KEVOS® MAKEOS · Manufacturing
Boring Bar Deflection
How far will this boring bar deflect under the cutting force, and is the overhang reasonable?
Tip deflection of a solid boring bar or long tool as a cantilever under the cutting force, with the overhang-to-diameter ratio, against an allowable deflection.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bar diameter | mm | Diameter of the bar shank (use the flat-to-round equivalent for flats). |
| Overhang | mm | Length from the clamping face to the cutting edge. |
| Bar elastic modulus | GPa | Modulus of the bar: about 210 GPa for steel, about 550–630 GPa for solid carbide. |
| Cutting force on the tip | N | Resultant cutting force, roughly kc × depth × feed (see the turning power tool). |
| Allowable deflection | mm | Part of the bore tolerance you can accept from deflection. |
Method and formulas
- I = π D⁴ ÷ 64.
- Deflection δ = F L³ ÷ (3 E I); stiffness = 3EI ÷ L³.
- Overhang ratio = L ÷ D.
- Example: a 20 mm steel bar at 100 mm overhang deflects 40.42 µm under 200 N.
Limitations
- Static deflection only; chatter depends on dynamic stiffness and damping.
- Clamping is assumed rigid; real holders add compliance.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose bar diameter and material for a deep bore
- Estimate size error from tool deflection
- Compare steel and carbide bars
Who it is for
- Machinists
- CNC programmers
- Manufacturing engineers
What you get
- Tip deflection
- Overhang-to-diameter ratio
- Bar stiffness
Interpreting the result
- Common guidance: steel bars to about 4 × D, carbide to about 6 × D, damped bars to about 10 × D; check the supplier’s limits.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 762–790, 1300. Topic reference; no source tables or recommended settings are reproduced.
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