How to Make a Segmented Bowl

A segmented bowl starts as rings, not a log. Each ring is a circle of short, mitered pieces of wood, the segments, glued end to end. The rings are stacked and glued one on another, a little wider or narrower each time to follow the curve of the bowl, and the stack is turned smooth inside and out.

Because you build the blank, you choose the wood for every ring and every segment, waste far less of it than with a solid blank, and the bowl stays stable: the grain runs around each ring, so it doesn't move the way a solid blank does.

Draw the bowl's profile, the outline of one side cut through the middle, at full size. Split it into rings: pick a height for each one (the thickness of the board you'll cut it from) and read off its outside diameter and how thick its wall needs to be.

Then check every ring sits on the one below it. When the bowl is turned, each ring's wall is cut back to one smooth wall, so each ring's wall has to overlap the wall underneath. Where it doesn't, turning cuts through the glue joint and leaves a gap or a step.

The free Segmented Bowl Designer does both: it draws the profile as you change each ring, warns you at any joint that overlaps by less than 3/8", and gives the cut list for every ring. It opens with this bowl, 3 rings in 12 segments with 3/4" walls and a 1/4" allowance, 4" tall. Every ring overlaps the next by at least 1/2".

Miter angle is 180° divided by the number of segments, set at both ends of every segment. Twelve segments is 15.0°.

Segment length comes from the outside diameter. The segments make a polygon, not a circle, and its flat sides have to reach the circle for the ring to turn down to size, so the long side of each segment is the diameter times tan(180° ÷ segments). Add the allowance on both sides first. A 10" ring in 12 segments with a 1/4" allowance: set the saw to 15.0° and cut each segment 2 13/16" long point to long point. The short side comes out 2 5/32".

Strip width is the ring's wall plus the allowance on both sides: rip a 1 1/4" strip for a 3/4" wall. The Segmented Ring Calculator works out any ring, and the Miter Angle Calculator does the same cuts for flat work like a hexagon box or an octagon frame.

Cut segments on a crosscut sled with an angled fence, or with a miter gauge set to the miter angle and a stop block set to the long side. Flip the strip over between cuts so the angles alternate and every segment comes out a trapezoid of the same length.

Make test cuts first. Cut a full ring from scrap, hold it together dry with a band clamp and look at the joints. A small error doesn't stay small: each segment has two cuts, so in a 12-segment ring a cut 0.1° off is 2.4° off around the ring, and the last joint opens about 7/32" at the outside of a 10" ring. Adjust the angle until the dry ring closes with no light in any joint.

Glue each ring as two halves. Glue the segments of each half on a flat board, with masking tape or a simple jig holding them in line, and let them dry. Sand or joint the two mating faces of each half flat on a disc sander or a sheet of sandpaper on a flat surface, then glue the halves into a full ring. Any small angle error is taken up in that last flat joint instead of leaving a gap.

Flatten both faces of every ring before stacking, so each glue joint is wood on wood. Then glue the rings together one at a time, centred on the one below, with the segments offset by half a segment so the joints form a brick pattern. That looks better and makes the stack stronger.

Mount the stack on a faceplate or a glue block and true it up. Glued-up segments are a polygon, so start slow and stand out of line with the blank. The example bowl is about 5 1/2" across before turning: start around 655 RPM, rough it round at about 1,091 RPM and finish at about 1,636 RPM. The Lathe Speed Calculator works out any diameter.

Turn the outside to the profile, then the inside, following the walls you designed: cutting deeper than the overlap cuts into a glue joint. Sand through the grits and finish as you would a solid bowl.

Tailstock is the turning app behind the designer. It's free for bowls up to 4 rings, with a cut list for every ring, saved designs and the profile drawn as you go, and it shares a design as an image. Tailstock Pro adds as many rings as you like and as many saved designs as you like.

Ready to plan yours? Open the free Segmented Bowl Designer in your browser.