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why Modeling Strategy Matters in Procedural CAD Modeling why Modeling Strategy Matters in Procedural CAD Modeling

Why does modeling strategy matter so much in procedural CAD? Two scripts can produce the exact same geometry while showing very different generation times.

Using a concrete build123d example, this article explains why certain operations, such as fillets, become expensive when repeated at scale, and how a simple change in approach can drastically reduce computation time.

A clear overview of the key challenges in procedural modeling, highlighting the direct impact of design choices on CAD engine performance.

A selection of custom 3D models

3D model of a round vent cover for ventilation in STL format. Its insertion diameter is 67 mm. The slats have an angle of 45° and a low thickness of 1.6 mm. A centered vertical reinforcement strengthens the slats. This vent cover features a thin flange of 5 mm. The overall diameter of this model is 77 mm.
Parameter Value Unit
male diameter 67 mm
slat angle 45 °
slat thickness 1.6 mm
flange width 5 mm
central reinforcement yes
Model of a pipe elbow with a 90° angle in STL format. This elbow has an outer diameter of 41 mm and an inner diameter of 38 mm. The tube thickness is therefore 1.5 mm. End fillets make it easier to assemble.
Parameter Value Unit
outer diameter 41 mm
inner diameter 38 mm
angle 90 °
end fillets yes
Oval pipe adapter provided as a STL 3D file. The internal cross-section on side A is 100x70 mm, while on side B it is 80x40 mm. You get a sleeve of 5 mm on side A and 10 mm on side B. The transition section is 20 mm long, for a final overall length of 35 mm. The shell is relatively thick, with a wall thickness of 4 mm. External chamfers are added at the ends to make it easier to insert the adapter into ducts or hoses.
Parameter Value Unit
side A internal width 100 mm
side A internal height 70 mm
sleeve length on side A 5 mm
side B internal width 80 mm
side B internal height 40 mm
sleeve length on side B 10 mm
thickness 4 mm
transition length 20 mm
Y offset 0 mm
Z offset 0 mm
end chamfers outside

📦 Model #1045

1 object(s)
- format STL
O-ring STL file ID 25 × CS 3 mm
Model of O-ring with dimensions ID (inner diameter) 25 mm / thickness 3  mm. External diameter (OD) resulting corresponds to 31 mm.
Parameter Value Unit
inner diameter (ID) 25 mm
cross section (CS) 3 mm
Download this rectangular protective honeycomb grid model in STL format. Mounting holes are placed at the four corners (center-to-center 210x110 mm), each with a diameter of Ø5 mm. The overall dimensions reach 220x120 mm, with very large 10 mm cell size for peak ventilation. This grid serves as both a protective guard and a ventilation panel.
Parameter Value Unit
length or center-to-center 210 mm
width or center-to-center 110 mm
mesh size 10 mm
dual color no
holes yes
hole diameter 5 mm
Download this 3D model in STL format of a round-to-rectangular tube adapter with an outer diameter of ⌀76 mm and a rectangular section with inner dimensions 200×20 mm. The shell thickness is 3 mm and the overall length is 200 mm. The adapter has an offset of 40 mm along the Z axis.
Parameter Value Unit
cylinder outer diameter 76 mm
cylinder inlet length 20 mm
rectangle internal length 200 mm
rectangle internal height 20 mm
rectangle inlet length 20 mm
offset Z 40 mm
offset Y 0 mm
total length 200 mm
thickness 3 mm
chamfer no chamfer
Small parts organizer with 4 drawers 75×75×50 mm STL file, thickness: 2 mm
View of object #0
Model of a storage box with drawers in STL format. This model includes 4 drawers, arranged in 2 rows and 2 columns. Practically speaking, this means 2 rows of 2 drawers. Each drawer has usable dimensions of 75 mm wide, 75 mm high, and 50 mm deep. The wall thickness is 2 mm. The external dimensions of the structure come to 165 x 161 x 56 mm. All the objects in this model were designed to be printed without support generation.
Parameter Value Unit
number of rows 2
number of columns 2
inner drawer depth 50 mm
inner drawer width 75 mm
inner drawer height 75 mm
wall thickness 2 mm
removable divider none

