Catching up with the 'Leader', a unique model of Bulleid's prototype.
Words by Kevan Ayling.
I have been a long-term Bulleid fan, and had constructed a rebuilt Merchant Navy in early '80s, so I decided to have a crack at the 'Leader'.
I bought a copy of Kevin Robertson's excellent book 'Leader - Steam's Last Chance' which I read from cover to cover, but remained unsure as to how I would obtain drawings and other details necessary for me to commence construction.
Following a chance conversation with a visitor to the Worthing Society, a 1/2" thick wad of of A3 size photocopies of Leader works drawings landed on my doorstep some days later.
Now I had to build it !
It soon became apparent that if I was to have a successful locomotive, I would have to make substantial changes.
I am not saying it would be impossible to build a 5 in. gauge version to works drawings, but I think it's chances of success would be slim indeed, bearing in mind that the expertise of two major railway workshops could not solve all the problems inherent in the full size design.
I began by making a full size bogie drawing from the works drawing.
A side elevation of Bulleid's Q1 cylinder and valve gear was obtained from a book and enlarged to approximately 1" scale by photocopying, then cut out and laid on the bogie drawing.
I could see that this would work as the Q1 chassis and Leader power bogie are fairly similar in size.
My only problem was where to put the piston valves; below the cylinders would take up room I had provisionally earmarked for the lubricators, and above would involve raising the floor in both driving cabs.
I eventually settled for the latter as in practice it didn't show, and allowed me to more or less to copy the Q1 cylinders and motion.
A length of 20 x 90mm black steel was bought, and worked started on the four power bogie side frames.
On the prototype these were of hollow box section fabricated by welding, but I decided to make them from solid.
Two weeks and a bucketful of swarf later, the horizontal mill had transformed the four 28 1/2in. blanks into acceptable copies of bogie side frames.
After clamping and drilling for stretchers and cylinder blocks, etc. the frames were taken to a small engineering concern where the 24 holes for the axlebox pedestals were drilled in the 20mm thick lower edge of the frames using a Bridgeport turret mill with digital read-out; 100% accuracy at this stage being essential !
The axleboxes were tackled next.
These are mild steel fabrications silved brazed on a specially made jig, three components per axlebox, twelve axleboxes !
They were then bored for ball-races, again using a jig made for the purpose.
The 48 bronze bushes needed were then pressed in and, with all this repetitive work completed, it was with some relief that each axlebox was slid nicely on it's pair of 12mm stainless steel pedastals.
The patterns for the wheels and cylinder blocks were made, and after consultation with [the late] Mr. Norman Spink [then of Chesterfield] they were duly despatched to darkest Derbyshire.
In the intervening weeks before an unliftable sack of castings arrived on my doorstep, I busied myself with such mundane items as frame stretchers, buffer beams and the like.
Work was also started on the four sets of Stephensons valve gear and although not all were made at the same time, a year or so passed before the tin of oil under my bench (I have rusty hands) contained four complete sets.
The wheel and cylinder castings duly arrived and work was started on the wheels.
The Harrison L6 made short work of these, and once the axles were turned I soon had two rolling chassis.
One bonus accruing from building the Leader is that the external chain drive removes the need to make coupling rods, or quarter the wheels.
The only quartering necessary was setting the built-up axles to 90 deg., simply accomplished with a square !
Once the lathe became free after turning the twelve driving wheels, it was time to fit the boring table and make a start on the cylinder blocks.
First, all surfaces other than the 'B' shaped undersides were flycut to size using both the horizontal mill and the lathe.
They then went onto the boring table and were bored out to 1 3/4 inch diameter.
The piston valve bores were machined to take Les Warnett's 9F piston valve liners which I used on my 2-8-2 and are excellent; in fact my design for the exhaust ways on the Leader cylinder blocks was based on them !
A little more time saved...
Each liner was machined and put on a mandrel in the dividing head and indexed for nine 3/16in. dia. ports.
These were then drilled and filed out square with a needle file.
Sounds easy ? Well, 8 liners = 72 ports = terminal boredom.
Seriously, the only way I could face this job was to square out two or three each morning before work.
It made little or no noise, and first thing in the morning (for me at least) reduced the likelihood of mistakes.
