What kind of machinery are you talking about?

George Washington realized by the 1760s that growing tobacco was a losing proposition. Not only had tobacco growing ruined the soil at Mount Vernon (so his yields were on a downward spiral), the only market for his crop was in Britain and since he had to rely on factors to sell his crop he never got the best price and the goods the factors bought on Washington’s behalf were usually inferior in quality and style. So, Washington abandoned tobacco in favor of grain that he could sell to his neighbors (who never grew enough to feed themselves because they were too busy growing tobacco and other crops for export). But, growing grain is far less labor intensive than growing tobacco (even without any machinery) and Washington was morally opposed to selling slaves against their will. By the time Washington died Mount Vernon had a large population of slaves, whose labor was not needed, but Washington took care of them anyway and not only freed them in his will, he also left money to pay for their transition to freedom after Washington had died.

A few slave owners at the time of the Revolution were personally opposed to slavery and some of them did free their slaves.

However, once cotton became such a profitable crop, many southern slave owners began touting the “benefits” of enslaving the “inferior black race”.