Peckforton Light Railway: A beginner's guide to 3D printing

I think it is fair to say the 3D printing has revolutionised model making. In the past developments in the world of modelling have had varying degrees of impact: injection moulding, resin casting, laser cutting, air-brushing; but the widespread availability of 3D printers, their cost effectiveness and the ease with which they can be used is, to my mind, unprecedented.

Why and how? I will attempt to support this claim by sharing my own experiences in designing, printing and constructing various models for my garden railway.

The process of creating a 3D printed object can be summarised as:

Buy a printer
Set it up
Download or draw a 3D image
Open the image in a slicer program (usually supplied with the printer)
Slice the image and save it as a GCode file (which contains the instructions needed by the printer to make the object)
Load the GCode file into the printer (via memory card/stick, wifi or cable)
Prepare the printer (level the bed, load the filament, pre-heat the bed and print-head)
Print the object
Remove the object from the print-bed
Switch off the printer

These processes are fleshed-out in more detail below

What is 3D printing?

PLA
ABS
PETG

Buying a printer

How to 3D print a model

Step 1 - Setting up the printer

Step 2 - Slicing the 3D drawing

Brims
Rafts
Skirts

Step 3 - Printing the object

How to draw your own 3D models
Conclusion

What is 3D printing?

Put simply, a 3D printer is a device which creates a three dimensional object. 3D printers can be used to create a full sized house in concrete or a precision mechanical part in metal but the printers we use for model making generally use plastic or resin.

FDM printers

The most popular 3D printers for creating models for hobbyists are Fused Deposition Modelling (FDM) printers. FDM printers force a thin stream of melted plastic through a heated nozzle to fuse repeated layers of plastic together. The nozzle and its associated heating element (ie the print head) are moved left and right (X axis), forward and back (Y axis) and up and down (Z axis) with electric stepper motors which are precisely controlled by a microprocessor (ie a computer chip). In reality, the forward and back (Y axis) movement is usually achieved by moving the print bed.

The plastic used for 3D printing is usually supplied on a drum as a filament - ie a long thread (a).

Source: https://www.cleanpng.com/png-3d-printing-rapid-prototyping-ciljno-nalaganje-fus-1318947/download-png.html#Personal

This is fed into the print head (b) at a steady speed so that it can be melted and forced through the nozzle on to the print bed (e). The stream of melted plastic is continuously moving and placed on to the print bed and/or the plastic which has already been deposited there to slowly build-up the object (c) in a series of layers.

Resin Printers

Resin printers work in a different way. I will cover that in another article to avoid confusion here (See A Beginner's guide to Resin Printing)

Printer filaments

The plastic used in FDM printers is supplied in a variety of different forms. The most popular are PLA (PolyLactic Acid) and ABS (Acrylonitrile Butadiene Styrene), though PETG (Polyethylene Terephthalate - Glycol modified) is beginning to gain favour with some modellers.

All melting plastics emit fumes which you should avoid inhaling and so your 3D printer must be installed in a well ventilated room. The fumes from ABS are considerably stronger smelling and more harmful than either PLA or PETG and so it is advisable to install an air extractor or some sort near the printer if you are intending to use ABS.

PLA

PLA is by far the most popular. As it is a plant-based plastic it is almost odour-free when printing. It is easy to use, bonds readily with superglue and doesn't require high temperatures during printing. It is also biodegradable. Some garden railway modellers are concerned about how long it will last in an outdoor environment and whether it will be adversely affected by sunlight. Biodegradability is not really an issue as PLA would take several decades to disintegrate in a landfill site and so should last modeller's lifetime, particularly if it is painted. However, PLA can be affected adversely by prolonged exposure to hot sunshine. It is unlikely to cause problems in a temperate climate such as that found in the UK, but garden railway modellers living in warmer climates might find ABS or PETG to be a safer option.

ABS

ABS requires higher temperatures to print and is harder and more durable than PLA. However, it is tricky to get good results with ABS. The printer has to be set up very carefully and it's advisable to place the printer in a draught-proof cabinet to help ensure the temperature doesn't fluctuate. In addition, the fumes which ABS emits when it is printing are very strong and considerably more toxic than those emitted by PLA or PETG and so should only be used in a well ventilated space and/or with some form of air extraction. ABS can be readily bonded with acetone and is much more tolerant of hot sunshine than PLA

PETG

PETG is a sort of half-way house between PLA and ABS. It requires a hotter temperature to melt the filament which can be bonded with some of the solvents used for styrene (eg Dichloromethane, methyl ethyl ketone (MEK), toluene, and cyclohexanone). However, these solvents are highly volatile and listed as carcinogens and so should be used with caution. PETG is, however, more durable than PLA and is less susceptible to environmental factors.

