I'd vote for Robin's suggestion of opto slot sensors.
I used Buy Photoelectric Sensors U-shaped thru-beam sensor,PMR44P Sunx PMR44P online from RS for next day delivery. for the X-axis on my lathe, and repeatability is good. They come in various mounting styles, so you can normally find one that will fit with minimal effort.


From experience, inductive sensors generally have quite a wide tolerance, both in range and switching time. I've tried using a few different ones to control hydraulics in the past, and I could never get them consistently detecting motion. Good old fashioned mechanical heavy duty limit switches worked far better, even though the occasional one would get wiped out when things moved.