Kitchenaid artisan mixer locking switch only locks 3/4 the way and motor head bounces when mixing dough, although is still locked down.

Make sure that the hinge pin is locked up firmly with the grub screw that is accessed with machine upside down on a towel. It is right up the middle of the pedestal. Next fit bowl & flat paddle and adjust head height with the screw that you can see when the head is raised up. The screw is right in by the middle of the hinge for the head unit. Screw it in (clockwise) a bit to lower and anti clockwise to raise. You want to screw it in enough to just hear the paddle tinging on the bowl and then anti clockwise the screw so it just clears. 1/4 turn from tinging is roughly it. If the head is still not locking down you may need to run a rat tail file through the locking slot to allow the lock better engagement. This is a last resort, if you file too much it is permanent and cannot be reversed so don't do it until everything else has been done properly. It's not a big job for your local Kitchen Aid service agent to sort out for you.