The instructions that come with new Taig pulleys, say not to use any kind of hammer to put them on. You can just put the pulley in a bowl full of boiling water for about 5-10 minutes. It should just drop right onto the spindle after that, at least it did for me.
A few hints on the procedure:
1) Put a sharpie mark on the top of spindle shaft that aligns with the flat spot on the shaft and one on the top and bottom of the pulley that aligns with the set screw. That way while your juggling the hot pulley you can line the the two marks up much easier than trying to find the set screw on the pulley and the flat spot on the spindle.
2) Sit the spindle on a tube or cup, if it's off the mill, that's taller than the bottom end of the spindle. That way the spindle is nice and stable when you drop the pulley on.
Also while you've got the pulley off, you can drill and tap the top so you can install the
magnetic spindle depth stop. This should be done on a lathe for good alignment. Don't know if it works with the regular Taig collets, but it's an excellent mod for the ER16 spindle.