The building has been sold and a new enterprise is to be set up.
When the business began, Stan Bulling recognised there was a business opportunity for second-hand tractor parts and refurbishing machinery.
In its early days the business had a reputation for being able to supply even the most unusual and difficult-to-find items for clients.
Stan Bulling, who is also known by the nickname of ''Steptoe'', was a contractor before starting the business and that gave him a good knowledge of farming equipment and farmers' requirements.
Iain Bulling joined the business in 1982 after working as an engineer at Checketts Engineering.
Thornbury Enterprises had been in existence for 49 years and Iain Bulling has been involved for 36 years.
''The business expanded quite considerably,'' he said.
Land levellers were just one item the business manufactured.
Demand for levellers was high in earlier years, he said.
At its peak the business sold 26 land levellers in one season.
Stan and his wife, Dot, ran the business as a team. Mrs Bulling took care of the administration.
The same pattern continued when Iain and Nicky Bulling took over the reins.
''It's been exceptionally hard work,'' he said.
''I'd been coming in at 7 o'clock in the morning to paint a land leveller, then build another one, then painting another one before finishing at 7 at night.''
But it had been a ''hellava'' lot of fun.
The technological advances in agricultural machinery such as tractors and cultivating machinery meant if there were problems with the new machinery diagnostics, computer technology was needed to right the problem, he said.
He described today's farmers as technologically ''savvy'' and eager to keep up-to-date with the latest mechanical developments.
Small businesses such as Thornbury Enterprises could not afford to buy the new diagnostic technology.
Add to the change in technology, government-imposed compliance requirements, and health and safety requirements, and it caused difficulties for small business, he said.
The couple believed it was time for a change and Mr Bulling had some health issues.
The business will close its doors on September 28.