Stupid newb question: Is a Z of +10 above or below the surface of the work material? I know Z=0 is the surface of the material (now).
Depends on how you have set things up with the polarity of your motors. But I think general convention is for negative to be downwards. You also zero in different places depending on the sort of cut you are going for. For instance the spoilboard can be zero if you want to ensure a clean cut through your material, or surface can be zero if you want to engrave a known depth.
To get a clean cut through the material on my CNC, it seems I would need the Z to be at least within 5 mm of the surface of the work material. My dremel bit that I have in the machine does not do side cutting. It does only end cutting.
Thanks for the reply, @Ben_Delarre .
So my technique up until recently was to zero the end mill by hand to the top of the spoilboard, first visually and then by moving down in 0.1mm increments and checking the rotation of the bit till it just starts to catch then I back off 0.1mm. Then I set zero at that position and back up to a safe position at least 3mm clear of my hold downs. I then setup the thickness of my material in my cam program and tell it where my zero position is. This then gives me nice precise cuts through the material without destroying my spoilboard. Taken a while to get my head around all this, there is a lot to learn in CNC land!
@Ben_Delarre I guess there is a lot to learn. I saw no such settings in the software that I tried using which means I should probably pitch it.
I have thus far used CamBam where the setting was called ‘Stock Surface’ so if my material was 10mm thick and I had zeroed to the spoilboard I would set Stock Surface to 10mm and have a clearance plane at something like 20mm depending on my hold down positions. I now use Vectric Aspire which frankly is a far superior tool but a little pricey, this makes it all a lot clearer as you get nice diagrams in the UI to show you what everything is relative to.
heh. I am a cheapass. I will probably only use Free software for the CAM software.
Ah if its open source you’re using then the setting is undoubtedly there somewhere, it’ll just be buried in a UI so hideous it makes me run away and have a nervous breakdown in the corner 
If using grbl you can move the end mill tip to barely touch the surface of the stock and located on the bottom corner of the area you want to start. Reset the board now and it will assume that as (0,0,0) location. From there on Z-coordinates are negative and X,Y positive (unless you did not position on the bottom left corner of the area of interest). CamBam will give you a few free rides. Cut3D seems simpler but not free. PyCam is free but not updated recently. Easel is available for ShapeOko users for free. MakerCam is free but only 2D.
I noticed the piece was below 0,0,0 and there was a button to put it above z=0 and start it near 0,0,0. Well, that fixes that problem.
My own unscientific method involves jogging X and Y to a coordinate close to where I want 0,0,0 to be then lower Z until it’s a few mm above the work piece. Make final X and Y adjustments then turn on the spindle and lower it by hand until the endmill just barely touches the material. Zero the machine with ‘G92 x0y0z0’ and start the job.
I really should start probing with GRBL to make life easier.
And CAMBAM gives you 40 evaluation sessions. I’ve been using it for some time now and I’m on my 12th session. 
Just don’t shut it down. And once the trial period ends I’m definitely purchasing it - totally worth $150.
@Matt_Miller It took me a bit to notice what was right in front of me. PyCAM does what you just said in about 2 clicks of the mouse. One to orient near 0,0,0 and one to +1 the Z. I imagine the +1 Z could also be done by sticking some scrap paper under the object. Hmmmm…We have tons of scrap paper at work.