This CNC Router/Dremel, is my first peek into the CNC world...

How are you supposed to find "zero" (top of the wood your carving)?

Are you supposed to use your router surface as zero, and then just figure in the height of the wood your working with? Dosn't sound to me like its such a good option, because the wood thickness varies too much.

"MY" method... is get the cutter, .0625 to .125 above the wood... loosen the collet, so the cutter falls down to meet the wood, and tighten the collet back up, with the bit resting on the wood.

What is the "right" way... or the most "common"?

Jog down slowly until you touch the surface, and zero the Z axis at that point. Some use a thin piece of paper and jog down until they touch the paper, then zero.

Or do something like this.

http://www.cnczone.com/forums/showthread.php?t=36099

Cigarette rolling papers work for me, get the same brand all the time and the thickness is remarkably consistent. Keep moving it with one hand, jog with the other and when it snags you know you're within the paper thickness of your material surface.

Oops, Double POst.. sorry. Too much E- numbers in my orange juice:)

Before I was using a SX3 I would use the paper method.
The SX3 has a quill, so I just jog to near the work.
Zero the DRO.
Manually move the quill down till the bit touches touches (spindle off)
Lock the quill. Zero the quill DRO (on the head)
Jog up 20-30mm.
Hit cycle start.

When I move the quill down there is a small amount of backlash in the gear that puts the quill down, and I overshoot just till you feel the gear free up.

Below 1mm drills/mills I use an eye glass as the quill weight used above becomes a bit scary.
I use drills as small as 0.2mm. Yes 0.008" !

Might make a touch sensor one day but this is a 5 second procedure so have not bothered to get any fancier.

Repeatability by using the quill weight is excellent. I love my quill and will never cut the handle off.
Using the quill readout you can make minor Z adjustments without fiddling with the gcode.

On my superduper lathe I stick an acellerometer (sp?) on the tool and jog in wearing a set of amplified headphones and you can hear it "hit" the surface on a 1 micrometer jog on Germanium.

That's for fine stuff though.

I use a brass feeler gage and drop z till I get a slight drag. This is not for super precision but fine for the router.