Brims, rafts, and skirts

Publish date: 2024-05-05
Brims, rafts, and skirts

15.4.5 Brims, rafts, and skirts

Sometimes, especially when printing an object with a small footprint on the build plate, an extra adhesion feature such as a brim may be helpful.

A brim is extra material, typically only one or two layers tall and several outlines wide, printed around the perimeter of the object touching the object, extending outward, to stabilize the object. A brim tends to be helpful with small or isolated parts of a model, e.g., hooves of an animal, to aid with adhesion of the small area of the object to the build plate by extending the area.

A raft is a few extra layers of material, printed as a horizontal latticework, extending under the entire object. Besides helping with adhesion, it can also provide a strong foundation for the rest of the print. The number of layers in the raft controls the height (and to some degree the strength) of the raft; the raft offset controls how far beyond the main object the raft will extend; the raft separation determines the distance between the raft and the object itself – typical distances range from 0.14–0.2mm – where you want to aim for a close enough distance to give adequate adhesion during the build, but not so close that it becomes very difficult to remove the raft from the object once the print has finished; the raft infill controls the density of the interior of the raft, where you want enough material to support the bottom of your main object but not so much that the raft is so solid that it bonds too tightly to the bottom of your main object.

A skirt is an outline of extra material printed surrounding the perimeter of the object, but not touching it, typically offset 3 or 4 millimeters from the object; it is thus similar to a brim that has been moved farther from the object itself. However, unlike a brim, sometimes a skirt might be quite tall – even the height of the object itself – rather than, like a brim, being only a few layers high. This is because a skirt is sometimes used to shield the object from drafts; as such, they tend to be used more with filament such as ABS where uneven cooling can cause warping. (With PLA filament such as the Polar 3D supplied filament, a minimal skirt might be generated more to establish a smooth initial flow of melted filament, rather than for adhesion/shielding purposes.)

Including a brim around small or isolated parts of a model object may aid in adhesion and stability of that portion of the build. Including a raft under a model object may aid in adhesion of model objects that have small footprints on the build plate, as well as adding stability and a solid foundation for the rest of the build, especially if the overall object is relatively large compared to its small footprint on the build plate. Building a skirt along with an object may help establish smooth nozzle flow, or may be used to shield especially thermal-sensitive filament material from thermal drafts during the print.

Only brims and minimal skirts tend to be of much interest when using PLA filament, such as that shipped with the Polar3D printer and sold by Polar 3D. Rafts and more extensive skirts, in contrast, may be of interest with other filament materials, such as ABS.

The Polar Cloud 2.0 has a feature whereby you can ask to add a brim, raft, or skirt to your object. Once you have selected an object and clicked “3D PRINT” to get ready to print it, then go to “PRINT SETTINGS”, (see Figure 15.16), and under “BASIC” settings scroll down to Support, (see Figure 15.17). Then under “Platform Adhesion Type”, use the drop-down menu to select “None (Skirt), Brim”, or “Raft”, as desired; see Figure 15.18. Then click the gear icon (to the right of “None (Skirt)”) to adjust the parameters (layers, outlines, raft infill, etc.) as desired; see Figure 15.19.

Figure 15.16: Polar Cloud build plate PRINT SETTINGS

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Figure 15.17: Polar Cloud build plate Support

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Figure 15.18: Polar Cloud build plate Platform Adhesion Type

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Figure 15.19: Polar Cloud build plate Skirt Settings

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