📦 Model #4476

1 object(s)
- format STL
Tubing adapter STL 3D file ⌀ 40–37 mm (Length: 115 mm)
Tube adapter ⌀40 mm to ⌀37 mm in STL 3D format. Length of this connector is 115 mm. The thickness of the tubes is identical: 5 mm. The larger-diameter tube has a sleeve length of 35 mm, the smaller one of 40 mm. The ends are rounded to facilitate the connection of the two tubes.
Parameter Value Unit
side A length 35 mm
side A outer diameter 40 mm
side A thickness 5 mm
side B length 40 mm
side B outer diameter 37 mm
side B thickness 5 mm
transition length 40 mm
axis offset 0 mm
ends fillet fillet on bo...

📦 Model #2152

1 object(s)
- format STL
Tube adapter STL 3D file ⌀ 115–100 mm (Length: 65 mm)
Inline tube adapter ⌀115 mm to ⌀100 mm in STL format. Total length of this sleeve is 65 mm. The thickness of the tubes is identical: 3 mm. The larger-diameter tube has a sleeve length of 30 mm, the smaller one of 30 mm as well. The ends have no fillet.
Parameter Value Unit
side A length 30 mm
side A outer diameter 115 mm
side A thickness 3 mm
side B length 30 mm
side B outer diameter 100 mm
side B thickness 3 mm
transition length 5 mm
axis offset 0 mm
ends fillet no fillet
Rectangular adapter provided as 3D STL file. Side A and side B share the same internal cross-section, 220x73 mm, with a rectangular profile. Each sleeve provides an insertion length of 50 mm. The transition section between the two sides is 120 mm long, for an overall length of 220 mm (side A sleeve, transition and side B sleeve). No chamfers are applied at the ends; both inner and outer edges remain sharp.
Parameter Value Unit
side A internal width 220 mm
side A internal height 73 mm
sleeve length on side A 50 mm
side B internal width 220 mm
side B internal height 73 mm
sleeve length on side B 50 mm
thickness 3 mm
transition length 120 mm
Y offset 0 mm
Z offset 0 mm
end chamfers none
Rectangular duct transition downloadable as STL 3D file. The internal cross-section on side A is 96x51.2 mm (rectangular), while side B is 40x26.2 mm (rectangular). Both side A and side B sleeves share the same insertion length of 30 mm. Between the two sleeves, the transition section adds 55 mm, giving an overall length of 115 mm. Inner and outer edges at both ends are left unchamfered. Relative to side A, side B is shifted by 25 mm along the Z axis.
Parameter Value Unit
side A internal width 96 mm
side A internal height 51.2 mm
sleeve length on side A 30 mm
side B internal width 40 mm
side B internal height 26.2 mm
sleeve length on side B 30 mm
thickness 2 mm
transition length 55 mm
Y offset 0 mm
Z offset 25 mm
end chamfers none

📦 Model #1272

1 object(s)
- format STL
Tube adapter STL file ⌀ 45–15 mm (Length: 90 mm)
Tube coupler ⌀45 mm to ⌀15 mm in STL format. Total length of this sleeve is 90 mm. The larger-diameter tube has a thickness of 2.5 mm and a sleeve length of 30 mm. The smaller-diameter tube has a thickness of 2 mm and a length of 30 mm as well. The ends are raw.
Parameter Value Unit
side A length 30 mm
side A outer diameter 45 mm
side A thickness 2.5 mm
side B length 30 mm
side B outer diameter 15 mm
side B thickness 2 mm
transition length 30 mm
axis offset 0 mm
ends fillet no fillet

