A beginner's guide to using 3D printers for your model railway

What are 3D printers?

filament vs. resin

They are exactly what they say they are. They are machines that can produce a three-dimensional solid object from a CAD (Computer Aided Design) file. They do this by building it up from thin slices of material one layer at a time until complete. The thinner the layers, the finer the detail, but the longer the printing process takes. There are a number of ways this can be achieved, using heat, light and even lasers. At the moment, there are two basic types of printer readily available at an affordable price to the average modeller.

FDM (Fused Deposition Modelling)

Also known as ‘Filament’ printers work very much like a very fine scale hot melt gun. They pass a thermo plastic (meaning one capable of being melted) material such as ABS through a heated nozzle that turns it molten. As the plastic is extruded, the nozzle is moved around the printer plate guided by the computer program to build up the model. The raw material for these machines normally comes in the form of filament cable reels, hence their common name.

DLP (Digital Light Processing)

Also known as ‘Resin’ printers work in a different way. They use a liquid material - the resin - which turns solid when exposed to certain specific wavelengths of light (normally ultraviolet light). The pattern of this light exposure is managed by the CAD file to create the required solid model, again a layer at a time. The resin is poured into a small vat with a clear base which is located over the light source. A build plate is lowered into this vat to within a very small distance of the clear base. This distance determines the thickness of the layers printed. The light source then ‘cures' the resin between the vat base and the plate to the necessary pattern and this now solid resin sticks to the build plate. The plate is then raised slightly and (hopefully) takes the first layer with it. Fresh liquid resin fills the void that appears and is exposed to the light source to create the second layer which sticks to the first layer. This process continues until the complete model emerges from the vat.

Each system has its own particular merits and drawbacks. Filament printers are the quicker of the two, and - depending on the type of thermo plastic used - can produce load bearing items capable of being used for brackets or drive gears. A key feature of any printer is how large a model it can print. This build volume is determined by the area of the build plate and how tall an object can be printed on it. In general, FDM printers can produce much larger models than DLP ones. Resin components have a reputation for being more brittle and less resilient. As well as the increased print time, one must take care when handling the resin, and the post production finishing is also more involved.

Where resin does score is in the quality and definition of the small details that they can replicate. This is because of the reduced layer height of each print pass. Filament printer layer thickness is dependent on the nozzle bore which is usually about 0.4mm (although specialist smaller nozzles can be purchased). Whilst it does occur on resin prints, they can also be more susceptible to shrinkage and distortion as the molten plastic cools. Resin printers layer heights can be adjusted as required, easily going down to 0.1mm thickness and beyond (I have mine set to 0.025mm). The difference between the two can be likened to the relative picture quality of standard and high definition televisions. And it was for this increased level of detail that I decided to purchase a resin printer.

Working safely with resin

Before beginning, it is appropriate to spend some time on the health and safety aspects of working with resin. As modellers, we already use a number of chemicals in our hobby such as paints, adhesives, lubricants, cleaners and solvents, and we all know they should be treated with respect. Once a 3d object has been properly printed, cured and rinsed, the resin should essentially be non-toxic. However, lengthy uncontrolled periods of exposure whilst it is liquid or only part-cured can sometimes lead to sensitisation and dermatitis. So, until the resin is fully cured, there are a couple of basic precautions that must always be taken. Skin and eye contact with uncured resin must be avoided at all times. I use disposable nitrile gloves, goggles, face mask and dedicated apron which is washed regularly. I have got into the routine of wearing these when pouring out the resin and during the cleaning and final curing. The equipment also protects you from any inadvertent exposure to the special solvent when cleaning down the parts and work surfaces. Any working areas should be away from food, cleaned down after each run and be well ventilated. Twelve months ago, such preparations would have sounded extreme. In these interesting times, they are just the normal prelude for a trip to the supermarket.

The next step

It is a statement of the obvious to say that before you start printing, you must have something to print. There are many CAD files readily available on the internet from sites such as www.thingiverse.com. Some require a fee to download, but many are free. They are a good way to get started, particularly when running the printer for the first time. At least you will be working with a proven model to discover the printer's settings and capabilities. These sites often have associated forums and blogs where you can benefit from the good – and bad – experiences of others.

Find out more...

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Need more advice? Take a look at the BRM Techniques page for all our latest guides and advice articles.

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