Portsmouth Block Mills

• 1. Introduction

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  In 1808, the Portsmouth Block Mills turned out 130,000 pulley blocks for the Royal Navy. The mills stood inside Portsmouth Dockyard in Hampshire, England, and were built during the Napoleonic Wars. A pulley block is a plain object. It is a wooden shell that carries a grooved wheel for rope. Yet the machines that made them are regarded as the start of mass production with all-metal machine tools. The same buildings also held the first stationary steam engines the Admiralty ever used. How did a dockyard on England's south coast take such a leap? Who designed the machines, and who actually got them running? And why did the rest of British industry wait so long to follow?

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• 2. Steam And Sawmills

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  The dock system at Portsmouth began with Edmund Dummer in the 1690s, who built a series of basins along with wet and dry docks. By 1770 one basin was no longer needed, and the plan was to turn it into a sump for water draining from the other facilities. Horse-operated chain pumps lifted that water out.

  In 1795 the Admiralty appointed Brigadier-General Sir Samuel Bentham as Inspector General of Naval Works, the first and only person to hold the post. His job was to bring in steam power and to mechanise production in the dockyard. His office employed engineers, draughtsmen, architects, chemists and clerks. It set up a plant for rolling copper plates to sheathe ship hulls, and forging-mills for metal ship parts.

  By 1797 work had started on extra dry docks and deeper basins. Bentham realised the old drainage system could not cope with the extra demand. In 1798 he installed a steam engine designed by James Sadler, a member of his own staff. It worked the chain pumps and drove woodworking machinery. It also drove a pump that sent water from a well around the dockyard for fire-fighting. That well lay some 400 ft away, and a horizontal wooden spear running through a tunnel carried the pumping motion.

  The Sadler engine sat in a single-storey engine house with its boiler built in. In 1807 a more powerful table engine from Fenton, Murray and Wood of Leeds took its place. In 1830 a Maudslay beam engine replaced that one. In 1800 a Boulton and Watt beam engine was ordered as a back-up and housed in a three-storey engine house in line with the first. James Watt and Co. replaced it with another engine in 1837.

  Space was tight, and the manufacturing facilities could not spread outward. So by 1802 the drainage basin had been filled with two tiers of brick vaults. The lower tier served as the reservoir, and the upper tier as storage. The roof of the upper tier was level with the surrounding land, which created new ground to build on. On it rose two parallel ranges of three-storey wood mills, designed by Samuel Bunce, the architect on Bentham's staff. The southern range held both engine houses with their chimney stacks, the chain pumps and some woodworking machinery. The northern range sat directly over the vaults.

  Bentham ordered woodworking machinery of his own design, mostly up-and-down saws and circular saws. Underdrives through the upper vaults carried power from the engines to the northern range. Vertical shafts then lifted it to the upper floors, and flat belts on pulleys drove the machines. The saws cut the many small parts used in shipbuilding, such as components for tables and benches and small turned goods like belaying pins. Until then, joinery of this kind had been cut by hand.

  The mills held more. There is evidence of a rotary wood-planing machine, though details are obscure. A pipe boring machine bored out straight elm trees to make pump dales, which could be up to 40 ft long and were fitted through a vessel's decks to bring seawater up to the deck. Another machine made treenails, the long wooden dowels that fixed a ship's timbers together. Yet one product of the dockyard still came from outside: the pulley blocks.

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• 3. The Block Problem

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  A typical ship of the line needed about 1000 blocks of different sizes, and over the course of a year the Navy required more than 100,000. Contractors made every one by hand. Their quality was inconsistent, supply was a constant problem, and the price was high.

  Bentham had devised some block-making machines himself but never developed them. How they worked is now obscure. In 1802 Marc Isambard Brunel proposed to the Admiralty a system of making blocks with machinery he had patented. Bentham saw that it was superior. In August 1802 the Admiralty authorised him to go ahead.

  There were three series of block-making machines, each built for a range of block sizes. They were laid out as a production line, so each stage of work passed naturally to the next. To house them, the yard between the two wood mills was walled off and roofed over as a new workshop.

  The first set, for medium blocks, was installed in January 1803. The set for smaller blocks followed in May 1803, and the set for large blocks in March 1805. Layouts changed and the plant was modified many times. By September 1807 it was judged able to meet every need of the Navy.

  The machines came in 22 types and numbered 45 in all. Two 30 hp steam engines drove them, and they included circular saws, pin turning machines and morticing machines. With them, 10 men could produce as many blocks as 110 skilled craftsmen. What each machine actually did to a block is a story of its own.

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• 4. Anatomy Of A Block

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  A pulley block has four parts: the shell, the sheave, the pin that locates the sheave in the shell, and a metal bush called a coak. The coak is set into the sheave to save wear between sheave and pin. Each part had its own line of machines.

  Shells began as slices cut from a tree trunk. Circular saws cut those slices into rectangular blocks. A hole was bored for the pin, and at right angles to it came holes for the morticing chisels. In the morticing machine the chisel moved up and down while the vice holding the block crept forward with each cut. A circular saw with angled guides then cut off the corners. Next, a wheel carried several blocks around its rim while a cutter swept across them in a curve set by a former. This shaped the four faces to a shallow curve, and the blocks were turned 90 degrees after each cut to bring up a new face. A final machine scored a shallow groove to seat the securing ropes.

