Page "James Watt" Paragraph 24

The field of application for the invention was greatly widened when Boulton urged Watt to convert the reciprocating motion of the piston to produce rotational power for grinding, weaving and milling.

Although a crank seemed the obvious solution to the conversion Watt and Boulton were stymied by a patent for this, whose holder, James Pickard, and associates proposed to cross-license the external condenser.

Watt adamantly opposed this and they circumvented the patent by their sun and planet gear in 1781.