1 day i i bought used crankset with dead bottom bracket and decide to replace the bearings. You can buy new bearings for cheap on Chinese marketplace. 

For this tool you will need m8*60mm bolt, m8 nut, wide washer (45mm) (or you can try to model and print it). Print long version bearing press. Short version require 15mm spacers or long socket.

Print with 4+ walls, 3+ bottom and top 30+ infill