01 · OverviewWhat this is

This packet documents an engineering prototype of a 21-string kora-inspired bridge-harp / harp-lute, driven from a parametric workbook (kora-design-table.xlsx) and a SolidWorks MasterLayout. It is not a traditional reproduction, not a production-ready commercial instrument, and not a claim of cultural authority. It is a learning build — segmented wooden bowl, through-neck/spine structural load path, tall notched bridge separating two string banks, hide or synthetic membrane head — held to a public-release-blocked status until cultural review, treble safety redesign, and proof-load tests pass.

Six coupled systems

The build packet balances six systems that move together — change one, document the cascade in the other five.

Cultural provenance

The kora is widely documented as a West African 21-string bridge-harp / harp-lute. The Met Museum collection notes describe a 21-string instrument from the Mande region with a calabash resonator, hide soundboard, long neck, handles, and a tall bridge. Britannica similarly describes a long hardwood neck passing through a hide-covered calabash resonator with 21 strings over a notched bridge. Background sources are listed in Section 15.

02 · CAD modelSolidWorks MasterLayout · KOR-000_KoraHarp

The assembly is built from a parametric MasterLayout part — bowl, rim, through-neck, crossbar, two hand handles, membrane, bridge pad, tall notched bridge, two sleeve bearings, and an eyebolt tail anchor. The basic shapes are modeled; final dimensioning, joinery, hand-post profiles, and tail-anchor hardware details still to come.

CAD viewer Loads cad/KOR-000_KoraHarp/KOR-000_KoraHarp.gltf — SolidWorks-exported glTF, 11 part buffers + leather texture.

SolidWorks QuadView — Front · Left · Top · Trimetric of the KOR-000_KoraHarp assembly. If the 3D viewer never replaces this image, the glTF at cad/KOR-000_KoraHarp/KOR-000_KoraHarp.gltf couldn't be loaded — see cad/README.md for the export route and serving notes (most likely cause: opened via file:// instead of localhost).

Assembly tree (from SolidWorks)

• KOR-000_MasterLayout — parametric layout part, source of truth for all driven dimensions
• KOR-000_Gourd — segmented bowl shell (168-stave substitute for calabash)
• KOR-000_Neck — through-neck spine (continuous structural load path)
• KOR-000_Crossbar — neck-to-hand-post / rim cross brace
• KOR-000_Handle ×2 — player hand posts
• KOR-000_Membrane — head (hide or synthetic, material TBD)
• KOR-000_BridgePad — bridge foot pad / cushion against membrane
• KOR-000_Bridge — 6.0″ tall notched bridge, two string banks
• 7815K21 ×2 — multipurpose flanged sleeve bearings (string termination hardware)
• KOR-000_Eyebolt — tail anchor (load-rated, rounded contact surfaces)

Drawings index

Photo shotlist

Production photography is gated by VAL-015. Until owned, permission-cleared visuals exist, all images in this packet are explicit placeholders. See photo-shotlist.md for the shot plan.

03 · String schedule21 strings · F3 → D6 · workbook-derived

Calculated from the workbook formula pattern (Mersenne–Taylor) using nylon density 0.04155 lb/in³, assumed breaking stress 44 600 psi, wound-string effective density factor 2.5×, and target tension ramp 8 → 14 lbf. This is a planning table, not a purchase-ready prescription.

21 strings · 17 nylon · 4 wound · highlighted rows above 85 % break · Σ planned tension ≈ 230 lbf — exceeds the 200 lbf threshold that triggers continuous through-neck / spine and load-rated tail anchor (see Section 5).

04 · Bridge & resonatorTall notched bridge · segmented bowl · membrane head

Bridge

The bridge is load-bearing and tone-shaping. It separates two string banks, maintains notch spacing, transfers load into the head without tearing, and must not rock under asymmetric playing loads. Workbook inputs: 6.0″ tall × 2.5″ wide × 0.75″ thick; 0.125″ slot clearance; ~0.273″ string spacing (6 / 22). The first bridge is sacrificial — built with extra footprint options for staged-load tests against the head.

Segmented bowl

168 staves (12 segments per ring × 14 rings × 0.75″ stave height) replace a natural calabash. This changes mass, stiffness, damping, and attachment options. Acoustic equivalence to a traditional calabash is not claimed; the first prototype is responsible for measuring open-bowl air resonance, head tap modes after membrane install, bridge-loaded head deflection at staged tension, and microphone response before and after any optional piezo install.

Membrane head

Material is either ethically sourced hide or a synthetic substitute. Final choice gates on supplier review and ethical / cultural notes. Tacks vs lacing attachment is open; both can split the rim or tear the membrane if spacing is wrong.

