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.

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?

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.

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.

Wheels

final pair of rear wheel rims

The rear wheels are only 97mm OD, hence my initial thought was to buy some thick walled 4 inch diameter pipe, but I just could not find any. I bought 100mm mild steel round bar, 2 off pieces at 1 inch long, I then had to machine the rims roughly to size.

Machining the treads at 7° to the wheel was tricky but rewarding. Machining a pair of wheels with handed angles at 7 degrees was tricky.

traction engine rear hub

The hubs need 8 slots machined on each face. The slots are 4mm wide and arranged so that the spokes on one side of the hub fit between the spokes on the other side.

The next stage was to make the spokes and then build the wheel up.

a pair of rear wheels
a pair of finished wheels
About Nigel 278 Articles
Have 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.

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