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A web-site by Rob Speare

   

Catching up with the 'Leader', a unique model of Bulleid's Master Class   -   Part 2.

Words by Kevan Ayling.          

Main Chassis

I always reckoned that 60% of the total work in building this locomotive was in the power bogies and that the main chasis, boiler and topworks would account for the other 40%.  With this in mind a start was made on a drawing of the main chassis.  This scaled out at 6ft long but was only 3in. deep on the fish-bellied central section which scaled at 56in. radius.  For this reason, I decided to have the mainframes laser cut from 10mm black steel.  The drawing was duly completed and taken to the laser cutting firm, causing amusement amongst the staff because the only paper I had available to make a 6ft drawing was a roll of 'Fred Flinstone' wallpaper.

A week later I collected the mainframes and was very pleased with the quality.  They only cost £30 each, the firm supplied the steel and the finished frames were free of distortion.  The only downside became apparent at a later stage when I had to drill some 3/32in. holes on the top edge and found the cutting process had left the suface very tough indeed.  This was compounded by the necessity of drilling said holes by hand, due to the length of the frames.  However, once the position and size of the stretchers were determined and fixed, I very soon had a chassis as tall as me !

The bogie pivots were fitted next and consisted of two 5in. diameter cast iron turntables, bolted to two 9 1/2in. lengths of 5/8in. diameter stainless steel bar, relieved in the centre to provide a flat bolting surface.  Each end of this bar was then fitted with an Oilite bush bearing bolted to each side of the chassis.  This allowed each turntable to tilt fore and aft, the lateral turning movement taken care of by the 1in. dia. spigot machined on the underside of the turntables.  At a later date I had to introduce a little play in one of these pivots to stop the front bogie derailing.

This is due to the length of the locomotive and our far from perfect miniature tracks, where the front of the loco can be on the super-elevation while the rear is still on the flat.  So with that in mind my next project, a Kitson Meyer 2-8-8-2, incorporates a spherical bearing on one of the pivots.

Now that I had a chassis and two nearly complete power bogies weighing about 140 lbs each, it was time to get the arc welder from under the bench and construct a trolley on which the embryo loco would live from this point on.  The bogies were fitted with my own system of cam operated drain cocks, placed on the trolley, and the main chassis dropped on.  Then more steelwork welded up and bolted to the floor of my van before setting off to the track to clearances, etc. and have a photo session !

Superstructure

The next task was to decide how to build the superstructure.  This was accomplished by adopting bulkhead and stringer construction.  Six bulkheads were cut and profiled to the body shape.  They were then all clamped together and two 5/16in. square slots milled in each side.  When separated and fitted in their respective positions along the chassis, the slots allowed the 5/16in. square stringers to fit flush, thus forming a sturdy framework on which to fit the 1/16in. thick mild steel body panels.  This thickness was chosen so that the compound curves caused by the narrowing of the chassis front and rear could be blended in by judicious use of the angle grinder.

To my dismay, I found on checking the reams of works drawings that I had no useful drawing of the cab ends, so these had to be made using a cardboard template made with reference to photographs.  The body panels were all bent on a large flypress using tooling made specially for the job.  They were then secured to the stringers and the angle fitted to the tops of the frames using a large quantity of 3mm countersunk machine screws bought by our Club secretary as a job lot at a boot sale.  By the time all the panels were finally in position I had tapped a couple of hundred 3mm threads.  Worse was to come.  In order to try to retain a scale appearance, the main side panels covering the boiler were secured with no less than 36 8BA bolts per side because of course, these panels had to be removable.  The tank section is sealed with several coats of car underseal, although it can be removed by undoing four 6mm stainless capscrews.

At the time the body was being assembled the smokebox had to be made and fitted since one of the bulkheads had to be bolted to it.  This is not conventionally circular but square, MIG welded from 3mm mild steel plate.  The top was made removable allowing the regulator, superheaters and associated pipework to be installed without the usual skinned knuckles, etc.

Boiler

I deliberately left construction of the boiler until most of the locomotive was complete.  This ensured that it would get at least one season's running, plus the inevitable steam trials such an usual design would demand.  I started by making a full size drawing guided by the Works boiler GA.  Full use was made of a CAD system for this drawing and what finally emerged from the printer was a boiler very similar in shape and size to the Bulleid/BR Pacific but with a larger firebox and a shorter barrel.  Obviously, the dryback firebox as used on the prototype was not entertained.

Construction is of wholly silver soldered 3mm copper.  The barrel is tapered and rolled from sheet, there are 240 stays in the firebox made from 3/16in. and 1/4in. copper rod.  Included in this total are four hollow stays in the backhead (for securing the fire door frame) and five in the throatplate (for the stainless steel arch).  These were turned from 5/16in. drawn bronze.  To complete the total there are also two 3/16 in. longitudinal stays also made from drawn bronze, these were pre-tensiled via adjustable nipples before the backhead was finally brazed in.  The barrel has twenty-six 1/2in. flue tubes and four 1 in. superheater flues, all in 16 gauge.

