Ringed Bowl Planner

Nested Rings Across Multiple Blanks, Cut with a Router Circle Jig

Getting Started with the Ringed Bowl Planner

This planner sizes the rings for a stacked-ring bowl that you cut from flat boards with a router and a circle-cutting jig, glue up, and turn on a lathe. It tells you how wide each ring must be, which board each ring comes from, the trammel setting for every cut, and whether the glue joints can hold the wall you plan to turn. Design a straight-walled bowl from numbers, or drag a curved profile into shape, then choose a wood for each ring and see the turned bowl in 3D.

How to use it

  1. Start from a preset (Classic 45°, Shallow Dish, Deep Bowl) or your own numbers.
  2. Set your stock and tool in section 1: board thickness, the blank size your boards allow, and your router bit.
  3. Choose how to describe the bowl in section 2, under Design from:
    • Angle: the base ring's diameter, the wall angle and the number of rings.
    • Diameters: the bottom and top ring diameters and the number of rings. The planner works out the angle. Use this when your lathe or jig sets the size, or you want a bowl of a given size.
    • Profile: a curved bowl. Drag the handles on the Profile & Ring Stack diagram to shape the outside; the Height and Max Diameter fields scale the whole curve. The inside follows at the finished wall, the height sets the number of rings, and each ring is sized for you. It starts from the straight-walled bowl you had.
  4. Enter the finished wall you plan to turn and a centering margin. Then set the ring wall, or press its Use button for the suggested width. (In Profile mode there's no ring wall to set: each ring gets its own.)
  5. Add your equipment limits in section 3 (optional): lathe swing and your jig's smallest and largest radius.
  6. Choose the woods on the Woods & 3D tab. Pick a Brush wood and click or drag over the rings to paint them; every other ring is the Base wood. The Blanks buttons paint every ring on one blank at once, and Clear sets them all back to the base wood. Rings on one blank come from one board, so painting them different woods puts them on separate blanks. When that happens a note says how many blanks the bowl now takes, with Undo and, where it fits, an offer to paint the ring's whole blank instead.
  7. Look at the bowl in 3D beside the rings. Drag to turn it, use Side, 3/4 or Top for a set view, and switch between Turned (the finished bowl) and Glue-Up (the rings stacked as cut).
  8. Check the warnings at the top of the sidebar and the summary under Bowl Dimensions.
  9. Compare ring counts on the Ring Count Options tab, and press Use on a row to load it. (Straight-walled designs only; the tab is hidden in Profile mode.)
  10. Go to the shop with the Workshop Cut Sheet (printable) and the Glue & Turn Guide.
  11. Save your work with Save Project: name it, set its status (Backlog, In progress or Complete) and add notes. Press Save again as you make changes. Projects lists your saved bowls, and My Projects in the site menu lists every calculator's. Projects are kept in this browser, on this device.
  12. Share with Copy link: the link opens a copy of this design for whoever you send it to. Reset starts over with the Classic 45° bowl.

Key terms

Ring
One layer of the bowl, cut from a board as a flat washer. Ring 1 is the base; in a straight-walled bowl the rings get wider going up.
Ring wall
The radial width of each ring, from its inside edge to its outside edge. In Profile mode each ring has its own, shown on the cut sheet.
Profile
The outside of the finished bowl, seen in cross-section. In Profile mode you shape it by dragging handles, and a smooth curve runs through them.
Step
How far each ring's radius grows over the one below: board thickness ÷ tan(angle). Steeper bowls step out less.
Glue ledge
Where a ring overlaps the ring below: ring wall − step. It's the only wood that runs through each joint.
Finished wall
The thickness you'll turn the bowl to, measured square to the wall. It crosses each joint on the bias, so it needs a ledge of finished wall ÷ sin(angle). The ledge sets the thickest wall you can turn, never the thinnest.
Centering margin
How far one ring might end up off-center from the next at glue-up. Each joint gets twice this much extra ledge.
Blank
One square of board that several rings are cut from, nested inside each other. A router cuts straight down, so neighbouring rings can't come from the same blank. The planner spreads the rings across the fewest blanks possible and letters them A, B, C…
Base wood
The wood of every ring you haven't painted. Changing it changes all of them.
Bit kerf
The router bit's diameter: the width of wood each cut removes. Rings on the same blank need at least this much space between them.
Trammel radius
The jig setting for a cut, from the pivot pin to the center of the bit. Outer cuts sit half a bit outside the ring, inner cuts half a bit inside.

Assumptions

  • All measurements are in inches, and angles are in degrees from horizontal.
  • Every ring is the same thickness, cut from flat stock. In Angle and Diameters modes every ring steps out by the same amount, so the bowl is a straight-walled cone before turning.
  • In Profile mode each ring reaches the centering margin past the outside of the wall and stops the same margin short of its inside, over the ring's whole thickness. Its radii are rounded away from the wall to 1/32". A ring whose hole would be narrower than the bit is cut solid.
  • Cuts are vertical: a router plunging straight down on a circle jig. Bevelled cuts (scroll saw or bandsaw) aren't modelled.
  • The turned wall is centered on the glue ledges (in Profile mode, it follows the profile). Joint strength is judged only by ledge width; glue type, grain direction and wood movement aren't modelled.
  • Blank sizes are squares just big enough for the outermost cut and its kerf, with no extra margin for tape, clamping or tear-out.
  • The lathe check compares the widest ring's full rough diameter with your swing, with no clearance. Leave yourself some.
  • When Ring 1 has a hole, another blank's center offcut can close the bottom; the cut sheet says which one, and the disc is that blank's wood. With no offcut big enough, it's a separate disc of the base wood.
  • Every ring on a blank is the same wood. The planner keeps rings of different woods on different blanks and uses the fewest blanks it can for each wood. Painted rings move to other blanks; the rest keep the blank letters they'd have in a one-wood bowl wherever they can.
  • The 3D preview is a guide to color and layout, not a finish sample: wood colors and grain are approximate. It glues each ring a quarter turn from the one below, and turns the bottom disc flush with the foot.
Open this guide again any time with the Getting Started button.
Presets:

How this planner cuts the rings

A router cuts straight down, so rings nested in one board can't overlap when stacked: each ring's hole is the next ring's outside plus a kerf. This planner spreads the rings across as many blanks as it takes, cutting each blank's rings concentrically with your circle jig. Neighbouring rings come from different blanks, so each ring can be wider than the step between them, and that extra width is the glue ledge. Rings that share a blank need one bit width between them, and the planner assigns rings to use the fewest blanks possible. A typical 45° bowl takes two blanks with the rings alternating; a steeper bowl or a wider ring wall takes more. Each blank only needs to be as big as its largest ring, so extra blanks are often offcuts.

The glue ledge is the only wood running through each joint, so it also limits the finished wall: the turned wall crosses the joint on the bias, and a wall T thick needs a ledge of T ÷ sin(angle), plus a margin for rings glued slightly off-center. Enter the wall you plan to turn, and the planner sizes the rings to suit.

To turn a curved bowl, design from a profile: drag the outside into shape and each ring is sized to hold the finished wall wherever it passes through that ring.

Stacked Profile Cross-Section

Glue Overlap Highlighted
R1 · AR2 · BR3 · AR4 · BR5 · AMax OD: 9.5"
Blank ABlank BGlue Ledge Holds WallLedge Too NarrowFinished Wall

Router Cut Layout (2 Blanks)

Fits Your Stock
Blank A: R1, R3, R5R1R3R5Blank B: R2, R4R2R4
Blanks: 2 × up to 10" x 10"Router Path Kerf: 0.25"Efficiency: 49.5%