3D Printing Brim vs. Raft: What’s the Difference?

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Anyone who’s ever tried their hand in 3D printing knows that it’s rarely a straightforward process. Depending on the filament you’re using and the design you’re printing, you might need to adjust a lot of parameters to get the best results. Printing brims and rafts are some of the most common troubleshooting methods that 3D printing professionals use. What’s the point of brims and rafts anyway and how are they different? When should you pick a brim over a raft and vice versa?

Why print with brims and rafts?

To put into context why brims and rafts are a common thing in 3D printing, we must first understand how warping happens. Warping (or curling) is one of the most common problems that 3D printing professionals encounter, particularly when printing at high temperatures.

In Fused Deposition Modeling (FDM), the filament material is melted in a hot end nozzle and set down on the build platform. As soon as the melted plastic leaves the hot end nozzle, it starts to cool down. This cooling process continues even as the first layer of the print is slowly being built. While this cooling process is spontaneous, there are a few factors that can affect its rate, such as its degree of exposure to the colder environment.

The warping problem comes about because the cooling of any layer of a 3D print is uneven. The outer layers, or those that are more exposed to the atmosphere, cool down faster than the inner layers. This leads to stress accumulation in the outer layers, particularly at the corners. With enough stress, the corners of the print tend to get detached from the build layer and “curl up.”

Brims and rafts are both meant to prevent warping. They are based on the same basic principle, but each alternative has its benefits and drawbacks.

What is a raft?

A raft is essentially an extra horizontal mesh layer printed below your actual print that is built wider than your first layer. This extra horizontal mesh provides a surface to which your actual first layer will adhere to. This filament layer will certainly have better adhesion to your first layer than the build platform. By building the raft wider, there is a larger contact area between the raft and the build platform, therefore also enhancing adhesion. A raft can be made of multiple layers according to your slicer settings.

What is a brim?

From a glance, you might think that a brim just looks exactly like a raft. However, the difference is easy to see upon closer inspection. In contrast to a raft that is essentially an extra layer underneath, a brim is merely an outward extension of the first layer. Although it’s also possible to print a brim made of multiple layers, a single layer brim is typically used.

How will I know which one to use?

Both rafts and brims improve first layer adhesion, and so are recommended for use whenever printing with a material that is exceptionally prone to warping, such as ABS or Nylon. When choosing between a brim and a raft, we like to stick to this rule: if a brim will do, then use a brim. If warping still happens with a brim, then it’s time to use a raft.

1. When to use a brim

Basically, a brim improves bed adhesion but only for designs that have a low risk of warping. While it does enlarge the contact area between the print and the build platform, it doesn’t create a “sacrificial” layer to which the first layer of the print will adhere to.

If you are printing a design that has a large base and therefore a large contact area to the build platform, then there’s a good chance that having a brim will be enough to prevent warping. A brim is also a good addition to designs that are exceptionally flat, as it provides material to pry off the print after it’s done without damaging the final product.

The reason why a brim is generally the more preferred solution is because it uses up less filament material and thus creates less waste. Since the first layer of the print is unaffected, its bottom layer retains a smooth finish. Rims provide very good first layer adhesion, but at times it can be too good – removing a raft can get so difficult that it could damage the print.

2. When to use a raft

Many consider printing with a raft the last resort when all other ways to improve bed adhesion have been exhausted. A raft is basically the ultimate solution to bed adhesion. By printing a preliminary mesh layer, the first layer of the print has something it can more reliably adhere to. A raft is generally a requirement if your design has poor contact with the build platform, such as when you have thin supports and a small base.

The superior adhesion of a raft comes at a price. Since the raft is composed of multiple mesh layers, a lot of your filament goes into printing it, which eventually becomes waste. You might also find your raft sticking a little too well to your print to the point that the print comes into risk of getting damaged while the raft is being removed. Even when you do manage to pry apart the raft from your first layer, the bottom surface of your print will come out with a rough finish. If you’d like to sell or display your print, then printing a raft may mean more time spent on post-processing.

Final thoughts

If you’ve been having layer adhesion and warping problems with your prints, then don’t worry: all 3D printing professionals and hobbyists have been through the same experience. Troubleshooting warping problems is only one of several steps you’ll take in mastering the intricacies of 3D printing. Before you know it, you’ll be taking on bigger hurdles such as clogged extruders or stringing in your prints.

Don’t forget that brims and rafts aren’t the only solutions to warping. You can try printing at lower temperatures, priming your build platform with an adhesive compound, or using a printing bed enclosure. When it comes to 3D printing, there’s always more than one way to skin a cat.