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.