A YARD CRANE FOR WALLINGFORD

In previous editions of the Gazette, I described the construction of various buildings for the Wallingford layout at the private Fawley Museum, near Henley-on-Thames. Readers may remember the museum as the venue for Channel 5’s The Great Model Railway Challenge in 2018 and 2019. For those who didn’t see the earlier articles, the layout is approximately 120 feet long and runs from a fiddle yard at one end, through a model of Watlington station to the terminus at Wallingford. Although the track was laid and most of the scenery was installed about 20 years ago, the station at Wallingford was never completed.

For the past 18 months, I have been constructing the missing buildings and progressing the scenery so that the layout appears complete although, in truth, what layout is ever complete?

The design of the Wallingford layout is based on drawings and photographs contained in Paul Karau’s book Great Western Branch Line Termini (Oxford Publishing Company.) With a copy of Karau’s book to hand, together with a copy of The Wallingford Branch by Paul Karau and Chris Turner, I have spent many happy hours creating, first, the signal box (see the November 2020 Gazette) followed by a variety of buildings within the station site (described in the May 2021 Gazette) as well as general scenery, fencing, walls and cattle pens.

Rather than trying to draft the crane elevations using a CAD programme, thereby developing my IT skills, I opted for a traditional drafting method using Rotring pens (remember them?) and graph paper. At this stage, I also decided that I would construct the model using a mixture of nickel-silver and brass, and that I would try to ensure that it functioned to some degree, rather than being an entirely static model.

At this stage, I must declare that I have little experience of cranes, either in model form or in real life. As a consequence, I shall probably use incorrect terminology in this article in describing some of the components. I apologise in advance for this.

So how does the typical yard crane work? The crane sits on a concrete base and has a central vertical pivot located towards the front of the crane body, so that the jib is counterbalanced by the bulk of the crane mechanism. This pivot is slightly conical over most of its height and is located in bearings in the main body at top and bottom. The sides of the body provide support for the winding drum and the gear reduction mechanism. Winding would normally be carried out by two men, using a double-ended crank handle, each man standing on a platform on either side and slightly to the rear of the main crane body. There is a friction brake on one side, to prevent the load from dropping uncontrollably. The winding shaft can be moved sideways between two positions, one to raise and lower the load and one to rotate the crane by means of a gear on the main crane body that turns against a toothed ring mounted on the base. Brakes are provided for both the winding drum and rotation of the crane.

Knowing my limitations, I decided that there was absolutely no way that I could produce all that level of detail so I decided to omit the geared rotation but make the crane capable of lifting loads through the winding mechanism.

I decided that the best way of constructing the model would be as a series of sub-assemblies which could be separately constructed and finished prior to final assembly. These would be the base, the main body (incorporating the winding gear) and the jib.

I started by creating the jib, cutting and filing two identical pieces out of 0.7mm nickel-silver sheet and then drilling the necessary holes required for the pulley and the top fixings. 0.3mm nickel-silver strip was soldered to the sides to provide the webs of the jib. Additional pieces of nickel-silver were then cut and soldered to produce the bracing lattice work, as close to the original photographs as I could achieve.

At this point, I managed to obtain 15mm and 12mm brass pulleys, which were approximately the correct size for the jib and the hook pulleys respectively. The pulleys were plain-sided, which didn’t look right, so each of the pulleys was machined in the lathe to produce an indented side that looks more like the real thing. The pulleys were then chemically blackened and put to one side for later installation.

With the jib completed, my attention turned to other parts of the crane assembly, starting at the base and working up. The real crane was mounted on a substantial square concrete block. To replicate this, three pieces of scrap foamboard, left over from the construction of the buildings, were glued on top of each other as a sandwich.

The top layer was cut as a 40mm diameter circle and the two lower pieces were cut as a 55mmx 55mm square. When dry, the foamboard was covered in air-drying modelling clay to provide an uneven surface. The base was painted in concrete colour and lightly dry-brushed with dirty black, which was also used to paint the circular zone beneath the crane body.

Finally, a hole was drilled in the centre and a brass tube glued vertically in place to provide a solid support for the root of the main pivot post. This would allow the crane to be removed in the future for cleaning or repair. At the same time, I drilled a matching hole in a piece of scrap timber to provide me with a construction base for the model and avoid me risking any damage to the completed crane base.

With the mounting hole defined, I turned a brass pivot post using my minilathe. The root of the post was machined to be a close fit in the base. At the same time, I turned two brass collars that would act as the top and bottom bearings for the crane. These would eventually be soldered into the main body of the crane, allowing it to rotate freely.

The next sub-assembly to be tackled was the body of the crane itself. The key to this was creating a pair of matching sides with accurately drilled holes to take the various axles for the working mechanism. At the same time, the metal parts for the bottom of the body and the operating platforms were cut out and set aside.

