What is a Segmented Bowl?
A segmented bowl is a woodturning project made by gluing together many small trapezoidal pieces (segments) into rings, stacking the rings, and then turning the assembly on a lathe. This technique allows woodworkers to create striking patterns using contrasting wood species, achieve larger diameters than single blanks would allow, and make efficient use of expensive exotic woods.
Each ring is composed of segments cut at precise miter angles so they form a perfect polygon that approximates a circle. When turned on the lathe, the polygon becomes a smooth circle. The accuracy of the miter cuts is critical for tight-fitting joints without gaps.
Segment Formulas
Common Segment Counts
| Segments | Miter Angle | Shape | Notes |
|---|---|---|---|
| 6 | 30° | Hexagon | Easy to cut, more material waste |
| 8 | 22.5° | Octagon | Good balance of ease and appearance |
| 12 | 15° | Dodecagon | Most common, looks great |
| 16 | 11.25° | Hexadecagon | Near-circular, small segments |
| 24 | 7.5° | -- | Very small segments, intricate |
Turning Tips
- Always add 1/8" to the segment width for turning allowance.
- Use a precision miter gauge or sled for consistent angle cuts.
- Glue rings one at a time, flattening between each with a drum sander.
- Use slow lathe speed initially; segmented bowls can come apart if unbalanced.
- Check that all segments in a ring form a complete circle before gluing.
Frequently Asked Questions
How many segments should I use?
12 segments per ring is the most popular choice. It provides a good balance between ease of cutting, visual appeal, and a shape close to circular. Fewer segments (6-8) are easier to cut but waste more material; more segments (16-24) create finer patterns but require more precision.
What glue should I use for segmented bowls?
Titebond III (waterproof PVA) is the standard for segmented bowls. It provides strong joints, adequate open time for assembly, and is food-safe when cured. Avoid CA glue for structural joints in turning projects as it can fail under lathe forces.
How do I prevent gaps in the joints?
Gaps come from inaccurate miter angles. Ensure your miter gauge is precisely set (use a digital angle gauge). Test-fit dry before gluing. Even a 0.1-degree error multiplied by 12 segments creates a visible gap. Also ensure segment lengths are consistent.