Shakuhachi — SHK-D4-P1

1.8-shaku D4 solid-billet hardwood prototype · open-pipe acoustics · headstock-driven deep-bore drilling
family · open-pipe pipeline · cnc-lathe status · scaffold → packet date · 2026-05-07

What this is

A small, manufacturable family of solid-billet hardwood shakuhachi — built on a Western luthier's lathe + drill press, not from split madake bamboo. The first prototype is SHK-D4-P1: 1.8-shaku D4 in cherry, with the long bore drilled using the headstock-driven deep-bore drilling technique on square stock before the outside is turned round.

This page is the public build log. The raw packet (design.md, BOM, cut list, validation, assembly manual) lives in the repo root; the parametric design table is shakuhachi-design-table.xlsx.

Cultural framing

The shakuhachi (尺八) descends from Tang-Chinese xiao ancestors imported to Japan in the 7th–8th c., and was central to the practice of suizen (“blowing meditation”) within the Fuke sect of Zen Buddhism (Edo-period komusō, or “emptiness monks”). The Meiji government banned the Fuke sect in 1871; the instrument survived in concert use, and modern Kinko-ryū and Tozan-ryū schools continue the tradition. Traditional makers in Kyoto, Tokyo, and Hamamatsu still use madake bamboo with urushi-lined bores.

The instruments built from this packet are Western luthier-shop adaptations that respectfully model the shakuhachi's acoustics and finger-hole logic without claiming to replicate the traditional craft. Where this packet diverges from tradition (solid billet, hardwood, straight bore, oil finish, no urushi), it is documented as such.

Governing model

Open-open pipe with two open ends — foot and utaguchi:

f = c / (2 · L_eff)
L_eff = L_physical + δ_foot + δ_utaguchi
δ_foot ≈ 0.6 · r_bore                    (standard open-end correction)
δ_utaguchi ≈ 1.5 · r_bore – 2.0 · r_bore  (empirical; shakuhachi-specific)
hole_distance_from_foot ≈ L_acoustic · (f_fund / f_hole)

The standard 0.6·r foot correction is well-validated. The utaguchi end is harder: a beveled notch with player jet excitation extends the acoustic open-point past the physical rim. Back-fitting from the canonical 1.8-shaku ↔ D4 anchor gives a per-end correction of ~1.7·r, which the empirical loop refines after the first measurement.

Empirical-correction guard: Tony's NAF K2 corrections do not apply here. They were derived from fipple-block + slow-air-chamber NAFs; the shakuhachi has neither. K2 columns in the workbook are intentionally blank for shakuhachi rows.

First prototype: SHK-D4-P1

Hole stations (acoustic first-pass)

Drawings

Build workflow

Validation criteria

• Bore wander < 0.020 / 0.040 / 0.080 in at 6 / 12 / 18 in (pine scrap pass)
• Bore ovalization < 0.005 in at any station
• Wall thickness ≥ 0.150 in at every quadrant
• Ro fundamental within ±25 cents pre-tuning, ±10 cents post-tuning
• All five holes within ±10 cents of target after filing
• Octave (Ro → Ro′) within ±25 cents
• 30-day pitch drift < 5 cents at constant 68 °F

Open assumptions

1. δ_utaguchi ~1.7·r is empirical; first measurement re-fits it.
2. Bore is straight cylindrical. Traditional madake bore tapers; documented divergence.
3. Hole diameters uniform 0.276 in starting size. Real shakuhachi often 8–10 mm — start small, file open.
4. Wood-species sensitivity unmeasured. Cherry first; backup species spec'd.
5. No urushi lining. Western prototype uses oil finish.
6. Player calibration absorbed into utaguchi correction. Test player = TK; cross-player corrections deferred.

Family roll-out (after SHK-D4-P1 validates)

The 11-key family in the design table (C4 through B4 + higher) reads forward from the corrected δ_utaguchi value. Re-cut sibling blanks only after the empirical loop tightens predictions to ±15 cents.

Cross-references

• instrument-maker#84 — headstock-driven deep-bore drilling
• tonykoop/flutes — NAF family (K2 reference; do not port to shakuhachi)
• tonykoop/fujara — long open-pipe stave-built sister
• tonykoop/transverse-flute — slip-cast open-pipe sister; packet template