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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

File in STL format of a round-to-rectangular adapter with an external diameter of ⌀120 mm and a rectangular section with inner dimensions 60×40 mm. The shell thickness is 3 mm and the overall length is 100 mm. The adapter has an offset of 10 mm along the Y axis and 10 mm along the Z axis. Chamfers are present on the outside of the cylindrical end and on the inside of the rectangular end to ease insertion.
Parameter Value Unit
cylinder outer diameter 120 mm
cylinder inlet length 30 mm
rectangle internal length 60 mm
rectangle internal height 40 mm
rectangle inlet length 30 mm
offset Z 10 mm
offset Y 10 mm
total length 100 mm
thickness 3 mm
chamfer chamfers on ...

📦 Model #1161

1 object(s)
- format STL
Tube adapter STL 3D file ⌀ 200–180 mm (Length: 80 mm)
Tube reducer ⌀200 mm to ⌀180 mm in STL format. Final length of this fitting 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 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 180 mm
side B thickness 3 mm
transition length 20 mm
axis offset 0 mm
ends fillet no fillet

📦 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 of an elbow with a 90° angle in STL format. This elbow features an outer diameter of 66 mm and an inner diameter of 63 mm. This results in a tube thickness of 1.5 mm.
Parameter Value Unit
outer diameter 66 mm
inner diameter 63 mm
angle 90 °
end fillets no
STL 3D file for an oval duct adapter. On side A, the internal cross-section is 100.1x100 mm (nearly circular), whereas on side B it is 80x40 mm (oval). 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. Wall thickness is generous (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 100.1 mm
side A internal height 100 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
Download this model of a U-shaped furniture handle. The overall dimensions are 50×140×14 mm. This handle has a circular cross-section and a 90-degree transition. The openings are 6 mm diameter with a center-to-center distance of 126 mm.
Parameter Value Unit
width 50 mm
length 140 mm
thickness 14 mm
shape (0:square,1:circle) 1
transition (0:right,1:rounded) 0
fillet radius 0 mm
hole diameter 6 mm
3D model in STL format of a round-to-rectangular tube adapter with an external diameter of ⌀150 mm and a rectangular section with inner dimensions 235×80 mm. The wall thickness is 2 mm and the total length is 235 mm. The adapter has an offset of 60 mm along the Z 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 150 mm
cylinder inlet length 30 mm
rectangle internal length 235 mm
rectangle internal height 80 mm
rectangle inlet length 30 mm
offset Z 60 mm
offset Y 0 mm
total length 235 mm
thickness 2 mm
chamfer chamfers on ...
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
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
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 20 drawers 50×30×60 mm STL 3D file, thickness: 2 mm
View of object #0
3D file of a DIY organizer in 3D STL format. This model includes 20 compartments, arranged in 5 rows and 4 columns. Specifically, this means 5 rows of 4 compartments. Each compartment provides an inside space of 50 mm wide, 30 mm high, and 60 mm deep. The wall thickness is 2 mm. The compartments feature 2 dividers each, which allows up to 3 sections per compartment and up to 60 compartments in total. The overall dimensions of the structure measure 228 x 174.5 x 66 mm. All the objects in this model were designed to be printed without support.
Parameter Value Unit
number of rows 5
number of columns 4
inner drawer depth 60 mm
inner drawer width 50 mm
inner drawer height 30 mm
wall thickness 2 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 #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 #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
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

📦 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

📦 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
Download this STL file of a simple U-shaped drawer handle. The external dimensions are 50×140×10 mm. This handle features a square section and a 90-degree transition. A fillet ensures a more comfortable grip. The holes are 6 mm diameter and have a 130 mm center-to-center distance.
Parameter Value Unit
width 50 mm
length 140 mm
thickness 10 mm
shape (0:square,1:circle) 0
transition (0:right,1:rounded) 0
fillet radius 1 mm
hole diameter 6 mm
3D file of a round vent cover for air circulation in STL format. Its insertion diameter measures 150 mm. The slats have an angle of 40° and a low thickness of 1.6 mm. A centered vertical reinforcement secures the slats. This 3D vent grille features a flange of 7 mm. The total diameter of the model is 164 mm.
Parameter Value Unit
male diameter 150 mm
slat angle 40 °
slat thickness 1.6 mm
flange width 7 mm
central reinforcement yes
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
Small parts organizer with 4 drawers 20×10×20 mm STL file, thickness: 2 mm
View of object #0
3D model of storage drawers in STL format. This model contains 4 compartments, arranged in 2 rows and 2 columns. Specifically, this means 2 rows of 2 compartments. Each compartment offers a storage volume of 20 mm wide, 10 mm high, and 20 mm deep. The wall thickness is 2 mm. The external dimensions of the box are 55 x 31 x 26 mm. All the objects in this model were designed to be printable without support generation.
Parameter Value Unit
number of rows 2
number of columns 2
inner drawer depth 20 mm
inner drawer width 20 mm
inner drawer height 10 mm
wall thickness 2 mm
removable divider none
Color-coded compartment box STL file: 32 compartments of 20×15×5 mm
View of object #0
This multi-compartment box with color markers design features 32 slots measuring 20×15×5 mm each. The total dimensions are 100×156×9 mm. Fillets of 3 mm applied to each compartment, make it easier to grasp items stored in the box. The dividers are particularly reinforced.
Parameter Value Unit
number of rows 8
number of columns 4
compartment length 20 mm
compartment width 15 mm
compartment height 5 mm
wall thickness 4 mm
compartment fillet (radius) 3 mm
row colors ABCDEFGH

📦 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 #3916

1 object(s)
- format STL
Tubing adapter STL file ⌀ 77–30 mm (Length: 140 mm)
Tube fitting ⌀77 mm to ⌀30 mm in STL format. Length of this sleeve is 140 mm. The thickness of the tubes is identical: 3 mm. The larger-diameter tube has a length of 30 mm, the smaller one of 50 mm. The ends are raw.
Parameter Value Unit
side A length 30 mm
side A outer diameter 77 mm
side A thickness 3 mm
side B length 50 mm
side B outer diameter 30 mm
side B thickness 3 mm
transition length 60 mm
axis offset 0 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
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...
Download this model of a support bracket with reinforcement in STL format. The dimensions are 180 mm in length, 180 mm in height, 20 mm in width, and 8 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 reinforcing bar enhances mechanical strength and includes two openings for fastening. No support is needed to print this bracket, placed flat directly on the build plate.
Parameter Value Unit
length 180 mm
height 180 mm
width 20 mm
thickness 8 mm
hole diameter 5 mm
chamfer on the holes yes
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
Small parts organizer with 15 drawers 40×25×25 mm STL 3D file, thickness: 2 mm
View of object #0
Model of a storage organizer in STL format. This model includes 15 compartments, arranged in 5 rows and 3 columns. Specifically, this means 5 rows of 3 compartments. Each compartment measures 40 mm wide, 25 mm high, and 25 mm deep. The wall thickness is 2 mm. The overall dimensions of the box are 141.5 x 149.5 x 31 mm. All the objects in this model are intended to be printed without support.
Parameter Value Unit
number of rows 5
number of columns 3
inner drawer depth 25 mm
inner drawer width 40 mm
inner drawer height 25 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.