BUILDING A

METRIC MINNIE

Part one by Franco Pucci

Introduction

Drawings for Metric Minnie were published on MEWS. We explained: “Large scale traction engines are attractive to operate, but they are not everyone’s favourite size to build. Storage and transport are also not practical for everyone.

“The Minnie scale is so much more convenient to handle and is a 'single-handed' engine. And it can be proudly displayed on the sideboard which you can’t do with a half-size Burrell. If there is a balance between building and operating a model traction engine then the Minnie is definitely biased towards building satisfaction.

“This version of the Minnie is geared to the newer workshop with metric tooling, tho most have little difficulty in moving between measures.

“Some time ago Arthur Groves set about producing a metric version of Len Mason's classic small traction engine design. There were a few dimensions missing, and the grouping of components was not easy to follow. We asked Julius de Waal if he would like to have go at re-presenting Arthur's design in a way more suited to publication. He agreed, and with astonishing speed re-worked things in Solid Works.

“Castings have been available for many years from several suppliers for the original imperial version and they should also be alright for Metric Minnie. However, as Len Mason pointed out when introducing the original design, there is no reason why most of the parts should not be fabricated.”


I started the project in February 2015 and completed the build 01 March 2017 ( except for leak testing and final commissioning). Pressure test of the boiler was done at the early stages and that went well.

Prior to this build, I had no experience in either model building or machining. I have had an interest in model steam engines since I was a little boy, when I was shown a small steam engine working with a methylated spirits burner, and I pretty much forgot about it until two years ago! I did not know at the time  what a large learning curve this would be. I must be honest, I chose this project because I was very lucky to be able to get the plans from Julius De Waal, and the fact that if I could pull this off, I may learn something about machining! I also managed to get a copy of the original book published by LC Mason from 1969 - which did come in handy from time to time, more for the explanations than the drawings - Julius's drawings are perfect for the build.

A lot of Youtube videos and website searches gave me both the basic knowledge and the inspiration to start the build - after seeing some of the amazing models that are out there.

Areas I had to do some really quick learning were::

1. Silver soldering - I had done plenty of soft soldering before being an electronic engineer but never any silver soldering - this stuff is absolutely awesome! The boiler presented me with probably my biggest challenge - soldering the entire thing together and making sure it did not leak was probably my biggest achievement - and boy did it feel good when it was completed!

2. Working the copper (dished ends, tender etc)

3. Hardening of tool steel (for various small parts like the lubricator ratchet wheel and the gear hob)

4. Machining - all aspects from tool grinding to sharpening, to well, everything really…

6. Acme thread for steering - had to make a hob for this, which I had never done before and after a few tries I eventually got it right.


Biggest challenges

1. silver soldering the boiler - had to scrap the first one due to the silver solder types I initially used - got some good advice from a few model makers which helped tremendously.

2. feed pump from solid piece - this was quite a challenge due to its shape. By this time I was able to do it right first time.

3. crankshaft was surprisingly easy - I probably took twice as long as a machinist but - so what.

4. most laborious (boring) was the making of the firebox stays from bronze and the wheel strakes

5. It was a little annoying always having to change between the lathe and mill on one machine so I will probably be looking to get a small mill in the future.

What's left

I need to do the final testing and tuning and then a wooden base of some sort for display. Although I did modify Minnie to run on a gas burner, It will run on coal if necessary, but for the moment gas will do.


Tools

The Emcomat 7 lathe and Mill combo was used for the entire build, and I must say, this is a magnificent little machine for hobbyists. It's got a great range of speeds and feeds, although at times I would have loved a larger mill.


Drawings

All the drawings were obtained from Julius De Waal. I used the book by LC Mason predominantly for build order, commissioning, and general knowledge on the build.


Front wheels and hubs

All the wheels were machined from aluminium - I tried to use only materials that would not rust as far as possible, so brass, bronze, copper, stainless steel, and aluminium were my materials of choice. There were a few cases where mild steel, tools steel or cast iron were used - more about this later.

Some of you machinists out there are probably cringing at the removal of  stock from the bar. stock using a boring bar, but hey, my first bit of turning - I still had a lot to learn!


Machining the wheel hubs:


Marking the holes for the spokes using a wood former with a centring pin - the spokes were laser cut.

One wheel done! Decided to use screws instead of rivets due to my absolute lack of riveting experience.
More to come…



Part one here  Part two  Part three  Part four  Part five  Part six  Part seven  Part eight 

Part nine  Part 10