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#

stock <Material> shape=round diameter=<expr> z=<expr>      // no grain argument
section axis=z [interp=linear|spline] [samples=<n>] {
    at z=<expr> { circle r=<expr> }                         // two or more stations
}

• shape= is rect (the default for every plain stock <Material> 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=<expr> { circle r=<expr> }. 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#

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 §6 ("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:

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:

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:

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:

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:

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:

circle r=rf

samples#

property; property in 23 of 116 examples (35 uses).

Shortest real use, from speaker_ported.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:

centering axis=z

pommel#

not used by any example yet.

Related terms#

• Pommel