Let’s get 4561 rolling
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.
The next job was to make and permanently insert the fitted bolts and nuts for the cylinder joint. The cylinder block was then taken off the ‘coffee table’ and turned over to stand on the floor upside down as seen in the photo. One of the extension frame blanks has been placed where it has to be fitted when after machining.
Each end of each cylinder bore 5 studs have to be fitted to reinforce the casting around the steam ports. Three of these studs are shown during manufacture – the one with the plain section to be fitted across a steam port. The ends are finished with square sections used to drive the studs into position when the squares are then cut off.
This photo. shows one cylinder end with the 5 studs in position and the ends dressed off. 3 can just be seen within the steam port and 2 between the cylinder bore and the steam chest below.
A close up view of the steam port showing the studs in position.
This photo shows one new extension frame plate on the milling machine preparatory to being set up for machining to size.
This photo shows the old extension frames which have been retained to act as patterns for the machining. The new plates will be thicker to resist cracking and/or bending when 4561 is next in service.
Having set the cylinders up the first check made was that both castings were sitting flat on the ‘table’. This was done between each casting and the ‘table’ top using a feeler gauge which was 0.002” thick – i.e. two-thousandths of an inch.
These photos show the joint between the cylinders secured with temporary bolts. In the centre is the hand tool made to skim the casting surfaces around each bolt hole to ensure that the fitted bolt heads and nuts when inserted can be tightened evenly onto the casting surfaces.
A further alignment check was made using a straight edge across the cylinder end faces and the edges of the cylinder flanges. The straight edge is an 8 feet long steel bar which has been ground true over its length which is kept solely for this sort of work. This check was also done using feeler gauges to ensure there were no unacceptable gaps compared with the GWR standard tolerances for machined parts.
Having prepared the two cylinder castings they were separated for the joint faces to be cleaned up ready for the application of the jointing compound. The photo shows the area involved.
This photo shows one of the cylinder faces liberally coated with the jointing compound.
The two castings were rejoined on the ‘table’ and the same alignment checks made to confirm all was well before the bolts were tightened. The photo shows the cylinder flanges with bolts in place and evidence that the jointing compound has squeezed all around the joint
Machining of the surface table to form a level datum for assembling the cylinders has been completed and the resulting block mounted on a welded steel framework. It is now referred to as the ‘coffee table’ although it is considerably more substantial than these normally are!
Two photos that show the new cylinders having been set up on the ‘table’ with temporary nuts and bolts through the central flanges to hold the two castings steady. Once Ryan is satisfied that these are correctly aligned he will make and fit new fitted bolts for these flanges to hold the two cylinders together in service. Note that a small screw jack has been set up under each cylinder casting to take some of the weight to assist making any movements needed.