Z axis stopped part way through print I got an Anet A8 for Christmas.

I am trying to print a calibration tower and the z axis stops lifting at approximately 100mm.

I checked that the gantry is able to travel along the full length of the threaded rods, and while resetting the bed height I noticed that the LCD display showed the extruder height above the bed.  It reads 0 at home (good) but goes back to zero when I manually turn the rods so that the gantry goes above the heigh at which the print stopped.

Any thoughts on what to check? I am double checking all the mechanical bits (connection to stepper coupling, ease of turning, etc...). 

My slicer is Cura 3.1.
I found two issues:


While cutting the cables to size, I made the cable for the z-axis too short.
In Cura the y height reset to 100mm rather than the 240mm I had earlier specified.  I assume the G-code I used was sliced with the wrong settings.