3D Printing part three
THE THIRD PART IN OUR 3D PRINTING SERIES LOOKS AT THE IMPORTANCE OF SETTINGS IN ACHIEVING AESTHETICALLY PLEASING RESULTS
We move up a level in our skills and print out a camera
In this third part of our series, we will address the 3D printer setting details by following a real-world creation: the model mock-up of the PONF camera (the official site is http://ponfcamera.com), an innovative project aimed at creating the first dual-back (digital and analogue) reflex camera.
This is a kind of 3D-printed item for which the aesthetic result is a key factor. Our goal is achieving (as much as possible) the same skeleton that the product will have. The process described here is not limited to the bare 3D printing of the STL files but also involves some interesting craftwork / post-production.
The first step was creating the design of the components with Rhino 5 CAD software — you can see some of the 3D renderings in the illustrations on these pages. The process described can be easily applied to plenty of 3D-printed static models.
Bed calibration
We mentioned in a previous article the importance of the correct bed calibration for a good printing job. To proceed to calibrate the 3D printer bed manually, we will adjust the four calibration screws, one at every corner. In an attempt to make things easier, some models provide only three calibration points. I had the opportunity to use both methods and found that I obtained better results with the fourscrew system. The procedure is not too difficult but should be precise.
Four-point calibration procedure
Position the extruder making the Z-zero at about .5mm from the bed. The 3D printing software has an auto-zero function to position the extruder nozzle at the axis origins.
Using the manual controls on the printer or the 3D printing software, move the extruder nozzle to the first corner. No matter what method you choose, check the distance of the nozzle from the bed surface with a .10mm thick feeler and rotate the corner calibration screw to the right distance. Repeat the same procedure on all the four corners.
The optimal distance between the nozzle and the flat bed should be .5–.7mm. However, one calibration on every corner is not sufficient — modifying the distance of one corner of the bed slant will affect the settings of the other three corners. So you will need to repeat the four- corner calibration until the distance value is constant at all the test points. It is important to note that the calibration process is not a stable condition — temperature variations during print jobs and other factors affect the settings. It is good practice to check the bed calibration frequently and always before starting a new job.
The process we describe can be easily applied to plenty of 3D printed static models
Automatic calibration
Alternatively, the manual procedure can be automated with a 3D printer auto-levelling sensor. This is a tool permanently applied to the extruder, which is able to detect the distance from the bed. The automated process has pros and cons and can be applied only with compatible 3D printers.
Pros: The automatic levelling sensor is a good choice if the user has no experience and is not sure of being able to carry out the manual calibration. The automatic levelling process is faster and can be very efficient if the bed is (almost) aligned correctly. After the sensor installation, it is easy to use.
Cons: The sensor is not expensive but not super cheap, either. If it is included with the 3D printer it can increase the cost of the device as a meaningful value-added. The extruder model and 3D printer should be compatible with the sensor installation. The 3D printer controller board should be compatible; an extra connector for the level sensor should be available on the board. A firmware upgrade is needed to make the sensor work correctly.
Unfortunately, the auto-levelling sensor cannot be considered 100-percent trustworthy. It can detect the bed slant but will not change its orientation. During the 3D printing process, the controller firmware applies the mathematical corrections to the G- code `instructions, compensating for the bed misalignment. This is as if the extruder were correctly moving over a non-plane surface. It risks introducing a systemic error, resulting in imprecise object generation.
During the past couple of years, this
tool has become more popular and there are always more 3D printer models arriving that are compatible with or include the sensor in their original build specs.
STL model control parameters
Starting from the same STL file we can achieve very different results and qualities depending on how we configure the slicing algorithm. Our choices depend on what kind of object we are creating and its usage. In our case, we are building a model, so aesthetics is more important than robustness.
The two parameters that influence the final quality the most are speed and layer-thickness settings.
It is important to keep the printing speed within an acceptable range, as the faster the extruder moves the greater the loss of precision. Consider that every filament has its own best 3D printing speed. Different materials have different fusion temperatures and
different physical characteristics. For example, ABS (acrylonitrile butadiene styrene) is more flexible than PLA (polylactic acid), has a higher fusion temperature (about 220°C) and the model may be more resistant to temperature changes, but it is more flexible. However, mechanical printed parts — especially mechanical moving parts — may end up being difficult to use and require a lot of refining.
In the past, I have tried to make motion pieces with ABS and experienced a lot of difficulty. PLA (which fuses at about 180°C) is easier to manage. I prefer to use PLA as I get more precise results.
When working with different materials, you should consider adopting different configuration settings (i.e., speed, kind of support, preferred nozzle diameter, etc.). The settings we use in this example refer to PLA filament.
