The Wehnelt was a bit harder to machine than I had imagined.
The problem is the ID is too small so tool clearance is an issue.
I had to use a 14mm drill to create the hole to clear the tungsten filament.
The venting hole was supposed to be perpendicular with the chamfer, but I don't have a good way to machine it in angle and rotate the right amount so I decided for this lateral milling and drilling operation that worked well, only problem I did not make a mandril to hold it so clamping from the edge distorted the part that does not get flush with the filament ceramics plate.
Also the tip of the filament is reaching out the small hole, so I will need to adjust the part height.