Article from Gazzette volume 20 number 7 - May 2018

Bob Gledhill, diagrams by the author, photographs by Charles Oldroyd

I've demonstrated 3D printing at several shows, and visitors are always fascinated by seeing a 3D printer at work. Often the comment is “I’ve heard about these but never seen one working”. So what questions do people ask about 3D printing and how should they be answered?

Virtually anything. However, unless you learn CAD skills, and we’ll come back to this later, you are limited to printing objects designed by others. There are thousands of 3D objects available on the Internet that you can download and print. Many of these are free, some you have to pay for. You don't even need a 3D printer as there are several '3D Printing Bureaus' that offer a 3D printing service. You send them the drawing file of the item and they print and post it to you. Some even offer 3D printing in metals. The advantage of using their services is that their printers print in high quality, and you have no outlay on your own printer, but the disadvantage is in the high cost of each item, especially if you need several, and the need to get the design 'right first time'.

Some of the capabilities of 3D printing.

A budget 3D printer kit from China will cost as little as £100, but you have to both build it AND get it working, so it’s best if you know someone with 3D printer experience. Mid-range printers, usually requiring a number of pre-assembled parts to be bolted together, cost £300 to £400.

The Genuine Prusa machine, generally regarded as one of the best for hobbyists, is about £600 as a kit, or £800 ready built. There are lots of clones of this machine advertised on the Internet, some good, some not so good.

Prusa i3 Mk2 printer.

In addition to the printer you will need the driver software, much like colour printers need software to make them work (now often incorporated into Windows).

The most common is 'Repetier Host' available as a free download, though higher end printers come with their own version of this program branded and 'tweaked' to suit individual printers. You will also need the plastic itself at around £16 to £30 per kilo, but a kilo makes a large amount of model.

Finally, you will also need a computer.

Flexi track sleeper base. 4mm Track chairs. Flexi track sleeper base, bottom, and at the top, a test fit of a short section of check rail chairs and rail.

98% of hobbyist 3D printers are basically computer-controlled hot glue guns. The 3D printing method they use is called Fused Filament Fabrication (Wikipedia is a good place to find out more). The plastic filament or rod, usually 1.75mm in diameter, is fed via a small toothed gear into the 'hotend' where it is melted at about 200c. The pressure created by the unmelted filament pushes the melted plastic out of the nozzle and this sticks to the bed/table. Once the first layer of the object has been printed, the nozzle moves up and prints a second layer of hot plastic which sticks to the first layer….and so on gradually building the plastic object from the bottom up. Getting the first layer to stick to the print bed is the tricky bit and requires some trial and error on the cheaper machines, more expensive machines now automate this process.

The standard nozzle has a hole of .4mm diameter, but it is possible for very detailed work to go as small as .15mm. Each layer is normally .3mm, but for detailed work .1mm or even less is possible. The process is not fast and the smaller the nozzle and layer height, the slower the printing.

Each layer leaves a tiny ridge, and these can be felt and often seen on the vertical surfaces of a 3D print, and are even more noticeable on sloping top surfaces such as the roof of a carriage or bus. This is often the main criticism of 3D printed parts from hobbyist machines. 3D printers costing several thousands of pounds (such as those used by 3D printing bureaus) overcome this by using different printing methods outside the scope of this article.

Once you have the drawing on a computer, the CAD drawing, you export the drawing as a file with the .stl (STereoLithography) file format. The file must contain the drawing as a 'watertight' mesh of triangles, and to ensure that this mesh is complete it is best to run it through a program to check it such as Netfabb (Netfabb.com) or MeshLab (meshlab.net), both have free non-commercial versions. Finally you send the file to your printer via its software, usually a version of Repetier Host or Cura, and print it.

This diagram shows the stages involved in 3D printing a model.

Point sleeper base.. Two points constructed from 3D printed sleeper bases and chairs.

To build and commission a 3D printer, requires an understanding of sometimes not very well written instructions, the downloading and installing of computer software and some 'tinkering' skills. Buying a ready-built machine only requires just the tinkering skills. Getting the best out of a 3D printer is still something of a black art.

Once you have the machine, and wish to make your own models, then you will need CAD (Computer Aided Drawing) skills in order to design them. There are several free CAD programs available as downloads and I always suggest trying at least four of them for a couple of hours each to see which is most suited to your needs and learning style. I did this and found I got on best with one called Sketchup which is available as Sketchup Free, Sketchup Make and Sketchup Pro, the first two being free and the last one, for professionals, has a cost.

Drawing an object in a CAD program on a computer is much like using a word processor. Using Shape and Action icons on the screen, (much like Bold and Italic in a Word Processor) you can amend and add things as you go along. It is obviously best to start with simple items, such as fencing, window frames, doors, before progressing onto chimney stacks, barrels, packing cases, etc. Note that unless you are already very skilled in CAD it will be some considerable time before you are drawing rolling stock and locomotives!

A CAD drawing showing, left to right, the stages in building a 3D object. This program is Sketchup Make, but several others are available free to use. Home and office furniture. 3D printing brings a whole new meaning to interior detail.

Once you have drawn your model you must export it in the correct file format, normally a .stl file for 3D printing. Most 3D drawing programs have this built in. For the free versions of Sketchup you must download and install a 'plug in'. Details of how to do this are on the Internet.

