3D Printing Rafts vs Brims vs Skirts: How to get started

These three FDM 3D printing techniques enable better bed adhesion and print stability. Here’s how and when to use them.

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25 Mar, 2022

FDM 3D printing techniques, like skirting, can improve build outcomes.

FDM 3D printing techniques, like skirting, can improve build outcomes.

If you’re struggling with proper bed adhesion and warping when 3D printing, there are some tried and true techniques for improving print results—especially for ABS and higher temperature materials. If used correctly, rafts, brims, and skirts each have their benefits and can make the difference between a successful or failed print. In the following article, we illustrate what each 3D printed feature is and when and how to use it for the optimal result.

3D Printing Raft

What is a Raft?

A raft is essentially a 3D printed platform on which parts are printed. A raft usually consists of a grid-like 3D printed structure, which sits underneath and extends beyond the borders of the first layer of the 3D model, acting as a base. 

In FDM 3D printing, first layer adhesion to the build platform is vital to ensuring that your 3D prints turn out well. Poor adhesion can lead to warped and defective parts. Rafts are a technique used by makers to improve first layer adhesion and stabilize parts throughout the printing process. 

When you Should use Rafts

Rafts can be very effective in certain circumstances. First and foremost, if you are 3D printing with ABS filament—a material prone to warping—a raft can improve adhesion by ensuring your print’s first layer sticks to the top layer of the raft. Higher temperature thermoplastic filaments like ABS are also more likely to warp without a printed heat bed. Using a raft if you don’t have a heated build platform can help lessen the chances of warpage.

Rafts can also be used in cases where the 3D model has an unbalanced structure–for example, a part with a heavier top and smaller footprint. In this case, using a raft can stabilize the object as it is printed. Another scenario in which a 3D printed raft has benefits is if your build platform is damaged or warped. A raft can create a flat, level base for your part to be printed on.[1]

3D model of raftRafts are 3D printed underneath the part, acting as a platform that anchors the part to the build platform. (Image: Simplify3D)

Slicer Settings for Rafts

Most slicer software programs, like Cura and Simplify3D, have raft integrations built in, so you don’t have to design them yourself. That being said, you may want to adjust some settings for the best outcome. The main slicer settings for rafts are:

  • Layer Thickness: There are three distinct layer thickness settings when it comes to rafts: base layer thickness, middle thickness, and top layer thickness. The former is the first layer of the raft to be printed. To promote optimal bed adhesion, this layer should be thickest (i.e. 0.36 mm).[2] Raft middle thickness will be smaller than the base layer and larger than the top layer. The top layer thickness should correspond to the layer thickness of the printed part (0.12mm is standard).

  • Air Gap: When printing a raft, there is the option to integrate an air gap in between the raft top layer and the first layer of your 3D print. This gap encourages raft removal.  

  • Extra Margin: In raft generation, the extra margin determines the surface area of the raft on the build platform. The larger the raft, the better the adhesion. Raft offset may also come up. This is the width of the raft from the edge of the printed model.

  • Print Speed: This setting determines how quickly your raft will be 3D printed. To maximize bed adhesion, a slower printing speed is suggested.

The Pros & Cons of 3D Printing Rafts

Pros

  • Improves bed adhesion, especially for materials prone to warping like ABS. 

  • Can create a level printing surface if the build plate is uneven or damaged.

  • Minimizes the risk of warping for parts made on non-heated build platforms.


Cons

  • The bottom layer of your 3D printed part may have a rougher surface than if it was 3D printed directly on a smooth build surface.

  • While removal of the raft can be easy, simply peeling away from the 3D printed part, that is not always the case. Removal of the raft can be difficult and time-consuming. In worst-case scenarios, it can even damage or break the final printed object.

  • Increases the overall amount of printing time.

  • Materials used for printing rafts typically end up in the waste.

3D printed shoe with raftAn object is 3D printed using both a skirt and a raft.

3D Printing Brim

What is a Brim?

A brim is a 3D printed border that extends from the edges of the 3D printed part. Unlike a skirt, the brim is actually connected to the 3D printed part, effectively giving it a greater surface area to adhere to the print bed. Unlike a raft, the brim does not go underneath the 3D printed part’s first layer.

Brims are an effective technique for securing a part to the build platform for better first layer adhesion, which in turn can minimize the risk of warping and part failure. Brims can also help to anchor the outer edges of the print to the build surface for better stability.

When you Should use Brims

There are a number of situations in which you might employ a 3D printed brim. For instance, if you are using a higher temperature filament with a greater ratio of shrinkage and warping—like ABS or PP (polypropylene)—activating a brim can promote better layer adhesion and subsequently reduce warping.

Brims are also handy for increasing the footprint of 3D printed parts. This is especially useful for parts with a small base or footprint that might become unstable in the printing process. Integrating a brim will effectively anchor the part to the print bed and stabilize it as the extruder deposits more layers.

