The 150m long TBM, named Phyllis, will start the drive from the Royal Oak Portal in west London running 4 miles east to Farringdon via Bond Street and Tottenham Court Road.
Over the next three years, eight tunnel boring machines will construct 13 miles of twin-bore tunnel under the capital.
More than 3,000 people are currently working directly on Crossrail.
And there are still plenty of chances for firms to win work on the job with another 4,000 contract opportunities to be advertised – providing huge economic opportunities for London and UK firms to get involved.
TBM name check
The first tunnel boring machine was named after Phyllis Pearsall who created the London A-Z. She walked 23,000 streets and a total of 3,000 miles to compile the map.
The second will be named Ada after Ada Lovelace who was one of the earliest computer scientists.
She worked with Charles Babbage on his “analytical engine”, and is regarded as having written the first computer program.
They were among the three winning pairs of names as voted by the British public.
The other winners were Victoria and Elizabeth and Sophia and Mary – these names will be used to name the next four tunnel boring machines.
Mary was the wife of Isambard Kingdom Brunel and Sophia was the wife of Marc Isambard Brunel who built the first tunnel under the Thames.
Crossrail Chief Executive Andrew Wolstenholme said: “Further machines will be launched later in 2012 and beyond. The extent of tunnels to be built under London are on a scale not seen for many years.
“By late 2014, over 21km of twin-bore tunnel will have been constructed.”
More than 50 firms are supplying materials and services for the construction of Crossrail’s western tunnels between Royal Oak and Farringdon.
Thirty-five of those companies are based outside London.
Companies such as DAM Structures in East Yorkshire, Eaves Machining in Bolton and Servaccom Redhall in Hull are already benefiting from Crossrail’s construction.
Steel fabricator DAM Structures plans to increase its workforce from 45 to 65 people by the end of the year as a direct result of Crossrail while Servacomm Redhall which produces prefabricated buildings have just taken on 10 extra staff.
Latest economic forecasts suggest that Crossrail will add up to £42bn to the economy as well as create thousands of skilled jobs and training opportunities.
Secretary of State for Transport Justine Greening said: “Crossrail will make a huge difference to generations of Londoners, reducing journey times, improving connectivity, supporting the economy and creating jobs. It’s exciting that we’ve reached this landmark for this world-class testament to our engineering excellence.”
Boris Johnson, the Mayor of London said: “Crossrail is set to build upon the transport benefits Londoners are already seeing as a result of the Neo-Victorian level of investment that has flowed from the Olympics and the upgrades being delivered on the Tube. The sight today of these mighty tunnelling machines primed for action is a significant step forward in the construction of this vital infrastructure project.”