Prior to this step, I bored the hole for the 1/2 - 24 thread. Next the hole for the valve stem was drilled and reamed, and the 45 degree face was cut., and the hole was tapped. I then removed it, screwed it onto a 1/2-24 threaded spud, and re-chucked to true the machining boss.
Here the casting is still attached to the 1/2-20 threaded spud, and chucked in a spindex on the mill. The holes for the fuel and air intake were machined 90 degrees apart. Next the spud was clamped in a 45 degree angle vise and V-Block, and the hole for the adjusting needle valve was drilled and tapped. The #65 hole for the fuel inlet was then drilled to intersect with the valve seat face. The fuel passageway was then drilled using another setup.
The various parts for the mixer are shown on the left, and the assembled mixer is above. I hand-lapped the valve for a while to obtain an air-tight fit in the seat. There is an excellent seal over the fuel inlet.
