Introduction: 3D Printed Super-Lightweight Interactive LG G4 Smartphone Cover

I have tried to show this step by step how-to for two reasons. The first is to explore a not easy to do 3D printed project and the second is to present a small product that has been designed trying to avoid the problems that arises when using a traditional smartphone cover.

I have found a lot of difficulties to find an original LG G4 cover to take the measures so I decided to get the measures directly from the device. The problem is that this smartphone model is not flat so multiple repere points should be used to take a reliable size for the cover.

Using a smartphone to shoot photos, use the screen, navigate etc. the presence of a cover, also the most usable, in my opinion represent a problem. The best solution will be able removing the cover when we use the device. The cover instead is useful, especially with the round circle showing the clock and some applications when we are moving, hearing music, and some other situations. So the project started.

You can buy this original cover on Drobott (and apply the Instructables 10% discount code DWQ0H19J to your purchase)

Step 1: The CAD Design

Parts design

The first image shows the two parts the cover is built in their relative assembly position. The design has been done with Rhino 4 extruding a curve that follow the curvature of the edged screen. As mentioned in the introduction using several repere points respect the bottom horizontal flat plane (measures has been taken in the real world ;) ) the points position has been used in the cad side view to create a couple of parallel Beziers then joined with two straight lines.Extruding the compound curve it was possible to create the flat surface: the base for the creation of both the components.

The round screen view is enabled alternatively to the normal full screen view by a small Neodimium magnet that when it is in proximity of the smartphone touch screen the feature is enabled. The effect occurs only in one specific position that has been found experimentally and measured with a caliper. For this model it has been used a Neodimium magnet 3mm diameter x 1mm thick and every flat surface is 1 mm thick.

The bottom component includes a 'L' shaped rail in the middle that is used to keep the cover in place when it is inserted on the smartphone.

The photography shows a detail of the finished part with the magnet inserted in it.

As you can see in the second 3D image the 3D printing position of the parts is different than the assembled example of the first one. We will see later the reason.

Step 2: The Front Customisable Logo

The bottom -yellow- part (nearby the smartphone screen) is made with a coloured filament. The top side (black or white, but any combination of colours can be used) replicates the screen hole and has a logo that can be customised as you want. The effect sounds nice, no?

In this example I have just used an enlarged Wingding TTF font character but as a matter of fact any logo can be applied to the surface.

The easiest solution seems to create the logo in vectorial format then exporting it in DXF format. DXF files can be imported in Rhino CAD as planar curves. Alternatively it is possible to use any TTF text taking account of some limitations as the logo is cut.

Step 3: Choosing a 3D Printing Strategy

As you can see in the making of video shown in the introduction step the top and bottom parts of the cover are thick and flexible. This is essential to adapt well to the smartphone giving the needed support to absorb as much as possible eventually shocks.

In this case it was very important choosing the right printing strategy considering the points detailed below.

Avoid screen scratch risk

To print the two cover parts we need to setup a support while printing; also in the case we remove with great accuracy (it is strongly suggested) he support side remain less refined than the opposite side. For this reason the top part should be printed with the top side (the side that will be visible to the user) on the top print area.

Vice versa the bottom part should be printed rotated so that the internal side (the side in contact with the smartphone touch screen) is the most refined.

When the 3D printing ends, after removing every support residue and refining the surface with extra fine sand paper this side remain always a bit rough. The same for the top part.

Following this method the two rough parts are the internal sides of the cover and are perfect to be glued.

PLA is not like metal and also when we slide the cover over the smartphone there is no risk to scratch the touch screen.

Choosing the right printing parameters

The two examples shown in the images of this instructable has been created with a 0.4 mm nozzle (the purple model "B") and a 0.3 mm nozzle (the orange model "A"). As you can see the differences are very few; as a matter of fact this is not the most important factor: we should consider instead that the final thickness of every part is just 1mm thick. To grant a very good flexibility and avoid the risk of layer separation after some experiments the better solution was to set a single layer thickness of 0.1 (the smaller available on the 3D printer). With this layer thickness also 1 mm of printed material is built of 10 different slices granting a good adhesion and flexibility.

Another important factor contributing to reach a good result is the fill factor. We should not be worried to spend more time during the printing process but in cases like this it is needed to set the slicer to 100% fill: solid material.

Other concurrent factors

As you see the printing step is not the only important phase of the entire project development; adopting the solutions described above implies to do the right choices also in the design phases.

As we are printing with a 100% fill factor we don't need to care too much to print very slow: is is important to use a set of differentiated parameter keeping the printing borders at least 30% slower than the internal parts. The reference speed I have adopted with my printer is variable between 45 and 70 mm/min. It is important to maintain the right difference between borders and internal filling, while the effective printing speed depends on the 3D printer model you own.

A and B: two models, both working

I have experimented two possible assembly solutions. The first model A (the yellow one) is assembled with some cyanoacrylate glue only along the two shorter sides. Keep them pressed for about half an hour and it is very difficult they break during usage.

The second solution instead, the model B (the purple one) has four pins so that - always adding a drop of cyanoacrylate glue around them before closing the two sides - that add a coloured touch and help to position perfectly the two parts of the covers when assembling.

That's all folks!

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Bio: Balearic Dynamics, owned by Enrico Miglino, is a R&D company located in Spain integrating technologies, creates new products and develop software and firmware components ... More »
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