
    "thread_angle_deg": 0
  },
  "expected_outputs": {
    "T_raise_Nm": 76.530612,
    "T_lower_Nm": 24.509804,
    "efficiency": 0.326667,
    "self_locking": "yes"
  },
  "working": "πdm=π(0.05)=0.157079633 m; l/(πdm)=0.1. T_raise=(10000×0.05/2)[(0.0157079633+π×0.2×0.05)/(π×0.05-0.2×0.0157079633)]=250[(0.1+0.2)/(1-0.2×0.1)]=250(0.3/0.98)=76.530612 N·m. T_lower=250[(0.2-0.1)/(1+0.2×0.1)]=250(0.1/1.02)=24.509804 N·m. e=Fl/(2πT_raise)=0.1(1-0.2×0.1)/(0.1+0.2)=0.098/0.3=0.326667. Since μ=0.2>tanλ=0.1, self-locking=yes."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json