8th May, 2018 by Steve Masters in Workshop Blog
5239 "Goliath" arrived from The Dartmouth Steam Railway and overhaul began in October 2017. Following is the latest news on the progress in the Workshop.
This week we were able to use the extremely accurate optical alignment equipment thanks to Andy Forster. A telescope is mounted in the aluminium disk fitted to the front of the cylinders. This disk is a very good fit in the end of the cylinder and the mounting for the telescope is machined perfectly concentric to ensure the highest accuracy. The telescope is aimed directly at a target plate at the rear of the loco frames. The main purpose of this telescope at this time is to ensure that we have set up our horn grinding plates perfectly upright and square to the frames. To achieve this, a straight edge is held against the horns and a precision mirror reflects a target back into the telescope. When the straight edge and grinding plates are perfectly square the target is displayed centred. If even a few thousandths of an inch out over the length of the 5 foot straight edge, the target appears miles off!
Having set up all the plates, the job of horn grinding could start. Our own design of horn grinder was used which tracks these plates to grind the opposite horn perfectly flat and parallel to it. Once done, the plate is removed, the grinder turned over and then the first face is tracked to grind the last face ending up with a pair of perfectly flat, parallel, upright and square faces.
Also this week, the wheels returned from the South Devon Railway after having the tyres, journals, thrust faces and crank pins turned. We have now made a start shot blasting and priming them.
This week we assembled and jigged the front dragbox ready for welding and drilling. We finished welding the tank supports and they were NDT crack tested before being machined to square up the ends and ensure that they are at the right length. Also, now that the frames have been levelled, the horn ties are being adjusted to ensure that they grip the bottoms of the horns securely and in the right place.
This week our main objective was to get the frames jacked up level and then supported along their length so that the frames were completely relaxed and not sagging anywhere. This is important for us in order to accurately set up and measure for axlebox alignment and also to check the fit of horn stays.
Work on the frames is still progressing nicely. All of the horn guides have now been fitted with their new interference fitted bolts. More priming of the frames has continued with just a small number of areas left to finish. The first of the tank supports have been welded up ready to be machined.
This week a lot of progress was made in fitting the horn block bolts. The holes are first reamed until they are parallel and continuous through both the frame and the block. The diameter of the hole is then carefully measured and the new bolts machined 0.002” bigger to give a tight interference fit.
Elsewhere there was lots more primer being applied to the frames and the very wasted front dragbox was cut off behind the bufferbeam.
The heavy snow this week didn’t hinder our progress too much in the workshop!
The trailing axleboxes do not have replaceable crowns, instead, they have replaceable bronze inserts at just the lower edges. The inserts are fitted into a dovetailed slot and are then pinned. These require renewing, as the axle journals are being skimmed and therefore will be a slightly smaller diameter. The bronze strips are very important and withstand the high piston loads transmitted through to the axle.
With the majority of the shotblasting and priming complete, work has started to refit the horn blocks which were found to be loose. They have all been roughly refitted on the frames.
The major task of shotblasting the frames is now complete meaning that the frames are now positioned at the back of the workshop where there is a bit more room to work on them. The boiler is now at the front of the workshop ready for work to start on repairing the lap joints and the crown stays.
Having completely stripped the frames, the job of shot blasting has started. Previously we have always needlegunned the frames which is very slow, noisy and isn’t good for the user due to the vibration. The shot blaster however is very quick, quieter without vibration and the finished results are far better.
Having removed the cab, tanks and bunker the week before, the cranes were booked finish the major dismantling. Firstly the boiler was lifted from the frames and the ashpan removed. The boiler was then put onto a wagon. Next the frames were lifted clear of the wheels and put onto the frame trolleys. Finally the wheels were lifted clear of the rails.
Having completed 41313 for the Isle of Wight Steam railway in June and then fast tracked 1719 Lady Nan through the workshops to give her a new ten year ticket, we were pleased to welcome GWR 2.8.0T number 5239 Goliath from the Paignton and Dartmouth Steam Railway for an extensive overhaul.