What is slicing a 3D print?
Slicing a 3D print is the act of converting a 3D model into a set of instructions that a 3D printer will understand to print your model. Quite literally, it 'slices' the 3D model into thin layers, and further determine how each layer should be printed (the tool path) to get minimum time, best strength, etc.
Each different brand of 3D printer, will have its own slicing software, although they will all work in a very similar way.
When you are slicing your 3D print, there are lots of different settings that can be adjusted. This page details the key concepts you will need to know in order to slice your prints successfully.
Layer Height.
What is layer height and why is it important?
FDM 3D printers build objects by printing layers on top of other layers. The height of these individual layers is defined as “layer height”. This could be anywhere, for example, from 0.05mm to 0.8mm. A larger layer height means the same model would have fewer total layers and visa versa.
Layer height is a crucial parameter that affects an object’s vertical level of detail, surface smoothness, mechanical strength and print time.
For most prints, the default values of layer height produce good results. Default layer height for Ultimaker is 0.15mm and default layer height is 0.2mm.
Why would I change the layer height?
Whether you change your print from the default layer height depends on the purpose of your print.
- If you want to print something fast and detail is less important, increase the layer height.
- If you want to print something small or delicate, reduce the layer height.
- If you want a strong, load bearing part, the default layer height is best.
You are most likely to notice the visual difference of layer height on curved prints, a large layer height will have visible steps whereas a smaller layer height will make it more smooth and may make the object seem smooth.
Reducing the layer height will only increase vertical (Z) level of detail, the horizontal (XY) resolution is only affected by nozzle size (e.g. a smaller nozzle can print in higher detail).
The smaller layer height, the longer your print will take as it is printing more layers.
Orientation and strength.
When thinking about layer height and part strength, orientation is also important. For example, a long thin rod printed standing up may have 400 total layers, whereas printed lying down it may have only 20. The surface area between each of the 400 layers would be very small and it would be much easier to break than the rod printed laying flat.
Adhesion.
What is adhesion and why is it important?
Adhesion is the ability of the print to stick to print bed.
If the first layer of the print doesn’t stick to print bed, your print will fail. The print will either fail immediately, be warped or fall over during printing.
Parameters that affect adhesion.
Levelling of the print bed
When 3D-printing, there must be a specific distance between the nozzle and the print bed to achieve good adhesion.
If the nozzle is too far away from the print bed, the print will not stick to it. Likewise the nozzle shouldn’t be too close.
All of uCreate's 3D printers automatically level the print bed.
Temperature
Some plastics shrink when cooling down. The nozzle extrudes molten hot plastic on the heated print bed.
Heated material is more adhesive than cold material. A heated print bed stops the plastic from cooling too fast and shrinking back off the build plate.
Different materials require different print bed temperatures for optimal adhesion.
Build plate
The state of the build plate will affect adhesion. If the build plate is damaged, scratched or dirty, adhesion will be reduced.
There are multiple types of print bed such as steel sheets, aluminium and glass. Some materials adhere better to different types of build plates.
For metal build plates, ask staff for an isopropyl alcohol wipes can be used to clean them if you are having adhesion issues.
Surface area
The more material in contact with a print bed, the greater the adhesion will be and thus the lass chance of the print coming loose.
In addition, the taller a print is, the more force that will be exerted on the base when the print head bump into the top surface (due to leverage). For this reason, a large flat print will likely adhere very well, where as a tall thin print has a very high chance of coming loose.
Types of adhesion.
Brim
A brim is an additional area around the outside of the first layer of a print that can increase the object’s surface area. It is printed adjacent to the models first layer.
It is effective against warping of the print and helps adhesion.
We recommend always printing with a brim.
Raft
A raft creates several layers on the print bed which the print is then built on top of. Using a raft can help when the print otherwise has little adhesion to the surface.
If your print does not adhere when using a brim, try using a raft.
Skirt
A skirt is a line surrounding the print on the build place but is not connected to the print.
It does not increase build plate adhesion but primes the nozzle and establishes a smooth flow of the filament.
Infill.
What is infill and why is it important?
Infill is the repetitive structures, such as triangles or hexagons, which fill the interior of your 3D print.
Infill is needed to ensure objects have enough structural integrity to stand on their own and also acts as internal support structure for the model to be built. By adjusting the infill density, it is possible to obtain the desired combination of object strength, weight and print time.
Common infill patterns and their uses.
Rectangular
Using rectangular infill offers reasonable strength in all directions and a fast print time.
For most slicers this shape is the standard type of infill.
Triangular
Triangular infill can be used to give extra strength in the direction perpendicular to the faces.
Concentric
Concentric infill can be used to make a part more flexible.
Infill density.
The infill density (or percentage), directly affects the weight, strength, and material usage. 0% infill percentage means the model is completely hollow, 50% would mean half of the interior space is filled with filament and 100% infill means a solid block. The higher the infill percentage, the more solid and heavier your print will be.
Infill percentage: 15-20%
Most slicing programs use this range as the default infill percentage as it offers reasonable mechanical strength in addition to low filament usage and print time. For most prints, this default value is appropriate.
Infill percentage: 50-70%
For prints such that require high mechanical strength (brackets, beams, other load bearing parts etc.) using 50-70% infill is recommended. At this percentage, print time is much higher but the model will also be much stronger.
Supports.
What are supports and why are they important?
Supports provide a surface for overhanging parts of an object (any part of a print that extends outwith the main body of the print) to be printed on top of. After the print, support structures are removed from the print.
When should I use supports?
Supports are used to hold up your model while it is 3D printing.
Up to a point, FDM printers can build objects by printing with small offsets in consecutive layers, in a stepwise manner. Your slicing software will automatically detect and add supports to the appropriate areas of a model if you select the support option. You should use supports when the overhang angle is more than 45°.
By changing the orientation of the object on the build plate, it is possible to avoid supports.
Support Types.
Single filament supports
Single filament supports are when you are printing your model and your supports out of the exact same material.
uCreate Bambu Lab, Ultimakers and print queue Prusa printers use single filament supports in PLA.
These supports are fast to print and are physically removed during post processing. In general, models with large flat external surfaces work best with this kind of support.
Some disadvantages of single filament supports are risk of damaging delicate parts during removal, practical difficulties in removing the support and inability to remove the support from internal cavities.
Dual Filament Supports (Non-soluble)
Dual filament supports are when your model and the supports are printed from different materials.
uCreate Ultimakers can use dual filament supports (non-soluble).
These supports tend to bind less strongly with the object material and therefore be easier to remove. 'Breakaway' material is specifically designed for this application.
Some disadvantages of dual filament supports (non-soluble) are similar to single filaments supports, but you are less likely to damage the model during support removal.
Dual Filament Supports (Soluble)
Soluble supports are when you use dual filament printing, but the second material can be dissolved instead of needing to be physically removed during post processing.
uCreate Ultimakers can use dual filament supports (soluble).
The soluble support we use is PVA which dissolves in water. It can allow you to support internal cavities, hard to reach places, parts with independent/interlocked pieces and is vital for printing anything delicate that could easily be broken otherwise.
Some disadvantages of dual filament supports (soluble) are that the print failure rate is higher and bulky support structures can take a very long time to dissolve.