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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

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
Color-coded compartment box STL 3D file: 15 compartments of 15×15×15 mm
View of object #0
This printable sorting box with colored collars features 15 cavities measuring 15×15×15 mm each. Overall dimensions are 57×93×18 mm. Fillets of 2 mm applied to all compartments, make it easier to grasp items stored in the box.
Parameter Value Unit
number of rows 5
number of columns 3
compartment length 15 mm
compartment width 15 mm
compartment height 15 mm
wall thickness 3 mm
compartment fillet (radius) 2 mm
row colors ABBBB
Small parts organizer with 6 drawers 40×40×75 mm STL 3D file, thickness: 2 mm
View of object #0
Download this file of a storage organizer in STL format. This model features 6 boxes, arranged in 2 rows and 3 columns. In detail, this means 2 rows of 3 boxes. Each box comes with an inner space of 40 mm wide, 40 mm high, and 75 mm deep. The wall thickness is 2 mm. The boxes come with 2 dividers each, which allows up to 3 sections per box and up to 18 compartments in total. The global dimensions of the box are 141.5 x 91 x 81 mm. All the objects in this model are intended to be printable without support generation.
Parameter Value Unit
number of rows 2
number of columns 3
inner drawer depth 75 mm
inner drawer width 40 mm
inner drawer height 40 mm
wall thickness 2 mm
removable divider two divider ...

📦 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 file in STL format of a round-to-rectangular adapter with an outer diameter of ⌀124 mm and a rectangular section with internal dimensions 156×176 mm. The shell thickness is 2 mm and the overall length is 50 mm. The adapter has an offset of 20 mm along the Y axis and 20 mm along the Z axis.
Parameter Value Unit
cylinder outer diameter 124 mm
cylinder inlet length 5 mm
rectangle internal length 156 mm
rectangle internal height 176 mm
rectangle inlet length 5 mm
offset Z 20 mm
offset Y 20 mm
total length 50 mm
thickness 2 mm
chamfer no chamfer

📦 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 design of a round vent cover for ventilation in STL format. Its insertion diameter is 91.9 mm. The slats have an angle of 45° and a low thickness of 1.4 mm. A central reinforcement strengthens the slats. This 3D vent cover has a thin flange of 5 mm. The full diameter of the model is 101.9 mm.
Parameter Value Unit
male diameter 91.9 mm
slat angle 45 °
slat thickness 1.4 mm
flange width 5 mm
central reinforcement yes

📦 Model #4017

1 object(s)
- format STL
Honeycomb grille STL 3D file, 150x100mm, mesh: 10mm
3D rectangular protective grid file in STL format. The overall size is 150x100 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 150 mm
width or center-to-center 100 mm
mesh size 10 mm
dual color no
holes no
File in STL format of a round-to-rectangular adapter with an external diameter of ⌀128 mm and a rectangular section with internal dimensions 60×110 mm. The wall thickness is 3 mm and the total length is 200 mm. The adapter has an offset of 40 mm along the Z axis.
Parameter Value Unit
cylinder outer diameter 128 mm
cylinder inlet length 60 mm
rectangle internal length 60 mm
rectangle internal height 110 mm
rectangle inlet length 60 mm
offset Z 40 mm
offset Y 0 mm
total length 200 mm
thickness 3 mm
chamfer no chamfer

📦 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
3D file in STL format of a round-to-rectangular adapter with an external diameter of ⌀100 mm and a rectangular section with internal dimensions 100×50 mm. The shell thickness is 3 mm and the total length is 100 mm. The adapter has an offset of 3 mm along the Y axis and 3 mm along the Z axis. A chamfer is applied on the outside of the cylindrical end.
Parameter Value Unit
cylinder outer diameter 100 mm
cylinder inlet length 30 mm
rectangle internal length 100 mm
rectangle internal height 50 mm
rectangle inlet length 30 mm
offset Z 3 mm
offset Y 3 mm
total length 100 mm
thickness 3 mm
chamfer chamfer on t...
Download this STL file of a simple U-shaped handle. The external dimensions are 35×140×14 mm. This handle features a square section combined with a right-angled transition. A light fillet along the edges produces a more pleasant grip. The openings are 5 mm diameter with a center-to-center distance of 126 mm.
Parameter Value Unit
width 35 mm
length 140 mm
thickness 14 mm
shape (0:square,1:circle) 0
transition (0:right,1:rounded) 0
fillet radius 1 mm
hole diameter 5 mm

📦 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
Download this enclosure with lid in 3D STL format. The dimensions are 120 mm long by 100 mm wide and 35 mm high. The lid is 10 mm high. Wall thickness is 2 mm. This enclosure has significant cooling area on the lid and under the base.
Parameter Value Unit
length 120 mm
width 100 mm
total height 35 mm
lid height 10 mm
wall thickness 2 mm
screw margin 0 mm
fit clearance 0.1 mm
cooling level 8
cooling zone(s) cutouts on b...

