Let’s get 4561 rolling
Having completed the assembly of the extension frames and cylinders with all the bolts fitted and tightened down the opportunity was taken to try the pony truck in position to confirm clearances would allow truck to swing adequately. Although the extension frames were thicker their profiles should have been unchanged but the lower bends at the front of the cylinders were more generous than desired. The photo shows this bend on LH frame highlighted to show lack of clearance from pony truck (light green).
The spare metal was removed by hand grinding both LH and RH frames to the required shape.
The next step was to try the complete extension frame assembly (which was still upside down) in position in the main frames. Using the shop overhead crane it was first lifted over to a clear section of the shop floor :-
With care it was lowered down to the floor resting on the back of the extension frames :-
These photos show the top of the smokebox saddle and the cylinders. By care in lowering and moving the crane away from the camera the whole assembly was slowly turned over to rest on the bottom of the cylinders on the floor. This allowed the crane slings to be adjusted for the next lift.
The second photo shows the assembly having been lowered into position within 4561’s main frames.
Nuts and bolts through the main and extension frames behind the cylinders and a frame stand to support the front of the frames enabled the assembly to be levelled and the crane slings removed. To judge appearances the opportunity was then taken to put 4561’s smokebox on its saddle.
With the extension frames and racking stretcher finally fitted in position on the cylinder block it was necessary to make and fit all the bolts and nuts needed for security. This photo shows the work in progress.
At this stage the racking stretcher plate has been bolted to the cylinder block with the corner angles either side bolted through their respective extension frames. The remaining extension frame bolts are being inserted and when fully driven in will be secured with the nuts that can be seen ready in the centre of the stretcher.
When a batch of fitted nuts and bolts is required it is usual to cut lengths of bar steel as blanks as in this photo. These can then be machined to cut and form the screw threads to fine limits depending on the type of fit required. Ideally the bar steel is supplied as a hexagon shape the size needed.
This photo shows a typical set up for a bolt being machined in a screw-cutting centre lathe. The head of the bolt is held in the rotating lathe chuck on the left, the other end of the bolt blank being supported on the tailstock centre. In between the cutting tool mounted on the lathe saddle tool post is traversing to the left as it profiles the shank of the bolt.
With the extension frame assembly almost complete attention has turned to the leading pony truck. The frame transverse assembly seen is to straddle the leading wheelset being ‘steered’ by the two arms to the left. In checking the condition of the main securing bolts these were found to be worn out and are being replaced. A reject bolt is seen on the RH arm with its replacement in the frame above.
A close-up of the defective bolt. It can be seen that the screw thread is severely worn and not capable of providing a strong fastening with its companion nut when fitted and tightened.
Having corrected the pony truck frame the opportunity was taken of setting it up in position in the main frame assembly as shown. It will be seen how the rear ‘steering arms’ are coupled to a pivot block mounted on the front horizontal frame stretcher. This block needs to be securely mounted to withstand the shocks in will experience when 4561 is in traffic.
When examined this block was found to contain badly worn bolt holes and signs of previous repairs symptomatic of having been allowed to remain in service with loose bolts. The mounting face is seen in the photo. and shows the variations in sizes of the four corner bolt holes. For rectification this block has therefore been sent to specialist welders experienced in the recovery of old cast iron castings. These holes will be filled in before being re-drilled the correct size in the right places.
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.
Having reduced the thickness of the extension frame plates where needed they were then set up flat on the milling machine table to create a curved profile where the thickness had been changed. This can just be seen above the lower handwheel. The machine spindle below the upper handwheel is fitted with a profiled milling cutter to generate the shape required.
This photograph shows the profile milling cutter in action during the early stages of this machining.
Having completed the shaping of the extension frame plates the next step was to drill each plate ready for where the 4561’s front buffer beam and leading pony truck frame stretcher will be fitted.
The 8 holes on the left will be used for the buffer beam angles and the 11 holes centre and right are for the stretcher.
The all new pony truck stretcher is tried in position against one of the extension frame plates fitted to the cylinder block to confirm alignment and dimensions are to drawing. The team has fabricated the stretcher from a central casting bolted into an assembly of steel plates and angles riveted and/or welded together. The frame plate mating faces have been machined to ensure a good fit between the 2 extension frame plates to ensure they are supported the correct distance apart.
This photo shows the assembly so far from the rear. It also shows the new rear cylinder covers in position on each cylinder.
The next stage was to fit the second extension frame plate in place as seen in the next photo. when the whole assembly of cylinder block, extension frames and truck stretcher was being checked to ensure all dimensions and alignment were correct.
A lockdown challenge for you:
This photo is taken from the front through one cylinder and shows the rear cover in position at the back. The central hole is where the piston rod will go. Bearing in mind that the cylinder block assembly is upside down what are the two holes to the left of the piston rod for – one in the back cover, the other in the cylinder wall?
As can be seen a frame extension (orange) is not simply a flat piece of steel plate. It is profiled to fit beneath the cylinder block but in front of that it has to be cut away to clear the leading pony truck wheels before being shaped to fit the front buffer in due course. With the cylinders upside down on the floor the LH extension is seen in position having been aligned and fitted to the block ready for all bolt holes to be reamed ready for the securing bolts to be made.
This view of the front of the extension frame shows how it is not part of a flat plate but has also to be tapered in thickness from the front of the block and joggled inwards to increase clearance for the pony truck wheels. This part of the work was done by our supplier. Apart from not wasting steel the reduction in thickness helps to keep weight distribution under control.
At the back of the cylinder block the frame extension is deeper where it will be bolted to the main frame plate in due course. In the photo. this section is still full thickness but this has to be reduced in order to provide clearance for 4561’s leading sandbox which will be fitted between the frames. This machining has to be finished in such a way as to minimise the possibility of creating any stress raisers that could cause frame cracking under heavy shunting impacts. The old extension frames are shown in the next photo. where it can be seen how this reduction in thickness has to be blended into the main part of the extension frame plate.
The old plates do show evidence of past cracking and bending under shunting impacts and the new plates are being thickened in this area to minimise this possibility in the future.
This photo shows the back of the other, R.H. frame extension set up on our large milling machine for the thickness to be gradually reduced in a series of steps using a slab mill. Once this has been done down to finished size the plate will be laid down flat on the machine table to be profiled to removed the cut edges and provide a smooth transition from the thinner section to full thickness.