05 · Neck & load pathThrough-neck · tail anchor · proof-load gates

The neck is interpreted as 51.2″ long. A traditional kora neck passes through the resonator; this hybrid packet preserves a continuous structural load path rather than relying on the bowl wall alone — total string load can exceed 200 lbf under the workbook tension ramp.

Minimum first-build requirement

• Continuous neck or internal spine through the bowl — no bowl-wall-only joint at full tension.
• Separate tail ring or tail bar with mechanical backup — load-rated hardware, rounded contact surfaces (no string-cutting edges).
• No full string load until joint proof-load (VAL-008) and bridge-foot tests (VAL-010 / VAL-011) pass at 1.5× planned total tension.

06 · Bill of materials17 line items · resonator · structure · bridge · strings · electronics · fixtures · finish

All costs are planning estimates. Sourcing and supplier RFQ are tracked separately in sourcing.csv and supplier-rfq.md.

07 · Assembly manualStep-by-step build, jigs, glue-up, head install, stringing

08 · CNC & drawings briefPre-CAM operation plan · jig accuracy gates

Jigs and fixtures dominate accuracy on this build. A miter-sled error of 1 ° multiplies across 168 bowl staves and 16 rim segments — fixture validation (VAL-005 / VAL-006) gates bowl glue-up and head install.

09 · Validation gates15 checks · 8 release-blocking

Every gate has a measurement method, tolerance, and an action-if-fail. Six block public release (cultural review, treble safety, fixture accuracy on miter sled, neck/tail proof-load, bridge-foot pressure / rocking, placeholder visuals).

10 · Run it — Wolfram CloudInteractive string + bridge + bowl model

The companion notebook kora-starter.wl implements the Mersenne–Taylor string model, the workbook bridge geometry, and the segmented-bowl parameter sweep. Once wolfram-cloud-sync sets the cloud object to Public-Execute permission, this block renders an interactive embed — change parameters in the browser, see the percent-break and tension cascade live, no Mathematica install required.

How the embed got here

1. wolfram-cloud-sync upload pass pushed kora-starter.wl to CloudObject["Musical_Instruments/strings/kora/kora-starter.wl"] under the wrfcoin account.
2. wolfram_publish.wls flipped permission to Public-Execute and captured the public URL.
3. URL pasted into the data-cloud-url attribute above. Once wolfram_emit_engineering_manifest.py --apply writes the URL into capstone-manifest.json as engineering.wolfram[0].cloud_url, the future generator will source it from there.

This iframe loads from wolframcloud.com — the one section of the explorer that requires an internet connection. The rest of the page is fully offline-capable for the static content.

11 · Risk registerCultural · string-tension · bridge · resonator · neck/joint · ergonomic

Red-team pass on the build. Six families of risk, all with explicit mitigations. Cultural and treble-tension risks block public release; bridge and neck/joint risks block full-tension stringing.

12 · Capstone deliverablesDeck · print packet · explorer

Three primary deliverables for the v4.3 challenge run plus this explorer.

13 · Learn to playWarm-up scales · easy tunes · intermediate motif · original

Starter songbook seeded by the sheet-music skill. ABC source + notes per tune; LilyPond / MIDI / audio render is downstream.

Tune names like Kaira and Tutu Jara reference traditional Mande repertoire as study material; River Crossing is an original Heifer Zephyr composition. Cultural review (VAL-001) covers how this folder is presented publicly.

14 · Supplier RFQString banks · head material · tail-anchor hardware

15 · Sources & provenanceMande / kora background · workbook · prior work

• Met Museum — Kora collection notes (21-string instrument, Mande region, calabash resonator, hide soundboard, long neck, handles, tall bridge): metmuseum.org/art/collection/search/501115
• Britannica — Kora (musical instrument): long hardwood neck through hide-covered calabash, 21 strings over notched bridge: britannica.com/art/kora-musical-instrument
• Workbook — kora-design-table.xlsx, sheet Kora. Mersenne–Taylor string model; segmented-bowl geometry; bridge slot spacing formula.
• Prior work — Heifer Zephyr sambuca packet (boat-shaped arched harp) re-uses the parametric MasterLayout pattern first developed for this kora repo.
• Cultural advisors — pending. Engagement plan tracked in VAL-001; no public claims until review is on record.

License

Repo is currently private review pending the release gates listed at the top of this document. Dual-license intent (matching the Heifer Zephyr workshop precedent): design files (cad/, drawings/, cnc/, bom.csv, family-spec.csv, sourcing.csv, cut-list.csv, validation.csv, kora-starter.wl) under CERN-OHL-W-2.0; written content and media (.md docs, capstone deck, print-packet.*, site/, learn-to-play/) under CC-BY-4.0. License file will be added at the public-release transition.

16 · ImagesConcept renders