I installed a spindle encoder on the spindle. Please see Bridgeport Series II Interact 2 Head diagram to see how the head looks like.
I made (on a Clausing 6913 Lathe), a spindle adaptor that you can see below. This adaptor fit nicely into the spindle (it was 26mm ID), and I made a few dimples on it with a center punch to provide extra grab. The green goo that you see on the thick part of the adaptor, is a Pennzoil marine grease that I put on, mostly, to prevent any rust. There is a tiny flange between the thick and thin portion, that you can see, that keeps the encoder adaptor from falling down below.
The Macaroni and Cheese cup is a temporary substitute for the encoder cover.
O100 sub G1 Z-0.03 F5 O100 endsub S1 M3 M8 O<apply_to_a_grid> call [0] [0] [0.5] [0.5] [5] [3] [0.01] [100] M2
O100 sub G1 Z-0.2 F3 O100 endsub S1 M3 M8 O<apply_to_a_grid> call [0] [0] [0.5] [0.5] [5] [3] [0.01] [100] M2
(Rigid tapping with 10/32 tap) O100 sub G33.1 Z-0.6 K[1/32] O100 endsub S1 M3 M8 O<apply_to_a_grid> call [0] [0] [0.5] [0.5] [5] [3] [0.01] [100] M2