The supports in resin 3D printing

In contrast to FFF 3D printing, in resin 3D printing it is always advisable to use supports. There are several reasons why supports should be used, but the most important ones are:

• Support cantilevers: As in FFF 3D printing, each layer must be supported by the previous one. This is why cantilevers require the use of supports.
• Accuracy of the first layers: It is common to use long exposures for the first layers to improve adhesion to the printing platform. This overexposure often results in thicker layers, dimensional errors and loss of accuracy. The use of a raft and supports makes it unnecessary to position the part on the base and therefore prevents overexposed layers from matching the part.
• Minimise the possibility of failure: During the printing process, the resin cures in contact with an FEP or PDMS film. When the platform is lifted, the interaction of the part with this film generates adhesion forces that are greater the more contact surface there is. This is why parts are often positioned obliquely, minimising the surface area per layer. This positioning generally results in a larger cantilevered surface that requires the use of supports.

Parts of the brackets

In resin printing, the substrates are divided into three parts:

• Base: This is the area of contact with the platform. The larger the surface area, the greater the adhesion with the platform, but the greater the resin consumption.
• Pillar or body: This is the lifting structure of the support. It is a column structure with a risk of buckling, so its diameter must be correctly adjusted according to its height and whether it is interconnected with other supports or not.
• Head: This is the junction area between the support and the workpiece. It is used to reduce the area of contact with the part. It is the weakest point and the one with the highest risk of failure.

Image 1: Structure of a pillar. Source: makezine.

Support parameters

Although it may vary from one software to another, there are several parameters that must be set correctly for a successful printout:

• Support density: This is the number of support pillars per surface that will be generated on the part. The greater the number of supports, the lower the risk of failure, but the greater the aesthetic impact on the part. Ideally, as few supports as possible should be used, without the part failing. It can also appear as a gap, where the value indicates the distance between supports.
• Type of supports: Generally, there are two types of supports: straight and shaft supports. Tree supports are more efficient as they require less material and a lower density, however, they may have a higher risk of failure than straight supports on tall parts.
• Height or elevation: This is the distance the part will be separated from the base. At least 3 to 5 mm minimum is recommended.
• Diameter: This is the diameter of the support body. A larger diameter will produce more stable supports, but will increase the resin consumption. The diameter of the support does not affect the visual impact of the piece, so the only negative point is the waste of material. It is advisable to increase the diameter in pieces that require high supports in order to avoid failures.
• Contact point diameter: This is the area of contact between the support and the part, and one of the most important parameters. A larger diameter will produce a better bond between the part and the supports, minimising the risk of failure, but will also have a greater visual impact on the part.
• Interconnected brackets: The interconnected brackets function creates bonding structures between the different brackets, giving them greater stability. Some software applies this function by default. It increases the resin cost, but drastically reduces the risk of failure.

Common problems with brackets

Some of the most common failures in resin 3D printing are related to the supports.

• The part separates from the supports: In order to reduce the visual impact of the supports on the part, the supports are narrowed in their contact area (head), minimising the contact surface. The lift-off forces between the part and the FEP or PDMS foil sometimes cause separation between the part and the supports. When this happens, the solution is to increase the contact area between the part and the supports, which can be done in two ways:
• Increasing the contact area, which will make the support marks more visible and increases the risk of notching when removing the supports.
• Increase the density of supports, which will also increase the visual impact on the part. The risk of notches on parts when removing them is reduced. Although the risk of the part separating completely is reduced, some supports are likely to fail.
• Some supports shift: In the case of tall supports, there is a possibility of buckling during layer change. This will cause layer displacements that will cause some supports to fail. The best way to avoid this is:
• Increase the diameter of the supports
• Increasing interconnection
• Reduce the lifting speed of the platform
• The holders are not easily removed / the workpiece is damaged when they are removed: This is caused by an excessively large contact area. It is advisable to reduce the contact area with the workpiece, which increases the risk of separation between workpiece and supports. To compensate for this, the support density can be slightly increased.

How to remove the supports

Some manufacturers recommend removing the supports before post-curing, while others recommend removing them after post-curing. It is best to remove the supports before post-curing, as they will be easier to remove, and to go over the marks once the part has cured.

Supports should never be pulled off by hand, as this will cause notching and small gouges in the workpiece. Supports should always be removed using cutting pliers and blades, cutting close to the point of contact. Once the part has cured, they can be sanded to reduce their visual impact.