The above image is not very encouraging; there are far too few triangles (7224 to be exact), making the model look too coarse. We will now have the 3D printing software build up this model into a preview. We use Simplify3D software for this, it has a very good slicer module, a lot of options and supports many printer models.
This is what the rough model looks like in the Simplify3D software previewer. The surfaces from which the model is constructed can be clearly seen. The print does not look very accurate (it is not a smooth circular shaped object), and will be difficult to finish by hand, if it is printed from material that should be sanded and polished.
We therefore want our model to look as accurate as possible. We are now exporting the model to an .STL file of our solid with the highest possible resolution.
The above model now consists of more than 1 million triangles. The density is so high that the model now looks black due to the multiplicity and density of polygons! There is now a tolerance of less than 0.5 degrees in each ’tile’ that represents the surface structure, which is why we need so many tiles. In the software of Simplify3D the preview looks much better:
Although we have now improved the quality of our 3D model, there are still a number of challenges. The first challenge is that our mesh must be printed with an infill of 100% to make it massive. We can specify this in the software, but where the printer starts to print more slowly, especially around the wind way, the 3D model becomes quite warm as the printhead is more than 200 degrees. We must therefore use cooling. This is done by built-in fans in the printer and can be controlled by the software. However we also have to make sure layers will stick on top of each other. Another problem is that if we print the model in this way, the ‘roof’ of the room may collapse; the filament (the thread with which it is printed) horizontally bridges the window, so it will have to be supported. We do this with help of the software using support structures. These are very thin ‘turrets’ that are co-printed to support the horizontal overhang. These can later be easily removed with a thin set of pliers. You’ll see this in Part V as we discuss the print results. The program automatically calculates when and where this support should be placed, based on our settings, however we can override the placement and amount of supports.
Supports are coloured dark orange in the above cross section.
In the software we can add or remove supports. The amount of parameters in the software that controls the printer often makes the process quite long to get to a usable model, as often times it requires trial and error. Issues such as temperature of the print head, print speeds, resolution, layer thickness, placement of supports, cooling, material, retraction of the filament to prevent droplets or blobs and the amount of filament feed can cause frustration and confusion. We now have a few years of experience with 3D printing at deQuelery, and this is really necessary to be able to estimate what it takes to produce a usable print that matches the original design (the solid).
In the end, the software converts the model into layers, while taking into account all the other settings that we have applied. In the image below you can see print speeds, the duration of the print (7 hours and 53 minutes), the number of layers that make up the print (1005 layers of 0.1mm) and the amount of filament needed to print the entire model: 11236.6mm , or more than 11 meters. The final weight will be about 33 grams. Other filaments, especially metal infills are much heavier. More of this in Part V.
The ring around the model is called a ‘brim’, and is needed to allow the right amount of filament to flow into the printhead before the model is actually printed. The thin platform on which the model is positioned is called a ‘raft’. First a few layers are printed to create a ‘foundation’, resulting in a nicer print.
The code (the so-called g-code) that the software produces controls the printer and consists of 652992 lines of code. This code controls temperatures of the print bed and extruder, where the print head should go and how much filament should flow through the nozzle. The fans are also controlled with this code. Below is an example of a few lines of g code:
G1 X0 Y0 F2400 ; move to the X=0 Y=0 position on the bed at a speed of 2400 mm/min
G1 Z10 F1200 ; move the Z-axis to Z=10mm at a slower speed of 1200 mm/min
G1 X30 E10 F1800 ; push 10mm of filament into the nozzle while moving to the X=30 position at the same time