Hi Kristijan, I guess you mean width. Depends what you're aiming to chunk. Branches with lots of curves or wide slabs may need some width but narrow blades (short shafts) will make a sturdier machine.
10 cm dia with 4 blades per shaft is perfect for making our size chunks. Bigger will use less force (better cutting angle) but longer chunks. Mine are 12 cm dia. The chunks get a little longer than I like (close to 3") when I'm chunking thin material (less than 1" dia).
I didn't. I used square tubing and pressed bearings into the the ends. The shafts are 20 mm dia bolts and they don't spinn. Only the square tubes do. They are attached to the gears. No bearings on the frame.
I've never seen anyone else go this route, so I had to try
3×3 cm solid shafts may be strong enough if you find a way to attach the blades from all 4 sides without weakening the shafts to much (drilling holes).