Complex sentence: Back home Johansson converted his wife's sewing machine (a Singer machine) to a grinding and lapping machine, he preferred to carry out this precision work at home as the grinding machines at the Rifle factory were not good enough.
Split into simpler sentences: Back home Johansson converted his wife's sewing machine (a Singer machine) to a grinding and lapping machine. He preferred to carry out this precision work at home, as the grinding machines at the Rifle factory were not good enough.