Complex sentence: In 1886, Martins and his two business partners, James William Heaney and A. Anderson, were supplying castings for industrial equipment in general, but primarily gold mining machinery consisting mainly of compression cylinder castings for large engines.
Split into simpler sentences: In 1886, Martens and his two business partners, James William Heaney and A. Anderson, were supplying castings for industrial equipment in general. Their primary focus, however, was on gold mining machinery, consisting mainly of compression cylinder castings for large engines.