The firebox has a combustion chamber and a 52 sq. in. grate.  There are four 8mm stainless steel tube radiant superheaters.  As there is no cleading the finished and tested boiler was sprayed satin/matt black.  The regulator is mounted in the smokebox and is a modified 15mm Crane ball valve, bought for less than a fiver at my local plumbers merchants.  The specification in the Crane catalogue showed it to have a bronze body with a stainless ball turning in a PTFE liner.  So I thought I would give one a try, and it has operated perfectly.  The valve is controlled from the cab via a 3:1 bevel gear.  The degree of control is excellent as, of course, it is unaffected by steam pressure, and it doesn't let by !

Well, all that remained was to get the steam from the regulator to the cylinders, and the exhaust back to my version of Bulleid's multiple jet blastpipe.  So it was off to the hydraulic hose firm and after a chat with the boss I returned with four tailor-made stainless braided, PTFE lined flexible pipes good for 260 deg. C.  After fitting, everything was tested as far as possible on air and the locomotive was ready for it's first steam trial.

Steam Trials

A cold Sunday morning in December 1998 saw me lighting a fire in the far from complete Leader.  Several Worthing club members had turned up to watch, including at least two with video cameras.  Things went well at first, the boiler seemed okay, there were no leaks from any of the fittings; so far so good.  So I cracked open the regulator and started warming the cylinders.  I was soon rewarded with condensate from all four cylinders, then disaster struck.  It seems that I moved the loco too early in order to clear the condensate from all eight cylinder ends.  The result was that three of the four pins on the swinging levers in the Stephenson valve gear sheared, leaving me with a one cylinder loco !  Even so, it went if I gave it a push (and at least the boiler had passed it's steam test).

Once back in the workshop the bogies were removed (one at a time) and the valve gear examined.  I had used 3/16in. silver steel shafts and 1/16in. roll pins to secure the swinging levers.  This was clearly not strong enough.  So, back to the drawing board for a re-design of this part of the valve gear.  The motion plate bearings were dismantled, the shafts removed and discarded and replaced with 9/32in. silver steel.  These were then secured with 1/8in. solid high tensile pins.  Sounds easy ?  Well, due to the previously mentioned zero accessibility, this extra work took another two weeks of precious spare time to complete.

Another cold Sunday morning and back to the track, this time with no video cameras watching; the Leader glided effortlessly around the track.  This resulted in the few spectators present rewarding the builder with a glass of champagne and a big cigar !

By this time it was mid-January so I decided on a timetable of fortnightly steam trials which would hopefully iron out all the bugs by the spring.  The plan was to persuade as many club members to turn up every second Sunday in order to gradually increase the load to see what the loco would pull, and more importantly, to see what would break first.  Well I didn't have to wait long, the load was about 18 adults when a loss of power and a huge cloud of steam brought the train to a halt.

As the loco was running minus it's side panels it was soon apparent that there was a problem with the flexible steam pipe to the front bogie, the PTFE liner having broken down completely.  A replacement was obtained and on the next trial, again with a similar load, the pipe gave up in about 12 minutes !
I don't know what temperature the superheated steam was reaching but it was obviously more than the 260 deg. C. rated pipes could stand.  Curiously the longer pipe run to the rear bogie was okay.  Perhaps the longer run meant the steam had cooled enough not to damage the PTFE ?  The PTFE liner in the regulator taking wet steam has always been okay even though it is in the smokebox !

What to do now ?  A further visit to the hose firm and another chat with the boss seemed necessary.  This time he produced a catalogue from a specialist hose firm, and I was shown a flexible stainless steel pipe guarenteed to withstand 600 deg. C.  It seems that this stainless tube is made for the chemical and food industries and consists of a braided outer covering over a concertina form inner, the unions being welded on.  These pipes can be made to any length according to customer requirements.
I duly ordered two, one to replace the failed front pipe, and not wishing to take any chances, one to replace the still satisfactory rear pipe.  The PFTE lined exhaust flexibles were left in place.  All four flexible pipes were terminated in 1/2in. BSP unions.  To date these pipes have never given any trouble.

Consummate Ease

Well there it is.  The locomotive was eventually completed, painted and lined out.  It has participated in two Southern Federation rallies, two I.M.L.E.Cs, a couple of Open Days and numerous public running sessions at the Worthing Society's track, and (until recently) has never given any trouble, but I must admit I do breathe a sigh of relief after each steaming !  It is of course, not an exhibition model, and was built to pull lots of people, which it does with consummate ease.  But it seems a shame that, after many years work, the children at the track on public running days still ask their parents if they can ride behind the diesel !