Construction of the body was carried out on my trusty sheet of toughened glass and it proceeded quickly, although it was tricky keeping it aligned in all three dimensions until a few spots of solder could keep it sufficiently rigid. In general, I used 188ºC solder which would allow me to do any later soldering work with 143ºC solder, without the earlier joints melting. With the main body assembled, the side rails and platforms were attached without too much difficulty.

The next stage was to fabricate the bracing steels that connect the top of the jib to the crane body. To enable possible disassembly in the future, I opted to install threads in the jib and the top of the crane body, which would allow the bracing steels to be secured in position with brass nuts; 10BA at the jib and 8BA at the body. I selected 1.6mm x 0.8mm brass strip for the steels as this looked about the right size compared to the photographs, while being sufficiently robust to cope with any rough(ish) handling. Lugs for each end of the steels were made from 0.018in nickel-silver. It was now possible to assemble the bulk of the crane as a prelude to fitting the winding motion.

It was obvious that painting the crane would be very problematic if it was left until the gear mechanism was in place, so it was time to put the sub-assemblies through the paint-shop. I primed the body with red oxide and the jib with grey primer using Halfords aerosols, before giving all the components a top-coat of Precision Paints early- BR (Pre-1964) wagon grey. In truth, I have no idea what colour the Wallingford crane would have been painted; probably whatever grey paint was sent from Swindon.

However, the photographs suggest that it was finished in a relatively light colour and this colour looked reasonable. This is rather academic as I weathered the crane subassemblies using Humbrol colour washes before fitting the winding mechanism and the chain.

With the body finished, painted and weathered, it was time to approach the fiddly bit of the project, the winding mechanism. This is effectively a two-stage gearbox with a pair of gears on each side of the body connected by three axles. There is a winding handle on each end of the input axle and a winding drum on the output axle.

When I planned the crane, I decided to use proprietary gears and, fortuitously, I had bought a pack of assorted clock gears from Squires Models a couple of years previously. For size, these proved to bear a reasonable resemblance to the prototype, so the centre-to-centre dimensions were worked out and the axle locations were drilled accordingly. The pack of gears comes with 2mm steel axles but, as these proved to be a hard material to cut to length, I substituted silver-steel rod which proved much easier to work.

The two largest gears needed to be modified from plain gears to spoked ones. To mark out the shape, I covered each gear with paper using double-sided tape and drew the cutting lines using geometric instruments and my trusty Rotring pen. The plastic material is very soft and was easily drilled, cut and filed to the required shapes. The spokes could, perhaps, have been a bit thinner but I didn’t want to compromise the strength of the gears and risk a breakage during manufacture. This is something that would have been improved by 3D printing the components but that is a skill that I have yet to master.

The winding drum was turned from brass rod on the lathe, to the scale dimensions of the one on the Fawley Museum crane. The drum was then drilled to take a loop of wire that would secure the chain to the drum. The winding handles were assembled from brass tubing, square section and wire. The ends of the input axle were machined so that the hollow handles slid tightly onto the axle, to be secured later with superglue.

With all the components prepared, the axles were chemically blackened and the gears were spray-painted in grey primer, before being hand painted to a grimy black/grey finish. Starting with the winding drum axle, the mechanism was gradually assembled, continually testing the mesh of the gears as each axle was installed. Very little adjustment needed to be made which proved that my original marking and drilling was as accurate as I hoped it would be.

With the gear train in place, it was time to plan and fabricate the gear guards that were the limited acknowledgements of health and safety requirements on these cranes. The required sizes of the guards, which are different on each side, were measured from the model and fabricated from nickel silver sheet and brass strip.

Having satisfied myself that these were the correct size, I painted them to match the main body of the crane and fixed them in place with superglue.

The hooks were fabricated from a double thickness of 0.028in brass and cut to a rough shape, before being painstakingly filed to shape. I had no dimensions for the real hook so I had to copy the one at Fawley. Working on the basis of ‘If it looks right, it is right’, I was satisfied that I had captured the essence of the shape.

With construction finally complete, the jib was attached to the body and the chain and hooks attached. The chain on the Fawley crane has 57mm links that, at O Gauge, equate to 19 links/inch. A rummage through my bits and pieces box found a variety of chains that I have collected over the years (“they’ll come in useful one day”) and one with 21 links/inch looked a good approximation. As a bonus, the chain was already blackened.

With all the parts of the crane finally completed, all that remained was to locate the model in its correct position adjacent to the Goods Shed, to match the photographs in the books as closely as possible.

The Wallingford yard crane has been the most complex scratch-built model that I have built and, despite a few issues along the way, by far the most rewarding. Apart from producing a much-needed addition for the layout at the Fawley Museum, it has provided me with an absorbing project to improve my metalwork skills, as well as giving me something to occupy my time during the Covid Finally finished lockdown.