A link coupling transfers rotation between shafts through connecting links and their joints. The permitted relative movement depends on the link geometry and construction. This calculator compares an ideal set of equally loaded tangential links; it does not determine the capacity or misalignment limits of a commercial coupling.
Flexible Link Coupling Interactive Calculator
Compare equal-share link tension and nominal tensile stress for entered torque, radius and net area. The fixed 250 MPa comparison is not a product rating.
Equation Used
The model assumes n links share torque equally, each with a tangential tensile force at radius r = D/2. Then F = T/(n*r) and nominal stress is F/A. For an inclined link, the perpendicular moment arm may differ from the pin-circle radius; that geometry is not solved here.
FIRGELLI Automations - Interactive Mechanism Calculators.
- Torque is shared equally by the loaded link plates.
- Pin circle radius r is one half of the pin circle diameter.
- Link force acts tangentially and is carried as pure tension.
- Stress comparisons use a fixed illustrative value of 250 MPa, not a verified material allowable or coupling rating.
Links carry torque between shafts
The driving member applies force through the connecting links to the driven member. The torque contribution of each force is that force multiplied by its perpendicular distance from the shaft axis.
Pivots allow links to change direction as the members move. Some designs also depend on elastic flexure. Whether a particular arrangement accepts parallel offset, angular offset or axial motion must be established from its actual geometry; a link coupling does not automatically eliminate bearing reactions.
The end-view illustration highlights pins, links and the load path. Its tension-only sketch is an idealization. Pin shear, bearing pressure at holes, local bending and retaining details are not calculated.
Where the comparison is useful
The calculator is useful for exploring how torque, effective lever arm, load-sharing count and link area affect an idealized axial load. It is not a catalogue selection tool.
Different coupling families carry torque through different elements. For example, Falk Steelflex is a grid coupling, using a flexible grid engaged with its hubs. Its product ratings cannot be applied to the pinned-link sketch on this page.
Equal-share tangential link model
For entered torque T in N·m, pin-circle diameter D in mm and n equally loaded links, the model sets r = D/2 and F = 1000T/(nr). F is newtons per link. With net link area A in mm², nominal axial stress σ = F/A is in MPa.
This assumes that every counted link has the same effective moment arm r and carries the same tensile load. Link inclination, clearance, changing geometry and unequal load sharing are omitted. For a real link, use its perpendicular moment arm rather than assuming it equals the radius.
The final two readouts are 250/σ and 100σ/250. The fixed 250 MPa value is an illustrative reference only. These ratios do not establish a safety factor, fatigue life or allowable service torque.
Example: ideal force and nominal stress
Enter 600 N·m torque, 200 mm pin-circle diameter, three loaded links and 100 mm² net area per link. The assumed radius is 100 mm, so each link carries 1000 × 600/(3 × 100) = 2,000 N.
Nominal stress is 2,000/100 = 20 MPa. The fixed-reference ratio is 250/20 = 12.5 and the stress/reference percentage is 8%.
Doubling torque to 1,200 N·m doubles link force and nominal stress. These arithmetic comparisons do not check whether the links, pins, hubs or shafts can withstand either load.
Checks beyond nominal link tension
Actual coupling selection depends on speed, torque history, direction reversals, alignment, environment and the manufacturer’s ratings. Different designs have different lubrication, retention and inspection requirements.
A complete link assessment includes net-section stress, hole bearing, pins, bending, stress concentrations and fatigue. A low value of F/A alone does not show that wear is negligible or that a smaller coupling will work.
Unexpected heat, noise, looseness or visible damage requires investigation using the applicable equipment instructions. This calculator provides no remaining-life estimate or permitted continued-running interval.
Frequently asked questions
Which links should be counted?
The model assumes the entered count shares torque equally at the same effective moment arm. An actual mechanism may distribute load differently, so the count must come from its load path rather than merely counting visible plates.
Why might pin-circle radius be the wrong lever arm?
Torque depends on the perpendicular distance to the force line. An inclined link can have a smaller moment arm than its pin radius. The calculator assumes tangential force.
Is the 250 MPa value a material rating?
No. It is a fixed illustrative reference. The calculator has no material, fatigue or product-rating inputs.
Does low nominal stress prove long life?
No. Pin wear, local stresses, unequal loading and fatigue are outside this calculation.
Does the tool calculate misalignment capacity?
No. It has no angular, axial or parallel-offset input and does not solve the link geometry through rotation.
Is Falk Steelflex the pinned-link design shown here?
No. Steelflex is a grid-coupling family. Use its own manufacturer data rather than treating this simple link calculation as a product model.
Further reading
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