Or how to answer the ‘what next’ question

By Simon Janvrin

I recently completed the 2015 Polly course run by the Society of Model and Experimental Engineers (SMEE) at their headquarters in deepest Brixton.This wonderful Victorian London house, adjacent to some typical railway arches, is reminiscent of Mrs Wilberforce’s home in that splendid Ealing comedy, The Ladykillers. The house is packed from basement to rafters with everything model engineering, from huge lathes, through every Model Engineer magazine, to wizzy CNC gizmos. These are a few of my personal recollections of the course

Who is the course for?

If you are on your third LBSC locomotive, it is probably not for you (though I would defy you not to pick up some things of interest).

If you are a complete beginner, it will be quite hard. However, one of our group was such a person. He had no workshop, but had done the SMEE Basic Training Part 1 Course (Polly is Part 2) of which he gave excellent reports. Because of the reorganization of the SMEE workshops (which he needed to use) during the first half of our Polly course, he was late starting his engine. However, with perseverance and some time in another course member’s workshop, by the end he had a working model. So it can be done.

My own circumstances were that I had a reasonably equipped workshop inherited from my father, which included a large lathe. This, the story goes, had ‘fallen off the back of a German U-boat’ while it was being dismantled in Northern Ireland in the 1950s. Though my father built an Allchin traction engine over many, many years, I did not take much interest in such things until recently. Before the course I had built a few simple Hemingway tools and a Stuart S50 horizontal engine, and had acquired a Chinese mini-lathe. My sort of ‘beginner with a little bit of experience’ is probably the ideal starting point for the Polly course.

Course format

It is important to realize that the course is not ‘hands on’. That comes later when you go back to your workshop. Techniques are demonstrated by the lecturer to the class. This may not sound the best way to learn practical skills, but it is augmented by an excellent live video system (run by a SMEE volunteer) which projects a close up view of the proceedings on a screen behind the demonstrator. Tools and parts, finished and unfinished, are handed round for close viewing.

During the lectures/demonstrations, behind the students, sit a phalanx of SMEE’s ‘Great and Good’. Thus on tap is always a huge wealth of experience to contribute to the proceedings, and one soon learns that there are many different ways to do the same thing in model engineering. The general banter (and quite good jokes) of such experts is always entertaining. When one lecturer, with perhaps half a century of working metal, was asked how deep a lathe cut should be taken, he replied: ‘Enough to stop the lathe, then back off a bit’! Time, in those days, was money.

Polly as a learning exercise

SMEE’s choice of Tubal Cain’s Polly for the course was an inspired one.  Although it is the first engine, in the first volume, of Tom Walshaw’s (two volume) Building Simple Model Steam Engines, practically every model engineering technique is covered in some small way during its construction. Perhaps the best way is to follow the build through with a few photographs. Here is a Polly complete and a Polly in bits.

The course is divided into modules to show the construction of different bits of the engine. First comes the boiler. Throughout the course, emphasis is put on making tools to complete a particular task. Here are formers to shape the ends of the boiler, and later, the top and base of the burner.

The boiler introduces us to annealing and shaping copper pieces, and then silver brazing them all together. For most of us this was a new technique, and I certainly found that a lot of practice with bits of copper plumbing pipe was a useful start. It came as a surprise quite how much heat was required before the silver started ‘flowing’. But when it did, it was very satisfying. SMEE has boiler testing equipment, so you can check your joints.

Sheet metal work next, to make the engine firebox and base. Note the nice sharp corners on the base, made possible by milling a groove along the inside of the radius. However, a hacksaw will also work, and Polly can be built without a mill.  The firebox is formed around a tube (a bit of scaffolding pole seemed about right), and then it is soft soldered onto the base. The bolts on the base hold a piece of lead cast to the size of the base to provide stability when steam is up.

More metal bashing and silver brazing to make the burner. Neither seemed very easy when using thin brass sheet, and as you can see on the right, disaster was often just round the corner!

The boiler fittings are a nice turning exercise. They screw into brass bushings on the top of the boiler. Tubal Cain had only one fitting, the safety valve, but the extra ones in the SMEE version give more flexibility when attaching the steam pipe to the boiler and when filling the latter with water.

The breadth of the Polly course is shown here. Even though steam fittings only cost a few pence from the suppliers, we were encouraged to grind an HSS tool to form the nipple. All these little extras add to one’s model engineering skill base.

The safety valve is shown here. The ball bearing in the centre is 3/16 ins. The complete valve is on the left and an exploded one on the right. In the middle is is a small chuck fabricated to hold the ball bearing in the lathe chuck while it is drilled and tapped 10BA. One also learns how to form the spring using hard brass wire fed from the lathe toolholder whilst it moves under power feed.

Finally the heart of the engine. The cylinder is fabricated from brass, and involves drilling, reaming, turning and soldering. The piston assembly can be made in three different ways, turning in a chuck, turning between centres or fabricating the piston, con rod and big end separately. The crankshaft and flywheel are turned, the latter from cast iron, steel or brass. The engine standard and pipe work includes more brass work, sheet steel forming, copper tube bending and soldering.

At the end comes finishing and painting. How can a lecture on paint drying be interesting you might ask - but it can be at SMEE.  Assembly of the model follows, and then, with suitable excitement - STEAMING!

During the course you realize that most of the time in model engineering is taken up by planning and then setting up the part to be turned, milled, soldered or whatever. This means that making more than one Polly is not as arduous or time consuming as it seems.

And then you get really enthusiastic about it all, and this happens!

The one in the middle is a .63 edition of Polly (so I could use 28mm plumbers tube for the boiler). The one on the right is the fourth model in Tubal Cain’s first book, named Jenny Wren, and here I used 22mm  plumber’s tube for the boiler. But a cautionary note to anyone building such small engines.  I found they needed a lot of heat  (a small blow torch) to maintain running on steam.  I was told by another SMEE member that this was because the (relatively) thick plumber’s copper tube loses too much heat too quickly, and needs to be thinned (bored out or turned down).  Tubal Cain used some thin brass tube from a child’s telescope.

The last Saturday of the course coincides with the SMEE December competition day, and their Christmas get together. We Polly builders had a quick session on how to judge model engineering exhibits (by a very experienced judge) and then off we went to judge our own efforts. I thought my Pollys needed some sort of theme, so I raided my grand daughter’s doll box, and...

...Polly goes STEAMPUNK!

If this has whetted your appetite, I suggest you click here.