Locomotive frames – With the engine’s frames erected, all the major frame stays, brackets, horn blocks, axle boxes & buffers have been cast and fitted using around 1,000 driven bolts.  With the tender tank undercoating complete it has been possible to remove the wheelsets from under the engine frames. This has permitted fitting of the remaining driven bolts and cold turned rivets in the outside motion brackets and the spring hangers.

We now have the profiles for the “shelf” under the back of the cab and Ian Matthews has started making some special tooling to facilitate hot bending of the 20mm thick plate to form the flanges on each end which mate with the outer Cartazzi frame plates. Normally, shaping like this is carried out cold using a brake press forming a series of small bends, however, the radius required in this case is equal to the thickness of the material necessitating the bending to be undertaken at red heat. In this condition the metal, which is 20mm thick,  will be sufficiently pliable to be bent using form tools in our 30ton press. As it is important that the finished article is a good fit between the outer frames, doing the work in house as opposed to by a plate bending firm will enable subtle adjustments to be made to ensure a tight and parallel fit.

The “shelf” bending jig – Leigh Taylor

When fitted to the frames, the shelf will complete the frame structure and enable Ian to start fitting the electrical trunking under the cab which is relatively complex as the 3D CAD view shows.

3D CAD view of the trunking on the shelf. – Alan Parkin

Tender – Steady progress with the tender frames continues at Ian Howitt’s works at Crofton. The initial machining of the hornblocks has been completed, the hornblocks dispatched to NVES in Darlington for welding on manganese steel liners (NVES, thanks to our activities over the years, maintain a welding procedure for welding manganese steel to cast or mild steel), and are now back at Crofton for final machining. Many details for the brake linkage and hand brake mechanism have been made including the brake cross stay and brake cross shaft.

Tender hornguides with manganese steel liners welded in place. – Daniela Filová

The hornguides being set up on the tender frames. – Ian Howitt Engineering

Alan Parkin has now produced several manufacturing drawings for the approximately 140 individual components which are required to fabricate the cylinder block. At the same time David Elliott is building up the scale 3D printed model to determine the best construction sequence to ensure that all seams can be fully welded. The intention was to issue a “request for expressions of interest” to a number of fabricators during December. The target is for an almost full set of manufacturing drawings at the end of January to enable shortlisted companies to quote for the whole job.

The latest cylinder CADs and the assembled scale model of the cylinder block. – David Elliott

In parallel with discussions are at an advanced stage with a specialist company in CFD (computational fluid dynamics) to model the steam flow through the cylinder block to ensure that we do not have avoidable pressure reducing features to enable us to optimize the detail of the design – there is little scope for significant redesign of the block as the steam and exhaust passages are already as large as practical within the tight limits of the envelope of the block, however some gains may be possible through increasing radii on the inner corner of bends etc.

It is expected that this work will lead on to a more extensive model to analyse steam flow from the regulator to the blast pipe which will assist in fine tuning the profiles of the cams and the diameter of the blast pipe tops.

A further use of CFD will be look at smoke lifting. The original P2 No. 2001 Cock o’ the North did not have smoke lifting issues as even at low powers, as students of the history of the P2s will be aware, but the second engine, No. 2002 Earl Marischal (as first built with Walschaerts valve gear and the same smoke box and smoke lifting plates as No. 2001), immediately suffered from drifting smoke affecting the driver’s view resulting in early fitment of large and rather ugly smoke deflectors. The main difference is that piston valves open and close the exhaust valves gradually, with very little cross section for gas flow at the start and end of each event resulting in the exhaust appearing to “leak” from the chimney encouraging it to stick to the boiler top, which with the cross winds and the Coanda effect draws the exhaust down on the leeward side of the boiler. By contrast, poppet valves open and close to full area quickly resulting in sharper edged exhaust beats. Whilst not a problem on No. 2001, with all the computer modelling to optimize efficiency and power, there is a risk that the “squareness” of 2007’s exhaust beats may end up less sharp. If a smoke lifting problem is identified it is anticipated that with 80+ years of aerodynamic development since No. 2002 appeared, some relatively unobtrusive aerodynamic fences or strakes could be applied to solve the problem.

A short-term lack of Solidworks drafting capability has been identified and steps are in hand to recruit addition resources to cover this to expedite production of the detailed drawings for the valve gear. Low risk items such as reversing gear, return crank gear boxes and cardan shafts, and casting and machining valve covers can then be put into manufacture. In parallel it is intended to prototype a cam/follower/tappet/valve assembly and subject it to some fatigue testing before committing to a full set.

3D CAD view of poppet exhaust valve. – David Elliott

Cylinder drain cocks – Considerable progress has been made (mainly by Ian Matthews) in installing Alan Parkin’s cylinder drain cock design onto the frames. The design is closely based on that on Tornado to eliminate the use of Bowden cables (as used on the original P2s).

Cylinder drain cock actuating linkages. – Ian Matthews