Since you have now given the lathe model number, I can tell you that what you experienced is not a unique problem. The main reason that this problem occurs is because the yoke mechanism is sloppy on many, if not most, of the 46-715 lathes. This results in a misaligned asymmetrical load being placed on the movable half of the pulley especially when making rapid speed changes with the control lever. The pulley is weak in the area near a bearing where it is likely to crack and separate from its hub.
Disassembling the lathe is very easy, but please do not ever use a hammer to drive the pulley from the spindle. There will be a lot more than the pulley that will need replacing if you hammer it off.
To start the disassembly process, first roll the belt off the pulley. Next, remove the three long socket head screws from the handwheel. Now remove the set screws from the fixed half of the spindle pulley and slide it off the end of the spindle. Note that there is a 4 mm square keystock so the pulley must come straight off the spindle.
In order to remove the variable half of the pulley, the yoke assembly needs to be disconnected from the headstock. Remove the screws on the control lever mounting and slide it free. Remove the remaining pulley half and yoke and bearing. If you need to remove the spindle because of damage, it is retained by internal snap rings to capture the bearings.
I mentioned that the yoke mechanism is sloppy. If you want to improve it, you will need to machine a new follower rod yourself that matches the hole in the headstock casting. The follower also needs to rigidly mate with the yoke -- same thing goes for the drive rod. Alignment of these three parts needs to be precise to prevent binding. Delta tried to avoid the necessity for precision machining by having all the parts fit together loosey-goosey. Unfortunately, the problem with a loosey-goosey fit is the failure that you experienced where the pulley cracked and separated from its hub.
I am very surprised at the price of a new pulley. It used to be around $30 or less. If I were you, I would insist that Delta eat the cost of a replacement since it is a defective design. The concept is good, but their processes and tolerances are completely unacceptable. I had to replace this part at least three times and Delta never charged me for it. Things worked much better after I machined my own yoke assembly, but I finally discarded the whole Reeves drive mechanism on this lathe.