Most of my models have been printed with PLA, though I have tried both ABS and PETG. I found ABS to be extremely temperamental and experienced a series of problems in trying to get successive layers to bond. It was a lot easier to print parts with PETG but I was disappointed with the level of detailing I could achieve with PETG as opposed to PLA.

PLA v PETG

The locomotive sandbox on the left was printed with PLA - the one on the right was printed with PETG. Maybe, with perseverance, I could improve the quality of PETG prints by adjusting the settings but the PLA print was successful with the default settings.

NOTE: Both prints are as removed from the print bed, with their 'brims' still attached. Brims help small parts such as these to adhere to the print bed (see below) and are easily removed.

Buying a printer

"You get what you pay for" is generally just as true of 3D printers as it is with most things in life. The more you spend, the better the quality. But what does that mean in terms of 3D printers?

Source: https://builder3dprinters.com/

3D printing technology is developing continuously and new models of printers generally build on the successes of what has gone before. Rather than providing you with a list of manufacturers and models of printers which would probably be obsolete the moment it is published, it is better for you to read a few recent online reviews as to which makers and models are currently considered to be the best value for money before parting with any cash. Simply search for "Best 3D printers 2021 (or whatever year you're searching)".

What you might need to consider when buying your first 3D printer is:

How much can I afford to spend?
How often will I be likely to use it?
Where will I put it?

How much can I afford to spend?

At the time of writing, FDM printers can vary in price from less than £100GBP to over £50 000GBP. The more you spend, the better will be the quality of the construction materials and components used and the higher will be the quality of what it prints. However, a lot will depend on your maximum budget. My first 3D printer cost me just under £80 GBP, when most hobbyist 3D printers at the time were well over £200GBP.

I wasn't sure about 3D printing and so wanted to try it out without forking out too much cash. It's fair to say that, to achieve that price, the manufacturers had cut a few corners, but I still have that printer and use it regularly to print out parts which don't require a high level of finish.

Since I bought that printer, the average price of printers has fallen and the quality of the sub-£100GBP computers has improved, so by shopping around you could pick up a bargain.

An example of a more recent sub £100GBP printer

At the time of writing, Creality and Anet have gained a reputation for good quality entry-level FDM printers and have sold millions, so for a novice they are a good investment as there is plenty of advice and good-value accessories available to help you through your early learning experience.

How often will I be likely to use it?

That really depends on what you think you might be using it for? Before I started creating my own 3D drawings, my use of my printer was limited to items which others had created and could be downloaded (for free) from the internet. So, my usage depended on what I could find which was suitable. However, in addition to small items such as suitcases, crates, churns, barrels and baskets, ......

All these items on the luggage rack were 3D printed

...... I downloaded the parts needed to build a small diesel locomotive and a beam engine.

Sources for downloadable 3D images suitable for printing include:

Thingiverse - a wealth of free downloads
Gardenrails.org - a selection of free models for large scale garden railways
Shapeways - a mix of free and paid-for downloadable models
Pinshape - free and paid-for models

These sources provided me with enough downloads to keep me busy for a few months but, before long I couldn't find anything else I needed and so taught myself how to create my own 3D drawings. After creating a few simple designs such as window frames, seats, roof tiles and gutters, ......

..... I developed sufficient skills and knowledge to start creating my own rolling stock.

My own Southwold wagons drawn and 3D printed

However, it took a while to learn the skills needed to draw objects in 3D (see below).

Where will I put it?

3D printers take up a fair amount of room. The space you have available on your desk or workbench will largely dictate what size of printer you can buy. Clearly, if you are intending to produce large scale models for your garden railway then it is useful to have a printer with a fairly large print bed. Most hobbyist 3D printers have a 200mm x 200mm or 220mm x 220mm print bed, which is suitable for the majority of models. However, a 300mm x 300mm print bed is very handy when producing rolling stock or buildings for use on a railway built to 1:20.3 (15mm:1ft) or 1:19 (16mm:1ft) scales.

My first (cheap) printer has a print bed of 200mm x 200mm which was fine when I was using it for printing small models, but once I started drawing and printing parts for coaches and locomotives, I quickly found that the need for a printer with a larger (300mm x 300mm) print bed.

Fortunately, I now have a dedicated workshop for my model making and so it was simply a case of clearing some space on my workbench to accommodate my two printers.

