Building the Merchant Navy class 'Ellerman Lines'.

words by John Heslop.

                                              
Among the reasons for deciding to build a 5" gauge Merchant Navy was that I like 3 cylinder locos, and the prototype incorporated many interesting and unusual features.  This is first Bulleid design I have built, and it has a certain get-up-and-go appeal.  My brother-in-law sailed with 'Ellerman Lines', so this seemed a natural choice, especially as the original is on display, albeit in sectioned form, at the N.R.M. in York.

I am working entirely from Works Drawings, and incorporating as much authentic detail as possible, including some details which will be hidden forever once the model is completed.  For this I obtained drawings (at a price) from the National Railway Museum after first viewing some 80 likely drawings from their collection, which took a couple of hours to go through.  I ended up purchasing copies of most, back in August 2004.

In some ways, using works drawings is easier because all the parts are shown, though it still takes occasional trips to the N.R.M. to see the sectioned 'Ellerman Lines' to understand it all.
I tend to scale the dimensions by dividing by 11.3 and writing in pencil on the drawing.  I have not so far used any castings, everything has been fabricated or machined from solid.

                                              
To create each driving wheel, a turned disk of mild steel was set up on a rotary table in the milling machine, and eight segmental cavities were machined away.  To finish the sloping sides, the end of a standard 3/16" cutter was ground to 30°, making 50 thou deep incremental cuts, the small ridges easily taken out with a small file.  The exercise was repeated on the other side, except that as the inside face is conical, the rotary table was slightly tilted.

Then sixteen 1/8" thick m.s. segments shaped like 'Kraft cheese' were cut out with edges angled to fit the hollows, sitting 25 thou proud of the surface; and brazed to each wheel.  After cooling, the wheel was set up on the rotary table and using a 5/8" cutter a 40 thou cut gave a flat surface.  A shaped cutter was used to carefully machine a curve in each end of the now 75 thou thick brazed inserts, to reveal the hollow segment.

Finally the tyres made from EN24T 55-65 tons tensile steel with an 8 thou interference fit, were heated on firebricks using a propane torch, and the centres dropped in.  The result is a relatively light set of wheels with the distinctive Bulleid recesses on both sides; about 4 days work per wheel.

                                              
The crank axle is in one piece, machined from a 4" diameter billet of EN24T.  The driving wheels are press fitted and keyed to the axles, unusually the key on the Merchant Navy is set at 30° from the crankpin, in the model this was achieved by setting a slotting tool up in a jig.

The centre axle eccentric strap follows full size practice to good effect; the flange is on the strap which has the effect of retaining oil better.

When British Railways rebuilt the class, although the outside cylinders were retained, a new inside cylinder block was used as the original had outside admission valves driven by a rocking shaft.  The new cylinder block also forms the lower part of the smokebox.

The outside cylinders are machined from 4" diameter grade 17 continuously cast iron, using the vertical mill in the lathe as a diving head; the bronzy colour comes from heating in a domestic oven in order to shrink in the valve liners.  The photo shows the end cover studs holes being tapped 8 b.a. using a device to to this safely.  This spindle is a running fit in the chuck, and the large ribbed wheel allows control while the tap stays in line avoiding breakages.

The inside cylinder started as 6" diameter mild steel (EN3B), with shrunk in cast iron liners for the main bore and the piston valve.

The leaf springs and coupling rods have been made, but of course there is still a long, long way to go.

                                              
Painting will be difficult, as I really don't want to take everything apart, so it may be a case of careful application with a brush.  At the time of writing, I have just made the steam operated drain cocks; next is the front buffer beam, more frame stays and the brake gear, so there's plenty to keep me occupied.

My machines include a Harrison milling machine, and a Myford ML7 lathe bought new for £48 and 5 shillings.  In 2005 I bought a digital read out for the milling machine; but I do not have C.N.C.

                                              
Editor's notes:   Below are a couple of pictures showing the recently completed buffer beam and steam drain cocks referred to in John's text.  I hope to bring an update when John has made more progress; but as he says, there is a lot of work ahead; the pony truck is quite complex, and he still has another 6 wheels to produce, just for the locomotive.

Where possible John machines virtually everything from solid.  This includes the steam operated drain valve bodies shown below, though quite how, I haven't worked out yet.  Where fabricated parts like stretchers are made from steel components, John prefers joining with Sifbronze as he reckons this gives a more reliable joint than silver-soldering.