Chatter-free spindle speed calculator (stability pocket candidates, speed zone)
From the measured chatter frequency fc, the number of teeth and the current spindle speed, this gives candidate speeds in the stability pockets and tells you whether changing the speed is likely to help at all.
Chatter speed calculator
n(k) = 60 × fc ÷ (N × (k + 1)) k = 0, 1, 2 … Tooth passing frequency = N × n ÷ 60 current k = fc ÷ tooth passing frequency Zones: k > 10 low speed (A) / 3–10 intermediate (B) / 0.5–3 high speed (C) / below 0.5 very high (D)
Above the line (reddish) chatters, below (green) is stable. The vertical axis is relative to the unconditional stability limit. The lobes are a schematic calculated for one mode with a natural frequency of 985 Hz, damping ratio 0.03 and 4 teeth; real lobes differ with each tool, holder, overhang and machine. Because the chatter frequency fc is slightly above the natural frequency, the candidates (dotted lines) fall slightly to the right of the pockets.
Notes
- Low-speed zone (A, k above 10): the candidates are too close together for speed selection to work. Lower the speed (process damping: the tool flank rubs on the short surface waves and absorbs vibration) or reduce the depth of cut. Most chatter in turning is in this zone.
- Intermediate zone (B, k of 3–10): the limit is close to the unconditional stability limit (the depth that is stable at any speed), so reducing the depth, shortening the overhang or stiffening the setup works better than changing speed.
- High-speed zone (C, k of 0.5–3): stability pockets are wide, so the candidate speeds are worth trying. In high-speed end milling, raising the speed into a pocket can stop chatter.
- Very high (D, k below 0.5): the tooth passing frequency is more than twice the chatter frequency. All candidates are below the current speed.
- The chatter frequency is slightly above the natural frequency, so the candidates come out slightly higher than the true pockets, and fc itself moves when you change speed. After switching to a candidate, measure fc again, recalculate and fine-tune step by step.
- A candidate does not guarantee a stable cut at your depth. If the depth is too large, every speed chatters. Even inside a pocket, the tooth passing frequency (or a multiple of it) can coincide with a resonance and leave forced-vibration marks.
- Do not use candidates above the spindle’s maximum speed or the rated speed of the tool and holder. At high speed, tool unbalance can cause runout and a separate vibration (check the balance).
- How to measure fc: use a smartphone microphone with an FFT (frequency analysis) app, or the machine’s chatter detection, and look at the peaks. Peaks at the spindle frequency (n ÷ 60), the tooth passing frequency and their multiples are forced vibration. A peak away from all of them is the chatter frequency fc.
- The method assumes one dominant vibration mode with the chatter frequency close to its natural frequency (Shamoto 2011, Denki-Seiko 82(2); Altintas et al. 2020, J. Manuf. Sci. Eng. 142(11); Munoa et al. 2016, CIRP Annals 65(2)).
See also
All values are guides. Start from the tool maker’s recommended cutting data and adjust for your machine, workholding and coolant. Calculations run in your browser; nothing you enter is sent anywhere.