3D models created for touch readers or people with low vision require particular attention at the finishing stages to ensure that they are smooth to touch, provide high contrast, and perhaps even provide textural details.
Smoothing
Smoothing is important to make sure that 3D prints are not potentially damaging to the skin, given that reading by touch involves movement across the surface. Don’t just rely on your vision – carefully use your hands to check the 3D print for any sharp points, rough surfaces or distracting artefacts that require smoothing.
Note that some 3D printing filaments, such as “silk” PLA, provide a smoother finish and will therefore require less finishing.
Removing rafts, supports and brims
The FDM 3D printing process can easily result in sharp points on a 3D print. In particular, any point where the printing head has lifted off the print (usually over the top of a curved surface) will feel rough due to tiny sharp strands of plastic. There may also be sharp or unwanted remnants where supports have been removed, and a sharp edge where a skirt has been removed from the base.
Tools for removing supports and sharp remnants
If rafts and supports have been printed using the same filament as the model, remove rafts and supports as soon as possible after printing, while there is still some flexibility.
Remove rafts using a spatula or sharp paint scraper. Remove supports using needle nosed pliers.
To smooth small rough areas, mini needle files or a dremel are recommended. Avoid using sandpaper as it is likely to scrape a large area and change the appearance of the print surface.
Brims can usually be removed by hand but may leave a thin sharp edge at the base of the print. This is best removed with a deburring tool.
Tools recommended for removing and smoothing parts on 3D prints
PVA rafts and supports
If you have a dual-head FDM printer, PVA filament can be used for rafts and supports for a smoother finish, however this is a more time consuming process.
Submerge the model in lukewarm water (less than 50°C). After soaking for ten minutes, remove the main supports by hand then continue soaking and changing the water until all remnants have dissolved. At least 3 buckets of water are usually required.
Smoothing methods
Note that any method for smoothing a 3D print is also likely to result in some loss of fine detail.
Chemicals
Epoxies such as XTC-3D can be used on either PLA or ABS. The epoxy needs to be mixed before being applied in a thin layer over a foil tray. Curing takes around 3.5 hours but can be sped up with a light heat source. The resultant print will be smooth, glossy and very strong.
3D Gloop! is a solvent designed specifically for 3D printing plastics, available for PLA, PET or ABS. While it is primarily sold as an adhesive for strong adhesion between two 3D printed parts, it can also be applied in small quantities to create a smooth surface.
An acetone bath can be used to achieve a very smooth finish, however it is only recommended when chemical safety procedures can be strictly followed. This technique works only on ABS and PET (not PLA). The cold vapour method is the safest. Line the floor and walls of a sealable container with paper towel or cloth soaked in acetone. If using a metal container (e.g. an old paint tin), use magnets to fix the cloth to the sides. Place the 3D print in the centre on a plinth/aluminium foil so it is not touching the acetone. Seal immediately (with a clear lid if possible). Leave for approximately 1 hour, remembering that some further smoothing will continue after the print is removed. The model will be soft to touch and needs to dry thoroughly for at least a day.
Heat
Heat is a quick way to smooth the surface of a 3D print. However, this technique is not suitable for models with small peaks that could become charred, discoloured or distorted with heat. Perhaps the best method is to use a wood burning tool with a flat tip. Run the flat end of the tool lightly over the surface of the 3D print. Alternatively, a few seconds with a gas lighter should be sufficient to slightly melt and smooth the surface without distortion. If using a heat gun, use a low heat and keep the gun moving quickly along the surface.
Sanding and painting
If an extremely smooth and professional finish is required for high use items, start by smoothing the whole model using a rasp and then sandpaper (beginning with rough, and getting successively finer). You could also use a filler and sandable spray paint such as Rust-oleum. When sanding is finished, improve the appearance by spray painting with any of the following products. Several layers may be needed:
- Rust-oleum Triple Thick Glaze
- a polish such as Brasso
- automotive spray paint
This technique can be very time-consuming and is only recommended for multi-use display items, such as in an art gallery.
Adding textures or colours
Textures
Textures are useful for better replicating the properties of the object being represented, or for distinguishing between different parts of the model, or for highlighting key areas. Textures may be incorporated into the 3D printed model itself, or added after printing.
Fine-grained textures such as sand or model-makers grass can be added to the surface of a 3D model. First, evenly spread a layer of craft glue using a spatula or piece of card. Then, spread your material on top. After drying, removing any excess materials that did not adhere properly. Be aware that some mending may be necessary for high-use items.
3D printed model of Parliement House in Canberra with model-makers grass added. Image courtesy of Braille and Large Print Services, NSW Department of Education
Fabrics such as felt, fleece or hessian can also be glued to a 3D model. If the model is shaped, you will need to cut the fabric accordingly.
Felt base for map with 3D printed icons. A laser cutter was used for accuracy.
A 3D printing pen can be used to add textured patterns or lines directly onto a 3D print. This method may be quicker and easier than incorporating textures and lines into the CAD model for a shape with with curved surfaces, and as an added bonus you can use filament with a contrasting colour.
3D printing pens are relatively cheap and most can use the same PLA or ABS filament that you use with your 3D printer. Some come with a low temperature nozzle, allowing safe handling by touch readers, however these pens do tend to suffer from more blockages. Note also that using a 3D pen does require some practice.
Colours
Colour contrast is important for students with low vision, and also for models that will be used by blind and sighted people together. Some 3D printers, including dual-head printers, enable full or dual colour printing. Another alternative is to add colour after printing is complete.
Small areas of contrast colour can be applied after a print is complete. For outward structures, water-proof paint pens (such as Posca brand) are recommended as they are convenient and effective. Nail polish and modelling paint also work well. If using water-based paints such as acrylics, an additional layer of varnish will be needed as a sealant. Oil paint adheres well but can take days to dry.
Markers are generally not recommended for use on FDM 3D prints as they will run along the printing line, however fine liners or thin pens may be a good option for adding contrast inside indented lettering.
3D printed tiles with nail polish on raised areas and fine liner in indented lettering
Construction
Joining
3D Gloop! is a solvent designed specifically as an adhesive for strong adhesion between two 3D printed parts. It is available for use with PLA or ABS.
Acetone can be used to join two pieces of ABS. Make sure the surfaces are flat first, then apply the acetone with a brush or cloth. Keep the pieces held together tightly until it has dried.
Super glue is usually sufficient to join two pieces of PLA.
PLA welding can give seamless joins when there is a small surface area or to repair cracks in poorly printed parts. Use a short straight piece of PLA filament in a power drill or dremel. With the drill on medium speed and held at a 45 degree angle, drag over the seam from right to left. The friction should melt the plastic together. For a strong seam or a deep channel, you may need to create the weld in several layers. Let each layer cool before starting the next. After welding, you will probably need to do some sanding for a smooth finish.
Applying a base
Often, it is more efficient to attach a 3D print to a base after it has been printed rather than 3D printing the base as part of the model. The base should be a solid material (not flexible) such as acrylic or wood. If you would like to add a texture to the base (such as sand, fake grass or fabric), it is recommended to glue the 3D print to the base first, then add the textures to the remaining base area.
Superglue should be sufficient to fix the 3D print to the base.
Map with 3D printed buildings on an acrylic and wood base