Refitting cannon pinions
We know that cannon pinions in clock movements need to be a tight fit on centre arbors. When such a pinion is removed by having the arbor driven through it with light hammer blows, and then replaced in a similar manner, the fit is not repeated exactly due to a slight enlargement of the bore by swaging.
To minimise this effect (during assembly) the pinion can be heated a little to expand it before refitting. I have seen a particularly tight pinion actually drop into place using this method.
Perhaps it would be sufficient to heat a pinion just by laying it on the sole plate of an upturned domestic iron - something to try some time!
R Dobson, UK
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