An Engineer in Wonderland – Lignum vitae bearings
A programme about a chair from the Caribbean from Radio 4’s A History of the World in 100 Objects mentioned the wood lignum vitae, which reminded me of the clocks of John Harrison.
According to the book Longitude, Harrison used the wood in clock bearings for its long-lasting and self-lubricating properties.
So little wear is experienced that the Royal Observatory Greenwich, I am told, runs three of the four Harrison longitude clock full time without fear of deterioration.
The fourth – the actual longitude clock – does not use lignum vitae and cannot be run for fear damage.
Anyway, I was googling away trying to find out why the stuff wears so little,
However, I did discover that not only has it been used for clock bearings, but it was the material of choice for great big applications including propeller shaft bearings in ships – even after the second world war – and plenty of people claim it was used for the same job in the world’s first nuclear submarine.
And it has also been used in the bearings of generators within hydroelectric power stations – where it has operated for 50 years – without maintenance claimed one site.
I read that for lack of porcelain insulators, replacements for the San Francisco cable car system were turned up from lignum vitae in 1906, a few of which were finally removed in 2009.
How much of this is true, I have no idea.
I hope it all is.
Does anyone actually know why the wear rate is virtually nil?
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