Round 5 Percussion · Lane 05 · v0.1.0-blueprint Bowed Frame Drum

Family Membranophone Frame drum

Archetype Irish bodhran, ~450 mm OD × 90 mm deep

Target pitch C3 (130.8 Hz) fundamental · A3 (219 Hz) overtone

Frame 1.0 mm CR steel, rolled cylinder, butt-TIG seam

Novel features Internal sympathetic tone bar (C4 ~257 Hz) · Optional rosined-wheel bowing drone

Status Explorer ready Private repo Build pending

Frame OD

450 mm90 mm depth

Head playing OD

430 mm18" Remo Skyndeep

Fundamental

C3 · 130.8 HzBessel f₀₁ mode

Tone bar pitch

~257 HzC4 − 27¢, trim-tunable

Wall thickness

1.0 mm CRASTM A1008

Est. build cost

~$107materials + head

Total mass

~900 gframe + hardware + head

Tension screws

6 × M460° spacing on OD

Design thesis: A bodhran-scale frame drum with a rolled 1.0 mm cold-rolled steel cylinder frame instead of traditional laminated wood. Inside the frame, a flat CR-steel tone bar (400 × 25 × 1 mm) on neoprene grommets vibrates sympathetically when the head is struck, adding an overtone shimmer near C4. An optional rosined brass wheel on a cantilevered arm produces sustained bowed drone from 80–400 Hz, transforming this percussion instrument into a hybrid membranophone/bowed instrument.

Sheet-Metal Challenge The frame ring is the simplest formed part in the Round 5 set — a single-seam rolled cylinder — but the internal tone bar suspension and optional rosined-wheel pivot arm add precision fabrication requirements. The butt-TIG seam on 1.0 mm CR stock requires coupon testing to dial in heat input before committing to the full blank.

EngineeringParameters

All dimensions driving fabrication and acoustic models. Source: parameters.csv

Name	Value	Unit	Source	Confidence

ProcurementBill of Materials

Source: bom.csv · ~$107 USD total estimated build cost

Part	Qty	Material	Supplier	Cost USD	Lead (days)	Notes

QualityValidation

Predicted values from Wolfram acoustic model. Measured column populated after physical build. Source: validation.csv

Metric	Predicted	Measured	Units	Pass/Fail	Tolerance	Notes

AcousticsWolfram Starter Model

First-order acoustic model covering circular membrane Bessel modes, tone bar Euler-Bernoulli bending modes, sympathetic coupling check, and rosined wheel excitation bandwidth. Source: bowed-frame-drum-starter.wl

Model Overview

Head f₀₁ (predicted)

130.0 HzC3 target — solved from T

Head f₁₁ (predicted)

~219 HzA3 natural overtone

Tone bar mode 1

~257 HzC4 − 27¢ (free-free)

Coupling delta

~17%f₁₁ vs bar mode 1

▶ bowed-frame-drum-starter.wl Wolfram Acoustic model source

Loading bowed-frame-drum-starter.wl…

BuildFabrication Plan

7-stage, 38-step sequence using Maker Nexus tooling. Source: fabrication-plan.md

Stage 1

Frame ringSlip-roll + butt-TIG

Stage 2

Rim stripsRoll + continuous TIG

Stage 3

Tone bar + bracketsLaser cut + brake bend

Stage 4

Internal assemblyRivet + grommet + bar

Stage 5

Rosined wheelPivot + rosin (optional)

Stage 6

FinishSand 120→320 + coat

Stage 7

Head installStretch + tension + tune

Coupon Tests Required 1. Slip-roll spring-back coupon (200 × 90 mm strip) before rolling frame blank — adjust roll gap until OD = 450 ± 1 mm. 2. TIG butt-weld coupon (150 mm test strip) before welding frame seam — bend to fracture to confirm full fusion.

CADFlat Patterns & Bend Table

DXF layer scheme: CUT (red), BENDS (yellow), ETCH (cyan), HOLES (magenta). Units: mm.

Part Summary

Part	Blank L (mm)	Blank W (mm)	Process
Frame ring	1414.7	90.0	Slip-roll → TIG seam
Rim strip (×2)	1414.7	12.0	Slip-roll → TIG to frame edges
Tone bar	400.0	25.0	Laser cut flat (no forming)
Mount bracket (×2)	30.0	25.0	Laser cut + 90° brake bend
Wheel arm	80.0	15.0	Laser cut + 2× 45° brake bends

Bend Table

Feature	Part	Angle	Inside R (mm)	K-factor	Thickness (mm)	BA (mm)	Seq
B01	Mount bracket	90°	1.5	0.44	1.0	3.21	1
B02	Wheel arm bend 1	45°	1.5	0.44	1.0	1.60	1
B03	Wheel arm bend 2	45°	1.5	0.44	1.0	1.60	2

AcousticsTuning Notes

Head Tuning Formula

f₀₁ = (2.4048 / (2π r)) × √(T / σ)

r  = 0.215 m  (head radius)
σ  = 0.35 kg/m²  (goatskin) or 0.25 (synthetic Skyndeep)
T  = surface tension N/m  (set by screw tension)
Target: f₀₁ = 130.8 Hz (C3)

Screw-to-Pitch Quick Reference

Turns (star pattern)	ΔT (N/m est.)	Δf₀₁ (Hz est.)
¼ turn	+12	+4–8
½ turn	+24	+8–15
1 full turn	+48	+15–30

Tone Bar Trim Table

Trim each end	Bar length (mm)	f_bar1 (Hz, approx)	Note
0 mm	400	257	C4 − 27¢
5 mm	390	270	C#4 − 4¢
10 mm	380	285	C#4 + 94¢ ≈ D4
20 mm	360	318	Eb4

EngineeringRisks

Manufacturing Risks

Risk	Likelihood	Impact	Mitigation
Spring-back → out-of-round frame	Medium	High	Mandatory coupon test before full blank
TIG seam distortion	Medium	Medium	V-block jig; short passes; cool between
Rim strip weld high spot	Low	High	Grind + straightedge check
Wheel arm angle miss	Medium	Medium	Cardboard prototype first

Acoustic Risks

Risk	Likelihood	Mitigation
Tone bar coupling inaudible (17% delta)	Medium	Shorten bar 20 mm → 318 Hz closer to A3 overtone
Rosined wheel: squeak only, no drone	Medium	More rosin; lighter pressure; slower bow
Head fundamental unreachable	Low	Switch to lighter synthetic head (σ ≈ 0.25 kg/m²)
Sympathetic bar rattle	Low	Add thin foam strip between bar and grommet

DocumentationImages

20 shots required for capstone deck. Placeholders shown below. See photo-shotlist.md for full list.

bowed-frame-drum — rosined wheel arm macro

bowed-frame-drum — suspended tone bar macro

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Frame ring blank

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Slip-roll in action

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TIG seam weld

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Roundness QC

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Tone bar suspended

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Rosined wheel detail

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Head installation

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Finished drum front

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Finished drum profile

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Tuner app C3

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Player holding drum

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Bowing demo

Interactive Wolfram Model

Live parametric explorer (empirical estimates — not fabrication authority).