Among gearbox performance metrics, bending stiffness (often overlooked compared to precision and torsional stiffness) directly determines the limits of CNC machine tool machining. HONPINE’s anti-backlash planetary gearbox is redefining these limits with its ultra-high parameters.

What is Bending Stiffness?

Bending stiffness (also called moment stiffness or tilting stiffness) simply measures a gearbox’s ability to resist "bending over." Its unit is Nm/arcmin – a higher value means less tilting under the same external force, i.e., a "stiffer backbone."
Example: 1 Nm/arcmin means applying 1 Nm of torque tilts the output shaft by 1 arcmin (1 arcmin ≈ 0.0167°).

How is Bending Stiffness Tested?

The measurement principle is intuitive (see diagram below):

• Apply forces F₁ and F₂ at the output end, with lever arms L₁ and L₂.

• Calculate bending moments: W₁ = F₁ × L₁, W₂ = F₂ × L₂.

• Measure the resulting angular deflection θ of the output shaft.

• Calculate bending stiffness: Nm/arcmin = W / θ.
  

Higher values = greater stiffness = less tilting under load.

Why Does Bending Stiffness Matter in CNC Applications?

Consider a CNC 5-axis rotary table (diagram below): A radial force F acts at distance L from the gearbox, causing angular deflection θ on the A-axis.Scenario:

 210mm table, A-axis under 100kg radial load (F), lever arm L = 240mm. Performance comparison:

Japanese Harmonic Drive® (Model 40)

Stiffness: 264.6 Nm/arcmin

Deflection: θ = (F × g × L) / 264.6 = 0.89 arcmin

Displacement at F: 0.062 mm

Japanese RV-Style Cycloid® (Model RV-40E)

Stiffness: 931 Nm/arcmin

Deflection: θ = (F × g × L) / 931 = 0.25 arcmin

Displacement: 0.0174 mm

German Anti-Backlash Design (Model 056)

Stiffness: 1,170 Nm/arcmin

Deflection: θ = (F × g × L) / 1,170 = 0.20 arcmin

Displacement: 0.014 mm

HONPINE Anti-Backlash Planetary Gearbox (Model H3K-40T)

Stiffness: 2,250 Nm/arcmin

Deflection: θ = (F × g × L) / 2,250 = 0.105 arcmin

Displacement: 0.007 mm

Summary: Performance Comparison Under Identical Loads

The HONPINE H3K-40T Anti-Backlash Planetary Gearbox achieves decisive superiority.

Consequences of Insufficient Bending Stiffness in CNC Machining

Plummeting Accuracy: Tool-workpiece misalignment → dimensional/shape errors.

Increased Vibration: Lower natural frequency → CNC chatter, poor surface finish.

Reduced Efficiency: Forced lower CNC feed rates → longer machining times.

Tool Damage: Vibration accelerates wear/brittle fracture → higher costs.

How HONPINE Achieves Ultra-High Stiffness

Integrated 3-row "YRT-type" turntable bearings

Needle roller races machined directly onto gearbox components (monolithic design)

Simultaneously delivers:

• Extreme bending stiffness

• High moment load capacity

• High axial thrust resistance

Minimal runout (face/radial) → maximum stability

This design enables the H3K series anti-backlash planetary gearbox to provide unparalleled support in compact spaces, effortlessly handling heavy loads and severe radial moments in high-precision CNC applications.

Bending stiffness dictates CNC machine tool precision, efficiency, and longevity. HONPINE anti-backlash planetary gearboxes prove that 2,250 Nm/arcmin is no longer theoretical – it’s now a reality for demanding CNC systems.