What machine crippled Tom Robinson's left arm in childhood?

The machine that crippled Tom Robinson’s left arm in childhood was a cotton gin.

Tom’s arm was caught in a cotton gin owned by Dolphus Raymond when Tom was a boy. The accident tore the muscles loose, leaving his left hand and arm useless and noticeably shorter than his right.

The injury becomes crucial during Tom’s trial. Mayella Ewell’s injuries suggest that her attacker used a strong left hand, but Tom cannot use his left arm. Atticus Finch uses this physical evidence to expose the weakness in the accusation, although the racist jury still convicts Tom.

A cotton gin is designed to separate cotton fibers from their seeds, not to harvest cotton. Eli Whitney’s improved gin, patented in 1794, greatly accelerated cotton processing and helped expand the plantation economy. The machine is therefore both a plot device and a reminder of the South’s cotton-centered history.