Boring · Released

Boring-Bar Deflection Check

Estimate boring-bar deflection and chatter risk from bar diameter, overhang, material, and cutting data. Excessive deflection causes poor surface finish, dimensional errors, and vibration.

Bar diameter (mm)

Overhang L (mm)

Bar material

Workpiece material

Depth of cut ap (mm)

Feed f (mm/rev)

L/D ratio

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Estimated deflection δ

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Cutting force Fc

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Radial component ≈ Fc × 0.3–0.5

Risk level

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Formula and theory

Deflection of a cantilever beam: δ = (F_radial × L³) / (3 × E × I)

Moment of inertia (solid round bar): I = π × d⁴ / 64

Cutting force estimate: Fc ≈ ap × f × kc (specific cutting force × chip cross-section)

Radial force: Fr ≈ Fc × (0.3 to 0.5) for steel turning; use 0.4 as a default estimate. The radial (passive) force is what pushes the boring bar away from the workpiece and causes deflection.

The L/D ratio is the single most important boring-bar parameter. Most shops recommend keeping L/D ≤ 4–5 for steel shanks and ≤ 6–7 for carbide shanks. Beyond that, deflection and chatter rise rapidly.