# Round Stock & Sections *Turned parts: round stock, circle sections, and the square pommel* **Names:** `shape` `rect` `round` `section` `interp` `circle` `samples` `axis` `pommel` ## When to use A lathe-turned part: a table leg, a spindle, a chess piece, a wagon-wheel hub. The blank is round or square stock, and a `section` of stations sets the turned profile. Turned parts are a bench operation in the fabrication pack (no CNC setup spins a spindle). ## Syntax ```text stock shape=round diameter= z= // no grain argument section axis=z [interp=linear|spline] [samples=] { at z= { circle r= } // two or more stations } ``` - **`shape=`** is `rect` (the default for every plain `stock x y z`) or `round`. Round stock takes named `diameter=` and `z=` (the length along the spindle axis), never a grain word: its grain is lengthwise by definition and naming one is rejected. - **`section`** stations are sorted by `z` at compile time, whatever the write order. Each is `at z= { circle r= }`. `interp=linear` (default) makes straight facets between stations; `interp=spline` resamples a centripetal Catmull-Rom curve through them (`samples=`, default 64). - **The declared `diameter` must be at least twice the widest `circle` station**, or the build refuses it (the blank is narrower than the part). - A turned part is a stock primitive, not a cutter: ordinary features (`hole`, a joint's mortise) still cut it. Anchors `top_center`, `bottom_center`, `center` are the spindle axis exactly. The corner anchors stay legal but sit in wood the lathe has removed. - **Square pommel (RFC-0127):** keep ordinary square `stock` (no `shape=round`) and give a `section` whose stations do **not** reach the part's top face. Above the topmost station the square stays untouched (the pommel); below it the part is turned. The last station must reach the part's own foot (`z = -leg_len`) exactly. The topmost radius may be up to half the stock width: equal for a flush transition, a little less for a small shoulder. A tenon goes into the **square** pommel, never the round part. ## Example ```kdl project name="Turned Leg" units=mm schema_version=1 { params { leg_dim 45.0 leg_len 700.0 pommel_h 90.0 foot_r 14.0 } materials { material Ash type=hardwood } component Leg role=leg { stock Ash leg_dim leg_dim leg_len section axis=z interp=linear { at z="0.0 - pommel_h" { circle r="leg_dim / 2.0" } at z="0.0 - leg_len" { circle r=foot_r } } mark MortiseFace_X x=leg_dim y="leg_dim / 2.0" z="0.0 - pommel_h / 2.0" normal=pos_x } component Pawn role=game_piece { stock Ash shape=round diameter=40.0 z=60.0 section axis=z interp=spline samples=48 { at z=0.0 { circle r=6.0 } at z=-30.0 { circle r=10.0 } at z=-60.0 { circle r=16.0 } } mark AxisTop x=20.0 y=20.0 z=0.0 normal=pos_z } assembly Root { part Leg_A instance=Leg { by top_sw; pos x=0.0 y=0.0 z=0.0 } part Pawn_A instance=Pawn { by top_sw; pos x=200.0 y=0.0 z=0.0 } } } ``` ## Pitfalls and diagnostics - **Not built (residual):** a `rect`-family `section` (a non-circular varying profile; only `circle` stations exist), and a mark on the curved turned surface (only the flat axis ends, `normal=pos_z`/`neg_z`, are reachable; a mortise cut into a curved face is not modelled). Another file in `INDEX.md` may lift these (faceplate and rectangular sections); the newer file wins. - A grain argument on `shape=round` stock is an error; so is a grain word on a `type=sheet` material. - A `section` that stops short of the foot leaves square material floating under a round run; the build refuses it. Make the last station land on `z = -leg_len`. - A station radius over half the square stock width is refused (the blank cannot hold it). - A tenon into the round part cannot be modelled: tenon into the pommel, or use a `round_tenon` (see `joinery-tenons`) on a turned member's flat end. ## See also - `docs/KDL_AUTHORING.md` ยง6 ("Turned stock"); ADR-0018; RFC-0020 (turned round stock), RFC-0127 (pommel). - `examples/chess_pawn.kdl`, `examples/spindle.kdl`, `examples/shaker_side_table.kdl`, `examples/wagon_wheel.kdl`, `examples/speaker_ported.kdl`. - `components-and-stock.md`, `joinery-tenons.md`. ## Names Every name this page declares, how the example library uses it, and the shortest real use. ### `shape` word-valued property; property in 66 of 116 examples (133 uses). Shortest real use, from `appalachian_ladder_back_side_chair.kdl`: ```kdl pin shape=round size=3.0 ``` ### `rect` stock shape; node in 15 of 116 examples (101 uses). Shortest real use, from `appalachian_ladder_back_side_chair.kdl`: ```kdl rect x_min=0.0 x_max=pw y_min=0.0 y_max=pd ``` ### `round` stock shape, expression function; value in 44 of 116 examples (89 uses). Shortest real use, from `appalachian_ladder_back_side_chair.kdl`: ```kdl pin shape=round size=3.0 ``` ### `section` feature, word-valued property; node in 47 of 116 examples (93 uses); property in 18 of 116 examples (36 uses). Shortest real use, from `pop_laminate_stepped_sideboard.kdl`: ```kdl section axis=z interp=linear { at z=0.0 { circle r="drum_d / 2.0" } at z="0.0 - drum_h" { circle r="drum_d / 2.0" } } ``` ### `interp` word-valued property; property in 41 of 116 examples (80 uses). Shortest real use, from `pop_laminate_stepped_sideboard.kdl`: ```kdl section axis=z interp=linear { at z=0.0 { circle r="drum_d / 2.0" } at z="0.0 - drum_h" { circle r="drum_d / 2.0" } } ``` ### `circle` node in 40 of 116 examples (933 uses). Shortest real use, from `windsor_round_stool.kdl`: ```kdl circle r=rf ``` ### `samples` property; property in 23 of 116 examples (35 uses). Shortest real use, from `speaker_ported.kdl`: ```kdl section axis=z interp=linear samples=2 { at z=0.0 { circle r=port_outer_radius } at z="0.0 - port_length" { circle r=port_outer_radius } } ``` ### `axis` word-valued property; property in 72 of 116 examples (173 uses). Shortest real use, from `arched_crest_side_chair.kdl`: ```kdl centering axis=z ``` ### `pommel` not used by any example yet. ## Related terms - [Pommel](/almanac/techniques#pommel)