Non-Wood Materials#

Ring stock, shrink-fit pre-stress, and external, bought-in parts

Names: stock ring constraint to substance tempered

status: partial. Built: stock shape=ring, constraint shrink, non-timber sheet goods (type=sheet substance=acrylic|solid_surface|glass|laminate, tempered=#true), the material-pair joint allow-list, and the SUPPLY section of the cut list (ADR-0033, ADR-0076). external_part (RFC-0121 Level 3) is rejected permanently — do not write it; it does not parse. For a bought assembly use a hardware catalogue entry and hardware_mount, or a proxy component (ADR-0017, ADR-0076, docs/KDL_AUTHORING.md §5). Stress, force and pull-out are not modelled; the shrink report is geometric only, not a structural check.

When to use#

• A part that is a rolled or forged band, not a sawn or turned one: a wagon wheel's iron tyre, a barrel hoop, a steel collar on a post. Material is type=metal.
• A band fitted by shrinking: made a little too small, heated, dropped on, left to cool. constraint shrink states the fit and the compiler checks it, so the deliberate overlap is not reported as a clash.
• Any part that is bought or made to order rather than cut from timber: a type=metal part is listed under SUPPLY in the cut list and left out of timber volumes, boards and blank sizes.

Syntax#

material Steel type=metal thermal_expansion=0.000012      // per kelvin

stock <metal> shape=ring diameter=<outer> section_w=<axial width> section_h=<radial thickness>

constraint shrink from=<ring part> to=<part> radial_interference=<mm> temperature=<degC> [ambient=<degC>]

• diameter is the outer diameter; the bore is diameter / 2 - section_h. The ring sits in its circumscribing square with its top face at z = 0 (D4), like every other part.
• shape=ring takes the material and no other positional argument: no x y z, no grain word. It needs all three of diameter=, section_w=, section_h=. Only a type=metal material may be a ring.
• constraint is an assembly-scope node, may sit inside a repeat, and to= takes the same {i} interpolation as part id=. ambient= defaults to 20 degC. The material of from must declare thermal_expansion=.
• What it checks: (1) the built overlap is the declared radial_interference (within 0.1 mm); (2) at temperature= the bore r (1 + alpha (T - T0)) clears to; it reports the lowest temperature that does, and the hoop strain interference / r.

Example#

project name="Banded Plug" units=mm schema_version=1 {
    params {
        plug_diameter  300.0 min=200.0 max=500.0 label="Plug Diameter"
        plug_len        20.0 min=10.0 max=60.0  label="Plug Length"
        band_th          6.0 min=3.0  max=12.0  label="Band Thickness"
        interference     0.5 min=0.3  max=1.5   label="Band Interference (radial)"
        heat_c         400.0 min=150.0 max=600.0 label="Band Heat (degC)"
        // Outer diameter of the band: the plug's diameter plus the band's wall, less what the
        // band is made too small by.
        band_diameter  "plug_diameter + 2.0 * (band_th - interference)"
        band_depth     "band_th"
        plug_r         "plug_diameter / 2.0"
    }

    materials {
        material Oak   type=hardwood
        // `thermal_expansion` is per kelvin; the shrink fit's heating arithmetic needs it.
        material Steel type=metal thermal_expansion=0.000012
    }

    component Plug role=plug {
        stock Oak shape=round diameter=plug_diameter z=plug_len
        // Round stock is only round once it is turned: a plain cylinder is two stations.
        section axis=z interp=linear {
            at z=0.0 { circle r=plug_r }
            at z="0.0 - plug_len" { circle r=plug_r }
        }
    }

