The FDM printed part comes out ready to use, but not with the surface finish of an injection-moulded part. Layers are visible, the underside bears a mark from the build plate, and places on supports may be rougher. For a functional bracket, this is often irrelevant. For a prop, mock-up or visible body, post-processing can change the result a lot.
Important clarification: we offer the printing of the part, but do not promise sanding, filling, painting or acetone smoothing as a service. The instructions here are for you if you are going to process the finished print yourself.
Start before sanding
The easiest mark to remove is the one that wasn't created at all. Orientation decides where the layer lines will stay, which side will touch the build plate, and where the supports will be. If the part has a visible face, note it when ordering.
For painting, it is good to anticipate how you will hold the part without touching the wet surface. In a multi-part model, it is sometimes more convenient to finish the parts separately and assemble them at the end. Other times, the joint must be caulked and filled first. The correct order depends on the model and material.
Sanding without loss of shape
Start with as coarse a sandpaper as is needed for the particular marks and gradually move to a finer one. There is no universal number: the appropriate range depends on the material, the geometry and the desired look. Make a sample in an inconspicuous place or on a discarded print.
Edges, embossed text and precise joints are rounded quickly. Work with support under flat surfaces and check often rather than pushing hard. In machine sanding, the friction heats the plastic; it can soften and smear. Slower work with pauses is more predictable.
TPU does not sand like hard plastic. The flexible surface moves under the tool and may become fuzzy instead of smooth. With it, the better result usually comes from proper orientation and a clean print, rather than aggressive processing afterwards.
Filling layers and joints
When the goal is a flat painted surface, sanding alone can take a lot of material. A suitable filler or primer can fill the low spots, then the surface is levelled. Check specifically whether the product is compatible with the particular plastic and test it on a small area.
Deeper joints between assembled parts are treated separately. The glue carries the bond and the filler shapes the surface; one is not necessarily a substitute for the other. If the joint is going to take a load, the geometric fit is more important than the cosmetic layer on top.
Apply thin coats and allow each to cure according to the manufacturer's directions. A thick layer may look fast, but it hides details more easily, shrinks, or stays soft on the inside.
Primer and paint
Clean off dust and grease before priming. Choose a primer and paint labelled as suitable for plastic and follow their instructions for ventilation, protection and time between coats. Compatibility depends on the material and the chemistry of the specific product.
The primer not only helps the paint. It shows scratches, joints and dents that are difficult to see on patterned or glossy filament. After this inspection coat, you can go back to local fill and smoothing.
Several thin coats of paint usually preserve detail better than one heavy coat. With a part that bends, the hard coating may crack. This is especially important with TPU: the paint must tolerate the deformation, and this depends on the chosen system and the movement of the part.
Bonding and chemical smoothing
There is no adhesive that is equally suitable for PLA, PETG, TPU, ABS and composites. Contact area, load and material determine the choice. Clean the surfaces, test on a sample and follow manufacturer's safety instructions.
ABS can be processed chemically, but that doesn't make the procedure a harmless homemade step. Solvents are flammable and their vapours require a controlled environment and appropriate precautions. We do not offer chemical smoothing as a service. If you are going to do it yourself, follow the material and product documentation, and when in doubt, opt for mechanical finishing.
Plan the final size
Sanding removes material and primer and paint add a layer. On a decorative surface, this is a small change; for a hole, sliding surface or joint, it can be decisive. Leave critical contact areas unpainted or treat them separately. The required allowance is approximate and depends on the model, material and chosen coating system.
If you already know when ordering that you will paint or assemble, write it in the note. We can accommodate the orientation of the print, but the post-processing itself remains your job.
See materials, read about part orientation or upload printable model.