Everything affects everything else
Waiting continues in respect of Crewe Heritage Centre’s approval for our visit to fit the cab footsteps, and for our drawing checker to return from holiday to pass off our frame stretcher and motion plate drawing so that we can activate the order for the latter. Hopefully they will both be cleared shortly.
Our dragbox is now in final draft, ready for review before submission for approval. The dragbox is a vital structural member, and as such interfaces with many other parts and functions. Lifting came up early on as Crewe used massive forged hooks to hook on the bottom edge of the buffer beam outside the frames and the equivalent on the dragbox. These forgings have no doubt long been melted down, but were hazardous in any case. I remember being warned to resist the urge to hasten out of Belt 3 pit in Crewe erecting shop after wheeling a locomotive while the crane lowered the hooks, which would crash into one another, perfectly timed to wallop the head of an unwary apprentice! Two holes for safety chains in the rear ‘buffer beam’ are made suitable for 30 ton lifting shackles.
More difficult was squeezing in the steam brake cylinder and brake operating crank, which needed quite an effort, but necessary as the LNWR arrangement had significant weaknesses. We are confident that that is good thanks to the stress analysis of various different load cases, from track twist to traction and braking forces by David Burrage. One image of this analysis is shown on the left, demonstrating how it is affected by a simulated collision force of 1000kN (100 tons) – at the drawbar. This is the same force that BR standard coach couplings can withstand without failure, so we have to demonstrate that our locomotive can withstand at least the same. Yes it can!
That leaves some of the proverbial known unknowns, such as pipe (and no doubt electrical cable) routing. Crewe got into a mess with its vacuum brake and steam heating pipes in particular. The two inch vacuum pipe was routed through swept bends and elbow fittings along and down through internal cab plating and the corner brackets before crossing from side to side under the rear of the dragbox. The steam heat pipe was nearly as bad. E. S. Cox complained about the cost of fixing leaks in the vacuum pipes of the Claughtons, but then neglected the simple and cheap works modification that would have fixed the problem. That modification would have been to replicate the arrangement of most narrow firebox locomotives and run all the pipes down the firebox back plate between the frames then backwards under the dragbox, which is what we propose to do. As can be seen in the CAD image on the right, there is room to route pipes this way. However, we still don’t know what pipes will go where under the dragbox, so rows of bolt holes are to be provided all round so that pipe brackets can easily be bolted up.
Expect some more news soon, and our autumn newsletter.