There are 3D printers with a fairly small footprint and so, if space is tight and you anticipate only producing small scale accessories for your railway, then something like this Labists Mini X1 printer with a print bed of 100mm x 100mm might be suitable

Alternatively, resin printers tend to have a much smaller footprint and produce very high quality prints - see A Beginners' Guide to Resin Printing

How to print a 3D model

There are slight variations in which FDM printers are loaded, adjusted and set-up but the general principles are the same. This section will show you what is involved in printing a model to give you an idea of what is involved.

Step 1 - Setting up your printer

All 3D printers need to be set up before they can be used. The three main processes involved in setting-up are:

Pre-heating
Loading with filament
Levelling the print bed

Pre-heating

Before the filament can be loaded, the print head needs to be heated. It's also a good idea to heat up the print bed at the same time.

Most (if not all) printers have a small LED or LCD screen which is used for setting-up and controlling the printer. Dependent on the type of filament being used, the print head (or hot-end) must be pre-heated so the filament can be fed through the nozzle.

Loading with filament

The filament is then threaded though the print head. The feed mechanism is slackened-off to allow the filament to be pushed through manually until it reaches the heated nozzle. It can then be fed through by hand until a stream of molten filament appears out of the nozzle.

Most printers now have some form of automation built into the filament-loading procedure with instructions as to what needs to be done next shown on the screen.

Levelling the print-bed

To ensure that the base of the model being printed sticks firmly to the print-bed, it must be perfectly level so the nozzle is exactly the same distance from the print bed as it moves across it. This is usually achieved by adjusting sprung-loaded screws at the four corners of the bed (though some printers have only three adjusters).

Usually, a sheet of normal printer-paper is used as a sort of feeler-gauge to determine the correct distance between the tip of the nozzle and the bed. The print head is moved around the bed and adjustments made repeatedly until the bed is levelled.

Auto-bed-levelling is available as an optional extra on most 3D printers. A sensor is bolted to the print head and a series of readings automatically taken at key points around the print-bed which are then stored by the processor and used to make adjustments as the print is made. These sensors can be quite tricky to set-up and, although auto bed-levelling sounds attractive, it is by no means straightforward.

Source: https://www.creality.com/blog-detail/the-necessity-of-a-bl-touch-for-auto-bed-leveling

Step 2 - Slicing the 3D drawing

3D drawings intended for 3D printing are usually saved as .STL or .OBJ files. These need to be imported in a program which slices them into the series of layers which the printer will lay down. 3D printers are supplied with a dedicated slicer program, though any could be used as they all perform the same job with varying levels of sophistication.

Once the drawing file has been imported, the slicing is done with the click of a button and the "GCode" file which contains the instructions to control the printer is either saved on an SD memory card, a USB stick or, if the printer is hard-wired to the computer, sent directly to the printer.

As you can see above, this object will take 51 minutes to print and will use 6g or 2.00m of filament. The GCode file for this object can now be saved to the memory card (or disk).

Slicing programs contain a wide array of settings which can be adjusted to suit the properties of the filament being used or to change the way the object is printed. Probably, the vast majority of modellers use the default settings which are generally set-up for the specific model of printer with which it was bundled. However, small objects or those with a narrow base will usually need some additional support to help them adhere to the print-bed. This most often comes in the form of a 'Brim' or a 'Raft'.

Brims

A brim comprises a series of concentric, overlapping strips of filament which surround the base (or bases) of the object being printed.

The greater the number of strips, the more additional adhesion is provided. The width of the brim can be adjusted in the slicer program. As it is only one layer thick (usually 0.1 - 0.3mm), then is is easily removed once the object has been taken off the print bed.

NOTE: This was printed on my £250GBP printer

Rafts

A raft, as the name suggests, is a slab which is printed first and upon which the object sits. The raft usually comprises a base layer, followed by a criss-cross pattern of supports sandwiched between an upper layer on which the object will sit.

NOTE: This was printed on my £80GBP printer

Rafts are particularly useful when the an object's base is not particularly flat or when ABS filament is being used as it can be quite difficult to get the first layer of ABS to adhere to the print bed.

The raft is broken-off the object once printing stops and the object is removed from the printer.

Skirts

Like a Brim, a Skirt is a series of concentric strips of filament surrounding an object but, unlike a Brim, the Skirt is quite separate and does not touch the object. It doesn't improve adhesion directly but can be used to ensure there is a clean and steady flow of filament on to the print-bed before the actual object is printed.

Source: https://www.trustfm.net/hardware/3DPrinter.php?page=FineCalibration

Skirts are also used to provide some protection from draughts for small delicate objects.

