The Axlebox crown is the gunmetal bearing pressed into the top of the Axlebox which sits on the journals of the axles. This crown has a soft white metal lining in the top and forms the bearing face. 

The crowns not only take the weight of the loco but also resist the forward and backward forces from the cylinders and so it is important that they are in good order to give long reliable service. 

The original crowns were a bit past their best. Either loose in the Axleboxes or oversize and made up with more white metal. 

As the journals are currently being skimmed and polished at Riley’s the decision was made to renew all of the crowns to restore the correct limits and fits onto the new journal sizes. 

To renew the crowns, six large cored gunmetal billets were ordered and these were then turned down on our vertical borer to give the correct interference fit into the Axleboxes. 

A CAD drawing was produced to detail the cut line for the lower dovetails and the serrations. These serrations are there to help the white metal stick and stay in place. 

The bearings were then sent to a wire eroding company to cut the dovetails and serrations. This used a wire submerged in water which slowly sparks away at the part following the accurate CAD file. 

Once this process is finished, we will white metal them and fettle them to give the correct press fit into the Axleboxes. 

This is an example of where modern techniques are now being used. Traditionally this would have been done on a spotting machine with quite a bit of set up time. This method is extremely accurate and provides a quick turn around.