Throttle Plate Chuck from Bolt

[metric_taper]

My moto cross friend had me enlarge a carburetor (throttle body as it's fuel injected) bore throat diameter, so I had to make a new plate. What I noticed was the original plate was manufactured so the top and bottom edges were parallel to the throat top and bottom (when this butterfly valve is closed). When closed this butterfly valve is at an angle to the bore relative to the throttle shaft that holds this plate. I made a guestimate on what that angle was, and took a round bar that could be chucked in the lathe 3 jaw on my mill and set that to the angle (I recall it being 8 degrees, where the throttle was closed), machined that round bar end to that angle. Then did a similar thing using the tail stock to hold the new plate in place and machined it into the ellipse shape with the top and bottom edges now able to seal the air flow when installed. It took a few tries to get this right. I used a piece of brass for the throttle butterfly plate, as the original one was made from that material.
Seems my description is hard to read.