Once the GCode file has been transferred to the printer (via memory card, stick, cable or wifi), printing can commence.

Step 3 - Printing the object

The actual printing of the object is probably the most straightforward part of the whole process, providing all the preliminary steps have been gone through.

Preparing the print-bed.

A lot of printers are now supplied with rubberised surfaces or a removable mat over the print-bed, to help with the adhesion of the first layer. Whilst it is possible to print directly on to a smooth aluminium or glass print-bed, the addition of some sort of medium over the surface is advisable. This can take the form of:

specialised sprays
hair lacquer spray
a thin layer of Pritt stick adhesive
a layer of decorator's masking tape

I've tried most of these and favour hair spray or sometimes Pritt.

The cheapest hair lacquer seems to be the most effective. A light coating is given to the print bed (carefully masking the print-head and surroundings with paper). Occasionally, the bed needs to be washed with diluted domestic ammonia to avoid a build-up, otherwise it's fairly foolproof and seems to result in very few failures.

On those odd occasions when hair lacquer doesn't seem to work, I use a very thin layer of Pritt, spread in one direction and then another at right angles. The Pritt needs to be reapplied to the areas where printed objects have been removed and after a few prints I generally scrape the Pritt off with a broad bladed chisel and vacuum cleaner or it can be washed off with warm soapy water or domestic ammonia.

NOTE: It's easier to apply a thinner layer of Pritt when the print bed is hot

Pritt can also be used with PETG and ABS. One application of Pritt seems to last for dozens of prints with PETG but ABS requires a good thick layer (and even then, in my experience, it doesn't always guarantee success).

Pre-heating

Preheating the bed and hot-end isn't an essential prerequisite with PLA, but is more necessary with ABS and PETG to help with adhesion.

Printing

Having made these preparations, it's then just a case of selecting the GCode file from the memory card (or sending the file to the printer from the computer) and waiting.

I usually monitor the application of the brim and sometimes the complete first layer to check the filament is flowing smoothly and sticking to the print-bed evenly. If the first layer looks uneven, I will tweak the bed levelling knobs to raise or lower the bed while the brim is being deposited. Rubbing a finger gently over the deposited rows of filament will soon reveal whether they are or aren't sticking properly!

If tweaking the levelling knobs doesn't work, then the print is aborted and the bed re-levelled from scratch.

With large prints, I check printing progress at least once every hour, to ensure all is well. Sometimes the print head can snag on the printed object and drag it off the bed - resulting in a mass of filament-spaghetti. These things happen from time to time; it's just a case of aborting the print and trying again. Alternatively, there may be a problem with the shape of the object or the way it was sliced (eg having insufficient support or a too narrow brim) and so it may result in a return to the drawing software and/or the slicer.

All being well, a successful print should be sitting on the print bed at the end of the printing process.

Drawing your own objects

Having tried to use several (free) 3D drawing programs and online tools, I eventually discovered TinkerCAD and, so far, I have not created an object with it which hasn't been accepted by my slicing software (Cura).

Unlike most other 3D CAD programs, that start with a 2D drawing which is then extruded into the third dimension, TinkerCAD tools are 3D objects, which are placed on the 'Workplane', manipulated (ie resized or reshaped) and then combined with other 3D objects.

To my mind, what is really clever about TinkerCAD is the way in which any object can be turned into a 'Hole'. When a 'hole' is combined (ie "grouped") with another object, the hole's shape is removed from it.

For example, to make a window frame, a box object is placed on to the workplane:

It is then resized to match the dimensions of the window (by dragging the white 'handles' on the corners of the shape).

Four boxed-shaped holes are then resized and positioned where the panes will be, ......

..... and, when the holes are grouped with the frame, the panes are created.

The window frame is then saved as a .STL drawing which can be opened up in the slicer, turned into G Code and printed. It really is that simple.

If you think about it, most man-made objects are made up from a series of simple shapes joined together. With a bit of effort, even the most complex shapes can be drawn in TinkerCAD by joining simple shapes together.

A more comprehensive tutorial on creating railway related objects can be found here - How I drew an open wagon with TinkerCAD

Conclusion

There are some things which 3D printing do very well and things which it is not so useful for - in terms of the technology as it presently exists. Who knows where it will be in another three, five or ten year's time? In the meantime, I have certainly found it to be an extremely useful adjunct to my arsenal of modelling techniques.

Here are just a few of the things I have created for my railway with my 3D printer - and this is just the tip of an, as yet undiscovered, iceberg!