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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 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 #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
Small parts organizer with 6 drawers 25×14×73 mm STL file, thickness: 2 mm
View of object #0
3D file of a storage case in 3D STL format. This model features 6 boxes, arranged in 2 rows and 3 columns. Specifically, this means 2 rows of 3 boxes. Each box offers a storage volume of 25 mm wide, 14 mm high, and 73 mm deep. The wall thickness is 2 mm. The external dimensions of the structure are 96.5 x 39 x 79 mm. All the objects in this model are intended to be printable without support.
Parameter Value Unit
number of rows 2
number of columns 3
inner drawer depth 73 mm
inner drawer width 25 mm
inner drawer height 14 mm
wall thickness 2 mm
removable divider none

📦 Model #2770

1 object(s)
- format STL
Tubing adapter STL file ⌀ 120–16 mm (Length: 25 mm)
Straight tube coupler ⌀120 mm to ⌀16 mm in STL format. Final length of this sleeve is 25 mm. The thickness of the tubes is identical: 2 mm. The larger-diameter tube has a length of 5 mm, the smaller one of 5 mm as well. The ends are not rounded.
Parameter Value Unit
side A length 5 mm
side A outer diameter 120 mm
side A thickness 2 mm
side B length 5 mm
side B outer diameter 16 mm
side B thickness 2 mm
transition length 15 mm
axis offset 0 mm
ends fillet no fillet
Enclosure with screwed lid in 3D STL format. The dimensions are 200 mm long by 130 mm wide and 60 mm high. The cover only is 10 mm high. Wall thickness is 3 mm. This enclosure features cooling area on the lid and under the base.
Parameter Value Unit
length 200 mm
width 130 mm
total height 60 mm
lid height 10 mm
wall thickness 3 mm
screw margin 0 mm
fit clearance 0.1 mm
cooling level 3
cooling zone(s) cutouts on b...
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 #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 #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...
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 STL 3D model of a basic U-shaped handle. The overall dimensions are 50×100×14 mm. This handle has a square section and a rounded transition. A light fillet along the edges ensures a softer grip. The mounting holes are 5 mm diameter and have a 86 mm center-to-center distance.
Parameter Value Unit
width 50 mm
length 100 mm
thickness 14 mm
shape (0:square,1:circle) 0
transition (0:right,1:rounded) 1
fillet radius 1 mm
hole diameter 5 mm
3D design of a round grille for air circulation in STL format. Its male diameter is 180 mm. The slats have an angle of 45° and a high thickness of 2 mm. A central reinforcement strengthens the slats. This 3D vent cover has a thin flange of 3 mm. The total diameter of this model is 186 mm.
Parameter Value Unit
male diameter 180 mm
slat angle 45 °
slat thickness 2 mm
flange width 3 mm
central reinforcement yes

📦 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
Single compartment box with colored ring STL 3D file – Dimensions: 15×7.5×5 mm
View of object #0
This printable single-compartment box with a color ring features a single compartment measuring 15×7.5×5 mm. Overall dimensions are 21×13.5×8 mm. A 2 mm fillet improves usability inside the box.
Parameter Value Unit
number of rows 1
number of columns 1
compartment length 15 mm
compartment width 7.5 mm
compartment height 5 mm
wall thickness 3 mm
compartment fillet (radius) 2 mm
row colors A

📦 Model #4468

2 object(s)
- format STL
Enclosure with screw-mounted lid STL 3D file: 100×85×70 mm
View of object #0
Download this enclosure model with lid in STL format. The dimensions are 100 mm long by 85 mm wide and 70 mm high. The lid only is 20 mm high. Side thickness is 3 mm. The enclosure does not have cooling.
Parameter Value Unit
length 100 mm
width 85 mm
total height 70 mm
lid height 20 mm
wall thickness 3 mm
screw margin 0 mm
fit clearance 0.1 mm
cooling zone(s) no cutouts
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 #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 of a round air vent for ventilation in STL format. Its insertion diameter measures 71 mm. The slats have an angle of 40° and a high thickness of 2.4 mm. A centered vertical reinforcement reinforces the slats. This 3D aeration grille has a thin flange of 4 mm. The full diameter of the model is 79 mm.
Parameter Value Unit
male diameter 71 mm
slat angle 40 °
slat thickness 2.4 mm
flange width 4 mm
central reinforcement yes

