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A Brief History of the Plumb Bob

Bruce Cynar

The history of the plumb bob is split by the Industrial Revolution, which doomed one usage, but created another. When early man first started building permanent settlements, someone must have realised that stone walls built truly vertical stood better than walls that leaned. Perhaps this same fellow noticed that a stone cradled in his sling caused the ropes of the sling to hang taut and straight down. By 2600 BC, we know the Egyptians had taken this concept and created the earliest surveying instruments: the plumb board, the A-Level, T-Level and plumb square. This was the first use of the plumb bob, against a wood frame that paralleled the surface being measured. The worker could then make a more precise visual judgment as to the trueness of plumb or horizontal level. These earliest bobs were stone and their shape, although often egg-like, really didn’t matter. These simplest of tools remained virtually unchanged for the next 4400+ years.

The invention of the spirit level, and the beginnings of the Industrial Revolution that allowed the level to be manufactured, both accurately and cheaply, began the demise of the ancient plumb tools. For establishing plumb and true horizontal the level is simply a better tool. It is quicker and easier to use and just as accurate. But there is one thing the level can’t do easily, and that is to transfer an exact point from one height to another.

The Industrial Revolution that almost did in the plumb bob also created new uses. The precision and manufacturing capacity brought about by this surge in technology, increased the need for the accurate transfer of points in taller buildings, steel bridges, machinery installation and deeper shafts. While the shape of bobs had been tapering to a point for years, suddenly there existed a need for; and the capacity to produce efficiently highly accurate coordinate transfer devices – also known as plumb bobs. An interesting history for a tool whose only claim to fame is that it obeys the law of gravity!

Appeared 1995 – Toolshop Auctions Catalogue

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