We are wanting to build a machine that uses a short "X" axis for the first and last few inches of each programed travel.   Basically the gantry will be wheel driven on the part itself and the secondary X axis would be used to travel beyond the drive wheels off each end.  We were thinking of using proximity switches to indicate when it should switch between X1 and X2.  I'm not sure how I would get Mach 3 (or 4) to control this.  The transition point/position would not need to be accurate, but it could not loose steps in the transition.  I am looking for some guidance on how this would be arranged and coded in Mach 3.