KEVOS® MAKEOS · Manufacturing
Lathe Chuck Grip Force and Speed Limit
How much grip does the chuck need to hold this cut, how much is lost at speed, and how fast can it safely run?
Workholding check for a jaw chuck: cutting and feed forces from the chip area and specific cutting force, the total jaw grip needed to resist the cutting torque and feed force by friction with a safety factor, the grip lost (or gained) to centrifugal force on the jaws at the spindle speed, the static grip to set, and the highest speed at which the chuck’s rated grip still holds the work.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Cut | ||
| Cutting diameter | mm | Diameter being cut. |
| Specific cutting force | N/mm² | Specific cutting force of the material. |
| Depth of cut | mm | Depth of cut. |
| Feed | mm/rev | Feed per revolution. |
| Feed force ÷ cutting force | Axial feed force as a share of the main cutting force. | |
| Chuck | ||
| Gripping diameter | mm | Diameter on which the jaws grip. |
| Gripping | choice | Outside gripping loses grip with speed; inside gripping gains it. |
| Friction at the jaws | Friction coefficient between jaws and work (about 0.1 for smooth hard jaws, 0.2–0.3 for serrated jaws). | |
| Safety factor | Safety factor on holding. | |
| Number of jaws | Number of jaws. | |
| Mass of each jaw set (base + top jaw) | kg | Mass of one base jaw plus its top jaw. |
| Radius of the jaw centre of gravity | mm | Distance from the spindle axis to the jaws’ centre of gravity. |
| Spindle speed | rpm | Spindle speed. |
| Maximum static grip of the chuck | kN | Largest static grip the chuck is rated for (from the chuck maker). |
Method and formulas
- Cutting force F_c = k_c a_p f; feed force = ratio × F_c.
- Grip needed while turning = n √[(F_c d_c ÷ d_g)² + F_f²] ÷ μ (the friction at the grip must carry the cutting torque and the feed force).
- Centrifugal force on the jaws = jaws × m r ω²; static grip to set = grip needed + centrifugal force (outside gripping) or − (inside gripping).
- Speed limit (outside gripping) where the rated grip minus centrifugal force equals the grip needed.
- Example: the default cut needs 40.249 kN of grip; at 1500 rpm the jaws lose 8.8826 kN.
Limitations
- Rigid part; thin walls deform under grip and need lower pressure with soft jaws.
- Use the chuck maker’s speed and grip curves; this does not replace them.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check that a part will not slip in the chuck on a heavy cut
- Find a safe spindle speed for heavy top jaws
- Set chuck pressure for thin-walled parts
Who it is for
- Machinists
- Manufacturing engineers
- Tooling engineers
What you get
- Cutting and feed forces
- Grip needed while cutting and centrifugal change
- Static grip to set and the speed limit
Interpreting the result
- Heavy top jaws can lose most of the grip at high speed: lighter jaws or a lower speed may be needed.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1084–1101, 3131–3134. Topic reference; no source tables or recommended settings are reproduced.
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