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Engineers, of Bourton, Dorset.
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Background: c.1750 Daniel Maggs built a flax processing factory powered by a waterwheel. The factory was later managed by Richard Maggs and Herbert Maggs. Daniel’s son David Maggs established a workshop to make and repair equipment associated with flax harvesting and processing.
By 1810, Daniel’s son, David, was making agricultural implements there.
In 1820, the Maggs built a new mill, and this later had a very large (60 ft diameter) breastshot waterwheel installed. This was illustrated in 'Hindleys of Bourton'. The site later became the engineering works of Maggs and Hindley, and then E. S. Hindley and Sons.
1819 Daniel Maggs (Jr?) built a waterwheel for Nether Cerne Manor. The remains are displayed at Sherborne Steam and Waterwheel Centre in Sherborne, Dorset. See photos. This is thought to be the oldest all-iron waterwheel for which anything remains. It worked from 1819 to 1949, before being discarded in the water course.
1840 Partnership dissolved. '...the Partnership heretofore, subsisting between us the undersigned, Daniel Maggs, of Bourton, in the county of Dorset, and Rachel Colbourne, of Silton in the said county, in the business of Flax-Spinners and Linen-Manufacturers, carried on by us at Bourton, and at Silton aforesaid, was this day dissolved by mutual consent...'
1842 Daniel Maggs (Jr?) listed as a manufacturer of tick, dowlas, sailcloth and shoe thread
Comment from a correspondent,
There were at least three Daniel Maggs. Richard Maggs and Herbert Maggs were not involved in Bourton Foundry nor the associated flax factory and neither was David Maggs.
The 'Hindleys of Bourton' book is unreliable. A better source, though not perfect is 'Maggs and Hindley. Two Families. Two hundred years. An industrial heritage at Bourton, Dorset.' Published 2014 by the author Robert F Mullins.
The 60ft diameter waterwheel was not installed until 1837. It served the flax factory, with another smaller overshot waterwheel. Upstream the family had another flax factory at Pen Mill, Penselwood with a waterwheel perhaps 45 or 50ft diameter.
The foundry was established before 1810. Possibly on the profits of the successful development of the flax factory at Bourton. Sand suitable for casting was also found nearby at Breach Close.
Further comment from a correspondent,
The earliest waterwheel was at Crocker's Farm, Compton Abbas, near Shaftesbury, Dorset:
'... invented and erected by Mr. Daniel Maggs, of Bourton, to the astonishment of a large company of spectators. What is most remarkable, the barn stands on an eminence, its floor is near 64 feet above the level of the water (leat from Sturkel brook), and the wheel full 336ft. distant from the machine. It went round remarkably pleasant and easy; scarce a straw either crippled or with a corn was to be found, and it threshed near three quarters of oats in one hour. Too much cannot be said of Maggs's mechanical genius ..'
Much later, around 1851-1852, Oliver Maggs cast a 30ft waterwheel for the Duke of Bedford's estate at Kilworthy, Tavistock Hamlets, Devon. Its wheelpit was blasted out of rock by local miners. But there were three foundries in Tavistock, all capable of casting waterwheels and in at least one case steam engines too. It seems that the Duke sent his agent on a tour of farms in Devon, Dorset, Somerset and Wiltshire. He met Lord Portman's steward at West Lambrook who introduced him to George Parsons who was later to set up the Parrett Works at Martock. Parsons may have recommended Maggs and may have supervised the installation of the wheel at Kilworthy. 
A large waterwheel and pump made by the Bourton Foundry in 1902 - (E. S. Hindley and Sons] is now displayed at Kew Bridge Waterworks Museum - or was in 1994 
Other Hindley waterwheels survive, for example, one at Stour Provost Mill, Dorset, cast in 1889.