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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 #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...

📦 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...
Download this STL file of a U-shaped drawer handle. The external dimensions are 50×140×20 mm. This handle has a circular profile combined with a 90-degree transition. The holes are 4 mm diameter and have a 120 mm center-to-center distance.
Parameter Value Unit
width 50 mm
length 140 mm
thickness 20 mm
shape (0:square,1:circle) 1
transition (0:right,1:rounded) 0
fillet radius 0 mm
hole diameter 4 mm

📦 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
Enclosure with lid in 3D STL format. The dimensions are 120 mm long by 60 mm wide and 75 mm high. The lid only measures 10 mm high. Side thickness is 3 mm. This enclosure features marked cooling area on the lid and under the base.
Parameter Value Unit
length 120 mm
width 60 mm
total height 75 mm
lid height 10 mm
wall thickness 3 mm
screw margin 0 mm
fit clearance 0.1 mm
cooling level 5
cooling zone(s) cutouts on b...

📦 Model #1365

1 object(s)
- format STL
Tube adapter STL 3D file ⌀ 160–90 mm (Length: 250 mm)
Straight sleeve ⌀160 mm to ⌀90 mm in STL 3D format. Final length of this adapter is 250 mm. The larger-diameter tube has a thickness of 4 mm and a length of 110 mm. The smaller-diameter tube has a thickness of 5 mm and a length of 100 mm. The axes of the tubes are offset by 25.4 mm. The ends have no fillet.
Parameter Value Unit
side A length 110 mm
side A outer diameter 160 mm
side A thickness 4 mm
side B length 100 mm
side B outer diameter 90 mm
side B thickness 5 mm
transition length 40 mm
axis offset 25.4 mm
ends fillet no fillet
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

📦 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
Download this file of a corner bracket with reinforcement in STL 3D format. The dimensions are 200 mm in length, 200 mm in height, 30 mm in width, and 11 mm in thickness. The holes are designed with a diameter of 5 mm. Chamfers are done to the holes to improve the seating of the heads. The central reinforcement bar improves rigidity and includes two clearances for screwdriver access. Support generation is not required for printing this bracket, printed flat directly on the build plate.
Parameter Value Unit
length 200 mm
height 200 mm
width 30 mm
thickness 11 mm
hole diameter 5 mm
chamfer on the holes yes
File in STL format of a round-to-rectangular adapter with an external diameter of ⌀105 mm and a rectangular section with inner dimensions 150×50 mm. The shell thickness is 3 mm and the overall length is 100 mm. The adapter has an offset of 10 mm along the Z axis.
Parameter Value Unit
cylinder outer diameter 105 mm
cylinder inlet length 30 mm
rectangle internal length 150 mm
rectangle internal height 50 mm
rectangle inlet length 50 mm
offset Z 10 mm
offset Y 0 mm
total length 100 mm
thickness 3 mm
chamfer no chamfer
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
Rectangular box with lid STL file – 99×74×20 mm, wall thickness 2 mm
View of object #0
STL 3D file for a rectangular box with a lid. The box measures 99 mm in length, 74 mm in width, and 20 mm in height. Wall thickness is 2 mm, giving the box a thin-wall design. The box has rounded edges inside and out. A clearance is provided for an accurate lid-to-box fit. The internal dimensions, excluding rounding, are 95 mm × 70 mm × 16 mm.
Parameter Value Unit
length 99 mm
width 74 mm
height 20 mm
wall thikness 2 mm
Round box with lid STL 3D file ⌀ 104 mm - Height: 54 mm, Shell: 2 mm
View of object #0
Get this circular box in STL format. Its diameter is 104 mm and its height is 54 mm. The wall width is 2 mm. A fillet located at the bottom of the box makes it easier to grab stored objects inside.
Parameter Value Unit
external diameter 104 mm
total height 54 mm
wall thickness 2 mm
fit clearance 0.2 mm
inner bottom fillet 2 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 a pipe elbow with a 90° angle in STL format. This pipe elbow features an outer diameter of 58.5 mm and an inner diameter of 52.5 mm. The tube thickness is therefore 3 mm.
Parameter Value Unit
outer diameter 58.5 mm
inner diameter 52.5 mm
angle 90 °
end fillets no

