# 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 ```kdl grammar material Steel type=metal thermal_expansion=0.000012 // per kelvin stock shape=ring diameter= section_w= section_h= constraint shrink from= to= radial_interference= temperature= [ambient=] ``` - `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 ```kdl 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`: ```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`: ```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`: ```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`: ```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`: ```kdl material Acrylic type=sheet substance=acrylic nominal_th=6.0 finished_th=6.0 color="#d8ecf2" ``` ### `tempered` not used by any example yet.