Looking back at the lockdown challenge from a couple of weeks ago:-
The central hole is where the piston rod will go. The hole to the left in the back cover is where the anti-compression valve (cylinder safety valve) will be fitted to the outside; the hole in the cylinder wall is where the cylinder cock (cylinder drain valve) will be fitted outside when 4561 is assembled.
Having completed the milling of the frame extensions the inner end of one is shown where any rough edges or machining marks have been finished off by dressing (de-burring or removing sharp corners from) the plate edges and around the bolt holes.
Each plate was then set up on the vertical milling machine in order to spot face a number of the bolt holes to a common depth for when each extension frame is bolted to its associated main frame plate. This is to compensate for having increased the extension frame thickness in order to minimise the possibility of cracking in service while maintaining adequate clearances between the fixing nuts and bolts and the leading pony truck.
This photo. shows the fully machined LH frame extension in position on the cylinder block. It can be seen that it is supported on the underside of the smokebox saddle and butted up against, and to be bolted to the back of the cylinder casting. The spot faced holes may be clearly seen.
A view taken from behind the assembly shows the profile that was machined on the inner end of the LH frame extension. This has been done to ensure adequate clearances are left between the frame extensions when finally assembled to accommodate 4561’s leading sandbox between the frames.
With the machining of both plates completed both are now in place in the cylinder block in order to check clearances and to confirm the dimensions between them for manufacture of the racking plate.
This is a horizontal frame stretcher to be fitted tightly between the frame extensions and bolted to the underside of the cylinder to provide reinforcement of the joint between the two cylinder castings and assist rigidity of 4561’s main frame assembly at the front where high stresses will have to be endured in operational service.
This photo. shows the racking plate in position fitted between the frame extensions in order to mark out and drill the bolt holes between it and the cylinder castings.