📦 Model #4503

1 object(s)
- format STL
Tube adapter STL 3D file ⌀ 125–80 mm (Length: 105 mm)
Straight tube coupler ⌀125 mm to ⌀80 mm in STL format. Total length of this junction is 105 mm. The thickness of the tubes is identical: 5 mm. The larger-diameter tube has a sleeve length of 35 mm, the smaller one of 40 mm. The ends are raw.
Parameter Value Unit
side A length 35 mm
side A outer diameter 125 mm
side A thickness 5 mm
side B length 40 mm
side B outer diameter 80 mm
side B thickness 5 mm
transition length 30 mm
axis offset 0 mm
ends fillet no fillet
3D model of an elbow with a 90° angle in STL format. This elbow features an external diameter of 156 mm and an internal diameter of 150 mm. This results in a tube thickness of 3 mm.
Parameter Value Unit
outer diameter 156 mm
inner diameter 150 mm
angle 90 °
end fillets no
Small parts organizer with 30 drawers 40×25×80 mm STL file, thickness: 3 mm
View of object #0
Download this model of a sorting cabinet with drawers in STL format. This model features 30 boxes, arranged in 6 rows and 5 columns. Specifically, this means 6 rows of 5 boxes. Each box comes with an inner space of 40 mm wide, 25 mm high, and 80 mm deep. The wall thickness is 3 mm, which makes the structure sturdy. The boxes include 2 dividers each, which allows up to 3 sections per box and up to 90 compartments in total. The overall dimensions of the structure are 250.5 x 192 x 89 mm. All the objects in this model are intended to be printable without support generation.
Parameter Value Unit
number of rows 6
number of columns 5
inner drawer depth 80 mm
inner drawer width 40 mm
inner drawer height 25 mm
wall thickness 3 mm
removable divider two divider ...

📦 Model #4497

1 object(s)
- format STL
Tubing adapter STL 3D file ⌀ 32–19 mm (Length: 65 mm)
Tube fitting ⌀32 mm to ⌀19 mm in STL 3D format. Length of this junction is 65 mm. The thickness of the tubes is identical: 2 mm. The larger-diameter tube has a sleeve length of 35 mm, the smaller one of 20 mm. The ends are not rounded.
Parameter Value Unit
side A length 35 mm
side A outer diameter 32 mm
side A thickness 2 mm
side B length 20 mm
side B outer diameter 19 mm
side B thickness 2 mm
transition length 10 mm
axis offset 0 mm
ends fillet no fillet

📦 Model #2390

1 object(s)
- format STL
Round air vent STL 3D file ∅ 115 mm, slat angle: 45°
3D file of a round grille for air circulation in STL format. Its male diameter is 115 mm. The slats have an angle of 45° and a high thickness of 2 mm. This ventilation grille has a collar of 10 mm. The full diameter of this model is 135 mm.
Parameter Value Unit
male diameter 115 mm
slat angle 45 °
slat thickness 2 mm
flange width 10 mm
central reinforcement no

📦 Model #3502

1 object(s)
- format STL
Protective grid STL 3D file, 60x60mm, mesh: 8mm
Download this 3D square honeycomb grid model in STL format. The overall size is 60x60 mm, with wide 8 mm cell size for optimal air circulation. This type of grid serves both protection and ventilation roles.
Parameter Value Unit
length or center-to-center 60 mm
width or center-to-center 60 mm
mesh size 8 mm
dual color no
holes no

📦 Model #4396

1 object(s)
- format STL
Honeycomb grid STL file, 250x250mm, mesh: 10mm
Square grid model as a STL file. The overall size is 250x250 mm, with very large 10 mm cell size for maximum airflow. This grid serves as both a protective guard and a ventilation panel.
Parameter Value Unit
length or center-to-center 250 mm
width or center-to-center 250 mm
mesh size 10 mm
dual color no
holes no

📦 Model #4338

2 object(s)
- format STL
Enclosure with screw-mounted lid STL file: 120×100×60 mm
View of object #0
Enclosure model with a screwed lid in 3D STL format. The dimensions are 120 mm long by 100 mm wide and 60 mm high. The lid measures 40 mm high. Side thickness is 4 mm. The enclosure does not feature cooling.
Parameter Value Unit
length 120 mm
width 100 mm
total height 60 mm
lid height 40 mm
wall thickness 4 mm
screw margin 0 mm
fit clearance 0.2 mm
cooling zone(s) no cutouts
3D square protective honeycomb grid model as a STL file. Mounting holes are placed at the four corners (center-to-center 107x107 mm), each with a diameter of Ø5 mm. The overall dimensions reach 117x117 mm, with very large 10 mm cell size for maximum airflow. This grid serves as both a protective guard and a ventilation panel.
Parameter Value Unit
length or center-to-center 107 mm
width or center-to-center 107 mm
mesh size 10 mm
dual color no
holes yes
hole diameter 5 mm

