V42 Electric Locomotive in G Scale for Garden Railways

In this instructable I would like to show how to build a locomotive
for your garden railway from scratch. This is not the instructable which will teach you how to use a 3D printer or a CAD software. I assume you already seen a locomotive modell, a printer and a 3D modelling program, but you're hesitating to before making your first modell. I also assuming you have the basic modelling knowledge in DCC programming, and you can use a solder to connect two wires. I was in the same situation a year ago, and I want to show my design and the product, to encourage you starting your project. It is not as hard as you think, but it will took more time than I thougt before. You will need the following things: -Basic 3D modelling skills -3D modelling program (Sketchup, DesignSpark Mechanical) -Drawings, blueprints and photos from the original locomotive -Motor blocks and wheels -Some free time for drawing -A 3D printer (any type will do it) -Sanding paper, paint sprays -LED's for ligths, some screws for assembly, hook couplings for the bogies, and a DCC decoder if needed -Basic modelling tools: sharp knife, sanding paper, etc First of all take a look of a garden railway loco. The details are sturdy, designed to be able to operate outside, heavy enough to pull a long train. Some details might missing, but it has to be easy serviceable, and the T&W parts had to be easy to replace (eg: pickup shoes). The loco in this instructable is my second design, and the first one in G scale. I choose the MÁV class V42 electric locomotive because there are a lot of blueprints, photos and other datas available, and I was able to find a mathcing powered bogie with etched wheels and pantographs from a manufacturer. This made the whole thing easier, I don't had to design and make this important parts. I suggest you for your first loco choose one which has enough information and datas, and there is a powered bogie available for driving it from a manufacturer. You can try to make powered bogies on your later designs, but for the first time don't waste time with this. Collect as many blueprint from your desired locomotive as you can: drawings from front, side and top view are necessary to make the 3D modell. If possible, go to a local locomotive repair shop to take photos and measurements from the real locomotive. This will allow you to make the small parts and details as the original. I think that's all we need to start designing a garden railway locomotive

You will need a simple 3D modelling program and basic modelling capabilities to design the modell. I'm using DesignSpark Mechanical, it is a very easy-to-use and free program, and can export the OBJ files which will be needed for your 3D printer.

Prepare the blueprints and have a calculator in hand. A G scale european modell for normal gauge (1435mm) is at about 1:26 scale. It varies for different countries and gauges, can be 1:32, 1:22,5 or 1:29, measure one of your G scale modells, because you have to calculate with the right proportion, to match your loco to the existing ones. I calculated with 1:26, because I have european modells for normal gauge. I printed the blueprints, each view to a separate page, and then converted the measurements to 1:26 and wrote them to the paper. The V42 class locomotive is a 4 axle one, with 2 bogies. I found out the PIKO powered bogie for their E94 locomotive is a close match in measurements and wheelbase to what I need for my loco. However, I altered some of the measurements on the modell to fit the factory bogies.
Take a look at your existing garden railway loco: you will need to design your new loco in the same way. You will need a strong base to attach the bogie and carry the chassis, and it has to be easy to remove. It has to be easy to remove the chassis from the base plate, you can use hooks, clips or screws. You have to design space for the DCC plate and the speaker (not necessary).
Then you can start drawing your first locomotive. Start with the easy parts first. You can add the blueprints as a background to your design program, it will help a lot, don't forget to scale the drawings to the proportion you choose.

After the easy parts are drawn, you can start adding details for your locomotive. Keep in mind: you have to print this locomotive with your 3D printer. Draw the loco to "be printable". What does it mean? Do not attach parts. Keep the parts of the locomotive body apart. You will print them separately and later will glue them together. Draw the roof and the small parts as a separate part: you also print those things separately and will attach to the body later. This will also make painting easier.
Use your photos to add as many details as you can. Like small parts to the roof, door hinges, etc.
To draw the bogie there is one important thing: it has to look like the original one, but it don't had to be work like the original one! You can draw all as one part, with a flat back side. Measure your powered bogie and examine it where you can attach your bogie frames. Add the holes for the screws, this will make your assemly work easier and faster.
For the chassis, add the holes for the assembly screws. Design the place for speaker and DCC plate carefully, the DCC plate can be hot and it will melt the printed chassis. Add the holes for the lamps wiring. If you're planning to have a sound loc, see your speaker measurements, and the sound holes also. Keep in mind that you will have to paint and assembly the whole locomotive, design it to make your work easy. The more details you add the more work you have, but more realistic loco you will have!
Do not forget to design places for ballast weights inside. Since your loco will be printed from ABS or PLA, it will be very light and unable to pull a train. You have to thing where can you hide some metal ballasting inside or under the loco body. I used 2cm x 2cm metal rods in the longer engine hood. It gave enough weight to pull a train consisting 6-7 european coaches.

