Starting Conditions for G-Code generation and Rule Checking.

[sliptonic]

For any given operation in HeeksCNC, two distinct strategies are possible:

1. Touch off the top of the material and mill 'down' to a target depth. That is Z=0 is the top of the material and we might step down 1mm at a time to a depth of z=-10mm.

2. Touch off the bottom of the material (top of the bed). That is Z=0 is the bed, The top of the material is Z=15, and our target depth is Z=5.

It's pretty easy for a new user to get confused and this confusion can cause the machine to crash the cutter into the bed, or plunge to an unreasonable depth for the first cut.

I think a user intuitively expects to tell the software something about the starting conditions of job. I'd like to see the following features:

1. A required entry for the material thickness. I guess this could take the form of either a value entered into the Program properties. A fancier version might be to add a solid to represent the raw material. User could change the length,width, and depth of the solid. Depth would translate into material thickness. Either way, this would default to being NOT SET.

2. A required entry for the locatoin of Z=0. This could be a Simple drop-down with options for 'top of material' and 'bottom of material'

3. Additional rules checks that would take this information into account. For example;
   If Z=0 is bottom and material thickness is 10, starting depth should should be >= 10. Final depth >= 0 and safe height > 10.

If Z=0 is the top of material, starting depth should be 10, Final depth > -10 and safe height > 0.

4. automatic rules adjustment should work with this as well.