I should note the feedback here has been noted and considered so far here.
I have avoided shaping the brush to a sharp point as I was observing how the other variac had a point but it was blunt on the end so I worked to mimic that, somewhat by slightly giving a flat roll off on on just the two ends.
Vertical lines represent contact area to windings.
|_ _ | < Brush
| | <Top view of contact area of brush
| | winding aligns perpendicular to this
These adjustments I am making are only brief and temporary, I am just experimenting to see how I can get the collector supply to 0 volts.
Obviously as noted I want to make absolutely sure the carbon brush is making a wide enough contact patch to prolong the life of the variac for the long term.
Also the brush was running off the winding on to a metalic platform. I observed the control slightly sticks as the brush has to overcome the lip of the first winding, as Chuck noted and as I obviously noticed, I don't want this to occur to avoid premature failure. I will readjust approximately.