Both the front and rear of the throttle shaft were machined to make a flattened surface (6.4 mm thick) and the edges were chamfered. The screws are countersunk and have flat faces.
The visual band at mid height is the remaining original surface. The actual transition is a smooth curve in this region.
The surface was polished and chemically anodized using a method used to promote air flow in jet engine passageways. (I work as a materials/manufacturing engineer in the aerospace & transportation field.) On a flow bench the TB flows +18-20% better than stock over pressure drops ranging from 3-10 in-Hg.
The throttle plate was not given a knife edge finish for two reasons: 1/ I wanted the best transition during tip in and elected to keep the beveled edge with very small radii at the corners, and 2/ the best leading edge isn't a knife edge anyway. the best leading edge actually has a curved surface with compund radii.
The work was done by a retired machiist friend from work. It cost me under $100 even paying the friend for his time and it does improve flow without compromising part throttle driving.
