Foreword
This article does not discuss the educational aspects of designing a model. Aspects such as the so-called “hand tactile space” etc. can be found in article “2. Principles in designing models for VI students”. This article focuses on technical aspects concerning the size of models.
Thinking about size in the design process of a model
When designing a model, work is done in absolute dimensions. For example, if a cube is being designed, its edge length is always part of the design process. Therefore, always bear in mind that the 3D model will not only exist virtually (in which case size would be irrelevant), but will also be printed out on a 3D printer. This is where the importance of the specific printer or the size of the build space comes into play. If there is only a very small printer available and the model is to be produced on this device, then the construction of a very large model probably makes little sense (see also the last section of this article).
Resizing a model after the design process is complete
After designing a model and exporting it as an STL file, the size can still be scaled. This can be done either in a special program (e.g. Netfabb) or directly in the slicer Cura. Here it is possible to distinguish between a uniform scaling and the scaling of selected axes only. For simple models without fine details or braille this can work and be helpful. A model of a square pyramid can certainly be enlarged or scaled down and is printable as well as usable afterwards in an educational context.
Models with braille can generally not be resized afterwards, because braille always has to be printed in the originally constructed size. The model always changes as a whole when scaled, so individual elements (such as the braille) will change proportionally. Line and point symbols as well as other details are also changed during scaling, which is probably why in practice only very few models can be scaled at a later stage.
Build space of popular 3D printers
A simple rule of thumb is that the larger the printer’s build space , the larger the models that can be printed. In the last few years, 3D printers have tended to become larger and larger. In addition, there are more and more XXL printers, which are significantly larger than average. One of the fundamental intentions of 3D printing for visually impaired people is now that models can be exchanged digitally and printed anywhere in Europe (or even the whole world). As a result, models should follow the standard dimensions of common 3D printers:
As a rule, models should therefore be smaller than the absolute maximum of 19x19x19cm , as this is currently (in 2023) the size of build space in the most common 3D printers.
If you have a large printer at your disposal, there is of course nothing to prevent you from designing a large model. However, if a design is uploaded to the database it is important that it is printable on a “standard device” (20x20x20cm).
Assembly possibilities with several small components
In some cases, there is no avoiding a large print (where the edge length is greater than 20cm), as many details, lettering or similar mean the model cannot be reduced sufficiently to be printed on a “standard device”. An example of this is the braille hundred square, which must be printed in four individual parts on a “standard device”. In this particular case, the 4 individual parts must be glued together after printing. Since this is a flat model, it should also be glued to a wooden plate for stability.
In general, gluing the individually printed parts together should be the most common method for connecting them (see Article 6.3). Nevertheless, in individual cases it is worth checking whether perhaps a plug connection, magnets, hook-and-loop tape or similar might also be considered. Bear in mind that these techniques play a major role if a model is to be taken apart afterwards. Please refer to Article 4.7 for more information.
Thinking about the printing time of a model
The size of an object has a fundamental influence on the printing time. Another factor that has a great influence on the printing time is the diameter of the print nozzle, as well as the layer height and the amount of infill used inside the model to support the walls and in particular the top surfaces of a model. All the parameters mentioned should be checked individually for large models in order to minimise the overall printing time as much as possible.