📦 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 #4348

1 object(s)
- format STL
Tubing adapter STL 3D file ⌀ 33–14 mm (Length: 40 mm)
Tubing reducer ⌀33 mm to ⌀14 mm in STL format. Length of this coupler is 40 mm. The larger-diameter tube has a thickness of 2.5 mm and a sleeve length of 15 mm. The smaller-diameter tube has a thickness of 2 mm and a length of 15 mm as well. The ends have no fillet.
Parameter Value Unit
side A length 15 mm
side A outer diameter 33 mm
side A thickness 2.5 mm
side B length 15 mm
side B outer diameter 14 mm
side B thickness 2 mm
transition length 10 mm
axis offset 0 mm
ends fillet no fillet
Round box with lid STL file ⌀ 30 mm - Height: 150 mm, Shell: 3 mm
View of object #0
Download this circular organizing box in 3D STL format. Its diameter is 30 mm and its height is 150 mm. The walls have a thickness of 3 mm. A large fillet located at the bottom of the box makes it easier to grip objects located inside.
Parameter Value Unit
external diameter 30 mm
total height 150 mm
wall thickness 3 mm
fit clearance 0.2 mm
inner bottom fillet 4 mm
Small parts organizer with 9 drawers 60×60×80 mm STL file, thickness: 2 mm
View of object #0
File of a DIY organizer in 3D STL format. This model contains 9 compartments, arranged in 3 rows and 3 columns. In detail, this means 3 rows of 3 compartments. Each compartment provides an inside space of 60 mm wide, 60 mm high, and 80 mm deep. The wall thickness is 2 mm. The overall dimensions of the box are 201.5 x 195.5 x 86 mm. All the objects in this model were designed to be printable without support generation.
Parameter Value Unit
number of rows 3
number of columns 3
inner drawer depth 80 mm
inner drawer width 60 mm
inner drawer height 60 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 of a pipe elbow with a 60° angle in STL format. This pipe elbow has an outer diameter of 32 mm and an inner diameter of 28 mm. The tube thickness is therefore 2 mm. The ends feature fillets to make it easier to assemble.
Parameter Value Unit
outer diameter 32 mm
inner diameter 28 mm
angle 60 °
end fillets 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
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
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 #3188

1 object(s)
- format STL
Tube adapter STL file ⌀ 110–90 mm (Length: 130 mm)
Tubing adapter ⌀110 mm to ⌀90 mm in STL format. Final length of this sleeve is 130 mm. The thickness of the tubes is identical: 10 mm. The larger-diameter tube has a sleeve length of 20 mm, the smaller one of 100 mm. The ends are not rounded.
Parameter Value Unit
side A length 20 mm
side A outer diameter 110 mm
side A thickness 10 mm
side B length 100 mm
side B outer diameter 90 mm
side B thickness 10 mm
transition length 10 mm
axis offset 0 mm
ends fillet no fillet
File of a corner bracket reinforced in STL 3D format. The dimensions are 180 mm in length, 180 mm in height, 14 mm in width, and 12 mm in thickness. The drill holes have a diameter of 5 mm. Chamfers are applied to the holes for a cleaner fit of the screws. The central reinforcement bar improves rigidity and includes two openings for fastening. This bracket prints without support, printed flat directly on the build plate.
Parameter Value Unit
length 180 mm
height 180 mm
width 14 mm
thickness 12 mm
hole diameter 5 mm
chamfer on the holes yes
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 #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
Small parts organizer with 1 drawer 75×70×75 mm STL file, thickness: 2 mm
View of object #0
3D file of a storage box with drawers in STL format. This model features 1 box, arranged in 1 rows and 1 columns. In detail, this means 1 rows of 1 boxes. Each box measures 75 mm wide, 70 mm high, and 75 mm deep. The wall thickness is 2 mm. The external dimensions of the structure are 83.5 x 76.5 x 81 mm. All the objects in this model are intended to be printed without support.
Parameter Value Unit
number of rows 1
number of columns 1
inner drawer depth 75 mm
inner drawer width 75 mm
inner drawer height 70 mm
wall thickness 2 mm
removable divider none

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.