3D Printing Raft – When Should You Use It

What is a 3D Printing Raft?

A lot of 3D printer users have issues with getting the first layer right. The layer does not stick, is uneven, has poor finish or, if they are printing with materials like ABS, then warping fails the print.

All of these problems are quite demotivating but they can be avoided if not eliminated with a simple fix. A 3D printing raft is a horizontal mesh of filament deposited directly on the build platform. Upon this layer, the first layer of the print is deposited. This is a handy way to get the first layer right and also keep the print grounded to the build platform.

Rafts are generally used while working with ABS filament as it has high chances of warping. 3D printing rafts are not only important for avoiding warping but also to increase bed adhesion.

In the above image, the raft can be seen in blue.

When to Use a Raft

Although a raft can be used for many different reasons, the following three are the most important:

1. Warping: ABS, along with many other filaments, is prone to warping issues. One way to reduce them is to use a heated bed and spread a sludge of acetone and ABS filament pieces on the bed. But even then, warping can occur. To eliminate the warping issue completely, another method is to 3D print the model with a raft.
2. Poor Bed Adhesion: Because the model is printed on top of it, the raft forms the first layer of the complete print. And where a model may not always have a completely flat base sticking to the build platform, a raft is a flat mesh on the build platform. This gives the entire piece added surface area, which increases bed adhesion. 3D printing a raft also acts as a precaution against a possible failure.
3. Tiny Legs: Some prints have tiny features at their base. In such cases, these parts may not have the strength to carry the load of the rest of the print. Here, increasing the contact area of those features can help them bear the load of the complete print. At such instances, it is recommended that a raft is built as a safety precaution against a failure.

Pros & Cons of 3D Printing a Raft

Like every technique, a 3D printing raft also has a few pros and cons.

Pros:

• Fewer warping issues with stubborn materials like ABS
• Improved bed adhesion leading to higher chances of a successful print
• Consistent print output
• Stronger first layer

Cons:

• Rough finish on the bottom layer of the model
• Difficult to seperate from model, especially with a denser raft
• Extra waste material
• Possibility of breaking the part while removing the raft, especially with tiny model components

Note: Take precaution while removing the raft as it can cause injuries while dealing with tough rafts.

Slicer Settings for 3D Printing a Raft

It’s important to note of any observations when experimenting with slicer settings. Subtle changes in settings, whether increasing or decreasing values, should be done incrementally. This will help you check the progress (or regression) in a gradual way, allowing you to easily fine tune your ideal settings.

These settings are dependent on the 3D printers used, the filament used, the ambient temperature and even the build platform. One setting may not suit all purposes. A trial and error process has to be followed to find the ideal setting.

Separation Distance

The separation distance is the height of the space between the raft and the first layer of the print. Or simply the distance between the mating layers of the raft and the model. This is undoubtedly the most important setting for a raft.

A tighter separation distance will make it hard to separate the raft and the model. In the above image, we can see the distance between the raft (blue colored patch) and the first layer of the model.

For starters, try a separation distance equal to half of your nozzle diameter. If you have a nozzle diameter of 0.4 mm, try printing a raft with 0.2 mm of separation distance. The results will help you understand the necessary modifications you need to make to the settings.

According to a number of experienced users, the ideal separation distance is 0.1 mm. If the distance is increased then the print is easier to remove from the raft but the first layer of the print has a poor surface finish

Raft Layers and Offset

Bottom Layer

This is the very first layer deposited on the build platform. Therefore it’s recommended that it be kept thick and printed at a slow speed. This will help to achieve greater bed adhesion. You obviously don’t want a raft with poor bed adhesion, so be generous and keep a thick layer. According to a number of experienced users, the ideal raft bottom layer thickness is 3 mm. If the thickness is increased then it gets difficult to separate the raft and the print and it also wastes material.

Top Layer

The top layer of the raft will mate with the first layer of the print. Since this layer will determine the surface finish of the bottom layer of the print it is recommended that you should use at least two to three layers to achieve a smooth surface.

Offset

Some slicers have a setting that determines the distance the raft will extend to outside the edges of the print. Keep it slightly outside the print but not too extended.

3D Printing Rafts in Different Materials

Rafts are only used in FDM 3D printing. A 3D printing raft has significant power to impact any print, but only with careful control. A regularly failing print can be successfully printed by accurately adjusting the settings.

3D printers with a single extruder will of course 3D print rafts with the same material as the print, but a dual extruder printer can be programmed to 3D print a raft in a different material.

Common support materials like HIPS and PVA, if used for rafts, can be extremely beneficial. For example, printing ABS with HIPS or PLA with PVA is common practice.

HIPS and PVA are soluble in D-limonene and water, respectively. As such, if rafts are printed with these either of these support materials, they can be easily dissolved in the appropriate solution, eliminating the need to remove material. This can also help when working with a tighter separation distance.