3D Printing Moving Parts Fully Assembled - 28-Geared Cube

Why did I create this? I recently decided I wanted to really test 3D printing's potential as a manufacturing technique, this did not mean see how well it can just print a boring plastic part that could have just be injection molded for a fraction of the price like many 3D pieces printed we see now through services such as Shapeways, this meant designing something that could only be produced using 3D printing (and it had to be awesome!) while showing 3D printing to be a potentially very useful technology in the future due to one of it's two main advantages; the first has already been well documented about; this is about how 3D printing can be used to produce complex 3D geometries that would be impossible to produce using any other manufacturing technique, however these complex 3D geometries are generally just created for their aesthetic appearance and while they are generally very impressive, they have no real potential use or meaning that could portray 3D printing as a more practical manufacturing technique than current techniques for mass production.
In this instructable, I attempt to explore this second advantage of 3D printing and this is it's ability to print moving parts by printing whole assemblies in one print with all moving parts printed fully assembled, unlike the other advantage, this advantage really has a potential to change the way we mass produce devices which have moving parts; by 3D printing all moving parts in place, this completely removes the need for assembly, either by the manufacturer, which costs them money to employ people, as well as the time for the assembly to take place, or by the buyer which is again time consuming and can be complicated.

What is it? To fully test out 3D printing's ability to produce complex mechanical parts fully assembled I designed the '28-Geared Cube' which is a 3D printed desk toy which, as it's name suggests, is a cube with 28 gears on it; by rotating any one of these 28 gears, the other 27 gears also turn in a mesmerizing pattern. This was 3D printed using the 3D printing service Shapeways in the White, Strong and Flexible material. While I did want to test 3D printing, I also wanted to design something that I felt looked good and really made you question what was going on when you turn the gears.
To achieve this, the 28 gears are arranged so on each of 4 sides of the cube are 7 gears: 2 large outer ones that move in opposite directions, the outermost gear has handles on it so it can be easily rotated, the motion between the 2 large cogs on each face is reversed due to 5 smaller gears set within the cube in a similar layout to a planetary gearbox to reverse the big gears' direction on each of these 4 faces. Each of these sets of 7 gears on the 4 faces are all liked through one of the big gears on each of the 4 faces meshing at 90 degrees with one of the big gears on each of the 2 neighboring sides. This means that if any one gear is spun, they all spin in a memorizing pattern.

Step 1: Designing

First you need an idea which requires moving parts, whether this has a practical use, or no real practical use at all and is just designed for fun (like my design) and then you need to design it in such a way on CAD software that it can be 3D printed and move as intended in your design:

When designing assembled moving parts for 3D printing, the main design constraint you have to follow is the required clearance between parts within the design that you wish to print as separate solid bodies, such the distance between meshing gears, so that these actually print as separate parts, this value can usually be found for various 3D printing techniques, for example, Shapeways, who I use to 3D print, clearly publish the minimum clearance between moving parts for each of their materials they 3D print in on the 'Material Portfolio' pages (white, strong and flexible material requires a 0.5mm clearance); if this value is used, the moving parts should print without an issue and should be able to move as designed (as long as the other design constraints are followed for the intended material such as minimum wall thickness).

My design took many hours to make, first as sketches on my ipad, then modelled using Autodesk Inventor Professional 2013. I decided to model this design as separate pieces and then virtually assemble the separate moving pieces to create the final design, this allowed me to animate the design to make sure everything would work as I wanted it to.

The design was then uploaded to Shapeways where it was 3D printed in their 'White, Strong and Flexible' material and then it was posted to myself...

Step 2: Improvements

Below is a video of the cube as it was after it left the 3D printer without myself modifying anything, you can probably notice that while the gears do move, they do not move as smoothly as I had hoped with continued motion in one direction being nearly impossible as the mechanism would quickly jam, this is most likely due to the high friction surface of this material as it has a feel to it of medium grain sand paper.

However, with one simple modification, the smoothness and reliability of this mechanism improved drastically! I sprayed the whole cube with a PTFE lubricant (this material is also known as Teflon and is quite often on frying pans etc due to its anti-stick and low friction characteristics). As you can see in the video below, this completely reduced the friction within the cube of all 28 gears turning at once and it completely stopped jamming!

The last improvement isn't really that relevant to 3D printing itself, I just thought that making the cube motorised would make it just that much cooler and also proves that the 3D printed mechanism can be driven by electronics.
To make the 28 Geared Cube autonomous I used a 6 volt battery, 6 volt geared motor, reed switch and small magnet, small length of stiff wire, piece of fibreglass sheet, some Kevlar thread, a couple of washers and some electrical wire.
When the small magnet is placed near the reed switch, the motor starts which rotates just 1 gear which rotates all 28 gears.

Step 3: Conclusion

In my opinion, 3D printing is definitely not ready just yet for mainstream mass productions of fully assembled mechanical devices due to the relatively large clearances required between moving parts, even with higher end 3D printers such as the Objet (now owned by Stratasys) 3D printer series I still believe it is not low enough to provide precise moving parts, this can be seen in the 28-Geared Cube with the large amount of backlash there is in the gears as the teeth of the gears had to printed so they were 0.5mm away from neighbouring teeth.

The friction within current 3D printing materials is generally quite high so would have to be greatly lubricated using some kind of lubricant, such as the mentioned PTFE lubricant, so this again makes 3D printing quite difficult at the moment to produce consumer ready mechanical parts as post production steps are still required to make it consumer ready.

Another problem at the moment is the lack of 3D printing accurately with metals and lack of a small clearance required between moving parts making it difficult to produce mechanical assemblies in metal and metal can be very useful in many precise mechanical assemblies.

Lastly is the problem that 3D printing is still very expensive and slow which may limit it's use as a mass production technique.

Although the above may seem very negative towards 3D printing's use as a viable manufacturing technique for mass producing consumer ready mechanical parts, I really believe with the speed that 3D printing is advancing at the moment that these issues will soon not be issues anymore with more precise, fast and cheap printers being developed with a larger range of materials that can print mechanical parts, such as metals and low friction plastics. 3D printer could maybe even be developed to 3D print oil and other lubricants straight into the assembly.

All in all, this instructable shows how the creation of 3D assemblies using 3D printing is possible and works and while 3D printing might not be ready to mass produce mechanical assemblies just yet, I believe that this instructable shows that the future is bright for this technology and the best is still to come...