In 1838 he invented the Pivotal Typecaster, and he patented it in 1845. This machine replaced men who worked as handcasters. Some of them saw the machine and felt so strongly about it that they plotted to tip the machine off the boat that was to ferry it back to the foundry. Luckily, David Bruce was able to foil the plot.
An example of the Pivotal Typecaster can be found in the Printing Museum of the firm of William Clowes at Beccles, Suffolk, England.