# Nyckelharpa Design Study ## Design Thesis This concept treats the nyckelharpa as a keyed bowed fiddle where the keyboard is not decorative hardware; it is the acoustic control surface. The L2 uplift keeps the instrument in shop-planning authority: it names the assemblies, interfaces, test rigs, and failure modes that a builder should review before any measured layout, CAD, DXF, tuning, or string schedule is claimed. The hard design problem is keeping tangent contact repeatable while the bowed strings vibrate, the sympathetic strings remain free to ring, and the player can service the keybox without disturbing the whole setup. ## Mechanism Overview The player bows the melody strings while the left hand operates keys. Each key slides in the keybox and carries a wooden tangent. When the key is pressed, the tangent contacts a melody string from the side and defines a stopped speaking point. The tangent must meet the string cleanly, avoid dragging during release, and return without rattling. Sympathetic strings are not stopped by the main key action. They are routed below or through the keybox so they can respond to the bowed melody strings. Their path must preserve clearance from moving keys and tangents, protect the strings from accidental contact, and leave enough service access for tuning, replacement, and resonance experiments. The bridge, nut, tailpiece, keybox, pegbox, and body are coupled. A change in keybox height, bridge crown, string path, tangent face, or sympathetic-string clearance changes action feel and tone. This packet therefore records named setup variables and shop-review fixtures rather than pretending a first-pass drawing is build authority. ## L2 Assembly Plan The first physical work should be split into small assemblies before a full instrument is attempted: - A bowed-string rail that holds one melody string over adjustable nut, bridge, and tail references. - A removable keybox cassette that can slide one or more keys against the test string without being glued into a body. - A tangent carrier that allows contact-face swaps, height adjustment, and release-clearance inspection. - A sympathetic-string underpass mockup that shows how resonance strings can pass below the keybox without being touched by moving keys. - A body and soundboard planning shell that only tests service access, load paths, and mounting order. Each assembly remains `pending_measurement`. The packet does not choose final dimensions or release any part as fabrication authority. ## Subsystems ### Bowed String Core - Melody strings are the directly bowed voices. - Bow response depends on bridge shape, string path, bow clearance, string material, and setup, all pending measurement. - The L2 shop plan adds a test rail for one bowed string so tangent contact can be assessed before a full keybox exists. - No tuning, string count, string gauges, or scale length are released in this packet. ### Keybox And Sliding Keys - The keybox needs straight, low-friction key travel and a stable reference plane. - Keys need return behavior that is quiet, repeatable, and serviceable. - Tangents should be individually adjustable during setup. - Key travel, key spacing, guide material, and return method are all `estimate_pending_measurement`. - The preferred L2 study object is a removable cassette so key friction, return, and side-play can be tested outside the body. - The cassette should include inspection access for the underside and the sympathetic-string path rather than trapping those decisions inside the case. ### Tangent Contact - The tangent face is the pitch-setting contact element. - Contact should stop the string clearly without crushing, buzzing, or scraping. - Tangent geometry must allow fine adjustment after the actual string path is measured. - First prototypes should separate tangent-contact tests from full instrument body work. - Contact behavior should be logged as clear stop, muted stop, scrape, buzz, double-contact, or missed return. - The tangent should be replaceable as a small part in the first rig so face material and grain orientation can be compared without rebuilding the key. ### Sympathetic String Path - Sympathetic strings need their own nut, bridge, tail, and tuning access. - The path must pass near the resonant body while avoiding key and tangent interference. - Resonance is a setup variable, not a guarantee. The first build should log which strings respond, which remain weak, and which cause unwanted noise. - The underpass path should be represented by a serviceable mockup before final body closure. - The path must reserve access for string replacement, tuning hardware, damping experiments, and cleaning. ### Body And Service Access - The body must support bowed-string load, keybox fasteners, bridge load, and sympathetic-string routing. - Removable or inspectable keybox panels are preferred for early prototypes. - The design should keep tangent adjustment, key cleaning, and sympathetic string replacement possible without full disassembly. - The body plan should identify removable panels, keybox fastener access, and non-destructive inspection routes before any exterior form is fixed. - Glue-ups, closed cavities, and decorative covers should wait until the keybox and sympathetic-string service model are reviewed. ## Build Sequence Intent 1. Build the one-string tangent contact rig. 2. Add one sliding key and one adjustable tangent. 3. Add a sympathetic-string clearance mockup below the keybox plane. 4. Add bridge, nut, and tail reference blocks that can be repositioned for measurement. 5. Review service access and remove any part that traps tuning or key repairs. 6. Only after those gates pass, draft a measured body/keybox layout for future L3 work. The numbered order is a review sequence, not fabrication instruction. ## Parametric Intent Future design work should use named parameters before any fabrication file is created: - `estimate_body_outline_pending_measurement` - `estimate_melody_string_count_pending_measurement` - `estimate_sympathetic_string_count_pending_measurement` - `estimate_key_count_pending_measurement` - `estimate_keybox_reference_height_pending_measurement` - `estimate_key_travel_pending_measurement` - `estimate_tangent_contact_face_pending_measurement` - `estimate_bridge_crown_pending_measurement` - `estimate_string_path_clearance_pending_measurement` These names are placeholders, not values. ## First Measurement Gates - Key action: verify smooth travel, return, and side-play on a bench keybox. - Tangent contact: test one adjustable tangent against one melody string before making a full keyboard. - Clearance: check tangent release and sympathetic-string clearance with a transparent or open keybox mockup. - Bowing: confirm bridge and string path provide playable bow access before finalizing body layout. - Resonance: document sympathetic response only after actual string paths, bridge contact, and body coupling are present. - Serviceability: prove a key, tangent, and sympathetic string can be adjusted or replaced without destructive disassembly. - Assembly order: confirm the keybox, bridge references, and sympathetic path can be installed and removed in a repeatable review sequence. - Documentation: log each failure mode with photos or notes before changing tangent face, guide material, or string path. ## L2 Boundary This file is a concept and shop-planning risk map. It does not provide CAD, DXF, tooling instructions, dimensions, tuning, string gauges, or a measured acoustic model. All physical values and future part blanks remain estimates pending measurement.