Conversation so far:
How did Ross Brawn's career get started?
His career in motorsport began in 1976 when he joined March Engineering in the town of Bicester as a milling machine operator.
How did he do there?
Soon afterwards he joined their Formula 3 racing team as a mechanic.
How long did he work as a mechanic?
Brawn was hired by Sir Frank Williams in 1978 as a machinist for the newly formed Williams team.

Question: What did he do there?
Self-contained rewrite: What did Ross Brawn do after being hired by Sir Frank Williams in 1978 for the Williams team?