Frame Assembly Phase 2

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For most of the photos on this page, you can click the image for a larger picture.

Once the bogie has been completed we intend to turn to the rear end of the frames for frame assembly phase 2. This is where we will assemble the components attached around the dragbox at the back of the frame extensions. The dragbox and frame extensions will be fitted in Frame Assembly Phase 1.

The class 7 Britannia frame assembly is very similar to class 6. Thanks to Nigel Fraser Ker for allowing us to reproduce this photo.

Ignore the truck in the lower half of the photo.

At the top of the photo is the hind beam totally obscured by other components fitted to it. In the centre is the intermediate rubbing block which has 2 manganese steel liners on the top and bottom curved faces. This connects to a similar plate on the tender. Either side of the central plate are 2 rubbing plates. Intermediate buffers on the front face of the tender press on these plates. The buffers were introduced as a result of early problems on the Britannias with a periodic surging when braking or the regulator was eased at speed. See Bill Harvey's book "60 Years in Steam" for details. Under the intermediate rubbing block in the centre you can see the protrusion from the dragbox with holds the pony truck centring pin. Underneath the outer rubbing plates you can see the gusset castings that strengthen the back corner of the frames and hind beam. Underneath the gussets are the domed bolsters that will engage with bolster cups on the pony truck.

	The hind beam is in stock but is currently buried under the front buffer beam. We need to check if all of the holes have been drilled
	James Conway has created the CAD model for the intermediate rubbing plate. The top and bottom liners are part of the model.
	The Gusset and Bolster Carriers are substantial castings that are fitted at the rear end of the frame extensions and to the hind beam. They strengthen this key part of the frame assembly and allow the weight of the rear end of the locomotive to be transferred to the pony truck (via the bolsters)
	The bolsters are bolted to the underneath of the gussets. The bolster in the image shows the lower face with the lubrication grooves. The bolster domes will engage with bolster cups on the pony truck.
	The outer rubbing plates are in stock and are ready to be fitted.
	The final component in Frame Assembly Phase 2 is the hind firebox support. There are 4 firebox supports. 2 front supports engage with the front firebox support stretcher and 2 hind firebox supports that engage with brackets fixed to the frame extensions and are located near the rear dragbox. All firebox supports "float" on liners and are restrained vertically and sideways by clips. However, they are free to move in a fore and aft plane. The front of the the boiler is fixed to the smokebox and the smokebox saddle. As the boiler expands, the firebox supports are allowed to move aft. The firebox support is the red component, the beige components are the restraining clips and the grey component is the bracket fixed to the frame extensions.
	This is the CAD model for the pony truck pivot pin. It is fitted to the frame stretcher that performs the additional task of the front firebox support. The height of the pin is 13 inches (330mm) and is 5 inches (127mm) wide where it engages with the bush in the pivot stretcher. This is the area with the lubrication hole, note that it has a slight radius of 18 inches, in common with the bogie pivot.
	The hind beam gussets are taking shape in the fabrication shop at CTL Seal. The yellow marks are where some fettling is required. The right hand face on the front gusset is where the trailing truck bolster will be bolted. An oilbox is fitted in the void above the face.
	This is the intermediate rubbing block that sits in the middle of the hind beam. The rubbing faces have curved manganese steel liners welded to the face to limit wear. The main engine/tender drawbar fits through the central hole. Once phase 1 welding is complete, the block will be sent to the machine shop where the correct radius will be created on the rubbing faces. Once the machining is complete, the liners will be welded in place.
	1 June 2020. The bolsters have been through the first stage of machining which requires a CAD machine to create the dome. Next stage is to create the oilways and grooves on the face together with the mounting holes.

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