How I used Tinkercad to create a locomotive - PART 1 Scaling down and deconstruction

 The prototype

After buying a secondhand book, "Stone and Steam in the Black Mountains" by David Tipper which details the building of Grwyne Fawr Dam and Reservoir I was very taken with a pencil drawing of one of the locos, Anita, which was used by the contractor on a three-foot gauge railway constructed to transport materials to the site.

There were no details about the origin of the loco, so I consulted my fellow modellers on the Gardenrails.org forum and, within a few hours, they had not only identified the loco but had provided me with a works photo.

It turned out to be a one-off design built in 1904 by Manning Wardle & Co., for Elliot's Metals Co., Burry Port with a Works number of 1630. Another, later photo showed that over the years the loco was renamed and modified slightly.

 I searched in vain for a scale drawing, but one of my fellow modellers provided me with a couple of key dimensions (the diameter of the driving wheels (2' 4") and the size of the cylinders (9.5" x 14")) and so I used these to work out other dimensions, using the Works photo.

 Incidentally, the method I use to plot dimensions from a photo is fairly straightforward. Knowing the wheels are 2' 4" (or 2.3ft) I measured their diameter on the photo (24mm) and worked out that in 15mm:1ft scale that should be 35mm. So, dividing 35 by 24 gives 1.46 (to 2 dp). Thus, to convert the other dimensions measured on the photo to 15mm scale, all I had to do was multiply them by 1.46. I jotted all the measurements I needed in one of my many notebooks, in which I keep track of my various projects.

[INSERT photo]

 

 The chassis

Although I have started to construct my own powered loco chassis, I was uncertain as to where I would be able to find spoked driving wheels of the right diameter but, when looking through my bits box of chassis components, I came across the chassis for what I think is a Bachmann Porter which another fellow modeller had exchanged with me for some Bachmann Lyn parts. The dimensions weren't an exact match for Anita, but close enough. Most of my loco builds are 'inspired' by the original locos rather than true scale models based on the principle of the 'rubber ruler' and so I was more than happy to proceed.

The reason I hadn't used this chassis previously was because it had no motor and worm gear. In the past, I have experienced great difficulty in finding worm gears to mesh with Bachmann worm wheels (see How I converted a Bachmann Lyn loco), so I was delighted to not only find a motor which fitted the cavity, but also a worm gear in another bits box which meshed.

 Deconstructing the loco

 Before I could start the process of creating the 3D drawings needed to build the loco, I had to decide how I would break it down into the various parts needed. Because my first 3D printer was very much a budget model, I developed the habit of keeping the parts being printed to the most basic form - being printed as flat to the print-bed as possible. Even though I now have a slightly more sophisticated printer, I still like to keep things simple.

I always start with the running plate. As I am using a commercial chassis, I need to make sure the loco will sit happily on top of it. The running plate on this loco is stepped and so, following my keep it flat, principle, I decided to break this down into two separate sections - the larger upper section and the smaller lower (footplate) section.

The next most obvious section for me to tackle was the cab. So the sides and rear were drawn. I couldn't draw the front until I knew the exact size and shape of the firebox as it projects through the front of the cab.

Next came the firebox. I wanted it to be hollow and open at the front to give room inside the loco for the electrics.

The cab front could now be drawn.

 Next came the boiler and the tank. I spent quite a while tinkering with the design for the boiler, as it needed to be hollow and accessible for installing and maintaining the electrics. The boiler was slightly recessed below the running plate and so access to the interior would have been very restricted from below, and so I decided that the tank would be removable. This meant I had to figure out how it would sit above the boiler.

 The smokebox came next. In fact, after I had drawn it and test-fitted it to the 3D model of the loco (see below), I had to go back and modify the boiler to ensure there were no gaps between the boiler and the smokebox.

The motion received my attention next. I decided to do away with the cylinders on the chassis, as they didn't really match the design of Anita's. New cylinders, based on those in the photo were drawn, and were test-fitted to the 3D model. This allowed for new slide bars to be drawn. They were a compromise as they needed to be functional with the Bachmann crossheads, but look right compared to Anita's motion.

 

As you can see, I split the cylinder in two so that the two sections could be printed flat on the print bed.

 Finally, came the fiddly bits - the smokebox door ......

(as you can see, I separated the door handle wheel from the door itself to aid the printing process).... 

.... the chimney, .....

 ..... the tank filler cap, ....

(again, this was divided into two sections to aid printing)

..... the backhead ....

(which is a vague representation as I have no idea as to how the real thing would have looked)

..... the cab roof, .....

 .... the steps 

..... the springs .....

.... brakes ....

..... and the sandboxes.

 Once more, the sandboxes were broken down into two components, the base and the lid, so that each could easily be printed on the print bed without the need for cumbersome supports.

As mentioned above, as each part was drawn, I copied and pasted it on to a drawing of the complete locomotive, so that I could check that it fitted alongside the other parts. This sometimes resulted in previously drawn parts having to be modified slightly to ensure they accurately joined to the new parts.

Once all these parts had been exported as .STL files, they were sliced and saved as .gcode files which were then uploaded to my 3D printer.

See Part 2 for the next instalment.