In 1795, Terry invented his first
Milling machine to produce
interchangeable parts. Terry crafted these milled movements until the Porter Contract. Soon after 1802, Terry's production of wooden clocks grew considerably. Like other Connecticut clockmakers, Terry knew that apprentices could cheaply rough-cut wooden wheels for more skilled journeymen to shape precisely into clockworks, making clocks slightly more cheaply. And Terry was one of a number of Connecticut clockmakers who began to substitute water-powered machines for apprentices in the production of these rough-cut wheels. In 1802 or 1803, Terry purchased a mill to produce wooden clock wheels, which still had to be finished by hand by skilled journeymen clockmakers. He purchased a grain mill and used the water wheel and main shaft to run saws and lathes, which helped speed the production of parts. He later created jigs and fixtures to produce a large number of interchangeable clock parts. This allowed for the rapid adjustment and assembly of clocks, freeing Terry from the task of fitting and modifying each individual piece of each clock. Using his own ingenuity and inventiveness, Terry was thus able to speedily cut wheels, pinions, and other important clock parts accurately and repetitively. In the year 1806, Terry signed the Porter contract to produce 4,000 wooden clock movements (other shops would make the cases). According to historian
Diana Muir writing in ''
Reflections in Bullough's Pond'', at that time a skilled craftsman could produce six to ten clocks per year. In the third year he produced 3,000 wooden clocks. He sold his manufactory to two of his assistants
Seth Thomas and
Silas Hoadley and retreated to his workshop to create the first machine in the world to be mass-produced using
interchangeable parts. Terry envisioned a new kind of clock, intended for
mass production from machine-made parts that would come from water-powered machines ready to go into clocks without any additional hand cutting by skilled workmen. This would be a shelf clock, costing less than a tall clock. It would be made quickly and be easily repaired. Terry's further innovations included the design of an escapement with removable verge. This later became a standard design feature of American clocks for the following century. The
mass-produced wooden clocks manufactured from
interchangeable parts that poured from Terry's factory beginning in 1814 were the world's first mass-produced machines made of interchangeable parts. As such he would
mass market an affordable, complete cased-clock to American consumers. Terry's first clocks were offered in plain wooden box cases. Terry is also credited with the design of the
pillar and scroll case. In his autobiography,
History of the American Clock Business for the Past Sixty Years and Life of Chauncey Jerome, Terry's employee and assistant
Chauncey Jerome, later a great clockmaker and owner of the world's largest clock factory, mentions building the first pillar and scroll in Terry's workshop with the master's design and under his direction. The pillar and scroll case provided a large, clear dial in a wooden case about thirty inches tall and six inches deep. The upper part was the clock face, the lower part was either a mirror or a picture back-painted on glass. Despite the small size of the clocks compared with traditional long case clocks, Terry was able to provide sufficient power through gearing for the clock to run a full thirty hours before it needed to be rewound. Anticipating a successful product Terry had the foresight to patent his arrangement of clockworks. At least five patents were issued to him through the years up to 1825 in order to protect his invention. According to
Diana Muir in ''
Reflections in Bullough's Pond'', within a few years, several hundred men worked in two dozen factories in the
Naugatuck Valley and Bristol produced virtually identical Terry-style thirty-hour wooden clocks. Salesmen innovated such now-familiar marketing devices as installment-plan purchases and model changes of the cases to induce consumers who already owned a functional clock to buy a more fashionable model. As noted Terry was granted many patents for his advances in clockmaking, most of which were immediately infringed upon by local competitors eager to participate in satisfying the demand for an affordable clock. Many competitors would note "patent clocks" on their label in order to prevent litigation. One lawsuit did develop as noted below. Terry also produced wooden-movement tower clocks, such as those found in the steeples of churches and meeting houses, one of which is still operational today in the town of Plymouth. ==Tower clocks==