There could be many things going on with your machine. Your description sounds like simple run outto me. However I have not seen the set up. The first question I have is why are you traversing towards the tailstock? If you are crossing centerline with the tool you will get a concave shape which can look like true taper. If this is a CNC machine don't screw with any alignment issues for .001 over six inches. Program it out. If you are getting a concave shape from the tool crossing centerline then it will be impossible to program it out. You typicaly have this problem from being out of level. If it is a boxway machine wear in the ways can cause the same issue. No way to tell without seeing set up.
.001 over six inches is not bad. Remember this is a turning machine. Holding less than .001 on a turning operation is not impossible but becomes very difficult. In a production environment less than .001 is usually reserved for grinding operations. |