The STL files were sliced with the Cura algorithm, slice thickness of .2mm and nozzle diameter of .4mm. A slice thickness of .1mm may generate more precise vertical surfaces but double the printing time. In this case, as we will be
To achieve good quality with a DIY 3D printer, don’t count on the maximum printing speed declared by the manufacturer
finishing the parts and spray painting, it is not necessary, so I have opted for the faster printing process.
The best solution when deciding the print speed should be based on tests on the printing model you are using. There are too many parameters that influence this value so that it is almost impossible to find a general methodology.
To achieve good quality with a DIY 3D printer, don’t count on the maximum printing speed declared by the manufacturer. The 3D-printed parts shown in the illustrations were produced with the following parameters: • global printing speed: 55mm/s • outer perimeter speed: 28mm/s • infill speed: 65mm/s.
Note: A more detailed view of the set-up used to print the camera mock-up model (and all the relative CuraEngine settings) can be found in the Issue No. 77 folder on The Shed magazine GitHub repository: https://github.com/alicemirror/Shed Magazine/tree/master/Issue77.
Positioning the model
In regards to model orientation, there are some good practices beyond the obvious. First, always try orienting the object with its largest side to the bottom. This will provide better adhesion. Second, the lower layer should, when possible, be the flattest surface of the model.
‘Brim’ is the first layer extra surface created by the slicer algorithm to increase the adhesion of the printed object on the bed. A good brim width is 5mm. Setting a larger value does not add any worthwhile improvement but instead consumes extra material that will need to be discarded. Brim setting is a must when printing small components, but it should be considered a good habit. I always enable this feature on all my print jobs.
Support set-up is not always needed. It is a means to automatically add building structures to the model to print ‘ impossible’ parts. For example, without a proper support setting you get very bad results on a vertical side with a rectangular hole in the middle.
The slicing technique is based on a progressive vertical construction of a 3D object. It is essential that the filament of every layer is extruded over the previous one. To avoid filament extrusion ‘on the air’, we need to create a support. It is a light grid — automatically added by the slicer algorithm — starting from the last layer, printed until there is no next solid layer.
Fill percentage
The CuraEngine supports a fill percentage of between zero and 100. With a 100-per-cent fill setting we make a solid plastic object. In my experience with many printing experiments, a fill percentage range between of 20 and 75 per cent covers most needs.
When a solid STL design needs to be printed empty, the zero-percentage setting is perfect, but the object should be open on top otherwise the 3D printer will try to close the object with the top surface, resulting in a bunch of melted plastic inside the model.
In some cases, when I need to print thin objects of 2–3mm, it is mandatory to set a 100-per-cent fill to avoid weakness. The two camera-back components of our project here were printed with a fill percentage of 20 per cent. They have no mechanical stress and should be as light as possible. The small parts, the ones metal painted, were printed with a fill percentage of 50 per cent to increase robustness. Also, as there will be no mechanical stress on these components, printing at full density would have been a waste of time.
Finishing the model
In most cases, the print process is the most time-consuming phase of the prototype production but not here. As shown in the accompanying images, there is a considerable difference between the bare printed components and the model. The 3D printing with black PLA filament, 1.75mm thick, was completed in one day, but the finished model required another three days of handcrafting. 1. Preparing the components Remove extra brim material from the parts with pliers and a small cutter. To remove the extra support material, you need rectangular-sized pliers and a small clipper. The support gets printed very near to the vertical surface, but it does not touch it, so it is not difficult to remove. To avoid damaging the model while
As there will be no mechanical stress on these components, printing at full density would have been a waste of time
removing the support, I suggest using a fill density not lower than 50 per cent.
2. Cleaning and refining the surfaces This is the hardest job. It is not good practice to use electric tools (like a Dremel) because when rotating relatively slowly (e.g., 800rpm — the lowest speed of my tool), PLA becomes hot very quickly and tends to melt and deform. The best results can be obtained with multiple sandpaper passages starting from 400 grade up to 1200. To remove a more consistent quantity of material I here used several types of files before the sandpaper. Remove the plastic dust and move to the last step.
3. Painting the model parts Common acrylic spray paint works very well on PLA and the colour will remain stable. Paint multiple, fast passes. It is a boring process but really does give the best results. Wait about half an hour then
repaint. I applied five layers of paint to achieve the best result. If you find small drops on the surface, be patient. Wait until the paint is dry, clean the drops with sandpaper, then paint it again. The final result can be seen on these pages. For the software download of this series of articles, head to https://github.com/ alicemirror/ShedMagazine