I just figured out how to install a spindle encoder on a Bridgeport 1J head. I made a web page at
with some pictures and description. Now I can do rigid tapping on it!
I recently did the same thing on my J-head. Those sensors work very well, just watch out for vibration caused by the magnet pulling on the teeth, you don't want the bracket to fracture inside the gear housing.
I epoxied my sensor in a plastic housing that mounts in a recess I milled with a wood router. Since I am using Mach3, I had to divide the sensor output by 81 with a little Atmel uP to get the 1 PPR that mach needs. Will have to think about quadatrue for the future.