It depends..... if you are using the A axis (4th axis) with tool path generation completely from CNC Wrapper, then the "correct" Z zero should be set to the center of the part. If you are setting the Z zero, by jogging your machine down to the surface of your work piece and resetting Z zero, this is WRONG! But, as I said, it depends.... If you are using CNC Wrapper to convert g code generated by another program, to WRAP it around a cylinder, then you SHOULD set the Z zero to the surface of your work piece. 4th axis tool paths are an entirely different animal to get your head around. But basically, it functions similar to a lathe. (The Z Zero on a lathe is always the center of the stock). The programmed diameter of the work piece stock, is what CNCW is working from. Therefore, if you have for example a programmed stock diameter of say 2", and you have jogged your tool down to touch the surface of your stock, and reset Z zero, then subsequent Z moves WOULD move UP instead of down! As CNCW is trying to cut the radius of the stock relative to the stock's CENTER. (Which will always be a positive move- if it were negative, it would mean that the tool had to plunge into your stock completely PAST the centerline of the stock!). And since you probably have your stock mounted between the headstock and the tailstock, would result in your work piece being completely severed between the headstock and tailstock of your lathe (4th axis assembly). I would recommend learning to generate a tool path, such as engraving your name for example, in another program such as LazyCAM. Get that working successfully, on a FLAT piece of stock. THEN save that tool path g code file. Import it into CNC Wrapper, and CONVERT it for "Wrapping" around a cylinder. The trick is, you have to get your math EXACT in terms of the Y axis limits of the FLAT tool path, which will be converted into A Axis moves in CNC Wrapper. I.E. the Circumference of your A Axis work piece must EXACTLY match the measurement of your Y tool path limits of the FLAT g code tool path. If it is not an "exact" match in measurements, the only thing that should happen, is that it will engrave your name all the way around the cylinder, until the first letter meets up with the last letter. If the circumference of your work piece cylinder is SMALLER than the actual Y measurement, then the work piece will continue to rotate until the last letter engraves on top of the first letter. If the circumference is LARGER than the actual Y, then it will leave a GAP between the last letter of your name, and the first letter. As I said, 4th axis is a different animal to learn. Especially if you are new to CNC. I would first concentrate on mastering 3 axis tool path generation. THEN try and tackle 4th axis later, once you gain a better comprehension of what's going on. It will get easier to understand. Hope this helps!