Oct 12, 2017
As 3D printing technology develops we are seeing a rise in final models being produced directly from the printer instead of just prototypes, opening up new possibilities for designers.
This is partly as the quality of the printers improves. But it’s also due to some interesting techniques which are starting to be used in the design process of the product to help improve our ability to print complex shapes and rigid models.
I have designed an example which showcases some of the best techniques which I use day to day to create complex models as good as manufactured parts. The design work for this model was done in SolidWorks but the techniques used can be translated to any design software.
This decorative pulley light fitting I designed shows the different techniques I used to make an object with hard to print shapes and added strength which I’m still happy to have on display in my living room.
In this blog I will go through each part and show you where I added strengthened areas, where I created custom support in hard to print areas and where I used the capabilities of the Ultimaker to achieve the standard I was looking for. So let's dive right in.
Making the model a little stronger
The main body of the light fitting is an area that could undergo severe stress, depending on what you are hanging from the pulley. This part will have to withstand the weight of the pulley, the light bulb and any lamp shade you wish to add.
During the design phase I added two 4.5 mm holes through the main strut. This cavity allows me to slide in two 4 mm threaded rod in there. Before sliding them in I dab some super glue on the treads to hold the rods in place. This will increase the amount of weight the strut can bear, but the rods are hidden away inside the model.
Change your infill
You can also increase the strength in certain parts of your model by increasing the infill in Cura. With the main body I increased the infill pattern to 40%. This means internally there is 40% plastic and 60% air within the body. The rest of the parts were decreased to 20% as they don't suffer as much stress.
But adding infill does have two main drawbacks. It will increase both your print time and material used, so it's important to find a balance which works for you.
The fork part that holds the wheel could have been printed in two orientations: option A or option B, seen in the images below.
I chose option B as it allows the layers to run linear to the U shape – along the length of the shape rather than across it. The reason is, I knew in order to install this wheel I would have to stretch open the fork to insert the axle. If I had printed it like option A, where the layers run along the area that needs to bend, it could have snapped due to the weak spots between the layers.
When designing, take into account the orientation that that you will print your object with. Thinking about this early can avoid problems later on.
Material choice can also be a big factor when designing a strong model. Each material comes with its own set of properties which can be highly beneficial to your project. Since this is such a broad topic, for now I will look at four of the most commonly used materials: PLA, ABS, nylon and CPE.
Ultimaker PLA: PLA is your standard 3D printing material. It’s universal and easy to print with, but fragile and will snap before it flexes. Plus it doesn't take well to the elements and has a low melting point. Dipping it in boiling water will allow you to bend and mold the part. So if your design is going outdoors in the sun or in a very hot area PLA is probably not the choice for you.
Ultimaker ABS: ABS is another popular material choice but just like PLA it has a few downsides. While it can flex more than PLA and withstand higher temperature and the elements, it can be difficult to print with. It's more susceptible to warping if the printing environment isn't enclosed and controlled and has to be printed on a heated bed. It also gives off unpleasant fumes which can cause irritation for some people, so as with any material you should print in a well-ventilated room and not sit right next to your machine throughout the print.
Ultimaker Nylon: Nylon is a more advanced material. Its chemistry means it is susceptible to moisture. So if you’re working in a humid place you’ll need to keep it in a dry container or bake the material in an oven to dry it out. High amounts of moisture in the material can significantly reduce the quality. But once you’re printing happily with nylon it’s a wonderful material. With high impact resistance and less susceptibility to wear and tear, this is the perfect material for mechanical fittings or parts that rub against each other. But just like ABS it can warp so keep that ambient temperature up!
Ultimaker CPE: CPE is a great engineering material with excellent dimensional stability. What this means is that it doesn’t undergo as much shrinkage as other plastics, so it's more dimensionally accurate to your original 3D model design. This makes it great for tolerances. A heated bed is also recommended for printing with CPE.
So depending on what you’re making, material choice is important and something that should be considered early in the design phase.
Support material can be your 3D print’s best friend but can also cause some problems. It’s great at helping you achieve those intricate shapes that can’t be manufactured in any other way, but its downfall is that it can sometimes be difficult to remove (unless you’re using PVA on the Ultimaker 3). The trick is to try to avoid support material as much as possible, but sometimes you need it to realise your design vision.
On my design, the main body has a twirl to help support the main beam and make it look pretty. The end of the curl and the tip clearly needs support but the support on the tip is extremely thin. This is worrying as the higher it gets, the more unstable it becomes and this thin piece of support needs to hold its own weight and the curl until it reaches the other support. This is risky and could lead to a failure.
So what I did is return to SolidWorks and design my own custom support structure. This can be done in any other design software too. This has a large footprint on the bed and is a lot more stable that the Cura generated support. I designed the support structure to be 0.3 mm offset from the tip so they could break away easy. This technique worked like a charm and allowed a very hard overhang be achievable.
Screws and inserts
Sometimes you may need to join your parts with more than a little glue. Screws can be helpful, but you may not want them to be visible. You can hide them in a number of ways. You could recess the screw and bolt so it’s only visible from certain angles, or you could create an insert to keep it completely hidden. This can be done by stopping the print at a certain point, dropping the bolt in, and continuing so the printer encloses the hole in the model.
There are two ways to do this. The first is to manually pause your print and put the bolt in, but this isn't very precise. There is an option in Cura to do this accurately. This feature is called “pause at height”. It’s a little hidden but it can be found if you go to the options at the top of your screen. Open “Extensions > Post Processing > Modify G-Code”. In here, select “Add a Script” and choose “Pause at height”.
Here you can set the exact height you wish to pause at, where you want the print head to move when paused and how far the bed should drop. Make sure you tell the head to park somewhere that won’t restrict your access to the print.
My suggestion would be to test this feature by creating a small block with your insert in, especially if this is your first time trying it.
Remember to turn off the pause at height option for your next print.
So these are the basic techniques you could use to help create more difficult shapes with custom supports, add a little strength to areas you might be concerned about and make your design more rigid. This is not an absolute “dos and don’ts” tutorial but more of a springboard to help inspire your own designs and creations.
Use this knowledge to help you create awesome projects and develop your own strengthening techniques. I love to see how this community pushes the limits of 3D printing further than ever before. Even if it's with a simple insert. Someone will learn from that and appreciate it. Happy printing!
Kirby Downey is a South African Designer living in London who enjoys educating others about what can be done with 3D printing and how to push the boundaries of the limitations of 3D printing. With over eight years of knowledge and experience in both FFF and SLS technologies, Kirby prides himself in learning everything he can to help others on the journey that is 3D printing.