Lathe speed calculator
Enter the diameter of your mounted blank to get a safe RPM range from the standard shop rule of thumb. The result is a starting band, not a fixed speed: run the low end while roughing and raise the RPM only after the piece runs true.
Unbalanced start
450 RPM
Very slow, out-of-round
Roughing
750 RPM
Once running true
Finishing
1,150 RPM
Balanced piece
The rule of thumb behind the numbers
A common shop guideline keeps the product of blank diameter and RPM in a working band. Diameter in inches multiplied by RPM around 6,000 is a sound roughing figure; near 9,000 suits finishing a balanced piece. Rearranged, that gives the speed directly:
RPM ≈ 6,000 to 9,000 ÷ diameter in inches
An 8-inch blank lands near 750 RPM for roughing and about 1,100 RPM for finishing. A 12-inch blank drops to roughly 500 to 750 RPM. A 2-inch spindle can spin near 3,000 RPM. The band widens the choice rather than pinning one number, because balance and grain matter as much as size.
Why speed drops as diameter grows
The danger is rim speed, not RPM. The edge of a 12-inch blank travels almost twice as far per revolution as the edge of a 6-inch blank, so at the same RPM its rim moves twice as fast. That rim speed is what flings a cracked blank apart and what makes a catch violent. Lowering RPM as the diameter climbs keeps rim speed in a controllable range, which is why large platters and bowls run slow and small spindles run fast.
Start slow on anything unbalanced
A fresh bowl blank is rarely round and rarely balanced. Start it well below the roughing figure, near diameter times RPM around 3,600, so a 10-inch rough blank begins near 360 RPM. Bring it round at that speed, feel for vibration, and step the RPM up only after it runs true. A blank that shakes the lathe is telling you the speed is too high for its current balance.
Three habits matter more than any calculated figure. Spin every mounting by hand before switching on to confirm nothing hits the tool rest or bed. Wear a full face shield, not just glasses, because a thrown piece arrives faster than you can react. Keep the tool rest close to the work so less tool overhangs and catches lose their leverage.
Speeds by piece type
Different work sits in different parts of the band. A green bowl blank straight off the chainsaw is heavy and out of round, so it belongs at the slow end until it is round and balanced. A dry, roughed-out bowl that already runs true tolerates the roughing figure and often the finishing figure once the walls are even. Spindle work, being narrow and well supported between centers, runs fast: a 1 1/2-inch table leg blank spins comfortably near 2,000 RPM. Thin finials and small ornaments run faster still, limited more by how steady your hands are than by the wood.
Sanding is its own case. Drop the speed to roughly half the turning figure so the abrasive cuts rather than burnishes and so heat does not build and check the surface. A bowl finished at 900 RPM sands better near 400 to 500 RPM. Applying a friction polish or a finish on the lathe usually runs slower again, in the low hundreds, to keep the rag and the heat under control.
Reading the machine, not just the chart
The calculated band is a place to begin. From there the piece guides you. Chatter, a humming lathe, or a surface that tears instead of slicing all say the speed is wrong for the cut. A heavier stand and a well-mounted blank let you run toward the top of the band; a light benchtop lathe or a long thin spindle asks for the lower end. Variable speed makes this easy: dial down at the first sign of vibration, then creep back up.