Engineering Guide

ISO 54 — Standard Modules

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Always select module from this preferred series. Non-standard modules are not interchangeable with standard tooling.

Spur Gear — Key Formulas

Pitch Circle Diameterd = m × z

Outside Diameterda = m × (z + 2)

Root Diameterdf = m × (z − 2.5)

Base Circledb = d × cos(α)

Center Distancea = m(z₁+z₂)/2

Addendumha = 1.0 × m

Dedendumhf = 1.25 × m

Whole Depthh = 2.25 × m

Circular Pitchp = π × m

Tip Clearancec = 0.25 × m

Power, Torque & Speed

Torque (N·m)T = P×9549.3/n

Power (kW)P = T×n/9549.3

Angular velocityω = 2πn/60 rad/s

Tangential forceFt = 2T×1000/d (N)

Radial forceFr = Ft×tan(α)

Normal forceFn = Ft/cos(α)

1 HP (metric)= 0.7355 kW

1 HP (imperial)= 0.7457 kW

Pressure Angle Selection Guide

14.5°Legacy standard. Weak root, quiet mesh

20°ISO standard. Best balance of strength & smoothness

25°Heavy load applications. Stronger root, more noise

Typical Stage Efficiency

Spur gear pair98.5 – 99.0%

Helical gear pair98.0 – 99.0%

Bevel gear pair97.0 – 99.0%

Worm gear (high ratio)50 – 80%

Worm gear (low ratio)80 – 92%

Planetary stage97.0 – 99.5%

Rolling bearing99.5% per bearing

Essential Unit Conversions

1 kW= 1.3596 HP (metric) = 1.3410 HP (imp)

1 N·m= 0.1020 kgf·m = 0.7376 lb·ft

1 MPa= 1 N/mm² = 145.04 psi = 10 bar

1 inch= 25.4 mm

1 kgf= 9.80665 N

1 rpm= 0.10472 rad/s

Planetary Gear Ratios

Ring teeth ruleZr = Zs + 2 × Zp

Fixed ring → carrieri = 1 + Zr/Zs

Fixed carrier → ringi = −Zr/Zs

Fixed sun → carrieri = Zr/(Zr+Zs)

Assembly condition(Zs+Zr) / N_planets = integer

Typical planetary ratios: 3:1 to 10:1 per stage. Two-stage planetary can achieve 100:1.