Confusion on setting Z after surfacing operation

[everettwcaudle]

So, I have searched and read but still remain confused on this.   Here is the issue:

I have a Carbide Create CNC and use the native (Carbide Motion) gcode sender.   My setup requires a re-zeroing of the Z axis after each bit change (i.e., no automatic bit changer and no bit-zeroing device).  Thus, when running a Fusion job with several operations and several bit changes, I must re-zero my Z after each bit change (though the X-Y settings, in this case set at stock center) remain the same.

I am new to 2D surfacing as a first operation, and what I am having trouble understanding is how I should set my toolpath settings requiring a different end mill subsequent to a surfacing operation.  So, that is, if I create a setup using stock from a solid, and that stock is .25" thicker than my model's top and has .25" of axial stock, if I run a surfacing operation first that skims off the excess .25" of top stock, how do I set the parameters for any operation (say a pocket using a different end mill) when I no longer have a "stock top" to which I can re- zero after the tool change?  What I am finding is that if I re-zero to the newly created stock surface, after making the tool change, and then  run the second operation, my pockets end up .25" deeper than modeled.

Should I be referencing Z from another location (say, the spoil-board)?  I originally understood that Fusion took into account that the surfacing operation removed stock above the model top and generated tool paths that accounted for this.

Thanks to anyone who can make this more clear or provide instructions that are straightforward.

[leo.castellon]

In my opinion, your best solution would be to reference your part when you program to have the origin/WCS on the bottom and also set your tool reference to the bottom. That way, if you have to change a tool or break a tool while machining, then you will have the same reference point. Your machine will not care if all your Z moves are negative or positive. If you look at the attached picture, you set your both your tool and part to the same place, the part bottom.

Leo C