spindle pulley on the taig mill

I just got my new mill. I thought that before I fully assemble it, I
will make some mods which I had already planned to do so that I only
have to align things only once.

One of the things I wanted to do is to put graduation marks around
the periphery of the pulley on the spindle assembly. The idea is to
make a rpm readout using my meter and a simple sensor arrangement ala
Tony Jeffree's setup. According to the drawing that came with the
mill, the pulley is only held by by a hex screw. I loosened that and
the pully refused to come off even with some determined effort. Since
I am new to this, I didn't want to really force the issue and damage
the spindle.

Does anyone has any experience taking off that pulley? Suggestions
are most welcomed.

ym