I have Mach 3 installed on a new mill conversion and have just started my first experiments. I have a very basic question that has defeated me.
 
Using FastCAD, I design a toolpath defining 4 levels of cut at 1.5mm depth increments from the surface of the stock, as 4 discrete layers in the file. The DXF file is imported to Mach 3 and the layer dialog used to define these Z depths of cut as -1.5, -3.0, -4.5 and -6.0mm. The fast plane is defined as +1.0mm. I have used ZERO ALL with the tool touching the stock surface, and the TOOL OFFSETS are also all set to zero.
 
In the tool path display there are 2 red rectangles: one above the work is presumably the fast plane (though I cannot find this described in the documentation) and the 2nd red rectangle I assume is the suface of the stock (also cannot find a description).
 
My problem is that the red surface plane is buried about -1.8mm down amongst the tool paths, not above it by 1.5mm, and hence the resulting cuts are at wrong depths. Having spent a day tackling this I am now desparate for a solution!

You need to update to Lcam that is in Rev2.x