📦 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
Small parts organizer with 10 drawers 150×20×150 mm STL file, thickness: 2 mm
View of object #0
Download this model of a drawer organizer in 3D STL format. This model features 10 compartments, arranged in 5 rows and 2 columns. Practically speaking, this means 5 rows of 2 compartments. Each compartment measures 150 mm wide, 20 mm high, and 150 mm deep. The wall thickness is 2 mm. The overall dimensions of the structure measure 315 x 124.5 x 156 mm. All the objects in this model are intended to be printable without support.
Parameter Value Unit
number of rows 5
number of columns 2
inner drawer depth 150 mm
inner drawer width 150 mm
inner drawer height 20 mm
wall thickness 2 mm
removable divider none
Small parts organizer with 12 drawers 40×80×50 mm STL 3D file, thickness: 2 mm
View of object #0
Download this 3D model of a DIY organizer in STL format. This model contains 12 boxes, arranged in 3 rows and 4 columns. In detail, this means 3 rows of 4 boxes. Each box has usable dimensions of 40 mm wide, 80 mm high, and 50 mm deep. The wall thickness is 2 mm. The global dimensions of the structure measure 188 x 255.5 x 56 mm. All the objects in this model were designed to be printed without support.
Parameter Value Unit
number of rows 3
number of columns 4
inner drawer depth 50 mm
inner drawer width 40 mm
inner drawer height 80 mm
wall thickness 2 mm
removable divider none

📦 Model #2403

1 object(s)
- format STL
Multi-compartment box STL file: 36 compartments of 3×3×75 mm
This 3D model in STL format features 36 storage spaces measuring 3×3×75mm each. The total dimensions of the box are 32×32×77mm.
Parameter Value Unit
number of rows 6
number of columns 6
compartment length 3 mm
compartment width 3 mm
compartment height 75 mm
wall thickness 2 mm
compartment fillet (radius) 0.5 mm

📦 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 of washer / gasket in STL file format. This part features an internal diameter of ⌀57 mm and an external diameter of ⌀71 mm. The total thickness is 5 mm. A fillet is applied on the internal diameter with a value of 4 mm.
Parameter Value Unit
inner diameter 57 mm
outer diameter 71 mm
thickness 5 mm
finish fillet
finish position inner
sides one side
finish value 4 mm
Small parts organizer with 6 drawers 100×10×50 mm STL 3D file, thickness: 2 mm
View of object #0
3D file of a storage organizer in 3D STL format. This model includes 6 boxes, arranged in 3 rows and 2 columns. In detail, this means 3 rows of 2 boxes. Each box comes with an inner space of 100 mm wide, 10 mm high, and 50 mm deep. The wall thickness is 2 mm. The overall dimensions of the box are 215 x 45.5 x 56 mm. All the objects in this model are intended to be printable without support.
Parameter Value Unit
number of rows 3
number of columns 2
inner drawer depth 50 mm
inner drawer width 100 mm
inner drawer height 10 mm
wall thickness 2 mm
removable divider none

📦 Model #1151

1 object(s)
- format STL
Tube adapter STL 3D file ⌀ 147–49.9 mm (Length: 140 mm)
Straight tube connector ⌀147 mm to ⌀49.9 mm in STL format. Total length of this connector is 140 mm. The thickness of the tubes is identical: 2 mm. The larger-diameter tube has a length of 30 mm, the smaller one of 40 mm. The axes of the tubes are offset by 48 mm. The ends have a fillet on the outside to facilitate the connection of the two tubes.
Parameter Value Unit
side A length 30 mm
side A outer diameter 147 mm
side A thickness 2 mm
side B length 40 mm
side B outer diameter 49.9 mm
side B thickness 2 mm
transition length 70 mm
axis offset 48 mm
ends fillet fillet on th...
Round box with lid STL file ⌀ 72 mm - Height: 190 mm, Shell: 3 mm
View of object #0
Download this circular box model in STL format. Its diameter is 72 mm and its height is 190 mm. The walls have a thickness of 3 mm.
Parameter Value Unit
external diameter 72 mm
total height 190 mm
wall thickness 3 mm
fit clearance 0.1 mm
inner bottom fillet 0 mm
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
Design of a round grille for air circulation in STL format. Its insertion diameter is 90 mm. The slats have an angle of 35° and a high thickness of 2.4 mm. A centered vertical reinforcement strengthens the whole structure. This aeration grille features a prominent flange of 18 mm. The total diameter of the model is 126 mm.
Parameter Value Unit
male diameter 90 mm
slat angle 35 °
slat thickness 2.4 mm
flange width 18 mm
central reinforcement yes

📦 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
Round box with lid STL 3D file ⌀ 50 mm - Height: 60 mm, Shell: 2 mm
View of object #0
Download this cylindrical box model in 3D STL format. Its diameter is 50 mm and its height is 60 mm. The wall thickness is 2 mm.
Parameter Value Unit
external diameter 50 mm
total height 60 mm
wall thickness 2 mm
fit clearance 0.2 mm
inner bottom fillet 0 mm

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.