A jaw or dog clutch transfers torque through interlocking teeth. One half can slide axially to engage the other. Unlike a friction clutch, its engaged torque path is a positive tooth contact. This calculator estimates equal-share jaw loads and the separating force produced by an inclined loaded flank.
Form Clutch Interactive Calculator
Adjust applied torque, jaw pitch radius, loaded jaw count and flank angle. The end section shows interlocking jaws; the enlarged developed section shows why an inclined loaded face creates an axial separating force.
Equation Used
- Equal tangential load among the entered jaw pairs at one pitch radius.
- Loaded face inclined by α from the shaft axis in a developed pitch-cylinder section.
- Frictionless contact; only the torque direction that tends to separate the halves is shown.
- No tooth-root stress, contact pressure, backlash impact, shift force or transient simulation.
This is an ideal equal-load jaw-contact calculation for the illustrated separating flank direction. It assumes zero friction and full engagement. Holding-force ratio compares only entered axial retention with calculated separation; it is not a strength or certified safety factor. The moving view shows a held, engaged pose even if the available retention is insufficient; no disengagement dynamics are predicted.
Interlocking jaws and an inclined loaded face
The end section shows blue and bronze jaws interleaved around a common shaft axis. The visible sector gaps are unloaded-flank clearance. Green marks identify the loaded contacts; the two halves rotate together in the assumed engaged state.
The enlarged lower view unwraps one contact at the pitch radius into an axial–tangential plane. A straight loaded face parallel to the shaft axis has no axial component of its ideal contact reaction. Tilting that face creates a separating component in the direction shown. The angle in this view is the working flank angle, not an entry chamfer.
The animation shows a clutch held in engagement. If the entered holding force is below the calculated separation, the result flags that shortfall. Predicting disengagement motion would also require axial constraints, mass and retention behavior.
Positive coupling of two rotating members
Jaw clutches provide an interruptible connection through mating tooth faces. A sliding sleeve or other axial mechanism establishes their overlap. The historical feathered-shaft example and the modern dog-clutch model cited below illustrate that distinction between rotational connection and axial engagement.
This drawing is a generic contact model, not a named machine, synchronizer or torque-limiter design. It does not prescribe engagement speed, tooth hardness, root dimensions or a particular detent mechanism.
Resolve the contact force
Applied torque T acting at pitch radius r gives total tangential force T/r. If n jaw pairs share that force equally, each carries Ft = T/(rn). Use r in metres with torque in N·m.
In the developed section, the contact normal is perpendicular to the loaded face. For face angle α from the shaft axis, the axial component per jaw is Ft tanα. Summing the n identical contacts gives Fax = (T/r)tanα. This is why changing jaw count changes individual loading but not total axial separation in this equal-share model.
The holding ratio is entered holding force divided by total separation; the margin is their difference. At zero flank angle, this ideal model has zero axial demand, so dividing by it would not produce a meaningful finite ratio. The result is shown as “No axial demand” at zero flank angle.
Worked jaw-load example
At 120 N·m, 30 mm pitch radius and four equally loaded jaw pairs, total tangential force is 4000 N and each jaw carries 1000 N. A 20° loaded flank produces 1455.9 N total axial separation. With 2000 N available holding force, the ratio is 1.37 and the axial margin is 544.1 N.
Increasing to eight jaw pairs halves individual tangential loading to 500 N. It leaves the total separating force unchanged. Setting the loaded flank angle to 0° reduces ideal axial separation to zero.
What the comparison means
A larger pitch radius lowers tangential and axial force for the same applied torque. More equally loaded jaws lower the load on each contact. A steeper separating flank increases axial demand. These changes are reflected independently in the calculator.
Real jaws may not share load equally. Contact friction, manufacturing tolerances, elasticity, impact and retention geometry can matter. This tool calculates the stated static force balance, not tooth strength or a rated coupling capacity.
Jaw-clutch questions
Why does jaw count not change total axial force?
More equal-share contacts reduce each jaw’s load in the same proportion. Summing their axial components gives the same total at the entered torque and radius.
Is the flank angle an entry chamfer?
No. It describes the loaded working face measured from the shaft axis in the developed pitch-radius section.
Does a positive holding margin prove the design is safe?
No. It compares only ideal separating force with the entered axial holding force. It does not evaluate strength, fatigue or engagement impacts.
Why does the animation remain engaged with a negative margin?
It is an inspection of the assumed contact geometry. A negative margin is flagged; disengagement motion would require another model with axial constraints, mass and retention behavior.
References & further reading
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