    // A rolled band: outer diameter, axial width, radial thickness. No grain word.
    component Band role=band {
        stock Steel shape=ring diameter=band_diameter section_w=plug_len section_h=band_depth
    }

    assembly Banded {
        part Plug instance=Plug {
            by top_center
            pos x=0.0 y=0.0 z=0.0
        }
        part Band instance=Band {
            by top_center
            pos x=0.0 y=0.0 z=0.0
        }
        constraint shrink from=Band to=Plug radial_interference=interference temperature=heat_c
    }
}

ww clash on it reports 0 clashes, the overlap as design interference, and the fit: 0.500 mm interference (bore r = 149.500, fit r = 150.000); at 400 degC the bore clears by 0.182 mm; it fits from 299 degC; the shrink asks 0.00334 of strain and heating to 400 degC supplies 0.00456 (labelled geometric only, not a structural check). A worked example with six felloes and six spokes is examples/wagon_wheel.kdl.

Pitfalls and diagnostics#

• Round stock without a section is a square block. The plug above needs its two-station section to be a cylinder; without it the ring "reaches" the block's corners and the fit fails with an interference of several millimetres.
• declared radial_interference=… but the built solids interfere by …: the ring's stock and the constraint disagree. The ring's bore is diameter / 2 - section_h; make the constraint say what the geometry says, or the geometry what the constraint says.
• … does not clear … the ring cannot be fitted; heat it to at least N degC: a steel ring grows about 1.2e-5 per kelvin, so 1 mm on a 49 mm bore needs about 1,700 degC. Interference is small relative to the radius for a reason: raise the radius, lower the interference or raise temperature=.
• … declares no thermal_expansion=: add thermal_expansion=0.000012 (steel) to the material.
• `X` is a wood joint, but the male part `Y` is Steel: wood joinery (mortise_and_tenon, dowel, lap, …) is refused on a non-wood part. Only butt and hardware_mount may touch one; hold a band with constraint shrink.
• A ring overlapping a part it has no constraint to stays an ordinary clash. So does one whose constraint failed.
• The tolerance is 0.1 mm. A flat tang end 0.083 mm proud of a curved tread passes, a 1 mm discrepancy does not. A constraint that only passes within the tolerance is a modelling artefact worth a comment, as in the wagon wheel.
• Not modelled, and not claimed: hoop stress, clamping force on the joints, wood crushing, yield. A constraint shrink is geometry and linear thermal growth only.
• kdl-check rejects a grain word on a type=metal material, an unknown constraint kind and a shape=ring stock missing a dimension.

See also#

• docs/adr/0033-non-wood-materials-levels-2-3.md (decisions, the measured wagon wheel)
• docs/rfc/0121-non-wood-materials-and-hardware.md (Level 3, external_part, not built)
• docs/adr/0017-hardware-and-materials.md (Level 1: type=metal, hardware)
• docs/KDL_AUTHORING.md §5 materials
• examples/wagon_wheel.kdl, examples/filing_cabinet_vertical.kdl (metal parts, supplied)

Names#

Every name this page declares, how the example library uses it, and the shortest real use.

stock#

feature; node in 114 of 116 examples (910 uses).

Shortest real use, from glazed_vitrine_whiplash_crest.kdl:

stock Glass dw 6.0 dh

ring#

stock shape; value in 1 of 116 examples (1 uses).

Shortest real use, from wagon_wheel.kdl:

stock Steel shape=ring diameter=wheel_diameter section_w=rim_width section_h=tyre_band

constraint#

node in 1 of 116 examples (2 uses).

Shortest real use, from wagon_wheel.kdl:

constraint shrink from=Tyre to="Spoke_{k}" radial_interference=tyre_interference temperature=tyre_heat_c

to#

word-valued property; property in 2 of 116 examples (3 uses).

Shortest real use, from blanket_chest.kdl:

distribute from="0.0 - (hinge_zone / 2.0)" to="hinge_zone / 2.0"

substance#

property; property in 1 of 116 examples (1 uses).

Shortest real use, from acrylic_panel_frame.kdl:

material Acrylic type=sheet substance=acrylic nominal_th=6.0 finished_th=6.0 color="#d8ecf2"

tempered#

not used by any example yet.