3D PRINTING FOR FOLESHILL STATION

Anthony Butler explains how the 3D-printed elements were created.

I’ve been using 3D printers for a few years, mostly to print buildings for my own model railway projects. I use a Prusa i3 MK3S printer, which is still winning awards even after many years. As standard, it can print layers as small as 0.05mm. With a standard 0.4mm nozzle, the filament width comes out around 0.5mm wide. This wasn’t going to be fine enough for our purposes, so I used a 0.25mm diameter nozzle instead, retaining the very fine layer height. Using this nozzle – and after many tests with objects of various width – I was able to get reliably extruded widths down to 0.35mm, which was deemed acceptable. To go finer, I’d be into experimental settings and nozzle sizes.

All the designs that Paul sent were of sufficient detail that I was able to create the objects using a simple software package called 3D Builder, which comes free on Windows 10 onwards. It’s a very basic package which doesn’t have the sculpting capabilities of more advanced software, but neither does it have the complexity or the steep learning curve. In 3D designing you can either build parts up by adding bits to them or you can subtract from larger shapes. I use a combination of both, but mostly I build up from very simple primitive shapes.

To design the side rails for the bridge stairways, for instance, I started with a default 40mm cube. I resized this to represent vertical bars of the individual balusters, and then created a series of half circles and circles to join the bars at top and bottom. Care had to be taken to make sure the thickness of the resulting rings was the same size as that of the vertical bars.

Once the basic baluster shape was created, I test-printed it individually, then joined multiple versions together to form the balustrade, until I was finally at the stage of printing an entire side of the stairway.

Including the mid-platforms, there are 27 individual balusters on each side of the stairways. After adding the stair tread detail, a whole side could be created. In contrast, the sides of the actual bridge span section, use a different pattern entirely, with straps in a criss-cross effect.

The next problem was to figure out how to support the stairs. Each set of stairs had two posts in the middle and two more at the top, then there are two further posts that supported the bridge deck itself. At the bottom of the handrail there was an offset pair of posts as well.

My first efforts were nowhere near acceptable. The filament printer couldn’t quite do the posts justice, so I used a resin printer, a Creality LD-002H, which has very

fine layer resolution and was brilliant for creating the pillars and curved mid-supports for the bridge deck. While the plastic I used (PLA) has some degree of flexibility, I found that making these a little narrower than the part of the bridge they connect to meant that they would flex and twist at the same time. Therefore, they had to be made to a very fine tolerance to be able to fit.

3D PRINTING AT HOME

3D printing at home generally takes one of two forms. One type of printer cures a liquid resin using light of a particular wavelength (usually UV lights of 405 nanometres), one layer at a time. The other uses heat to melt rolls of thin plastic filament and extrudes it in layers.

I have both types of printers and usually employ a filament material called Polylactic Acid (PLA). This holds detail well and has sufficient strength for most modelling purposes. Like many people who use resin printers, I use a material that has ‘Abs-like’ properties. The two technologies are quite different. While both create components in layers, the end results can be quite different.

Resin printers are excellent for tiny details, such as the lamps I put on my model locomotives. But they can be messy. The common resin materials are hazardous and must be handled with the utmost care.

3D printing at this stage in its development is not for the faint-hearted. Neither is it suitable for anyone with limitations on what they can do with their hands. Both forms of printers require regular maintenance. There is a high likelihood of component failure, which requires taking a machine to pieces to replace some tiny part deep in its bowels. To get the best out of a printer takes time to configure the machine and your software.