I mean like a thread for somebody like me that is not a machinist!
I design electronics for a living - but am currently tasked with getting a combo mill/lathe (Shoptask) machine up and running to run prototype quantities of mechanical parts for our products (LED lighting).
I need to get this done by next week - so no pressure

What I need to do here is use this machine as a sort of automated drill press to drill holes in a sheet metal "pan" that is ~18" square. These holes will be for mounting 4X LED PCB to the pan - the finished product being a 24" square light fixture.
I would imagine that my required accuracy would be on the order of +/- 10 mil across a dimension of ~18" in the Y axis and ~8" in the X axis. I am basing this requirement on the size of the fastener (screw) and the size of the hole in the PCB. Due to the 10" limitation of movement about the X-axis - the pan will need to be rotated 180 degree during the process.
This machine has three stepper motors to drive three axis - X,Y, and Z. Currently I just need to use for drilling sheet metal which I would imagine would be a maximum of 100 mil thickness (probably less) and the material would be steel.
I have managed to perform a cursory calibration of the machine as far as movement goes with the Mach3 software. I do not have a set of gauge blocks so first "roughed in" the calibration using a steel ruler for 4" moves - and then fine tuned it using a dial indicator for 1" moves. I currently have the Y-axis +/- 1 mil, X-axis +/- 3 mil (this can be improved), and Z-axis +/- 6 mil (the Z-axis on this machine has a problem).
Is this calibration technique adequate for my needs?
Will the "pan" need to be pre-punched to guide the drill?
Should I use normal drill bits or pilot drill bits?
Is there some "convention" as to what is "zero" for each axis? I currently have dead center of the X and Y axis as zero - and Z-axis zero is fully retracted - i.e. Z only moves in a negative direction. Is this "normal"?
What about feed rate? I know from using a manual drill press that this matters - but I am not sure I understand the concept using Mach3. Is this simply a function of the acceleration profile setup during the motor tuning calibration - or are there other ways to control this?