A wood splitter is a very helpful tool, especially if you have knotty wood.
We used a lot of steel to build our splitter to make the whole thing very stable. The main frame is 2 steel C-sections 160 mm and a flat bar 200x12.
The gear is driven by a 2.2 kW gear motor with an output speed of 20 revolutions per minute.
The toothed rack is a 2 x M4 (40x40) module, unhardened, and the gears of the same module have 18 teeth.