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.

TEMPLATE ID: PRE-SHT-007 250 × 150 × 180 mm (T=1.2mm) Pre-Verified 1:1 Static Files Ready

250mm to 150mm Concentric HVAC Sheet Metal Duct Reducer & Exhaust Hood Flat Pattern (DXF)

Interactive Parametric 2D & 3D Studio

Live 2D Dieline, Interactive 3D Fold Preview & Custom Size Generator

Pre-loaded with 250→150mm HVAC Duct Reducer (250×150×180 mm, T=1.2mm)

1:1 CAD ENGINE READY

250mm to 150mm Concentric HVAC Sheet Metal Duct Reducer & Exhaust Hood Flat Pattern (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)250 mm

Top Outlet Width (W mm)150 mm

Vertical Duct Height (H mm)180 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 1034.86×222.82mm === 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 (2.26m) CREASE/SCORE (3.75m)● 1 Loops · Est. Cut: ~96s

1:1 Synced · Blank: 1034.86 × 222.82 mm

2D 1:1 Unfolded Vector BlueprintBlank: 1034.86 × 222.82 mm (40.74" × 8.77")

3D Interactive Fold & Orbit (Kraft Board)

80%

0%100%

Camera:

Yaw: -28°Pitch: 24°

⟳ Drag Anywhere to Rotate 3DL=250 × W=150 × H=180mm

DUCT FACET #1250→150mm (H=180)

DUCT FACET #2250→150mm (H=180)

DUCT FACET #3250→150mm (H=180)

DUCT FACET #4250→150mm (H=180)

Unfolded Sheet Size

1034.9 × 222.8 mm

True Slant Length

186.82 mm

Base → Top Opening

250 mm → Ø150 mm

SMACNA Collar Flanges

18 mm Top & Bottom

Direct Pre-Generated 1:1 CAD Files

Download Static Ready-to-Cut Files (250×150×180 mm)

These static files are pre-calculated for 1.2mm material thickness. Click any format below to download the pre-built static file, or export custom dimensions directly from the interactive Studio above.

↓ Download .DXF AutoCAD / LightBurn ($INSUNITS=4) ↓ Download .SVG Illustrator / Corel (1:1 mm) ↓ Download .PDF 1:1 Print + 50mm Scale Bar

Product Manufacturing Specification Sheet

Calibrated Physical Clearances & Material Stock for 250→150mm HVAC Duct Reducer

Parent Parametric Engine: HVAC Duct Transition / Reducer →

Target Physical Product Size

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

Engineered Internal Cavity & Clearance

True Slant Height S = 186.8 mm + 20 mm Top/Bottom Attachment Collars + 18 mm Lock Seam Tab

Recommended Board / Sheet Stock

1.2mm (18 Gauge) G90 Galvanized Sheet Steel or 1.2mm 304 Stainless Steel

Grain / Flute Orientation Rule

Isotropic Galvanized Coil Stock

Production Engineering Note: Unfolded single-piece 4-facet development eliminates multi-piece corner welding.

Structural Geometry & Material Reference (SMACNA HVAC Duct Construction & True-Length Triangulation Standard)

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.

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.

Internal CAD Silo & Related Ready-to-Cut Templates