Railway modelling: How to 3D print at home

I have bought a few printed items over the years and seen many that don't seem to warrant the excitement their sellers seem to think they should. At the TCT 3D Print show, I spent some time on the Monoprice stand, which seemed to be selling the cheapest printers in the large NEC hall. The representative was happy for me to prod and poke the machines, then offered to lend BRM one to have a play with for a month. Could a 3D printer in the workshop convince me of the value of them?

The printer that arrived in a big box from the USA is the IIIP, and first impressions are very good. This is a well-made piece of kit. The main parts are made from a decent thickness of metal. I'd taken the precaution of ordering some 50g sample packs of filament from www.ooznest.co.uk after chatting on their helpline to make sure I bought the right ones for the printer specification. The main thing to check was the nozzle diameter – 1.75mm rather than 3mm – other than that, choice of colours and materials was mine.

I realise that a budget Fused Deposition Modelling printer, where layers of plastic are built up one at a time, wouldn't give me the same results as the resin-based machines used by figurine manufacturers such as Modelu. However, at the same price as the average larger OO gauge locomotive, does it have a place amongst my tools?

Part of the setup process involves printing a 6cm-tall Chinese Good Luck Cat. It shows the limitation of the process. All the curves are made from steps and if you rub your fingers over it, you can feel lots of ridges. My next stop was the internet where I could download something more train-shaped. The printer required gcode files and a quick search took me to www.thingiverse.com where you find hundreds available for free download. Downloading designs is a sensible early step. I'm not looking to get into 3D design at the moment. That's a hobby in itself - and one I suspect many people won't be worried about. The chances are you can download a design to suit your needs without much effort.

Printing a toy locomotive provided me with a subject for the biggest challenge I expected to face – smoothing all the print lines. Part of the learning process involves understanding the materials involved. Printing using PLA is easy, non-smelly and provides a model that can be sanded if required. Although the specification says it will work, I struggled to persuade the printer to feed ABS. One problem was working out how much filament will be required. If the design includes lots of supporting materials or infill, you can find the stuff disappearing at quite a rate.

Time is another problem. A small locomotive takes 2.5 hours to print, a cat just over 3 hours and a larger (10cm long) toy, over 6 hours. Fortunately, once the first few layers have been laid down, the machine can be left to get on with the job.

1

The machine arrives fully assembled in the box. Only a spool support has to be clipped to the side, there's no screwdriver or spanner work. A separate transformer plugs into the back. Turn on the switch and everything appears ready to go.

2

Control menus are accessed by turning and pressing a knob. There are three main menus – Printing, pre-heating the nozzle and bed and one for moving the head around manually. It doesn't take long to work out where things are located.

3

Before printing can commence, the distance between the bed and nozzle has to be set to the thickness of a sheet of paper. You move the head around and slide paper between the two. Adjustment is made with an Allen key turning a bolt in each corner. The movements are small, but important. Too great a distance and the plastic will cool before it hits the bed and won't stick.

4

Files for printing are stored on a micro USB chip that slots in the side. You can plug a computer in instead, but this isn't recommended. When your computer goes to sleep because it's not being used, the printer can stop.

5

Before feeding the filament into the hole at the top of the printer, the end needs to be cut at an angle using scissors or better still, wire cutters. If you are using a reel, it can be hung on the side of the machine. My tests are with 10-metre-long spools, so I let them sit on the desk beside it.

6

Dial up the cat file and press print. The machine runs a test bead along the left-hand edge of the plate to get the filament flowing, then starts to build up the layers of material. It's mesmerising to watch for a while and quite nice on the ears too. Imagine R2D2 from Star Wars singing to you.

7

It's nearly impossible to see if the filament is moving into the machine but I find a mark from a felt-tip pen solves this and doesn't affect the printing process. Presumably the tiny amount of ink is destroyed by the heat of the nozzle.

8

Three hours later, I am the proud owner of a plastic feline, and happy the printer is working properly. The wide area printed around the base is a sacrificial layer called a ‘brim’ to help the filament stick to the bed. It's a useful guide, because if the brim doesn't stick, nothing else will, so you can stop the printer.

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Printed cat tested, I want to print something more railway-orientated so it's off to www.thingiverse.com, where thousands of free-to-download files are available. Put your subject into the search box and a list of projects appears. Other similar websites exist.

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To open the files, a free piece of software called Cura is supplied on the SD card, or can be downloaded from www.ultimaker.com. It allows you to open and rescale a file before saving it to the micro SD card for use in the printer. Essentially, the software takes the design and slices it horizontally so the print nozzle knows where to move during printing.

