This project introduces some tips to make a flexible but robust non-flat surface and some other common issues, explaining a possible solution through the making of a smartphone cover full 3D printed.

## The object

First of all the finished object.

The creation shown in the making of video required four main steps and some experiments:

1. Taking the model dimensions
3. 3D printing the components
4. Assembling the components

## Calculating the model dimensions

Finding some difficulties to buy an original cover fast and at a cheap price I decided to take the measures directly on the LG G4 smartphone.

TIP #1 : When you should measure a real object to make something 3D printed consider that it is a good practice to exceed your dimensions of about 0.1mm This is just the excess that you find when - also in the case of a perfect 3D printed object - you will use some kind of support when printing. This depends on the kind of object you measure but the suggested value is always the worth to take in account. When printing holes that will host screws (e.g. Allen screws, not conical Parker) a minimal extra amount of material is present in the holes at the end of the printing process. So if the screw is 4 mm you should design the holes 4.1mm You will see that the screw will fit perfectly without problems and you save a lot of time to complete the printed object with hand tools.

When a magnet is positioned in a specific point The smartphone screen changes showing a round watch giving access to a minimal number of easy apps. Making some experiments a 3mm x 1mm Neodimium magnet is sufficient to generate the screen switch effect but should be positioned very precisely. Also in this case the exact position has been acquired manually to design a hole in the cover bottom side at the right point. The following image shows the final result with the magnet embedded in the bottom part of the cover (the side in contact with the screen).

## Two sides, two colors

Making a flexible and robust plastic cover in two different colours sounds nice, yes? But this choice has a reason. This is the case when we convert a limit of the 3D printer in a good aesthetic effect. The following tip can be applied to almost all the cases when this is generalised issue will occur.

TIP #2: To successfully produce a well done and robust 3D printed object a support is needed.

This extra plastic thin filament is generated by the slicer (depends on the user settings) making possible the creation of objects else impossible to 3D print. Unfortunately it is very difficult that after removing the support from the finished object things remain perfect as we can read here and there... As a matter of fact the printed side in contact with the support is very difficult to make clean and neat.

When designing an object for 3D printing and important factor to take in account is the need of a support extra filament: it is better to create the entire object in two parts or more to be joined in the final assembly than accepting the compromise of a bad refined surface.

This is the case where a better result in the printing phase is decided during the design.

The cover should follow the smartphone screen form factor: not a planar surface but a slightly curved one. The next images shows how the support printing process has been done:

Also after a very accurate removal of the support material this side remains with rough surface. IN our case the solution was to make a couple of 1mm thick slices - better in two different colours - printed with support one to the opposite side of the other. Assembling the two components the rough surfaces remain internal and are no longer visible. The following group of images shows the second part of the cover, printed with described method. The last image shows the dark side of the printed element after the support removal: As you can see it is rough and few refined than the opposite side.

## Object design and components positioning

With the right dimensions of the parts and the cutting positions written down the 3D model has been designed using Rhino 4. The CAD choice depends most on the everyone personal experience and preferences: the best application in this case is always the one we know better. It is important to use a CAD program supporting the 3D model export in STL format ready for the slicing algorithm.

Note the images above: the first shows the assembled object, while the second shows the components correctly positioned to be exported in STL format

TIP #3: Based on my personal experience I consider a best practice before trying to print a 3D model to setup it assembled on the CAD as it should really be. This is a useful method do debug the design being reasonably sure that the finished parts, when printed, fit as expected and we have not forgot some important detail in the model. The further step is orienting the component(s) aligned to the x-y plane at 0,0 coordinates. When the STL file has been loaded in the 3D printer application it is again possible to reorient it, rotate, mirror etc. but what happens if you forget to apply the right transformation? Better to prepare it in the CAD environment.

## Setting the printing parameters

When all is ready we can finally slice the object(s) and print them. As many users know very well setting the 3D printer parameters is not always so obvious and it is almost impossible to apply the same setup to all the objects we create. Settings depends on the form, the usage, the nozzle diameter, the material and more and more. It is almost impossible to analyse all the parameters in a single article but the very important aspect is to focus what are the most influencing settings to reach the best result with a certain object. Depending on the object mechanical characteristics and shape these key settings may differ a lot.

The above images shows the assembled object with a correct (Is really correct? Anything is subject to further perfection) printer settings.

TIP #4: On top of our consideration any suggestion is always conditioned by the kind of filament we use; PLA has different rendering behaviour than ABS, Nylon etc.

Despite the settings strictly related to the filament quality (some colour filament have different behaviour than white or black, also of the same material) there are some general considerations that it is the worth to consider.

Printing thick surfaces we need to reach good reliability and flexibility. We should consider the thickness of the material in terms of printing layers. To get a good result with a 1mm thick object we should print a reasonable number of slices: it is a best practice adopting - when possible - a nozzle diameter 0.3mm or less for a good precision. Another good suggestion is to apply a 100% internal fill. Maybe the printing process will be slower but this gains in material consistence. For the same reason it is strongly suggested to slice 0.1 mm layers: we can count on 10 layers for the better robustness also for thick surfaces.

A last note: don't be too worried to print slow; 60-70 mm/sec with a well calibrated printer can be easily supported making a compact solid object.