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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

📦 Model #1929

1 object(s)
- format STL
Tube adapter STL 3D file ⌀ 94–80 mm (Length: 50 mm)
Tube reducer ⌀94 mm to ⌀80 mm in STL 3D format. Final length of this reducer is 50 mm. The thickness of the tubes is identical: 2 mm. The larger-diameter tube has a sleeve length of 20 mm, the smaller one of 20 mm as well. The axes of the tubes are off-center by 5.9 mm. The ends feature an external fillet.
Parameter Value Unit
side A length 20 mm
side A outer diameter 94 mm
side A thickness 2 mm
side B length 20 mm
side B outer diameter 80 mm
side B thickness 2 mm
transition length 10 mm
axis offset 5.9 mm
ends fillet fillet on th...

📦 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 #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 #4484

1 object(s)
- format STL
Tube adapter STL file ⌀ 54–44 mm (Length: 80 mm)
Inline sleeve ⌀54 mm to ⌀44 mm in STL format. Length of this sleeve is 80 mm. The thickness of the tubes is identical: 2 mm. The larger-diameter tube has a length of 30 mm, the smaller one of 30 mm as well. The ends have a fillet to facilitate the connection of the two tubes.
Parameter Value Unit
side A length 30 mm
side A outer diameter 54 mm
side A thickness 2 mm
side B length 30 mm
side B outer diameter 44 mm
side B thickness 2 mm
transition length 20 mm
axis offset 0 mm
ends fillet fillet on bo...
Download this file in STL format of a round-to-rectangular tube adapter with an outer diameter of ⌀106 mm and a rectangular section with internal dimensions 50×50 mm. The wall thickness is 3 mm and the overall length is 100 mm. A chamfer is present on the outside of the cylindrical end to ease insertion.
Parameter Value Unit
cylinder outer diameter 106 mm
cylinder inlet length 15 mm
rectangle internal length 50 mm
rectangle internal height 50 mm
rectangle inlet length 60 mm
offset Z 0 mm
offset Y 0 mm
total length 100 mm
thickness 3 mm
chamfer chamfer on t...

📦 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 3D file of a U-shaped drawer handle. The external dimensions are 35×100×20 mm. The handle has a square cross-section and a right-angled transition. A fillet produces improved handling. The holes are 4 mm diameter and have a 80 mm center-to-center distance.
Parameter Value Unit
width 35 mm
length 100 mm
thickness 20 mm
shape (0:square,1:circle) 0
transition (0:right,1:rounded) 0
fillet radius 1 mm
hole diameter 4 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
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
Rectangular-base box with lid STL 3D model – 84×45×20 mm, wall thickness 2 mm
View of object #0
Rectangular-base box with a lid provided as a STL 3D file. Overall dimensions are 84 mm long, 45 mm wide, and 20 mm tall. The box features thin 2 mm walls. Interior and exterior edges are rounded. A small clearance is included to ensure a precise fit between the box and the lid. The internal dimensions, excluding rounding, are 80 mm × 41 mm × 16 mm.
Parameter Value Unit
length 84 mm
width 45 mm
height 20 mm
wall thikness 2 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
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
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 #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 #1801

1 object(s)
- format STL
Tube adapter STL file ⌀ 110–100 mm (Length: 35 mm)
Tube coupler ⌀110 mm to ⌀100 mm in STL format. Final length of this adapter 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 raw.
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 no fillet

📦 Model #2186

1 object(s)
- format STL
Tube adapter STL file ⌀ 52–25 mm (Length: 105 mm)
Tube junction ⌀52 mm to ⌀25 mm in STL 3D format. Final length of this junction is 105 mm. The larger-diameter tube has a thickness of 6 mm and a sleeve length of 40 mm. The smaller-diameter tube has a thickness of 3 mm and a length of 50 mm. The ends have a fillet to make tube connection easier.
Parameter Value Unit
side A length 40 mm
side A outer diameter 52 mm
side A thickness 6 mm
side B length 50 mm
side B outer diameter 25 mm
side B thickness 3 mm
transition length 15 mm
axis offset 0 mm
ends fillet fillet on bo...

