One of the most important aspects of any print is the first layer. The first layer sets the foundation for the rest of the print.
If you’re not careful, bed adhesion issues can cause problems during printing.
Luckily, you can adjust Cura settings to achieve better bed adhesion. Printing with a skirt, brim, or raft improves sticking, prevents warping, removes clogs, and regulates nozzle flow.
In this post, I’ll cover each of the three adhesion assistants and cover when to use a 3D Printing raft vs brim vs skirt.
Skirt
A skirt is a set of contours that trace the perimeter of the part before printing the actual part. The one-layer tall line of filament helps prime the extruder nozzle before printing.
Skirts are the least intensive of the three and don’t help your print adhere to the print surface. That’s because the skirt doesn’t attach to your 3D print.
Although skirts don’t provide any bed adhesion benefits, they play a vital role in ensuring a smooth first layer.
After many hours of printing and sitting, print nozzles will begin to collect dust and debris from the dirty filament. Excess material can get lodged in the nozzle resulting in clogging.
Since printing a skirt effectively purges the extruder nozzle, it can help clear out any dust before beginning the printing process.
In addition to cleaning the nozzle and reducing the chance of clogging, the skirt will also help regulate the hot end temperature and helps regulate the flow.
It’s essential to pay attention while your 3D printer extrudes the skirt. Any significant issues become immediately apparent. If there’s no filament extruding, you know you have a problem and should stop the print.
Watching the skirt print is an excellent way to diagnose 3D printer bed leveling issues. You want to see consistent filament extrusion and print surface adhesion around the perimeter of the skirt.
If you see gaps or squished filaments, you know you have an issue with your base level.
Observing the skirt while it’s printing helps prevent material waste by catching issues before wasting hours of 3D printing time.
Here are the three Cura settings you can use to get the most out of skirts:
- Skirt Line Count: This parameter sets the number of times the nozzle will go around the part. The larger you set this number, the more contours there will be, resulting in longer print times and more material usage. I usually recommend using three lines, but if you have a very small part, you may want to increase the line count to 6 or 7.
- Skirt Distance: Skirt distance is the distance the skirt will be away from the print. Setting a higher value will result in the skirt being further from the part. The default setting of 10mm works great for most prints; however, you may want to decrease the distance to save build volume while printing larger objects. If you have a large part and a large skirt distance, the 3D slicer may tell you that the model exceeds the print volume because it counts the size of the object and the skirt.
- Skirt minimum length: The Skirt minimum length sets the minimum required linear distance for your 3D printer to print a skirt. In other words, if you set this value higher and have a very small part, the slicer may not print the skirt if the perimeter is below the skirt minimum length. The default setting of 255mm works great for most prints, but you may need to adjust it downward for smaller objects.
Brim
The brim is similar to the skirt in that the brim also traces the contours of the part; however, unlike the skirt, the brim contacts the perimeter of the part.
Printing with a brim effectively increases the surface area of the part on the build plate. Giving your object a larger surface area provides more contact space with the build plate, resulting in better bed adhesion.
Brims are especially beneficial if you don’t have a heated bed.
Since the brim attaches to the base of your print, it ensures that the edges of the 3D models don’t curl away from the build plate while the filament cools during the printing process.
In addition to mechanically securing the part and preventing warping, brims also purges the nozzle and help remove contaminants that can result in a clog or under extrusion.
The downside of printing with a brim is that they use significantly more material than skirts. And the contact points between the print and the brim may leave raised bumps.
Below are some settings to configure your brim in Cura:
- Brim Width: Brim width sets the width of the brim. It is similar to the skirt’s line count. The larger the brim width, the more contours your 3D printer will trace the perimeter of your part, providing better adhesion to the build plate. The default settings work great, but you may need to increase them if you’re struggling with base adhesion or warping.
- Brim Distance: Brim distance sets the separation distance of the brim from 3D models. The default setting is zero, meaning the brim attaches to your print. It’s recommended to keep the brim distance set to zero. Otherwise, you won’t get any of the bed adhesion benefits.
