| Information on Screw Threads
It is considered by some that the screw thread was invented
in about 400BC by Archytas of Tarentum (428 BC - 350 BC). Archytas
is sometimes called the founder of mechanics and was a contemporary
of Plato. One of the first applications of the screw principle
was in presses for the extraction of oils from olives and juice
from grapes. The oil presses in Pomeii were worked by the screw
Archimedes (287 BC - 212 BC) developed the screw principle
and used it to construct devices to raise water. The water
screw may have originated in Egypt before the time of Archimedes.
It was constructed from wood and was used for land irrigation
and to remove bilge-water from ships. The Romans applied the
Archimedean screw to mine drainage. The screw was described
in the first century AD in Mechanica of Heron of Alexandria.
The construction of the screw thread depended upon the eye
and skill of the craftsman. Advances on this occurred in the
eighteenth century. Antoine Thiout, around 1750, introduced
the innovation of equipping a lathe with a screw drive allowing
the tool carriage to be moved longitudinally semi-automatically.
Screws with fine pitches are essential in a wide variety of
instruments - such as micrometers. To construct such a thread
a lathe was essential. Jesse Ramsden in 1770 made the first
satisfactory screw-cutting lathe. Using his lathes a long
screw cut be cut from a carefully cut small original. Precision
screws allowed precision instruments to be made to allow the
construction of steam engines and machines tools. By their
use in surveying instruments they assisted in the construction
and development of canals, roads and bridges.
Screw threads for fasteners were cut by hand but increasing
demands deemed it necessary from them to be factory made.
J and W Wyatt patented such a system in 1760. The lack of
thread standardisation made fastener interchangeability problematical.
To overcome these problems Joseph Whitworth collected sample
screws from a large number of British workshops and in 1841
put forward two proposals:
1. The angle the thread flanks should be standardised at 55
2. The number of threads per inch should be standardised for
His proposals became standard practice in Britain in the 1860's.
In 1864 in America, William Sellers independently proposed
another standard based upon a 60 degree thread form and various
thread pitches for different diameters. This became adopted
as the U.S. Standard and subsequently developed into the American
Standard Coarse Series (NC) and the Fine Series (NF). The
thread form had flat roots and crests that made the screw
easier to make than the Whitworth standard that has rounded
roots and crests.
Around the same time metric thread standards were being
adopted in continental Europe with a number of different thread
flank angles being adopted. For example the German Loewenherz
had a thread flank angle of 53 degrees 8 minutes and the Swiss
Thury thread an angle of 47.5 degrees. The standard international
metric thread eventually evolved from German and French metric
standards being based upon a 60 degree flank angle with flat
crests and rounded roots.