Segmented Turning Calculator
Segmented bowl and vessel turning requires cutting individual wood pieces at precise miter angles so they assemble into rings without gaps. The miter angle depends only on the number of segments per ring. This calculator computes the miter angle, the included segment angle, and (given an inside diameter and segment width) the segment length for cutting on the miter saw. These values let you set up your saw and cut all segments to the same angle for a perfect circle.
Segmented turning formula
Included angle = 360 / segments
Miter angle = 90 - (180 / segments) = 90 - included angle / 2
Segment length = 2 × (inside radius + seg width) × tan(180 / segments)
Outside diameter = inside diameter + 2 × seg width
The included angle is the central angle each segment subtends in the ring. The miter angle is half the included angle subtracted from 90 degrees, which is the saw setting from perpendicular. The segment length is calculated from the outside ring radius using the tangent of the half-angle. Outside diameter adds two segment widths to the inside diameter.
Segmented turning tips
- Cut all segments for one ring from the same board if possible to match grain colour and avoid visual inconsistency at joints.
- Number the segments as they come off the saw and arrange them in ring order before gluing to verify fit.
- Clamp the ring on a flat surface using a band clamp or rubber bands; check for flatness and close gaps before the glue sets.
- Flatten each ring on a flat surface with a hand plane or drum sander before gluing it to the next ring.
- Offset the joints between rings by rotating each ring half the segment angle to improve the finished appearance.
Segmented turning calculator: frequently asked questions
What is segmented turning?
Segmented turning is a woodturning technique where individual wood pieces (segments) are glued together to form a ring, and rings are stacked to build up a vessel form such as a bowl or vase. The segments are cut with precise miter angles so their glue faces meet seamlessly when assembled into a circle.
How do I determine how many segments to use per ring?
The number of segments per ring is a design choice. More segments produce a rounder ring with smaller glue-face angles. Common counts are 8, 12, 16, and 24 segments. Eight segments per ring is simple to cut; 12 or 16 create more options for wood pattern arrangement.
What is the miter angle formula for segmented turning?
Miter angle = 90 - (180 / segments). For an 8-segment ring: 90 - 180/8 = 90 - 22.5 = 67.5 degrees. For a 12-segment ring: 90 - 180/12 = 90 - 15 = 75 degrees. This is the angle from 90 degrees perpendicular, as marked on most miter saws.
How do I calculate the segment length for a target ring diameter?
Segment length = 2 * (target inside radius + segment width) * tan(180 / segments). The outside diameter is the inside diameter plus twice the segment width. This calculator returns the segment length based on the target inside diameter you enter.
Why does glue joint quality matter so much in segmented turning?
When a segmented piece is turned on the lathe, the tool exerts significant shear stress on each glue joint. A poorly glued joint will blow out during turning, sometimes violently. Every glue joint must be flat, properly cleaned, and firmly clamped. Use a strong PVA (yellow glue) and apply even clamping pressure around the entire ring.
Official sources
- USDA Forest Products Laboratory: Wood Handbook, FPL-GTR-190 (adhesives and joinery).
- USDA Forest Service: FPL Homepage.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.