SMACNA HVAC Duct Construction & True-Length Triangulation Standard 1:1 DXF · SVG · PDF Default Spec: 200 × 120 × 140 mm (T=1.2mm)

HVAC Sheet Metal Duct Transition & Trapezoidal Hopper Reducer Flat Pattern Generator (DXF)

1:1 CAD ENGINE READY

HVAC Sheet Metal Duct Transition & Trapezoidal Hopper Reducer Flat Pattern Generator (DXF)

1CAD Style & Material SetupSheet

Select CAD Style / Model (36)Search & Filter

Material Stock Preset (Auto-Sets Caliper T & Kerf K)

Display Units

Scale Lock

1:1 True Scale

2Dimensions (1:1)Millimeters (mm)

Bottom Inlet Width (L mm)200 mm

Top Outlet Width (W mm)120 mm

Vertical Duct Height (H mm)140 mm

Thickness (T mm)

Laser Kerf (K mm)

3Brand Logo & 1:1 ExportZero Login

2D & 3D Brand Logo Mockup:

📤 Upload Logo

Print Artwork Bleed Guide:

Embed Spec Sheet & 50mm / 1" Scale Bars (Added on separate DIMENSIONS layer)

Pre-Flight Geometry Audit8/8 PASSED

PASS
Closed Outer Contours: 1 closed LWPOLYLINE cut loop(s) verified
PASS
Zero Duplicate Cut Paths: 8 unique segments (0 laser double-burns)
PASS
Flute & Kerf Tolerance Guard: T=1.20mm, K=0.000mm within structural limits
PASS
ISO Layer Color Separation: CUT (Red), CREASE (Blue), SCORE (Emerald), DIMENSIONS isolated
PASS
1:1 Physical Unit Header: Explicit mm/in SVG viewBox + DXF $INSUNITS=4 + 50mm PDF bar
PASS
Exact 2D Cut Bounding Parity: Cut Bounds 834.86×181.6mm === Blank Size
PASS
2D ↔ 3D Kinematic Model Sync: Archetype 'sheet_metal_transition' synced (1 3D component(s))
PASS
True Vector Sheet Nesting Sync: 1:1 vector paths mapped to multi-up sheet grid

100%

CUT (1.83m) CREASE/SCORE (2.97m)● 1 Loops · Est. Cut: ~77s

1:1 Synced · Blank: 834.86 × 181.6 mm

2D 1:1 Unfolded Vector BlueprintBlank: 834.86 × 181.6 mm (32.87" × 7.15")

3D Interactive Fold & Orbit (Kraft Board)

80%

0%100%

Camera:

Yaw: -28°Pitch: 24°

⟳ Drag Anywhere to Rotate 3DL=200 × W=120 × H=140mm

DUCT FACET #1200→120mm (H=140)

DUCT FACET #2200→120mm (H=140)

DUCT FACET #3200→120mm (H=140)

DUCT FACET #4200→120mm (H=140)

Unfolded Sheet Size

834.9 × 181.6 mm

True Slant Length

145.60 mm

Base → Top Opening

200 mm → Ø120 mm

SMACNA Collar Flanges

18 mm Top & Bottom

Structural & Manufacturing Specification Summary

Quick Default Download: ↓ .DXF ↓ .SVG ↓ .PDF

Unfolding a sheet metal HVAC duct reducer, exhaust hood, or pyramidal hopper transition requires true-length 3D triangulation because the vertical elevation height (H) is shorter than the true sloped slant height of the four trapezoidal facets. Our parametric sheet metal unfolder computes the exact true slant height (S_true = sqrt(H² + ((D_bottom - D_top)/2)²)), develops all four contiguous trapezoidal facets into a single radial flat pattern with a Pittsburgh/spot-weld lock seam allowance, and adds top and bottom flanged attachment collars.