A selection of window frames. Signal box section. The layered effect of the window frames is impressive.

Being able to design and produce your own bespoke items for your model railway is very empowering. The actual plastic cost per item is very small, so you can start with a basic design, print it, refine it and print it again until you are happy with the final result. This is especially useful when you require multiple copies of an item, such as window frames, chimneys, fencing etc. You can also print items for others (and you will be asked).

An increasing number of modellers are acquiring 3D printers, so the best place to start is with a fellow club or Guild member who owns one. Perhaps they could bring their printer to a club night and demonstrate it working, or run a small workshop on CAD for beginners to pass on what they have learnt to others. They needn't be an expert, often an enthusiastic beginner has more relevant up-todate experience.

Another free source of information and help might come from 'Maker Spaces' and 'Fab Labs' where you will find 3D printers and enthusiasts who know how to use them. Most will also have the facility to 3D print your designs 'at cost'. The Internet is probably the best source of upto- date information although bear in mind machines and CAD programs are changing and being updated all the time. Search the Internet for reviews and make your own decision based on your own needs and budget.

Based on first-hand experience and since I have owned or own of the following, I suggest looking at the reviews of each:

• Budget 3D printer: Colido DIY 3D Printer, also called the Print-Rite DIY 3D Printer. £199 from Amazon.co.uk who have an excellent returns policy should you need it. Just five or six subassemblies to put together and some well-labelled leads to attach to the controller. No heated bed so it’s limited to using PLA (the most popular plastic anyway) but gives excellent results. A good machine to start with on a budget.

• Mid-range printer: Wanhao i3 V2 3D Printer. £300 from Amazon.co.uk. Good metal-bodied printer with heated bed allowing you to try out different plastics. Just two parts to put together. Good solid printer. An updated version is now sold for £60 more.

• Best hobby printer you can buy: Original Prusa 3D Printer. Buy as a kit or ready-built, Mk2s or Mk3 from £570 to £900. Buy directly from Prusa3d.com. These are superb printers with excellent features, such as auto-bed levelling so your print sticks to the print bed reliably. There is also great on-line support direct from Prusa Research. FILAMENT (plastic) Start with a good quality PLA filament and gain some experience before trying cheaper or more exotic types. Your printer will be supplied with some filament to get you started. • PLA filament comes various colours but white is always the best for prototyping as you can see the detail. Rigidink.co.uk has 1.75mm PLA filament at £32 per Kilo. Their filament is of a consistently good quality. All the printers above use 1.75mm filament but always check you are ordering the correct size. SLICING SOFTWARE All the printers above come with a USB stick with the manufacturer's version of Repetier Host/Slic3r software. This takes the .stl output from your drawing program and 'slices' it into G-Code so your printer knows how to print each layer of your model. Prusa have modified and improved this software. • The best software for 3D printing is currently Simplify3D from Simplify3D.com. It costs $149USD (currently about £112). Not required if you have a Genuine Prusa machine, but for others this will give you more control and better print quality. Don't purchase until you have some experience of your printer and the software that comes with it.

3D models are made up of a triangular mesh which must be complete and 'watertight' for the model to print successfully. Two of the many programs which will examine your model and correct any problems with this mesh are:

• Netfabb from Netfabb.com. A Free version is available for non-commercial use.
• Meshlab from Meshlab.net. Free program.

The best web site to illustrate and help with problems is Simplify3d.com. Click on SUPPORT at the top of the screen and MORE on the Quality Guide icon. Clicking on the picture of each 'problem' brings up further help. Some of this is specific to settings in their program, but much is valid for other slicing and printing programs.

3D printers have developed to the stage where they are genuinely useful to railway modellers. O gauge is a good scale to exploit their capabilities. 3D printers are available for reasonable cost. The new skill you will need to master them is that of CAD. Only when you have the skills to draw the models you require can you truly exploit this new and powerful modelling tool.

G scale wagon body print.

www.shapeways.com - for 3D models to have printed. Search for ‘O Gauge’ to see what's available in 7mm, and 'railway' for general railway models. Note the larger the object the larger the price. There are other 3D print bureaus on the Internet.

• For 3D printers, Prusa.com is a quality starting place, search Ebay and Amazon for cheaper alternatives.

• For machines with a larger print bed - (up to 500mm x 500mm) which you may feel you need for some 7mm scale projects, search for 'creality 3D printer'. These are available in different sizes, so make sure you are looking at the largest! They get good reviews from users.

• General Internet searches on 3D printing will bring up plenty of links, as will a similar search in YouTube. Many of the 3D printer reviews are now done as video reviews in YouTube.

• For CAD programs, once again an Internet search for 'free 3D CAD programs' will bring up a list. Try each, but only try to learn one.

• For a list of Fablabs and Makerspaces in the UK to see if there is one near you go to Fablabs.co.uk and click on the 'makerspaces' link at the right of the screen. This opens up an interactive map. Bob Gledhill is the author of the book Laser Cutting and 3D Printing for Railway Modellers published by Crowood Press (available as a printed book or download). ISBN-10: 1785002260

A 3D printed G scale wagon.