Source: https://guthlabs.ai/docs/instruments/screw-jack-power-screw-torque-calculator/
instrument / verified-clean
# Screw Jack / Power Screw Torque Calculator
The current ledger marks this instrument verified clean within the source-bound verification corpus.
Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**
## Inspectable records
[01**Overview**Purpose and lifecycle]()[02**Mechanism**Method and assumptions]()[03**Implementation**Binding and validation]()[04**Qualification**Evidence and errata]()
## 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`