📦 Model #3631

1 object(s)
- format STL
Multi-compartment box STL file: 6 compartments of 100×80×80 mm
This STL file includes 6 cavities measuring 100×80×80mm each. The total dimensions of the box are 316×172×84mm. Fillets of 2mm applied to all compartments help with item retrieval stored in the box. The dividers are particularly reinforced.
Parameter Value Unit
number of rows 2
number of columns 3
compartment length 100 mm
compartment width 80 mm
compartment height 80 mm
wall thickness 4 mm
compartment fillet (radius) 2 mm

📦 Model #1092

1 object(s)
- format STL
Box STL file with dimensions 100×100×60 mm
This box design offers a single compartment measuring 100×100×60mm. The total dimensions are 108×108×64mm. The fillet of 2mm helps with item retrieval inside the compartment. The separators are particularly reinforced.
Parameter Value Unit
number of rows 1
number of columns 1
compartment length 100 mm
compartment width 100 mm
compartment height 60 mm
wall thickness 4 mm
compartment fillet (radius) 2 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
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
Small parts organizer with 25 drawers 40×40×40 mm STL 3D file, thickness: 2 mm
View of object #0
Download this model of a storage case in 3D STL format. This model contains 25 drawers, arranged in 5 rows and 5 columns. Specifically, this means 5 rows of 5 drawers. Each drawer comes with an inner space of 40 mm wide, 40 mm high, and 40 mm deep. The wall thickness is 2 mm. The overall dimensions of the box are 234.5 x 224.5 x 46 mm. All the objects in this model are intended to be printable without support generation.
Parameter Value Unit
number of rows 5
number of columns 5
inner drawer depth 40 mm
inner drawer width 40 mm
inner drawer height 40 mm
wall thickness 2 mm
removable divider none
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
Model of a corner bracket with a central reinforcement in STL format. The dimensions are 180 mm in length, 100 mm in height, 25 mm in width, and 5 mm in thickness. The mounting holes have a diameter of 5 mm. Chamfers are applied to the holes for a cleaner fit of the screws. The central reinforcement bar enhances mechanical strength and provides two openings for screwdriver access. This bracket prints without support, placed flat on the print bed.
Parameter Value Unit
length 180 mm
height 100 mm
width 25 mm
thickness 5 mm
hole diameter 5 mm
chamfer on the holes yes

📦 Model #2060

1 object(s)
- format STL
Tube adapter STL 3D file ⌀ 110–100 mm (Length: 35 mm)
Diameter adapter ⌀110 mm to ⌀100 mm in STL format. Length of this fitting is 35 mm. The thickness of the tubes is identical: 3 mm. The larger-diameter tube has a sleeve length of 20 mm, the smaller one of 10 mm. The ends are rounded on the outside to ease the connection.
Parameter Value Unit
side A length 20 mm
side A outer diameter 110 mm
side A thickness 3 mm
side B length 10 mm
side B outer diameter 100 mm
side B thickness 3 mm
transition length 5 mm
axis offset 0 mm
ends fillet fillet on th...

📦 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
Square protective honeycomb grid model as a STL file. Mounting holes are placed at the four corners (center-to-center 65x65 mm), each with a diameter of Ø4 mm. The overall dimensions reach 73x73 mm, with regular 5 mm cell size for balanced airflow and protection. This grid provides both mechanical protection and airflow.
Parameter Value Unit
length or center-to-center 65 mm
width or center-to-center 65 mm
mesh size 5 mm
dual color no
holes yes
hole diameter 4 mm
Download this 3D model in STL format of a round-to-rectangular tube adapter with an outer diameter of ⌀60 mm and a rectangular section with internal dimensions 48×52 mm. The shell thickness is 3 mm and the total length is 200 mm. The adapter has an offset of 55 mm along the Z axis.
Parameter Value Unit
cylinder outer diameter 60 mm
cylinder inlet length 40 mm
rectangle internal length 48 mm
rectangle internal height 52 mm
rectangle inlet length 50 mm
offset Z 55 mm
offset Y 0 mm
total length 200 mm
thickness 3 mm
chamfer no chamfer

📦 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 container in STL 3D format. This model can be used for organizing small parts in a workshop or on a desk. The shape is almost straight, with a inner height of 40 mm, a inner diameter at the top of 122 mm, and a inner diameter at the bottom of 121 mm. The total height is 41 mm.
Parameter Value Unit
inner bottom diameter 121 mm
inner top diameter 122 mm
inner height 40 mm
wall thickness 1 mm

📦 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...
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 #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

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.