A word here on the bore and stroke.
The 1 3/4in. bore was chosen in order to provide a power output approximately 1/3 greater than my 2-8-2.
It must be remembered that I was in uncharted regions with this locomotive, and that for it to be competitive in IMLEC
it had to be as good as or better than the 2-8-2.
Once the cylinder blocks were bored, the inlet and exhaust ways were drilled and manifolds made, shortly followed by pistons, rods, covers, crossheads, slidebars and motion plates.
Each rear cover has four slidebars made from 5/16in. square silver steel, the crossheads being made from cast iron.
Each slidebar was reduced to 3/16in dia. for 1/2in. and threaded 2ba for 5/16 inch.
Each motion plate was cut from 6mm black plate and the eight slidebar locating holes drilled on the vertical mill, 100% accuracy being essential.
On final assembly the liners were assembled with a smear of Hermetite and bolted up; they were then reamed in position with a brand new adjustable reamer bought and kept solely for this purpose.
Pistons, rings, rods, covers, slidebars, crossheads etc. were all assembled, then the motion plates were fitted on the ends of each set of eight slidebars and nutted up.
The entire cylinder block and motion plate assemblies were then put in the frames, aligned, and the blocks bolted in with 6mm capscrews.
The holes for the motion plates were drilled, tapped and bolted last.
Next, the valves were tackled.
I always use separate cast iron heads floating on collars silver soldered on a 3/16"in. stainless shaft, this enables me to rough turn and part off all eight valve heads (plus some spares !)
These are then mounted in turn on a turned-in-position mandrel and ground to size using a toolpost grinder.
This method ensures a really good fit in the previously reamed liners.
No rings are necessary, a couple of oil grooves are enough.
Once the cylinder blocks were complete it was time to assemble the valve gears.
The eccentrics were made and pinned together in pairs at the correct angle of advance, a jig being made to ensure that all four pairs finished the same.
They were made and fitted at the same time as the crank axles were fabricated.
All the pins were turned from 5/16in. silver steel, the bearing diameter being 3/16in., they were then drilled and tapped 6BA and hardened.
When fitted in the forked ends the length was adjusted (on the belt sander) to finish a few thou short so that on assembly, a 3/16in. 6BA Allen bolt and washer just nipped them so that they could not turn and, more importantly, couldn't fall out !
It wil be appreciated that a pin falling out in service on a loco as complex as Leader with zero accessibility would be a major disaster, to the extent perhaps to persuade the builder to take up a different hobby !
The accessibility aspect has always worried me, and became painfully clear on the first steam trials when three of four pins on the swinging levers sheared !
More on that later ...
The chain sprockets caused some headscratching.
I tried without success to obtain a second-hand 8mm Reynolds chain sprocket cutter.
Buying new was an option, but the cost was unrealistic for a one-off job (are they gold-plated ?), so I modified commercial made sprockets.
These were brazed to a substantial backing plate and bored to fit a collar mounted on the axle ends, each spocket was then secured to it's collar with six 4mm capscrews.
Finally, after more than three years of spare time, the valves on No. 1 bogie were adjusted, some hastily thrown together pipework connected, the compressor switched on and the wheels began to turn !
This moment (for me at least) makes all the hundreds of hours standing in a sometimes cold workshop all worthwhile.
Once both power bogies were running on air, my thoughts turned to the brake gear.
This is very complex, with clasp brakes on each on the twelve driving wheels, 24 brake blocks in total !
There were also 28 forked ends to be made from 5/16in. square bright steel.
These last items were made in one batch, and made easy by borrowing a self-centring 4-jaw chuck.
Likewise, the brake blocks were made in one batch.
The blanks were profiled and slotted on the horizontal mill and then radiused in a jig fitted to the rotary table on the vertical mill.
Although vacuum brakes were fitted to the prototype, I decided on air brakes for the model.
Tests have shown that as little as 10 psi is enough to lock the wheels.
At the time of writing, the compressor and driver's brake valve have yet to be made.
The lubricator drives took a bit of working out; I eventually settled for a drive taken via a small crank from the leading axle on each bogie.
Click here for Leader Part 2.