Just getting into this hobby – I wondered what slicing was with regards to 3D printing and why I needed to do it. I’ve always found that analogies really help me understand things that are new and unfamiliar to me. By relating a totally foreign concept to something I am much more familiar with – greatly speeds up and solidifies my comprehension of the new concept, idea or process. In this post – that is exactly what I attempt to do for those of you just beginning in this hobby of 3D printing, to help you understand the role of slicing in 3D printing process.
What is Slicing for 3D Printing?
Slicing a model for 3D printing “slices” the model into successive horizontal layers (2 dimensional cross-sections along the X & Y planes) that can be printed on top of each other – or stacked – to create a 3-dimensional shape. This “slicing” is done – because most 3D printers print one layer at a time, and then move up a notch to print the next layer on top of the previous layer. This is how a 3D printer slowly produces a 3D shape from a bunch of very thin 2-dimensional layers!
That is the narrow definition of what slicing is.
In a broader sense, slicing has commonly come to mean the part of the preparation process for 3D printing a model where you take care of setting up the mechanics of printing your 3D model. It is very similar to what is done through the printer dialog box when you are printing on paper with a regular printer.
When you print something on paper – the printer dialog box is where you select your margin width, any scaling, type of paper, whether you want to print on both sides of the paper, and if so – how to flip it. In similar fashion, it is the slicing software for 3D printing – where you are setting a bunch of variables and parameters for printing your 3D object like the size of the print, the fill pattern, and the types of supports to use. Slicing a 3D model for printing provides the printer with specific instructions (via g-code) on how each layer is to be printed and the path the nozzle is to take to print each layer.
Is it a perfect analogy, no – but one that I think is helpful to the beginner to understand the role of slicing in the 3D printing process.
Slicing the Model into G-code Instructions for the 3D Printer
So you have located an object you want to print on your new 3D printer. You may have located it on Thingiverse or even constructed it on TickerCAD. Then you saved the object to the hard drive on your computer as either an .STL or .OBJ file.
But how do you go about actually printing it now?
Well the printer can only understand g-code – a numerical control programming language that is used in computer-aided manufacturing. This code is predominately used to direct manufacturing and machining tools that are automated and controlled by computers. The slicing software is what generates this code.
The slicing software uses the object information contained within the .STL or .OBJ file, along with the parameters you select and indicate through the various options in the slicing software, to generate the g-code that controls the precise movements of the 3D printer head (or build plate) of the printer.
With these instructions received from the slicing software, the extruder of the printer then traces out, layer by layer, your 3 dimensional object.
Common Slicing Parameters to Consider & Understand for 3D Printing
In the slicing software the 3D model can be moved (so it doesn’t print in the middle of the bed), Scaled (change it’s size), and rotated. Additionally, below you will find some of the more basic parameters you might want to better understand and become more familiar – as they might be the first ones that need to be adjusted to get better 3D printing results!
Quality (Layer Height): The smaller (or lower) the layer height – the better the print quality will be. However, the print job will be longer – since the printer has more layers to print.
Infill / Fill Pattern: – This is the inside of the model – the part you cannot see. It still affects the object – because it is a big factor in the rigidity of the object. The more infill – the heavier the object will be, more filament will be used (and hence the cost higher), and the longer the print time will be.
Supports: – When printing a 3D object with overhangs – it may be necessary for supports to be printed underneath certain areas of the model to prevent warping and distortion of the object during the printing process. Overhangs are when only part of a higher layer is supported by the previous layer. Remember – the 3D printer is essentially a giant (but sophisticated) glue gun – in that it is extruding a melted plastic – which has to cool somewhat before the extruded plastic provides any structural value. So stacking melted plastic hanging halfway off the previous layer of melted plastic will tend to distort and warp if the angle of the overhang is too great. It is generally recommended that for overhang angles greater than 45 degrees- that supports should be used. Type of filament, temperature, and printing speed may be other factors that influence whether or not supports are required for a successful print.
Rafts, Skirts & Brims: These are all strategies that involve putting layers of filament down on the build plate before printing the 3D model.
