There are several reasons why you might want to print a part directly on the build platform, without a raft. For example, if a model contains no unsupported minima, then it is self-supporting and can be placed directly on the build platform.

Take the following considerations into account when printing directly on the build platform:

Choose a flat surface of the model to function as a base

When printing directly on the build platform, choose a flat surface of the model to function as a base during printing. Ensure that the chosen flat region of the model has a surface area sufficient to resist the forces experienced by the part during the printer’s peel process. Experiment with different flat surfaces of each model to determine the best area to function as a base.

Vertical compression and Z-axis dimensional accuracy

Formlabs printers compress the first several layers of every print to ensure adhesion to the build platform. This compression shrinks the vertical height of a print’s early layers. When printing with a PreForm-generated raft and supports, the compression does not affect the part’s dimensional accuracy because the compression only affects the generated raft and supports. When printing a model directly on the build platform, expect each model to be approximately 0.5 mm shorter than designed along the Z-axis in the model’s first layers. The exact compressed height varies between printers and build platforms.

Early layer merging

PreForm automatically revises the first 0.75 mm of all on-build-platform prints to increase adhesion. Early layer merging combines and extrudes the shapes—the perimeter and fill area—of all layers contained in the first 0.75 mm to ensure that printed parts have a completely flat surface in contact with the build platform. Slide the Slicer tool through the early layers to view the uniform, combined geometry.

Model compatibility

The On Build Platform feature works best for model geometries with at least one flat surface that can face directly parallel to the build platform. Shapes without any flat areas, such as spheres or organic shapes, are not recommended for the On Build Platform feature because these geometries will print with slightly flattened base layers due to early layer merging and compression.

Part removal

Take special care when removing parts printed with the On Build Platform feature, especially when there are no printed features for the removal tool to easily separate the part from the build platform. The flush cutters may chip the part. Separate the part from the build platform at the face that is least critical for the part's application or aesthetics.

To reduce post-processing effort by printing directly on the build platform:

1. Select the model in PreForm. Manipulators are overlaid on the model.
2. Click Orientation. A dialog box opens.
3. Click Select Base…. The pointer becomes an orange arrow.
4. Click on a flat surface of the model to become the base. The model reorients.
5. Click Done. The window closes.
6. Click the orange Print button when you are ready to print directly on the build platform without supports.

Choosing to print without a raft doesn’t mean you have to print without supports. To add supports to a model that is already directly on the build platform:

1. Select the model in PreForm. Manipulators are overlaid on the model.
2. Click Supports. A dialog box opens.
3. Click Support Structure. The panel expands.
4. Scroll to the Raft section.
5. Click the Raft Type dropdown and select None.
6. Click Auto-Generate Selected. Supports are added to the selected model.