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Two and half hours later, a locomotive, of sorts. It's very basic, but serves as a useful test piece. As a guide, a 50g spool of filament is enough to print a 60mm tall cat and two and a half 45mm long locomotives.

To see the use of CAD by a railway modeller, click here to read about Les Green’s Liverpool Lime Street. 

Did you know

All filaments can be mixed with other materials such as wood or metal if desired, giving the resulting items some of the properties of wood or metal. I tried a wood-infused PLA but had great difficulty feeding it through the printer. If your machine will print infused filament, the results can be very impressive.

There are three main materials used for 3D printing:

PLA – Poly Llactic Acid is a biodegradable polyester derived from corn starch or sugar cane. When heated for printing, the fumes (if you can smell them) are sweet. They may be harmful for youngsters, so printing in a well-ventilated room is a sensible precaution. The resulting models can be sanded smooth with normal abrasives. As the material is bio-degradable, it can be disposed of in a compost bin, apparently taking 6 months to dissolve. Nozzle temperatures of around 200ºC are required but while a heated print bed is desirable, it isn't essential.

ABS - Acrylonitrile Butadiene Styrene is a plastic that will be familiar to many modellers, or children - it's what Lego bricks are made from. A much harder material than PLA, it requires higher nozzle temperatures, around 240ºC and a heated print bed is essential. Fumes given off during printing can be unpleasant and many choose an encased printer for this reason.

PET - PolyEthylene Terephthalate is the most popular plastic in the world. Water bottles are made from it. More flexible than PLA and requiring slightly lower nozzle temperatures than ABS, it's also available in semi-transparent forms. Very sticky white printing, adhesion between layers is excellent, although peeling the model from the print bed can be more of a challenge.

Improve the surface of 3D printed items

1

The biggest problem with Fused Deposition Modelling is you can normally see the layers of print. This is especially apparent on curved surfaces such as boilers and cab roofs but even flat areas such as cab sides show a series of lines.

2

PLA can be sanded flat using normal abrasives. Work hard using increasingly fine grits and the resulting surface will be glass-smooth. The trouble is, you are likely to create dips in some areas and getting into all the nooks and crannies can be difficult. I couldn't get the sanding stick under the cab roof when I experimented with the locomotive print, and it's not a very detailed model

3

XTC-3D is a two-part epoxy-based brush-on coating. It claims to eliminate 90% of post-finishing work. Not only this, a coat will protect your model from moisture and help paint stick.

4

The two liquids are mixed following the instructions and the resulting gloopy liquid painted all over the model using a disposable brush. The foam brush I'm using seems ideal. I'm aiming for a very thin coat all over.

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Drying takes a couple of hours, although leaving the model overnight in a dust-free box is a good idea. The model looks like it has received a thick coat of gloss varnish at this stage.

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A spray with matt grey car primer shows XTC hasn't done a bad job. In many areas the lines have vanished but at the expense of the model now appearing soft. I'm not convinced this product would be much help on a highly-detailed surface.

7

For PLA prints, the Internet suggests that coats of paint and polyurethane varnish are the way to go. In theory, the varnish sinks in to the printed parts, smoothing the lines without harming detail. You need to leave each coat for at least 20 minutes to dry, so it's a time-consuming process. I gave the model a couple of coats of paint and three of varnish, leaving the last to dry overnight as recommended.

8

The worst of the lines have vanished, but at the cost of losing the crispness of the original. The primer doesn't seem too happy with the varnish either, which could be a problem if the model is to be painted.

The Verdict

Overall, I am impressed with the printer. It’s simple to use, well-made and reliable. If you want to dip a toe into the world of 3D printing, it's a good machine, but don’t expect injection moulding quality. I want to try to do more and make something useful. I don't care what, just something that isn't ‘plastic tat’.

I'd also like to persuade the ABS to print as there are some useful techniques for smoothing this which avoid the slightly melted appearance of the ones made from PLA and allow for greater detail printing. There needs to be more experimenting with sticking the material to the printer bed for that to work.

I'm a long way from a convert to 3D printing everything, but it’s more fascinating than I expected. Making printing work seems to be a matter of understanding the limitations of the technology rather than pretending they don't exist. I can see how printing could become a hobby in itself and that's not what I want, but at the price, I may see how this printer could justify a place on the workbench.

Looking for some advice on painting 3D model figures? Phil Parker shows how it’s done in this step-by-step video. 

Click here for even more easy-to-follow practical articles and videos from the team behind BRM magazine.