May Day 2023

Subsequent to the Easter working party, Andrew found time to go into Boston Lodge Works on several days to start the manufacture of the tender brake weighshaft. A suitable length of bar was obtained and cut to length to form the shaft itself. Centres were turned in each end so that the shaft could be mounted in a lathe for truing up later.

The brake weighshaft is fitted with four cranks. These were profile cut by an external company and supplied to us last year. However, a change in design was necessary and only two of the existing cranks were suitable. Therefore Andrew carefully marked out and cut the two new ones from 25mm plate using an an oxy-acetylene torch. The edges were then finished with a grinding disk to neaten them up. The cranks are designed to be 22mm thick so both of the new cranks was machined down on one of the mills to the required thickness.

The most critical dimensions are, of course, the hole centres. Andrew first drilled the holes in the ends of each crank. This was then used to mount each crank in the 4-jaw chuck of one of the big Dean, Smith and Grace lathes. The second hole could then be drilled and bored out to fit over the brake weighshaft.

Andrew finished drilling and boring the cranks on the Saturday of the working party. Simultaneously, Dave drilled and bored a piece of bar which was to form the thrust collars on the weighshaft assembly. These were parted off to form each collar.

With all the components completed, the next step was to weld them all together. Not so easy as it sounds though, since it is important to get all the cranks at the correct angles relative to each other. Andrew devised a means of clamping the cranks, one at a time, in their correct places and angles while they could be welded into place. First were the two middle cranks, followed by the two thrust faces.

Since welding causes distortion, we wanted to skim the bearing journals on a lathe to true them up after welding. But due to the throw of the cranks, it was not going to be possible with the end cranks in place. Fortunately they are fitted at the very ends of the weighshaft, which will greatly reduce the likelihood of distortion when they are welded on. But even without the end cranks fitted, finding a lathe with large enough throw to accommodate the middle cranks was a challenge.

The only suitable lathe available to us was the Swift, normally used for wheelset turning. The weighshaft assembly was mounted on the lathe using the centres in the ends of the shaft, drive being provided by the 4-jaw chuck clamping onto one end of the shaft. The saddle feed on this lathe is quite course, so Andrew wanted to use the compound slide on the saddle. But it soon became apparent that the alignment marks on the saddle were not reliable, so Andrew had to spend some time with a dial test indicator aligning the compound slide.

The Swift lathe is a big machine, the sort that you stand on to set up the job. That also means that operating the feeds by hand requires quite a lot of effort, especially when they are operating in a part of their range which they are not often used in. But after an afternoon's work, the bearing journals and thrust faces had been skimmed and are true. All that now remains is to weld on the final two cranks. A job for the next working party.

Paul decided to finish the shed tidying exercise which had been started at Easter. There are a number of pallets in the C2 Shed which carry various components. But as we have fitted parts to the locomotive, the occupancy of the pallets has become less, and hence the space is used less efficient. A day of shuffling pallets around, moving components from one to another, creating a workbench from trestles and putting other parts underneath that bench, and so on, has had a dramatic effect on the space in the shed. We can now move about easily, and the components which we will be working on next are the most readily accessible.

Paul was asked to drive a train on Sunday morning, but was available again for more C2 work in the afternoon. He dug out the Vesconite blocks we had purchased to make the tender brake weighshaft split bearings, and started to consider how we were going to machine them.

Chris cut a couple of lengths of steel strip to form washer plates for the bearings. Dave then marked out the bolt hole centres and drilled them. Dave then used the washer plates as templates to drill holes in the Vesconite blocks. The holes in the Vesconite will need to be enlarged for the alignment tubes to be fitted, but that is a job for the next working party.

To react the shear forces imparted to the tender brake weighshaft bearings by the steam brake cylinder, Paul designed and started to manufacture a reaction bracket.

Zoe joined us again on Saturday afternoon and Sunday. She has completed shaping one of the front slidebar packing pieces, and made good progress on the second. We hope that we can get these packing pieces completed at the next working party, by using the surface grinder to get them each to precisely the correct thickness.

The rear slidebar packing pieces are rather more complex to make. We want to bush the holes in the motion bracket, but the slidebars are attached with fitted bolts which would likely drive out a normal bush. So we have designed the bushes to be integral with the packing pieces. Zoe found and cleaned up a billet of steel from which we will make the rear slidebar packing pieces.

The whistle on the C2 is mounted on a branch on the side of the dome. The Chinese design results in the top of the whistle being very high up beside the top of the dome; a position which we are concerned will be foul of gauge. To try and alleviate this problem, Dave has altered the design for the new boiler, so that the branch is mounted lower on the dome, and is slightly closer to the locomotive centreline (where the gauge is higher).

During the proposed gauging test run we want to check that the repositioned whistle will be within gauge, so Dave and Chris calculated where the top of the repositioned whistle will be relative to the existing whistle branch. Chris then found some pipe fittings and a length of tube to make up a dummy whistle. It may not look pretty, but it will allow us to measure clearances to tunnels and footbridges.

Erle has continued to study the screw reverser. In particular, he has looked at the screw reversers used on the Welsh Highland Railway's Garratt locomotives and the NG15 which is currently being rebuilt. These have various features to eliminate backlash in the screw reverser mechanism, something which the existing C2 screw reverser does not have.

On Monday afternoon Erle, Paul, Andrew and Dave inspected the screw reverser of a Garratt stabled at Boston Lodge. It features collars on the ends of the die nut. The collars are not threaded, so do not influence axial play in the reverser. However, they do prevent the die nut "rocking" on the screw thread. Erle was of the opinion that much of the play in the C2 screw reverser is due to rocking rather than axial clearance, which puts a very different light on matters. It may be that we do not need a new screw reverser after all; just something to stop the die nut rocking. More measurement of the parts we have are needed to confirm this before we make a decision on how to proceed.

In summary, we carried out a number of minor but important tasks, as well as making significant progress on the tender brake weighshaft and its bearings. We didn't quite finish all the tasks, but they shouldn't take long to complete at the next working party. So a satisfying amount was achieved, along with a good deal of socialising in the sunshine on Saturday and Monday.