Test concept
The first prototype locomotive I’m developing for the City of Newcastle Museum for the Model Newcastle: Big Stories Little Things project is the C38, as I’ve outlined in my previous blog.
Most important is testing the mechanical element of the model which I will be working on as a priority. I am creating a chassis that will be as close to the final version as possible, without some of the things like bogies and some details which won’t be necessary. I need to stress test the chassis and wheels under full operating load for a long period of time on a rolling road to test its reliability and it makes sense this is the first thing to complete so time is on my side.
Turning wheels
I will be creating the wheels with a resin printer and a laser cutter. The tyre will be printed separately and electroformed in nickel, while the centre of the wheel, which needs to be painted, will be laser cut from ABS. I’ve found printing a part that is to be a different colour separately is a faster and cleaner way of manufacturing in this scale than masking things off. The combination of materials in the wheel will make it strong and reliable that will last for many thousands of scale, or even real miles.
I’m currently producing an extremely small device that in operation can be considered a lathe. The software I currently use doesn’t render round objects to a standard I am completely satisfied with and I will use my micro lathe to ensure the tyres are perfect.
Conductivity and electroforming
Electroforming is a method of adhering a layer of metal to a non-metallic object. A nickel anode, a lump of metal, is submersed in an electrolyte solution and positively charged from a power supply. The item to be plated is covered with an electro-conductive paint and submersed in the same solution and negatively charged. Microscopic parts of nickel move through the solution from the positively charged anode to the negatively charged part, which is called the mandrel.
This set up has two anodes. The mandrel is not in the picture.
The wheels are being electroformed for a dual reason:
Longevity
Track power
The locomotive must draw current through the wheels – think of a Hornby style model on a very large scale. Each drive wheel will be conductive. A brush, like what you may find on the bottom of a Scalextric slot car, will contact the back of the wheel and draw current into the chassis where it then completes a circuit with the motor.
As my dad always reminds me, your wheels are the most important part of your car – those are the bits that obviously connect you to the road and if they go wrong, especially at some speed (I never exceed the road limit – ahem), you’ll quickly realise the meaning of your motor vehicle has been lost and it becomes an abstract art installation, or a nuisance to other drivers, or both.
If all goes well, by next Sunday 9th December I’ll have some electroformed wheels to test - see you then!
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