  Sheaves were made from Lignum Vitae. A slice was cut across a trunk while the log rotated against the saw, which kept the thickness equal. A leadscrew set the log's position for each cut. A rounding saw then turned the slice into a disc, boring out the middle and shaping the edge in one pass. A profile was milled on each face to take the coak, which was inserted and held by a riveted retaining ring. The hole in the coak was broached out to the size of the pin. Finally a special lathe faced both sides and machined the rope groove.

  Pins were forged slightly oversize with a square left on one end. They were turned to size on a special lathe and given a burnished finish between hardened dies. One source says they were also tinned to protect them from rust.

  Coaks were cast in bell-metal. The mould left grease-retaining grooves in the inner bore. One end carried a flange, and a loose ring fitted the other end. Together they gave a seating for the rivets that fixed the coak to the sheave.

  Only the last steps were left to human hands. Workers smoothed the shells with a spokeshave, then assembled sheave and pin. The finished blocks were stored in the Block Mills and issued as the fleet demanded.

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• 5. Firsts In Machine Design

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  Boring a block left small indentations that later machines used to find it again. The clamp that held the block made these gauging points, so every later tool met the block in precisely the right place. Several features like this appeared in the Block Mills for the first time, and they have since become commonplace in machine design.

  Several of the machines had cone clutches. Brunel used detachable tool bits held in tool holders very similar to those on general purpose lathes today. Expanding collet chucks gripped the inside bore of the sheaves to hold them during certain operations. Some machines used two-jaw gripping chucks, which were precursors of the three-jaw chucks on modern lathes. The morticing machines could be set to stop on their own once a cut was finished.

  Sheaves and pins were interchangeable, because neither was married to a particular shell. The range of block sizes meant the work-flow is perhaps best described as batch production. It was basically a production-line system all the same.

  The whole system was designed for labourers rather than apprentice-trained craftsmen. Each man learned to run two or more machines and could be moved around the plant as needed. This way of working did not catch on in general manufacturing in Britain for many decades. When it finally did, it was imported from America.

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• 6. Building The Machines

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  Brunel's patent specification showed wooden-framed machines. They displayed many of the principles of the installed machines but bore little resemblance to the final designs. The machines Brunel submitted to the Admiralty for evaluation are now in the National Maritime Museum.

  Once the Admiralty contract was placed, Bentham engaged Henry Maudslay to build the machines. The final designs clearly drew on Bentham, Maudslay, Brunel himself and Simon Goodrich, mechanician to the Navy board. Bentham was away in Russia, so it was Goodrich who brought the block mills into full production. Brunel's payment was based on the saving the Navy made with the new system.

  The machines were almost entirely made by hand. The only machine tools available were lathes for circular parts and drilling machines for small holes. There were no milling, planing or shaping machines, so every flat surface was made by hand chipping, filing and scraping. There is evidence that flats were also ground to reach a near-precision finish.

  Each nut was made to fit its own bolt, and the pairs were numbered so they could be put back correctly. That was before the days of interchangeability. The builders used cast and wrought iron, brass and gun metal. Metal throughout gave far greater rigidity and accuracy than wooden frames, and that standard carried over to later machine tool manufacture. The finished system drew curious visitors almost at once.

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• 7. Visitors And Fame

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  On the morning of the day he embarked from Portsmouth for the Battle of Trafalgar in 1805, Admiral Lord Nelson visited the Block Mills. Another visitor came as part of her education: Princess Victoria, at the age of 12. Through the Napoleonic Wars, until 1815, a stream of foreign dignitaries and military men came to learn from what they saw.

  Major reference works of the day described and illustrated the machines, starting in 1811 and continuing in 1812 and 1817. Later reference works drew their accounts from these earlier ones. Almost all of this writing concentrated on the block-making machinery and ignored the saw-milling side of the mills. As a result, modern commentators have not discussed that part of the story either.

  The sawmills mattered. They let Brunel develop ideas that he later used in his private veneer mill at Battersea. He applied them again in the Royal Navy sawmills at Woolwich Dockyard and Chatham Dockyard. He also designed mills for private concerns, such as Borthwick's at Leith in Scotland.

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• 8. Survival

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  The Block Mills have stayed in constant Navy occupation, which is why they are not open to the public. Manufacture of blocks on the original machines declined over the years and finally stopped in the 1960s. Some of the original machines, part of the transmission drives and the engine-house shells still survive in the buildings.

  The National Museum of Science and Industry in London holds a selection of machines donated by the Admiralty between 1933 and 1951. Others are on display in the Dockyard Apprentice Museum at Portsmouth. Several websites claim the Smithsonian Institution in Washington, D.C., also has machines from Portsmouth. According to the Institution, that is a myth.

  Much of the original pulley system remains in place, though in poor repair. The building itself is in poor repair too, and it is a high priority for both English Heritage and the Ministry of Defence. Since 2003 English Heritage has been carrying out a detailed survey of the buildings and the records relating to the machines. As of 2006 a project is under way to ensure the building and its contents are preserved, if not restored.

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