CUT LAYER #EF4444 (ACI 1)

CREASE / BEND #2563EB (ACI 5)

SCALE HEADER $INSUNITS=4 (1:1 mm)

SIMULATION 2D + 3D + Nesting

Pre-Calibrated Industry Sizes (2)

Standard Product Presets Built on This HVAC Duct Transition / Reducer Engine

200 × 150 × 150 mm (T=1.2mm)

200→150mm HVAC Duct Reducer

200 × 200 mm (8") Bottom Inlet Reducing Concentrically to 150 × 150 mm (6") Top Outlet

Load Preset Spec →

250 × 150 × 180 mm (T=1.2mm)

250→150mm HVAC Duct Reducer

Transitions 250 × 250 mm (10") Trunk Duct to 150 × 150 mm (6") Branch Duct Over 180 mm Vertical Rise

Load Preset Spec →

Structural Geometry & Allowances

Mathematical Blank & Tolerance Formulas

True Facet Slant Height (S_true)

S_true = sqrt(H_vertical^2 + ((W_bottom - W_top) / 2)^2)

Applies the Pythagorean theorem to convert vertical elevation height (H) and radial offset into the true flat-pattern facet length.

Facet Side Edge True Length (R_edge)

R_edge = sqrt(S_true^2 + ((W_bottom - W_top) / 2)^2)

Computes the true length along the four corner bend lines where adjacent trapezoidal facets meet.

Total Unfolded Blank Width (W_flat)

W_flat = 4 * W_bottom + Seam_Lap

Spans all four lower base edges plus the spot-weld / rivet lock seam tab.

Pre-Press & Production SOP

Step-by-Step Export & Assembly Guide

1 Enter Bottom Inlet Width (L), Top Outlet Width/Diameter (W), Vertical Transition Height (H), and Sheet Metal Thickness (T).
2 Inspect the developed 4-facet flat pattern in the 2D CAD view showing the RED outer cut perimeter, top/bottom attachment collars, and BLUE press-brake bend lines.
3 Verify the 3D frustum transition geometry in the 3D Fold Preview tab.
4 Export as 1:1 .DXF for CNC plasma or fiber laser cutting, brake the 3 internal corner bends and top/bottom collars, and spot-weld or rivet the side lock seam.

Board Caliper, Laser & Die-Cutting Reference

Material Thickness, Creasing Matrix & Laser Kerf Settings

Material / Sheet Stock	Caliper Thickness (T)	Recommended Tooling / Laser Setup	Allowance / Kerf Spec	Primary Use Case
20 Gauge / 1.0mm–1.2mm Galvanized Steel (G90)	1.20 mm (18–20 ga)	CNC Plasma / Fiber Laser + Box & Pan Brake	Pittsburgh / Spot-Weld Seam Allowance: 16 mm	Commercial HVAC supply/return duct transitions, dust collection hoods
1.5mm 304 Stainless Steel Sheet	1.50 mm (16 ga)	Fiber Laser + Press Brake + TIG Seam Weld	K-Factor: 0.42 / True Slant Triangulation	Food-grade hoppers, commercial kitchen exhaust transitions, chemical chutes
14 Gauge / 2.0mm Mild Steel Plate	2.00 mm (14 ga)	CNC Plasma / Laser + Press Brake	Heavy industrial chute tolerance	Aggregate material hoppers, CNC chip chutes, industrial cyclones

Packaging & CNC Engineering FAQ

Frequently Asked Questions — HVAC Duct Transition / Reducer

Why can't I use the vertical height (H) directly on the flat sheet metal pattern?

Because the walls of a reducer slope inward from the larger bottom opening (L) to the smaller top opening (W), the true length along the sloped wall (S_true) is longer than the vertical height (H). Cutting a flat pattern using vertical height results in a duct transition that is too short.

Does the flat pattern include top and bottom flange collars?

Yes! Every facet includes top and bottom straight flange collars separated by BLUE bend lines so you can easily connect the reducer to upstream and downstream ductwork.

What seam allowance is included on the right edge?

A tapered 16mm to 22mm lock seam tab is automatically appended to the fourth facet for spot-welding, pop-riveting, or Pittsburgh seam locking.

Can I use this generator to make a square-to-round adapter?

Yes. By braking the four corner lines and rolling or cross-breaking the top collar to match your round collar connection (diameter = W), this pattern serves as both a concentric rectangular reducer and a 4-piece transition.

Topical Silo Navigation (Sheet Metal & HVAC)