Slicer Settings for Brims

Depending on the slicer software, generating a brim around your 3D model might fall under the Skirt settings. If this is the case, simply set the skirt offset (the distance of the skirt from the edge of the part) to zero. Below are some of the key slicer settings to be aware of for using brims:

  • Brim Width: This measurement designates how wide the brim around your 3D printed part will be. In most slicer settings, the default width will be about 8 mm. In general, the wider the brim, the better the first layer adhesion.

  • Brim Lines: This setting is also related to the brim width. Here, you can choose how many lines your print head extrudes to create the brim.

3D printed model with brims3D printed brims anchor the edges of a 3D printed part to the build platform, reducing the risk of warping.

The Pros & Cons of 3D Printing Brims

Pros

  • Can prevent warping by anchoring the part to the build platform through a wider surface area.

  • Improves first layer adhesion for the printed part, especially for warp-prone materials like ABS and PP.

  • Compared to rafts, parts printed with brims have a smoother first layer surface finish.

  • Brims consume less filament than rafts. 

Cons

  • Brims must be removed from the actual print. In some cases, removal consists simply of peeling the brim away from the part. In others, however, you may require a tool to remove it.

  • Printed parts with brims may need post-processing, such as sanding, to smooth out the contact points on the edges where the brim was connected.

  • While using less material than rafts, brims still generate material waste.

3D Printing Skirt

What is a Skirt?

In 3D printing, a skirt is a printed border around the 3D printed object, which does not touch the printed part. If you opt for a skirt, the 3D printer will begin by extruding filament lines to create the border before starting to build the rest of the part. 

This technique helps to prime the nozzle ahead of printing the 3D model and can lower the risk of filament blobs, which can cause defects in final prints.[2] Printing the skirt as a border around the part’s perimeter is also helpful for checking calibration. It allows makers to identify any potential problems with a level bed before the real printing begins.

3D printed skull with skirtSkirts are 3D printed before the part is deposited, allowing for the nozzle to be primed.

https://www.shutterstock.com/image-photo/3d-printer-prints-white-plastic-model-1758751424 

When you Should use Skirts

Skirts can improve printing results for most FDM 3D print jobs. The printed border on the build surface allows the melted filament to start flowing smoothly before the critical initial layer of the part is deposited. In other words, any filament inconsistencies in the first minutes of printing will be in the skirt, not your final part, leading to better first layer adhesion and minimizing the chance of warping. 

Unlike rafts and brims, skirts do not offer any physical support to your 3D printed part. So, while they do encourage better first layer adhesion thanks to nozzle priming, they may not provide the support needed for certain part geometries. 

Slicer Settings for Skirts

Slicer programs allow users to customize a number of settings related to skirts to control the distance of the skirt from the part, the thickness of the skirt, and more. These are the main skirt slicer settings to be aware of:

  • Line count: you can choose how many lines you want your skirt to consist of. While some slicer software programs have one line as the default, it can be beneficial to choose more. This allows you to confirm any leveling or setting changes made after the first line are working.

  • Distance: Skirt distance determines the separation distance between the perimeter of the printed part and the skirt.

  • Layers: You can set the number of layers your skirt should consist of. Usually one layer is sufficient, but adding another can make the skirt easier to remove from the print bed.[3]

The Pros & Cons of 3D Printing Skirts

Pros

  • Skirts are effective for priming nozzles and ensuring that by the time the first layer of the print is extruded, the filament is flowing smoothly.

  • Can also be used to validate bed adhesion and surface levels. Inconsistencies can be detected before the print starts, preventing failed prints before they occur.

Cons

  • Skirts do not provide physical support to improve first layer adhesion for the printed part.

  • While using a minimal amount of filament, skirts do still generate material waste.

Conclusion

Rafts, brims, and skirts are helpful tools in every maker’s toolkit. Now that you know what each 3D printing feature does and where it offers the most advantages, you’ll be able to improve your 3D printing outcomes.

References

[1] ModBot, August 7, 2021. “How And When To Use Skirts, Brims, And Rafts For 3D Printing”. [Internet] https://www.youtube.com/watch?v=p4R3F1as-1I [Accessed March 23, 2022].

[2] The 3D Printer Bee. “Cura Raft | Best Settings to Ensure Good Bed Adhesion”. [Internet] https://the3dprinterbee.com/cura-raft-settings/ [Accessed March 24, 2022].

[3] Simplify3D, 2022. “Rafts, Skirts and Brims”. [Internet] https://www.simplify3d.com/support/articles/rafts-skirts-and-brims/ [Accessed March 24, 2022].

25 Mar, 2022

Based in Montreal, Tess is a freelance content writer and editor with over five years of experience in the technology and manufacturing fields. She has a background in media studies, and holds a master’s degree from the University of Amsterdam.

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