As you finished the modell you can start preparing the files for printing. Do not start to print the loco until you are 100% sure, your design is printable. This step needs some 3D printing knowledge.
Do not lay the parts flat. I printed the locomotive in 3 big groups:

-Base plate: this is the base of the loco, the bogies and chassis will be attached to that. This is a thick object, required time and material, but this will hold your loco in one. Since this was too big to print in one piece, I designed it in 2 parts, with holes and parts to glue them together
-Chassis: this consisted 9 parts. 4 big one for the chassis walls, 3 roof parts, 2 parts for the engine room roofs. All of this attached together with glue.
-Bogies and small parts: the bogie frames are consisted 5 parts each, and there were several smaller parts (insulators, pantograph holders, lamps, hinges, ladders and other detailing parts)

For the best output you have to know your 3D printer capabilities: some parts will require different layer height. Lowering the value of layer height will increase the printing time, but you will get way better results. I printed the whole chassis on 0,1mm layer height. It took a day to print all the chassis parts, but it required minimum sanding.

If needed, do some test-prints: resize your parts to minimize printing time or prints only smaller pieces of the whole modell, to test different values. Allways check the GCODE view in your slicer software: check twice print once.

After the long hours of printing now you can finally assembly your loco. If you're using PLA as I did use a very high quality glue only (Henkel, Pattex, gel glues). Be careful of the gases while glueing the parts together. Use a solid, smooth plate to assembly the parts in-line.

Most 3D printed parts has a specific surface pattern. Now there is the hard part, to eliminate this surface patterns. After glueing the parts together, you have to apply a ground coating to it first. Use a fast-dryer one. If you printed your locomotive from PLA you can use 1K or 2K sprays, if you're using ABS be careful, some sprays will harm it and make the surface rough and you may have to print it again. Let your primer dry. Then you have to sand this layer down from the whole modell. You can start with a rough sander, use a waterproof one and apply water to the surface when sanding. After the ground coat sanded down, apply another one, and sand it down again, until the surface will be smooth enough. If there are bumps, and thick layers, you can apply putty to them. Putty also needs to dry completely before sanding, and you can only apply a thin layer at once. Be sure to use a putty which is re-paintable and your spray won't burn it! While sanding, be careful with the small parts and surface details. Cover them if necessary with masking tape. I had to apply putty to the roof parts to make them smooth, and the sides sanded down two times before final painting.

When all of your parts has a smooth surface, clean them thorougly, and apply the base coat again, and then you can paint it. Use a matching content paint and primer only! Apply at least two layers of paint, your loco will be used outside, the paint layers are for protecting, not only for decorating. Let the paint dry wholly before starting assembling the loco. Altough the spray can said 3 hours are enough, I waited one day between the two layers.

Assembly your new loco very carefully. If it is possible, test each part separately. For example, after assembling the powered motor blocks with the bogie frames, test them if they are running smoothly, even in the bend track sections. Apply grease and oil before assembling the bogies. Check the power pickup shoes surface and clean if necessary. Before the final assembly program your DCC decoder (if installed) and test it. Add as many parts as you can using screws, it will alllow you to remove and repair if necessary. Test the weight needs and add only the needed amount of ballast to avoid damaging the motors or decoder. Adjust the decoder settings to match your track and train needs. This will require a bit if testing. Add connectors to the wiring to make removing the chassis easier: for example the lights are fitted to the chassis and the decoder is on the base plate, add a connector to the wiring to be able to remove the chassis without needed to cutting the wires.

Now you have your own designed and printed locomotive. I made mine this way, it took more than 60 hours of printing from 0,5kg PLA, another 70 hours of sanding, priming, painting and assembly, and it works fine. By using factory motors and gears maintaining is easy, wide range of spare parts available. Good luck to your first design!