Lathe Vibration Calculator

An out-of-round or off-center blank spinning on a lathe generates a centrifugal force at every rotation, and this calculator works that force out directly from physics: F = m·r·ω², where m is the workpiece mass, r is how far its center of mass sits off the lathe's axis (the "imbalance offset"), and ω is angular velocity derived from RPM. Everything is converted to kilograms, meters, and Newtons for the physics, then converted back to pounds for display. The key comparison the calculator makes is that centrifugal force against the lathe's own weight, expressed as a "vibration severity" percentage — under 2% reads as smooth, 5-15% as rough, and above 15% as genuinely dangerous, since a heavy lathe absorbs imbalance forces far better than a light benchtop one.

From there it works backward to a safe starting RPM: it solves for the angular velocity that keeps centrifugal force at or below 5% of the lathe's weight, then compares that against a separate diameter-based cap (6000 divided by workpiece diameter, a standard roughing-speed rule) and recommends the lower of the two. The mass ratio output — lathe weight divided by workpiece weight — is a quick sanity check, since a ratio below about 5:1 tends to feel wobbly regardless of what the math says. A common mixup is guessing the imbalance offset too low: a rough bark-covered blank fresh off the chainsaw can easily be 1-2 inches off-center, not the fractions of an inch you'd assume for a pre-rounded blank, so err generous until you've knocked the corners off.