· So after a ton of rock crushing with a posthammer and heavy prybar, i decided to do the Google Patents and look at rock crushers, I also looked at buying a 800 rock crusher. After all of this I decided to build one (took 3 days of goofing off in the garage)! Items: 1. 1947 3" Irrigation pump (broken motor) was 28 at the junk yard but wieghs ...