I work in a machine shop in Western New York. We have an old Poreba Engine Lathe that was retro-fitted CNC with an Analiam Series 1200 controller about 10 years ago. We recently were awared a contract were we have to thread some large parts with this machine. We built all the bracketry and installed it along with an encoder. For some reason the machine looses track of the timing between the rev's and the Z travel and doesn't start the thread in the same place when taking multiple steps at depth. If we take only one pass the thread is perfect but when we come back to take another pass it wipes out the threads. This machine is old and we don't have all the manuals for it. I did find something about using an encoder with a "zero-marker". I am not sure how to spec this out or where to purchase it from. Any help would be appreciated. Thanks