First-Class Finishing For Your FDM Prints

With any FDM print, the finishing stage is what will take your end result from just ‘good’ to truly professional, whether it’s an attractive display piece or a durable, functional part. Here are a few practical tips to make your finishing process both efficient and effective:

Remove any support structures first

Any FDM print requires support structures to avoid drooping or deformation, so these will need to be removed before any other post-processing can take place. We’ve already looked at support structures in detail on the blog, so refer back to that tutorial for advice on how to remove yours effectively, whether you’ve incorporated them into your design, or utilised dissolvable support materials.

Smooth out your part’s surface

Once the supports are removed, you’ll need to gently sand your print to remove any leftover material and avoid the ‘stair effect’ that is an inevitable side-effect of this printing method. When doing so, consider the grade of sandpaper you’ll need. Generally, it is best to start with a coarser paper, then gradually work down to a finer one, but if you’ve printed your part with very fine layers, you may be able to move straight to a finer grade paper. Consult your material specifications if you are in any doubt, and always use a light touch when sanding, to avoid damaging any fine details and to maintain your part’s dimensional accuracy.

If you are concerned about fine details being lost, or the amount of time it will take to sand an intricate part, there are several alternative methods for smoothing the surface:

• Vapour smoothing is a popular choice for parts that will later be electroplated or will come into contact with liquids or gases, as it eliminates the natural porosity of many FDM materials. Unfortunately,  it does not deliver a completely smooth finish and may affect the mechanical strength of certain materials.
• Beadblasting can deliver an attractive matte finish (and so is often used in conjunction with vapor smoothing) and works with all FDM materials, although it will usually require input from a specialist to get the best possible result, as the media size and level of abrasion will need to be tailored to your specific part.
• Tumbling is a great choice if you are printing with more durable FDM materials and need to finish multiple parts quickly and consistently, although depending on the media used, dimensional accuracy may be affected.

Get ready to fill any holes

If you’re printing with dissolvable support materials, you may find that small holes appear in your part when they are removed. These are caused by the support material leaking into your part during printing. Smoothing the finish may also reveal small holes, caused by incomplete layers. If this occurs, you’ll need to fill the holes and ensure they are sanded smooth, but if this is done properly, the holes should be virtually invisible. Autobody filler is a good option, as it is strong, bonds well with plastic, and can easily be sanded or painted once it has set. On the other hand, if you are printing with ABS, you can create a filler by mixing a small amount of your original filament with acetone, so the filler will be of the exact same colour and surface quality as the rest of the part.

Clean your part

Before the final finish is applied, it’s important to clean your part, to remove any dust, dirt or leftover material. Our next tutorial will cover everything you need to know about cleaning FDM prints.

Choose the right finish

Once the above stages are complete, it’s time to apply the finishing touches. There are several options here:

• Metal plating. This is a good option for functional parts, as the metal finish will deliver an increase in mechanical strength. There are a wide range of options in terms of both materials and techniques at the time of writing. Some of these can be applied in-house, while others will require a specialist’s input. We’ll be looking at metal plating in depth later on the blog.
• An epoxy finish. This is a simple, versatile option that helps seal an FDM part, making it suitable for use with liquids or gases. The finish can either be brushed on by hand, or by immersing the part in epoxy, then using a vacuum to create a watertight seal, which is a good choice where preserving fine details and dimensional accuracy is essential. Bear in mind that polyjet materials are naturally watertight, and so will not require a finish of this sort.
• Painting. FDM materials can easily be primed and painted to deliver attractive, full-colour results. We’ll be taking a close look at the different processes for creating coloured FDM parts in a future blog post.

When considering which finishing techniques are right for your part, be sure to consider the part’s intended purpose, the level of detail in your design, and whether or not you will be producing them in large numbers. This will help you implement a finishing process fits seamlessly into your wider project workflows. The result: first-class results from every FDM project!