Wood-lathe speed calculator
The right spindle speed for a bowl blank depends on its diameter, the species, and how rough the surface is. Most calculators ignore all three. This one gives you a target SFM range, then converts to RPM for the largest and smallest diameter your blank will see — because the diameter at the rim changes as you turn it down.
Calculator
Why bowl blanks need lower RPM than spindle work
Spindle turning (between centres, work like a pen blank or table leg) is balanced. Bowl turning is face-plate work, and the blank is unbalanced until you've trued the rim. Until then, centrifugal force scales as radius × RPM² — doubling RPM quadruples the force. A 12″ wet blank at 800 RPM has 6× the rim force of a 4″ spindle blank at 2400 RPM.
That's why wet, large bowl blanks get spun at 200–500 RPM. The lathe doesn't care; the bearings don't care; the floor does.
Increase RPM as you turn
The calculator gives you two RPMs — start (large diameter) and end (small diameter). As you work inward, the rim shrinks, and the same SFM target requires a higher RPM. The conventional rule is to keep increasing RPM after each major turning pass. With a variable-speed lathe, do it without stopping; with a stepped-pulley lathe, plan ahead.
Limitations
- Assumes the blank is reasonably balanced. A wildly out-of-balance blank (intentional or not) needs a slower speed regardless of diameter.
- SFM is a starting point. Tool geometry, sharpness, and finish quality matter as much.
- Doesn't predict tear-out for figured wood. Test cuts on a small piece of the same blank first.
- Doesn't replace your judgement — if the lathe is shaking, slow down, no matter what the calculator says.
Frequently asked questions
Can I just spin everything at max RPM?
For small spindle projects, often yes. For anything large or off-balance, no — the rim speed becomes dangerous and the tool pressure gets weird. Don't exceed the SFM target by more than about 50%.
Why does wet wood turn so differently?
Wet wood wants to chip and grab at the tool; dry wood shears. Wet blanks come off the lathe looking polished but warp badly as they dry. Most production turners rough wet, finish dry.
What about segmented turning?
Segmented rings are usually glued-up dry blanks — same SFM target as any other hardwood turning. Watch glue line tear-out at high speeds; it's the most common segment defect.