📦 Model #1483

1 object(s)
- format STL
Tube adapter STL file ⌀ 200–50 mm (Length: 80 mm)
Tube reducer ⌀200 mm to ⌀50 mm in STL 3D format. Total length of this junction is 80 mm. The thickness of the tubes is identical: 3 mm. The larger-diameter tube has a sleeve length of 30 mm, the smaller one of 30 mm as well. The ends have no fillet.
Parameter Value Unit
side A length 30 mm
side A outer diameter 200 mm
side A thickness 3 mm
side B length 30 mm
side B outer diameter 50 mm
side B thickness 3 mm
transition length 20 mm
axis offset 0 mm
ends fillet no fillet
3D file of a mounting bracket with a central reinforcement in STL format. The dimensions are 150 mm in length, 150 mm in height, 14 mm in width, and 6 mm in thickness. The screw holes are designed with a diameter of 6 mm. Chamfers are applied to the holes to improve the seating of the heads. The central reinforcement bar reduces bending and provides two clearances for screwdriver access. No support is needed to print this bracket, printed flat on the build plate.
Parameter Value Unit
length 150 mm
height 150 mm
width 14 mm
thickness 6 mm
hole diameter 6 mm
chamfer on the holes yes

📦 Model #1901

1 object(s)
- format STL
Tube adapter STL 3D file ⌀ 70–42 mm (Length: 80 mm)
Inline tube junction ⌀70 mm to ⌀42 mm in STL 3D format. Total length of this coupler is 80 mm. The thickness of the tubes is identical: 3 mm. The larger-diameter tube has a length of 30 mm, the smaller one of 30 mm as well. The two axes of the tubes are offset by 13.8 mm. The ends are raw.
Parameter Value Unit
side A length 30 mm
side A outer diameter 70 mm
side A thickness 3 mm
side B length 30 mm
side B outer diameter 42 mm
side B thickness 3 mm
transition length 20 mm
axis offset 13.8 mm
ends fillet no fillet

📦 Model #2799

1 object(s)
- format STL
Tubing adapter STL file ⌀ 10–9 mm (Length: 25 mm)
Tube reducer ⌀10 mm to ⌀9 mm in STL format. Total length of this coupler is 25 mm. The thickness of the tubes is identical: 2 mm. The larger-diameter tube has a length of 10 mm, the smaller one of 5 mm. The ends are not rounded.
Parameter Value Unit
side A length 10 mm
side A outer diameter 10 mm
side A thickness 2 mm
side B length 5 mm
side B outer diameter 9 mm
side B thickness 2 mm
transition length 10 mm
axis offset 0 mm
ends fillet no fillet
Round box with lid STL 3D file ⌀ 134 mm - Height: 20 mm, Shell: 2 mm
View of object #0
Get this circular box model in 3D STL format. Its diameter is 134 mm and its total height is 20 mm. The wall thickness is 2 mm. A fillet located at the bottom of the box makes it easier to grip objects.
Parameter Value Unit
external diameter 134 mm
total height 20 mm
wall thickness 2 mm
fit clearance 0.2 mm
inner bottom fillet 1 mm

📦 Model #4120

1 object(s)
- format STL
Multi-compartment box STL 3D file: 6 compartments of 39×5×35 mm
This parametric compartment box includes 6 storage spaces measuring 39×5×35mm each. The total dimensions are 43×44×37mm.
Parameter Value Unit
number of rows 6
number of columns 1
compartment length 39 mm
compartment width 5 mm
compartment height 35 mm
wall thickness 2 mm
compartment fillet (radius) 1 mm