📦 Model #3713

2 object(s)
- format STL
Enclosure with screw-mounted lid STL file: 90×80×36 mm
View of object #0
Download this enclosure model with screwed lid in STL format. The dimensions are 90 mm long by 80 mm wide and 36 mm high. The cover only is 10 mm high. Wall thickness is 3 mm. The enclosure does not have cooling.
Parameter Value Unit
length 90 mm
width 80 mm
total height 36 mm
lid height 10 mm
wall thickness 3 mm
screw margin 0 mm
fit clearance 0.1 mm
cooling zone(s) no cutouts

📦 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 #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 #3096

1 object(s)
- format STL
Honeycomb grille STL 3D file, 210x148mm, mesh: 10mm
Download this rectangular protective grid file in STL format. The overall size is 210x148 mm, with very large 10 mm cell size for maximum airflow. This grid provides both mechanical protection and airflow.
Parameter Value Unit
length or center-to-center 210 mm
width or center-to-center 148 mm
mesh size 10 mm
dual color no
holes no
Model of a support bracket with a central reinforcement in STL format. The dimensions are 200 mm in length, 120 mm in height, 20 mm in width, and 8 mm in thickness. The holes have a diameter of 6 mm. Chamfers are done to the holes to seat the screw heads. The reinforcing bar enhances mechanical strength and includes two passages for fastening. This bracket prints without support, printed flat directly on the build plate.
Parameter Value Unit
length 200 mm
height 120 mm
width 20 mm
thickness 8 mm
hole diameter 6 mm
chamfer on the holes yes

📦 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 #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 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 #3645

1 object(s)
- format STL
O'ring STL file ID 12 × CS 4 mm
Model of sealing ring with dimensions Internal diameter (ID) 12 mm / CS 4  mm. Final diameter resulting corresponds to 20 mm.
Parameter Value Unit
inner diameter (ID) 12 mm
cross section (CS) 4 mm
Download this 3D file of a mounting bracket with a central reinforcement in STL 3D format. The dimensions are 152 mm in length, 152 mm in height, 26 mm in width, and 9 mm in thickness. The drill holes are designed with a diameter of 5 mm. Chamfers are applied to the holes to improve the seating of the heads. The central reinforcement bar improves rigidity and provides two openings for screwdriver access. This bracket prints without support, printed flat on the print bed.
Parameter Value Unit
length 152 mm
height 152 mm
width 26 mm
thickness 9 mm
hole diameter 5 mm
chamfer on the holes yes
Download this model in STL format of a round-to-rectangular adapter with an outer diameter of ⌀78 mm and a rectangular section with inner dimensions 30×200 mm. The shell thickness is 3 mm and the overall length is 100 mm.
Parameter Value Unit
cylinder outer diameter 78 mm
cylinder inlet length 20 mm
rectangle internal length 30 mm
rectangle internal height 200 mm
rectangle inlet length 50 mm
offset Z 0 mm
offset Y 0 mm
total length 100 mm
thickness 3 mm
chamfer no chamfer
File in STL format of a round-to-rectangular tube adapter with an external diameter of ⌀250 mm and a rectangular section with internal dimensions 250×150 mm. The shell thickness is 3 mm and the total length is 165 mm. The adapter has an offset of 15 mm along the Z axis. Chamfers are applied on the outside of the cylindrical end and on the inside of the rectangular end to ease insertion.
Parameter Value Unit
cylinder outer diameter 250 mm
cylinder inlet length 50 mm
rectangle internal length 250 mm
rectangle internal height 150 mm
rectangle inlet length 80 mm
offset Z 15 mm
offset Y 0 mm
total length 165 mm
thickness 3 mm
chamfer chamfers on ...
Round box with lid STL file ⌀ 50 mm - Height: 45 mm, Shell: 2 mm
View of object #0
Get this cylindrical organizing box in STL format. Its diameter is 50 mm and its total height is 45 mm. The wall thickness is 2 mm.
Parameter Value Unit
external diameter 50 mm
total height 45 mm
wall thickness 2 mm
fit clearance 0.1 mm
inner bottom fillet 0 mm

📦 Model #1095

1 object(s)
- format STL
Tube adapter STL file ⌀ 149.6–99.6 mm (Length: 80 mm)
Straight sleeve ⌀149.6 mm to ⌀99.6 mm in STL 3D format. Total length of this coupler is 80 mm. The thickness of the tubes is identical: 4 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 20 mm. The ends have a fillet to ease the connection.
Parameter Value Unit
side A length 30 mm
side A outer diameter 149.6 mm
side A thickness 4 mm
side B length 30 mm
side B outer diameter 99.6 mm
side B thickness 4 mm
transition length 20 mm
axis offset 20 mm
ends fillet fillet on bo...

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.