With the huge metal shredders that can shred an entire car or a bus, they can shred parts like the axle and engine which are large solid chunks of metal, just like the massive spinning shredder blades.
So why does the car get shredded and not the shredder? Are the blades made from harder/stronger metal, or is there something about their shape that makes them stronger (they just look like large plates with notches on)?