- Skirting is usually just a thin line around the object to be printed – and is done to essentially make sure that the extruder is hot enough, unclogged and ready to print. It’s like a warm up lap for the printer – to make sure it is primed and the filament is flowing properly. Think of a skirt as an outline of the object that doesn’t directly touch the object itself.
- A raft is generally referred to as a horizontal layer of printed material beneath the actual model – so the 3D model is not resting directly on the build plate. It is used to help with build plate adhesion and stability of objects with smaller footprints. If your 3D model doesn’t adhere well to the build plate it is likely your build will fail – or at least be warped or distorted.
- A brim is like a baseball hat brim – it doesn’t reside directly beneath the 3D model, but rather extends off the edges of the 3D printed object. It is primarily used to ensure the edges of the print do not come off the build plate.
Speed: Just like for printing a document – there is usually a compromise between speed and quality. So to with 3D printing. The quicker the printing process – the more compromise is made with regards to the precision of the print.
Temperature: You can set the temperature of both the extruder (printing head) and the build plate. The temperature of the build plate is important in getting good adhesion of the 3D model to the plate – so it does not slip or move during the printing process – which would greatly reduce the quality and accuracy of the build, or might even lead to a printing fail. The temperature of the extruder will need to adjusted for different types of filament, and may need to be tweaked depending on speed of the print job or if you are experiencing clogging at the extruder.
Retraction: Retraction refers to the distance the filament is retracted back (pulled back) into the extruder or printing head. Increasing the retraction can be one of the most important settings in reducing the strings associated with a 3D print.
Filament Type: The filament is the material with which you print to produce the 3D object. Selecting the the best type of material to use for your model will depend on what your objectives are. If you are printing parts for a machine and their durability is important – nylon filament would probably be your best choice. For prototyping a model that just needs to show a concept – PLA my be you best choice – since it is easy to work with and the model doesn’t need to be that durable.
Your options will also be impacted by the 3D printer you have. Some printers can use a wider variety of filaments than others.
Continuing on with my paper printing analogy – the filament type is similar to the type of paper you are using, If you are using card stock paper in your regular printer – the printer needs to know that fact so it accommodate the thicker paper by making adjustments to the distance between certain parts so the paper doesn’t get stuck in the printer. In similar fashion – the 3D printer needs to know if you are using PLA filament or ABS- because the material needs to be handled differently. For example – PLA requires a lot lower temperature to be printed (extruder temperature ~185C- 205C) versus ABS (220C – 240C).
Slicing Software to Use
There are many different slicing applications that you can use to prepare you print jobs – some of the more popular of which are: Cura, CraftWare, MatterControl, PrusaSlicer & MakerBot Print (All listed are free).
We use Cura – which is opensource software (developed and maintained by Ultimaker), which many consider to be the gold standard in slicing. It also works with OctoPrint – which we use to control our 3D printer remotely.
We like that with Cura you can control which parameters you want to see – while “hiding” the others. It helps keep the process a little simpler and less intimidating for the beginner. However, those more advanced options are there – and easily accessible by users ready to tinker with such settings.
Downloading & Installing Cura – Software for Slicing & Preparing a 3D Model for Printing
If you are downloading and installing Cura on a Windows (Windows 10 64 bit) computer with certain integrated Intel graphics cards – you might not be able to install and use the latest version of Cura. There are some known issues with versions 3.6 – to the present 4.4.1 version with such configured computers. (You can read more about it here if you are interested in learning more). If you find yourself in such a situation, I would strongly recommend that you download and install Cura version 3.5.1 – which you can obtain here. I hope to see this issue resolved soon – but it has been ongoing at least through 2019 and into 2020.
Conclusion
I’ve used a paper printing analogy in this post to, hopefully, make the concept of slicing and the role it plays in 3D printing a little more clear for those that are new to 3D printing.
Slicing is an important part of the 3D printing process and is where you may be able to turn prior failures into future successes. I have outlined some of the most common parameters you should become familiar with and learn to manipulate to increase the likelihood of your success when printing a 3D object. Many problems and failures in printing 3D models can be overcome by simply tweaking some of these parameters through your slicing software..
Sincerely,
