Brims, rafts, and skirts

14.4.5 Brims, rafts, and skirts

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

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

A raft is a few extra layers of material, printed as a horizontallatticework, extending under the entire object. Besides helping withadhesion, it can also provide a strong foundation for the rest of the print. The number of layers in the raft controls the height (and tosome degree the strength) of the raft; the raft offset controlshow far beyond the main object the raft will extend; the raftseparation determines the distance between the raft and theobject itself – typical distances range from 0.14–0.2mm – whereyou want to aim for a close enough distance to give adequateadhesion during the build, but not so close that it becomes verydifficult to remove the raft from the object once the printhas finished; the raft infill controls the density of the interiorof the raft, where you want enough material to support thebottom of your main object but not so much that the raft is sosolid that it bonds too tightly to the bottom of your mainobject.

A skirt is an outline of extra material printed surrounding theperimeter of the object, but not touching it, typically offset 3 or 4millimeters from the object; it is thus similar to a brim that hasbeen moved farther from the object itself. However, unlike a brim,sometimes a skirt might be quite tall – even the height of the objectitself – rather than, like a brim, being only a few layers high. This isbecause a skirt is sometimes used to shield the object fromdrafts; as such, they tend to be used more with filament such asABS where uneven cooling can cause warping. (With PLAfilament such as the Polar 3D supplied filament, a minimalskirt might be generated more to establish a smooth initialflow of melted filament, rather than for adhesion/shieldingpurposes.)

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

Only brims and minimal skirts tend to be of much interest whenusing PLA filament, such as that shipped with the Polar3D printerand sold by Polar 3D. Rafts and more extensive skirts, incontrast, may be of interest with other filament materials, such asABS.

The Polar Cloud 2.0 has a feature whereby you can ask to add abrim, raft, or skirt to your object. Once you have selected an objectand clicked “3D PRINT” to get ready to print it, then go to “PRINTSETTINGS”, (see Figure 14.16), and under “BASIC” settings scrolldown to Support, (see Figure 14.17). Then under “PlatformAdhesion Type”, use the drop-down menu to select “None (Skirt),“Brim”, or “Raft”, as desired; see Figure 14.18. Then clickthe gear icon (to the right of “None (Skirt)”) to adjust theparameters (layers, outlines, raft infill, etc.) as desired; see Figure14.19.