
Designing digital models
Design or Discover?
Have you ever had to replace a large, costly item just because a small inexpensive part was broken?
Has a board game become less playable because one of the parts is missing?
Using a 3D printer to make a new replacement part is now a reality, as long as you have the required part as a digital “STL model” file. But, what do you do if you don’t have the necessary file yet?
Before we discuss the process for creating a new digital CAD file, it is always worth considering whether someone else has already done the hard work for you.
If the part you need has a specific name, it is definitely worth putting the name of the object and “STL file” into Google to see if there are any existing models that can be downloaded. These are often free for personal use, but some designers (myself included) sometimes charge a small fee for some of their designs.
There are dedicated websites that host libraries of 3D models – not all are designed for 3D printing though, some are intended for art work or computer game environments and may not be useable, so do check whether the model was designed for printing before you pay for anything.
Here are some links to sites worth searching in:
If you are fortunate enough to find exactly what you are looking for, all you need to do is download a copy of the STL file (or in some cases, a collection of STL files contained in a Zip file) and then either send the file(s) as an email attachment, or send me a link to the download site.
However, many common objects have not yet been modelled and made available online, and, of course, if you have an idea for a completely new object then there is no alternative but to have the digital model created from scratch.




How can we make a digital copy of a real object?
There are several possible methods, each of which will be appropriate in different scenarios.
Scanning solutions
High-end commercial 3D scanning is highly accurate and sophisticated, but beyond the reach of most small home projects.
Smaller and less expensive 3D scanners are more widely available and I do own and use one of these. They are less accurate but are sometimes the best option for large, irregular decorative items – or a model of someone’s head!
Photogrammetry is like digital scanning but only requires an ordinary camera and lots of photos of the object taken from every angle. The results can be variable but when successful the resulting models can certainly be 3D printed.
CAD solutions
Using Computer Aided Design software is fundamentally different from scanning, but is often the best method of creating a digital model of a part that needs to be reproduced as a functional object.
The process involves drawing accurate sketches with precise measurements of all the relevant dimensions and then pulling, or extruding these sketches into the third dimension to create a ‘solid’ model inside the computer. This is gradually extended, added to, cut away, and connected to other parts until the digital model is an accurate copy of the target object.
If you have a physical copy of the object (even if it is broken) then this can be used to take measurements from and make the sketches accurately.
If no physical model is available then you will need to supply some basic sketches of the desired object with relevant dimensions, so that the CAD model can be created.
Just supplying a photo of a part that needs to be reproduced is not likely to work since accurate measuring will be difficult or impossible.
How much does it cost?
I charge £30 per hour for CAD modelling and 3D scanning work with a minimum starting at just £10.
I will be happy to advise you on the most appropriate method for creating new digital 3D models.
I am a self-taught, hobbyist designer and I will only take on projects that I believe I can complete successfully.
I know my limitations!
Can you do the modelling work yourself?
Certainly!
There are many 3D modelling programs available now, ranging from completely free to hugely expensive. Many people find the free software to be perfectly adequate as long as one is prepared to devote time to learning how to use it.
There are a couple of different kinds of programs and it is important to understand the difference between them.
Constructive Solid Geometry programs
CSG models are some of the best for 3D printing because the software treats the objects as solid items. Always export an STL file for printing but also send a STEP file to allow for minor adjustments.
Mesh modelling programs
Mesh models can be printed if they are “watertight”. The STL mesh file describes the surface skin of the model but may contain holes or overlapping surfaces which will cause problems. These models always need checking to see if they are printable.
Here is a selection of programs suitable for home use.
TinkerCAD – great for kids and beginners wanting to make a start with CSG modelling
FreeCAD – stand-alone CSG software that doesn’t require a network connection to run
* Fusion 360 – the current favourite CSG choice for many amateur and small business designers
* Onshape – powerful CSG modelling in a web browser or an iPad app
Shapr3D – another iPad design app; the free version is only useful for evaluation purposes
* OpenSCAD – CSG modelling for programmers; create solid models using code
* Blender – a really great mesh modeller with lots of features but with a steep learning curve
SketchUp – was popular with some users for a time, but has a reputation for creating some of the least printable models
MeshMixer – as the name suggests, this fun program can be used for combining models to make strange hybrid shapes
The programs that I regularly use are highlighted with an asterisk.