Plastic Printing

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It may not have escaped your notice that there is a minor revolution going on in how things are being manufactured. Not all things, but quite a lot of things, ranging from small lattice-work tubes on which body tissue can be grown (or sewn) to facilitate transplants and repair arteries, to large chunks of Her Majesty’s warplanes. I refer to 3D printing, which is rapidly coming into its own after a period when it seemed stuck in the curiosity/hobbyist category.

For those who don’t know what it is, or have failed to generate the enthusiasm to find out, 3D printing involves a heated nozzle (or sometimes two, to make multicolour prints) arranged vertically downwards fractionally above a glass plate. A fine thread of melted plastic, or other material, is squeezed out of the nozzle, which moves around the plate to make a layer of plastic in the shape of the base of the desired object. The plate then indexes down and the process repeats, building up the shape of the object layer by layer. A small fan attached to the nozzle ensures the plastic solidifies quickly and doesn’t collapse.

The main advantage of the method is the ease with which a component can be produced from just a drawing. No moulds or machining are required, and awkward shapes are easier to handle, with less waste. The range of materials that can be printed is growing rapidly. It started with thermoplastics, which melt readily in the nozzle at just over 200°C. Now machines exist like mini-foundries, which can laser-print metal. A novelty perhaps is a plastic material containing wood chippings, which gives the finished product not only a timber-like appearance but a definite woody smell. For the ultimate sophistication in DIY vase construction, go for a ceramic printer, with or without firing kiln, or for the fashion-conscious don’t bother with tedious, old-fashioned fabric, but just print your own clothes.

So what does this mean for the average railway modeller? For the big manufacturers, printed components have made little, if any, headway into their models. I’m not aware of the likes of Hornby or Bachmann doing production runs of a fully-printed body as yet. Speed (and therefore cost) compared with injection moulding for large production runs is a key issue, although printing of prototypes at the design stage is a well-established means of quickly seeing how an idea looks in the flesh. Hornby (under both the Humbrol and Airfix brand names) have tried selling home printers, with limited success. But that didn’t stop one well-known retailer selling a 3D printer for nearly 40% more than Amazon and calling it a bargain…

Amongst the more niche suppliers things are definitely happening. In 16mm for instance, several small (meaning one man and his dog, or maybe just the dog) businesses have sprung up, offering small wagons and the like from the printer in the spare room. One is even doing complete battery-powered locomotives in kit form. Low overheads, small production runs and free Facebook promotion make the activity worthwhile, although I doubt if anyone is making their fortune. The amount of detail which can be achieved is impressive, with no expensive tooling or sub-contracting required. As well as ready-to-run rolling stock, small scenic items such as barrels, drums and boxes are straightforward to do, and train crew and passengers can also be printed. Larger items such as buildings are feasible if constructed in sections, as I hope to demonstrate in due course.

Another option is to have someone else do your printing for you. You upload the design, drawn using 3D CAD software, or selected from a catalogue of existing models, and the company prints it for you, sometimes with a ‘choose your scale’ option. Not always the cheapest way of doing it, but the results are usually good from the professional machines they use.

The cheaper, and more adventurous, way is to do it yourself. Home machines start from around £400, less if you are brave enough to try a kit. They can appear a bit incongruous, as the need to get the printing nozzle to every part of a 6 x 6 x 6in envelope means you have an assortment of rods, gears, belts and motors whirring back and forth and up and down, all controlled by a computer chip reading your model’s file off an SD card. They look as if they shouldn’t work, but they do. In my experience it’s the mundane problems that get in the way of a perfect print. Things like a blocked nozzle (poked clear with a bit of brass rod) or a slippery bed plate (covered with masking tape and coated with hairspray, perfume immaterial). Trying to print in mid-air is a common problem, the nozzle needs to start at the bottom of the model and work up. A good design will include temporary scaffolding to ensure that, for example, the outstretched arm of a driver is supported during the printing process.

Getting a good design in the first place can be a challenge if no-one has been down that particular path before. If they have, there’s a good chance the requisite file will have been uploaded to one or other of the online repositories, for others to play with. Some rather ambitious projects have tried to laser-scan a complete full-size locomotive, to produce scale models for printing. However they tend to be more preservation projects than commercial ventures - maybe the kit is just too fancy to be cost-effective amongst a crowd of impecunious modellers. Mini-scanners are available for domestic use, some just using the humble smartphone and some clever software, but otherwise it’s down to learning how to use a 3D CAD program. I shied away from this until recently, fortunately the one I chose to try out (Sketchup) seems easier to pick up than others, although I still get my fair share of ‘I never told it to do that’ and ‘what’s happened now?’ moments. I can do simple boxes and cylinders, and it’s surprising how many components can be generated with these basic shapes.

Depending on the size of print and the quality selected, printing can take a while, but the machine can safely be left to its own devices, particularly if it’s in a cold workshop and a warm, well-stocked kitchen beckons. Only once (so far) have I accidentally switched the machine off mid-print, which is the sort of finger-trouble I can well do without. And yes, I di have to start all over again. And since you asked, I’m just making a Darjeeling D Class Garratt, in 16mm. Nothing too ambitious.

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