Bluebell Railway Villa Team

Birch Grove's firebox stays - Knobbling over the ends

The final stage of fitting the firebox side stays is the knobbling over of the exposed ends. This performs two functions: it seals the thread to prevent leakage past the threads, and on the inner end it prevents the stay end being burnt by the fire. The job is performed with a pneumatic rivetting gun, using three types of tool. The copper is sufficiently soft that it can easily be worked without heating.

[View of a stay end before knobbling over] The end of a side stay protruding through the firebox outer wrapper plate, with about 4 threads showing. [Click on the images for full-size picture.]

The first stage is to swell out the end of the stay using a round-ended tool. This spreads the stay within the plate to seal the thread against leakage, and outside the platework to form the head overlapping the plate. The pictures show Ian Collins in action:-

[View of first stage with round tool] [View of knobbling-over in progress] [View of stay head swelled out]

The second stage is to use a flat tool to fold the edges of the stay head outwards over the plate:-

[View of second stage with flat tool] [View of the tool being used] [View of the stay head after folding over]

The third stage is to use a rectangular tool to tuck the edges of the stay head tightly against the plate:-

[View of third stage with rectangular tool] [View of the tool being used] [View of the stay head after tucking in]

The outer ends of the stays are done first so that the stays are firmly fixed in the steel plate before they are knobbled over on the softer copper plate side.

[View of the boiler] The stay knobbling at the stage where all those on the outside of the throatplate and the backplate have been done, and a few of the inside ends. [View of knobbled-over stays inside the firebox]

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Last updated: 7-JUL-1998 LAN
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