- Brim Minimum Length: The brim minimum length tells your 3D printer the minimum size to print a brim. If you are printing a smaller part or a part with small build plate contact sections, you may need to decrease this setting for the brim to print everywhere your object touches the build plate. The default setting of 250mm works fine for most prints, but you may need to decrease it to 100mm when printing small parts.
- Brim only on the outside: This setting selects whether or not you want the brim to be placed on the outside of the perimeter only or would like it on the inside and outside. For example, if you have a hole on the inside of a part and want the brim to be printed on the inside and outside, make sure you toggle this setting off, and it will place the brim on the inside and outside. I recommend using the setting especially if you work with structures with a lower surface area and a hole in the center. If you’re printing a solid object, you won’t need to worry about this setting.
Raft
A raft is the third print adhesion technique offered by the Cura slicing software.
A raft is several layers thick and essentially builds a platform for the part to sit on.
Since 3D printing filament adheres well to itself, brims provide the ultimate bed adhesion. They provide a large surface area for contact with the build plate and an excellent surface for your part to print.
Rafts also extend slightly past the base of the part. The extension provides the same benefits as a brim in reducing warping and increasing first-layer adhesion.
As an added benefit, any scratches in the build plate won’t affect the surface quality of the part because it’s not printed directly on the print bed. Unfortunately, a raft makes achieving a smooth surface on the first layer difficult.
Once you remove the raft, you may be left with raised edges where the raft made contact with your print.
Here are some Cura settings to fine-tune your raft:
- Raft Print Speed: How fast your raft is printed. Unlike the skirt and brim, Cura allows you to control the print speed of the raft. Like regular 3D printing, it’s recommended to keep the initial layers of the raft much slower than the regular print speed. Cura’s default setting of 25mm/s works great for most prints.
- Raft Air Gap: The distance between your raft’s top layer and your printed object’s bottom layer. This setting sets the raft slightly further from your part and helps the filament cool before contacting it. Cura sets the default to 0.3mm, but upping it to 0.35 or 0.4 mm makes removing the raft from your print easier and reduces bumps along contact points. Reducing the raft air gap to 0.2mm results in better adhesion but makes removing prints from the raft more difficult.
- Raft Extra Margin: Raft extra margin tells your 3D printer the distance the raft will extend from the part in the x and y orientation. Cura’s default of 15mm is good unless you have small parts which may require more surface area to adhere to the bed. Large parts may do better with lower raft extra margin as they already have a large surface area.
- Raft Top Layers: Raft top layers is the height of the raft. Too few layers may result in poor bed adhesion, while too many layers use a lot of filament and add extra print time. You may want to play around with this setting to find what works for you. In our experience, the default setting in Cura works best.
When to Use a 3D Printing Raft vs Brim vs Skirt
When to Use a Skirt
Skirts are best used if you don’t anticipate any bed adhesion issues while 3D printing.
A skirt is best used to prime your 3D printer before it begins printing your 3D model. If you don’t need the bed adhesion benefits of a brim or raft, use a skirt to test your bed leveling and prime the extruder nozzle.
Skirts use the least amount of filament and have the shortest printing times. Printing with a skirt is recommended if you need to conserve filament or decrease total print time.
When to Use a Brim
Brims are the best choice for most 3D printing. They provide excellent bed adhesion and prime the 3D printer for the work ahead.
A brim is a middle ground between skirts and rafts, providing the benefits of both alternatives; they don’t use much 3D printing filament, have relatively short printing times, reduce warping, and provide excellent build plate adhesion.
However, because the brim attaches to your model, it affects the dimensional accuracy creating raised edges along the first layer. If dimensional accuracy or design is essential, you may prefer to print with a skirt to avoid creating imperfections along the contact points between the raft and your print.
When to Use a Raft
Rafts are best used when build plate adhesion is essential, such as for smaller objects with less surface area.
Rafts provide the ultimate surface adhesion but at the cost of using more filament material and longer print times. They have more contact points with your model resulting in imperfections along the first several layers.
The extra contact points help to reduce warping. If you’re printing a model without a heated bed or a large model with sharp corners, a raft helps prevent warping and lifting along the edges.
Rafts are not commonly used outside of small objects and ABS. If you’re printing ABS filament, rafts might be the only choice to achieve good bed adhesion, as it doesn’t stick well to the print bed.
