Miniature Traction Engine Boiler

The miniature traction engine boiler design is to heat partly from underneath and with through tubes from the firebox. This means I can make a simple copper boiler and fix this into a steel firebox. I wanted to share with you the thought process, design process and finally all of the engineering of the actual boiler. For more general information on boiler terminology and design you might like to visit a page dedicated to this subject.

What is the right angle for the boiler to sit relative to the road surface?

traction engine boiler angle

I calculated the efficiency of the engine and boiler so I could work out the water and fuel consumption and check the size of boiler was consistent with run time and fuel requirements.

One of the first things I needed to learn was how to make the boiler endplates. Forming the endplates over a shape took some time to master, but ended up a rewarding skill to learn.

boiler endplates

The materials used in boiler construction are important, brass fittings need to be avoided. This has been particularly important in thinking about how I mount the cylinder to the top of the boiler, my original intention was to use a brass bracket. However, with steam flowing through this and full working pressure it wasn’t such a great idea.

boiler endplates and tubes

The miniature traction engine boiler internals.

As pointed out by Ken on the HMEM forum this would be better with two more flue pipes at the bottom. Also, Ken calculated I need to add stays at the top or a stiffening plate. Both of these modifications will be dealt with.


Barrel shape Boiler Heat Loss Test Object

The boiler will be wrapped in a thin layer of insulation and an outer brass sheet. However, as I don’t feel like I know enough about thermal insulation I thought I should look at how to optimise this.

small vertical boiler

Before finalising the design of the traction engine boiler I decided to test my skills. For this I made a small vertical boiler.

This also meant that I could work out how to do the safety tests such as hydraulic testing.

2 thoughts on “Miniature Traction Engine Boiler”

  1. Hi Nigel,
    Just wondering the logic behind having your boiler endcaps “dome in”.
    Most copper boiler plans I’ve seen have them (well, the front one) the other way around!

    • Hello Andrew, I’ve dome the end plates in or made them concave as I want to rivet the smokebox to the boiler and at the other end the firebox to the boiler. Hence I need some material that is external to the boiler volume. What I’m not sure of is whether this is a problem? Best regards, Nigel


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