Miniature Traction Engine

miniature traction engine drawing

This is a work in progress around the research, design and building of a miniature Burrell 6NHP traction engine.

Cherry Hill's model engines a book by David Carpenter

My son bought me this book for my birthday as I’ve seen a number of Cherry Hill’s models and they are inspirational.

This book has made me think about my approach, my research and as I’ve got older how I can more calmly make parts and remake parts.

The main image shows the elevation view of this traction engine printed on a sheet of A4 paper. This is meant to be a small traction engine that works and make to enchant.

Basic dimensions:

  • Length: 263mm
  • Width: 122mm
  • Height: 176mm
  • Bore / Stroke: 12/17mm
  • Rear wheels:
    • diameter: 97mm
    • width: 22mm
  • Front wheels:
    • diameter: 70mm
    • width: 12.5mm

I wanted to work out the scale of this miniature traction engine. So, I’ve looked at a number of drawings, images and specifications. All information that I can find online. My conclusion is it is 1/20th scale.

Axles

front axle

The front axle was quite simple to design and make. A tapered 3/16″ square mild steel with machined ends to accept the wheels directly.

This axle then rocks and rotates on the axle pivot that is located under the smokebox.

Boiler

boiler endplates

The 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. Firstly I need to learn how to make the boiler endplates.

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

I calculated the efficiency of the engine and boiler so I could work out the water and fuel consumption.

The materials used in boiler construction is important, brass fittings need to be avoided.

Chimney

tapered chimney barrell

The chimney was produced in a number of sections. The lower section has some compound curves and was machined on the lathe and milling machine.

The mid-section of the chimney was made from 3/4″ round mild steel and machined to a thin 1.2mm thick wall at 2.5°, this was quite tricky but rewarding.

Crankshaft

One of the initial design questions was around the clearance between the crankshaft and the top of the firebox, in particular the clearance to the conrod bigend.

Firebox

firebox silver soldered

The firebox on this small model has been designed to be separate to the boiler. Manufactured from mild steel and silver soldered together.

The boiler is going to be clamped to the firebox.

The firebox door is a simple single hinge and latch design.

Plans and Kit of Parts

niature traction engine plan and parts

The parts made and bought laying on top of the engine plans.

Could this be a set of plans for sale or a kit of parts?

Smokebox

smokebox and lower chimney assembled

The smokebox is gradually taking shape with some basic dimensions being sketched out and then I’ve machined the main ring out of mild steel.

The lower chimney is curved and some of the turning was done freehand, with this you need to keep tool overhangs to an absolute minimum. Plus take your time and use very fine cuts. I wear a pair of heavy duty gardening gloves when I’m turning like this to minimise damage to my hands.

brass etching

For the lettering around the door I bought a Genmitsu 3018pro CNC engraver, but after a few upgrades I still reverted to a tried and tested etching technique using Ferric Chloride.

I then found a way to simply do brass etching. Silver soldering the hinge and ensuring it was all aligned was quite scary.

I then started again with the door lettering and etching.

Wheels

The front wheels are just 70mm OD and the rear wheels are 97mm OD. A total of 64 parts and 60 rivets go into making the four wheels.

traction engine wheels
burrell traction engine

The engine has not quite made it onto the wheels, but I do now have a Burrell on “Matchboxes”.

This have given me the ability to visualise it more clearly and think carefully about the next parts.

About Nigel 357 Articles
I've been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

4 Comments

  1. Nice work. I like small models – among other things, negotiations with the domestic manager for workshop space are easier!

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