Sunbeam Mixmaster - Variable Speed Control - Explanation

I have Sunbeam Mixmaster Model 1-8B, which has had some intermittent variable beater speed issues. I'm pretty capable at most any repair, and I've determined that there's no problem with the resistor or the capacitor on my model - and I generally see/understand how the depth control in the rotated speed controller works . . . and how the depth adjustment screw functions.

I'm a little unfamiliar with how the vertical variable speed control contact interacts with the circular hole in the static horizontal metal contact point. It's obvious (because I tested it), that the further the contact moves into contact with the circular hole - the higher the beater RPM. I've adjusted the depth screw and now the beater motor engages at the 1-2 setting (the beater motor wouldn't even start previously until it reached the 7-8 setting).

Mostly, I was hoping someone could better explain how the power contacts function when the speed control is actuated (turned).