Hi Jet_Deck, this is a nice challenge.
I confirm the bowl is designed according to the arms trajctory. Here we call the putter-shaped arm bras pétrisseur
= kneading arm, and the other one bras fraseur
= strirring arm.
On antique diving arms mixers, and according to the old bread-making process, only the stirring arm was adjustable : the 2 arms where used few minutes in order to form the dough, and then the stirring arm was raised up and the kneading arm was finishing the job alone. In this configuration the diving arm mixer was running such as a "Diosna mixer" ( see example here :
) and the gap between the bowl's edges and this arm must be as low as possible. This determines the kneading'efficency.
I measured the mobile parts of my mixer, and I modelised the trajectory of the arms here :http://imageshack.us/m/11/166/40737021.jpg
The red lines are the connecting rods, the blue lines the arms and the black dotted curves the trajectories.
If you need more photos or information on the mechanics, don't hesitate to ask me I will try to reply so far as possible by taking a peek inside my mixer.