📦 Model #4475

1 object(s)
- format STL
Tube adapter STL 3D file ⌀ 40–37 mm (Length: 118 mm)
Straight tube fitting ⌀40 mm to ⌀37 mm in STL format. Total length of this connector is 118 mm. The thickness of the tubes is identical: 5 mm. The larger-diameter tube has a sleeve length of 38 mm, the smaller one of 40 mm. The ends have a fillet to make tube connection easier.
Parameter Value Unit
side A length 38 mm
side A outer diameter 40 mm
side A thickness 5 mm
side B length 40 mm
side B outer diameter 37 mm
side B thickness 5 mm
transition length 40 mm
axis offset 0 mm
ends fillet fillet on bo...
3D model of washer / gasket in STL 3D file format. This part features an inner diameter of ⌀3.9 mm and an outer diameter of ⌀6.9 mm. The total thickness is 4.3 mm. This part has no finish applied.
Parameter Value Unit
inner diameter 3.9 mm
outer diameter 6.9 mm
thickness 4.3 mm
finish none
3D model in STL format of a round-to-rectangular adapter with an external diameter of ⌀140 mm and a rectangular section with internal dimensions 190×25 mm. The wall thickness is 3 mm and the total length is 200 mm. The adapter has an offset of 37 mm along the Y axis. Chamfers are applied on the outside of the cylindrical end and on the inside of the rectangular end.
Parameter Value Unit
cylinder outer diameter 140 mm
cylinder inlet length 25 mm
rectangle internal length 190 mm
rectangle internal height 25 mm
rectangle inlet length 100 mm
offset Z 0 mm
offset Y 37 mm
total length 200 mm
thickness 3 mm
chamfer chamfers on ...

STL: Advantages and Disadvantages for 3D Printing

The STL format is, without question, a cornerstone of 3D printing. This exchange format has established itself as the universal standard for representing 3D models ever since the early days of stereolithography. Its main strength lies in its simplicity: it describes the surface of an object using countless small triangles that form a mesh. This approach, known as tessellation, makes STL 3D files universally compatible with nearly all CAD software and slicers. If you’d like to learn more about this format, check out our article STL: What Is This 3D File Format?.

One of the major advantages of the format lies in this universality: whether you’re using a complex modeling program or a simpler design tool, you can export your 3D models in STL 3D format with near certainty that they’ll be interpreted correctly by your 3D printer. This ease of exchange has played a key role in the widespread adoption of 3D printing, allowing anyone to share and print objects without worrying about software compatibility. Once again, simplicity is its greatest strength.

However, that same simplicity also brings certain limitations. The triangle mesh, while effective for describing geometry, contains no information about colors, textures, or materials. For more advanced projects requiring these details, the STL format starts to show its weaknesses. Additionally, print quality depends directly on the fineness of the tessellation: too few triangles can lead to rough or faceted surfaces, while an overly dense mesh can make the file unnecessarily heavy.

Another notable drawback is the lack of unit management. An STL file doesn’t specify whether dimensions are in millimeters, centimeters, or inches, which can sometimes cause scaling errors when importing into a slicer. Despite these limitations, the STL format remains the go-to standard for converting your 3D models into G-code — the language your printer understands. It continues to be the preferred choice for its robustness and broad compatibility, even as newer formats like 3MF emerge for more specialized needs.

What is parametric modeling?

Parametric modeling is a fundamental approach in computer-aided design (CAD) that reshapes how 3D models are created and managed. Far from being a simple drawing technique, it represents a genuine design philosophy where objects are defined not by fixed shapes, but by variables and intelligent relationships.

This method makes it possible to modify the length, width, or diameter of a part and have the entire design adapt automatically, without the need to redraw everything. At the core of the process are parameters—numerical values (length, angle, thickness, etc.)—linked together through constraints and formulas. For instance, the diameter of a hole can be defined as half the width of a plate; if the width changes, the hole’s diameter instantly adjusts, ensuring the consistency of the design. This interdependence makes 3D models flexible and responsive to changes. One of the main advantages of parametric modeling lies in its ability to simplify customization and enable rapid iteration of designs.

Whether through modeling software such as Fusion 360 or FreeCAD, or through code-based libraries like build123d, this approach allows effortless exploration of a wide range of variations. Such flexibility is especially valuable across multiple fields—from mechanical engineering and architecture to consumer product design. It saves considerable time, reduces errors, and improves the performance of parts.

By defining design intent from the start through these parameters and constraints, the model preserves its integrity and functionality even after numerous modifications. It is a powerful way to transform an idea into a tangible object, ready to adapt to new situations.