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Mechanical

Mechanical features help you model real-world hardware quickly—smooth pipe transitions, printable rods, and robust screw threads. All measurements are in millimeters and the Z-axis is the default axial direction.

ThreadSpec

ThreadSpec captures all parameters needed to generate compatible external (rod) and internal (cutter) threads. It’s based on a fit diameter centered at the pitch radius, so the same spec can drive both male and female parts with predictable clearance.

Create & Normalize

local ts = ThreadSpec.new()
ts.fitDiameter = 20.0 -- at pitch radius × 2
ts.pitch = 2.0 -- mm per revolution
ts.depth = 0.9 -- radial depth from pitch radius
ts.clearance = 0.20 -- extra clearance for FDM
ts.segmentsPerTurn = 48 -- smoothness
ts.handed = "right" -- "right" | "left"
ts.tip = "cut" -- "sharp" | "cut"
ts.tipCutRatio = 0.4 -- 0.0..1.0 (only used when tip="cut")

ts:normalize() -- clamp/validate fields (recommended)

Fields

  • fitDiameter (number) — pitch radius × 2 used for both mating parts
  • pitch (number) — axial advance per turn (mm/rev)
  • depth (number) — radial thread depth from pitch radius to crest/root midline
  • clearance (number) — extra radial slack; typical 0.10–0.30 for FDM printing
  • segmentsPerTurn (integer) — tessellation density (more = smoother)
  • handed ("right"|"left") — winding direction
  • tip ("sharp"|"cut") — crest style
  • tipCutRatio (number) — truncation fraction for "cut" tips, usually 0.3–0.5

Practical guidance

  • Use the same fitDiameter and pitch for mating rod/nut pairs.
  • Increase clearance for tighter printers/materials; reduce for precision fits.
  • segmentsPerTurn of 32–64 is a good balance for most parts.

Pipe Adapter

pipe_adapter(rIn0, rOut0, rIn1, rOut1, length, steepness?)

Builds a smooth, revolved transition between two coaxial pipes. The adapter’s axis is Z; radii are taken at z=0 and z=length.

-- Transition from a 20×26 pipe (ID×OD) to a 12×16 pipe over 40 mm
local adapter = pipe_adapter(
    10,
    13, -- rIn0, rOut0 (ID=20 -> rIn0=10; OD=26 -> rOut0=13)
    6,
    8, -- rIn1, rOut1 (ID=12 -> rIn1=6; OD=16 -> rOut1=8)
    40, -- length
    8 -- steepness (optional, 4..12; higher = gentler blend)
)
emit(scale(adapter, 0.2))

Parameters

  • rIn0, rOut0: inner/outer radius at z=0
  • rIn1, rOut1: inner/outer radius at z=length
  • length: axial distance along Z
  • steepness?: smoothing factor [4..12] (defaults to a balanced value)
  • Returns Shape — a watertight revolved solid

Notes & Tips

  • Use for reducers/expanders between hose or pipe standards.
  • Keep wall thickness reasonable: rOutX - rInX should reflect manufacturable walls.
  • Increase steepness for a longer, gentler transition (better flow, less turbulence).

Rod

rod(diameter, length, chamferBottom?, chamferTop?)

Creates a cylindrical rod with optional end chamfers—handy as a starting shaft or as a carrier for threads.

-- 8 mm × 30 mm rod with a small chamfer on both ends
local r = rod(8, 15, true, true)
emit(r)

Parameters

  • diameter: outer diameter (OD)
  • length: along the Z-axis
  • chamferBottom?, chamferTop?: booleans to ease starts and reduce elephant-foot
  • Returns Shape — solid cylinder with optional chamfers

Threaded Rod

threaded_rod(totalLength, threadLength, threadSpec)

Generates an external threaded shaft and returns both the solid and the actual major diameter applied after any adjustments for tip style and clearance.

-- M20-ish printable rod: 60 mm long, 45 mm threaded section
local ts = ThreadSpec.new()
ts.fitDiameter = 20.0
ts.pitch = 2.0
ts.depth = 0.9
ts.clearance = 0.20
ts.segmentsPerTurn = 48
ts.handed = "right"
ts.tip = "cut"
ts.tipCutRatio = 0.4
ts:normalize()

local tr, major = threaded_rod(15, 10, ts)
emit(tr)

Parameters

  • totalLength: full shaft length (mm)
  • threadLength: axial length of the threaded section (0..totalLength)
  • threadSpec: a validated ThreadSpec
  • Returns
  • Shape — the threaded rod solid
  • number — actualMajorDiameter (mm)

Patterns & Tips

  • For partial threading, set threadLength < totalLength (e.g., leave a smooth shank).
  • Use handed="left" for reverse threads in anti-rotation features.
  • For small pitches or brittle materials, prefer tip="cut" with tipCutRatio≈0.4.
  • Increase segmentsPerTurn for close-up aesthetics or metal printing.

Gotchas

  • Units & axes: All distances in mm; axial features are aligned to Z.
  • Validate specs: Always call spec:normalize() to clamp and sanity-check inputs.
  • Wall checks: Ensure rOut − rIn stays positive and realistic for printing or machining.
  • Mating threads: Reuse the same fitDiameter/pitch for male/female; tune clearance for your process.
  • Geometry complexity: Extremely tight bends, tiny pitches, or abrupt transitions may challenge meshing—raise segmentsPerTurn or adjust dimensions.

These mechanical tools give you parametric, fabrication-ready parts—smooth pipe transitions, robust rods, and threads that actually fit.