In your 3D printing career, you’ll come across terms like skirts, rafts, and brims. These settings are found even in the basic settings of your slicing software, so you may be womdering what the differences between these things are, and how and when to use them.
Skirts are used to prime the nozzle before a print to get the filament flowing. Brims and rafts are used to help increase bed adhesion for materials or models that have a tendency to warp and lift off the bed.
What is a brim?
Much like the brim of a hat, a 3D printing brim is a layer or multiple layers of filament that extend outside the perimeter of your print. The brim starts at the outer edge of your model and extends out onto the build plate for as many millimeters as you set in the slicing software.
Why should you use a brim?
A brim provides extra adhesion to the outer edges of your model. It’s very useful when 3D printing very narrow objects that may easily get knocked over or lift off the bed.
It’s also useful for printing with ABS, as it has a tendency to warp and lift off the bed.
On the flip side, brims can also be used to pry prints off of the bed if they’re stuck too tightly to the bed. You can use the brim as a stepping stone to get the palette knife under it and pry the rest of the print off.
What settings should you use for a brim?
Brim width is how far the brim will extend from the print. That’s really the only setting you need to change.
If you’re using Simplify3D, there’s no dedicated brim setting: instead, just set the skirt offset to 0mm to get it to start right at the edge of the model.
Advantages of brims
- Can help prevent warping
- Helps with bed adhesion for delicate and narrow models
- Brims cut away quite cleanly and you won’t be able to tell there was ever one
- Comparatively less material is used than a raft
- The bottom finish will be much better than with a raft
Disadvantages of brims
- Brims will use a bit more material than if you did not enable them
- Even though they cut away easily, you’ll still need to sand them
What is a raft
A 3D printing raft is a flat base of filament that is laid down on the print bed. Your model is then printed directly on the raft. Rafts are usually a few mm thick.
Why should you use a raft
Rafts provide even better bed adhesion than brims. This is because you’re depositing the first layers of your model directly on filament instead of on the build plate. Like the brim, this is useful for models that have unstable initial layers(like a model that has thin legs but a big, heavy body on top).
Rafts also help prevent warping when printing with filaments like ABS. Warping happens at the point between the bed and the filament, so if you use a raft, it will be the raft that warps, not your print.
What settings should you use for rafts
There are lots of settings that you need to tweak when 3D printing with a raft. The first is separation distance.
Separation distance determines how much of a gap there will be between the top layer of the raft and the first layer of your print. If the separation distance is too little, then it can be very difficult to remove the raft from the model. Start with a distance of 0.1mm, and tweak up or down as necessary.
I suggest that you print a few calibration cubes or other small models using rafts with varying separation distances to see which one provides the best stability while still being easy to remove.
The next setting is the Raft Bottom Layer. This is much like the bottom layer of the print in a regular 3D print. It determines how well the raft will stick to the print bed. Use at least two bottom layers.
The Raft Top Layer is the layer on which the 3D printed model will start being deposited. This layer determines how the finish of the bottom layer of your model comes out, so use at least two to three layers to get a good bottom finish in your model.
Finally, Raft Offset(not available in all slicers) determines how far the raft extends outside your print. If you were to print a 20 x 20mm calibration cube and used a raft offset of 2 mm, that means your raft would have an area of 24 x 24 mm, since it extends on all sides.
Keep the raft slightly offset so you get some leverage for removing the raft after your print is complete.
Advantages of rafts
- Can help prevent warping with ABS and similar filaments
- Helps increase bed adhesion, reducing the likelihood of a failed print
- Bottom layers will be stronger
Disadvantages of rafts
- Bottom layer of your model will no longer be smooth
- Can be very hard to separate even with pliers
- Increases the amount of material you use
- If the raft is stuck too strongly, you might break the part as you try to remove it
What is a skirt?
Skirts are simply an outline of filament that is laid down at an offset from the perimeter of your print. The skirt never touches your print, but can be used as a way to get filament flowing correctly before your print starts the critical first layer.
The skirt also helps you eyeball whether the filament is properly sticking to the bed or not.
Why should you use a skirt?
Printing a skirt around your model is quite standard practice in the 3D printing world. The main function is to get filament flowing. It usually takes a few mm of nozzle movement and extruder movement to get the filament flowing correctly, and the first few mm of the skirt will also remove any impurities or flecks stuck on and inside the nozzle.
What settings should you use for a skirt?
Skirts have two main settings you need to adjust.
The Line Count is how many outlines of the skirt the 3D printer will lay down. Use at least 2 outlines, since this will get the filament flowing correctly. In some cases, a single outline will not be enough. Use 3 for smaller prints.
Skirt distance is how far the skirt is from your model. This is important when you’re printing large models! If you’re print a 200 x 200 object on a 205 x 205 bed, the maximum distance you could use for 2 outlines is 4mm. Otherwise, the printer will try to print the skirt outside the bed!
The skirt goes around the perimeter of the entire print, so if you are printing multiple parts in a single go, the skirt will only be laid down on the furthest perimeter, not around each individual part.
Advantages of skirts
- Helps to get the filament flowing by priming the extruder and nozzle
- Lets you eyeball the first layer before the model starts printing
- Lets you eyeball if your print will fit on the bed without any problems
Disadvantages of skirts
Some may consider the fact that the skirt is extra material to be a disadvantage, but in reality, the amount of filament extruded to lay down a skirt is really minimal. The filament you’ll save from catching a bad first layer before the print starts thanks to the skirt will be a lot more than the filament you use in the skirt.
How much extra material do brims, rafts, and skirts use?
I tried slicing a standard 20mm calibration cube with default settings for brims, rafts, and skirts:
- With skirt: 5 grams, 36 minutes
- With brim: 5 grams, 36 minutes (since the model is so small, there’s very little extra material used)
- With raft: 7 grams, 47 minutes
For most of your prints, you’ll definitely want to use a skirt as priming the nozzle is a very critical part of a successful print.
You may also find yourself using brims for very delicate or thin parts, brims will be quite helpful to prevent the print from getting knocked over.
I have tried rafts a few times but have found them to be a huge pain to remove, so I tend to avoid them unless I am printing with ABS. However, you can usually print anything you need in either PLA or PETG which have good bed adhesion anyway.