Another question about leveling/squaring

I have recently acquired a Techo-Isel gantry table. It is an older Model
I, and all assembled from bolted-together aluminum extrusions. In the
manual, Techno quotes a flatness of .020" per foot for the table, and
cautions against machining the table itself (rather to use a sacrificial
surface and skim that down.) The basic table is X-Y, and the Z axis bolts
onto T-slots on the X-arriage on the gantry. All motion is nice
ball-on-rod recirculating bearings, and the leadscrews are anti-backlash
ball too. It's driven by size 23 steppers with 2A chopper drives (General
Gontrols).

I'm in a quandry over how to set up this machine. I know that I need to
start from the Y axis and move up, but that's as far as I can wrap my head
around. I don't have a table that is known level with respect to the X-Y
plane, to start. I need to set up the Z axis to be perpendicular to that
theoretical plane, and then set my toolhead up so that its spindle will be
parallel to the Z axis. And that's after I've leveled the base as well as
possible, I assume.

The only thing I can think of to start is to mount up the sacrifical
surface (aluminum tooling plate) and attack it with a "single-point"
tool--i.e. a ball endmill. If I crisscross, spiral, etc. the surface
enough that should produce a plane that is parallel to the X-Y motion
without knowing the state of the Z axis at all (just that I keep it at a
fixed height while I'm doing the machining). I could then put a
machinist's level on that surface and sweep it vertically with the test
indicator in the spindle to set the Z axis perpendicular to it, and then
tram in the spindle.

Is that way out in left field? Am I on any kind of the right track? Or
am I overlooking something really fundamental that I'll end up slapping my
forehead when it's pointed out to me?

Thanks,

Randy

Randy Gordon-Gilmore ,----.___________ ______________ _________________
ProtoTrains // = = === == || == == == = || == == == = == =|
Rio Vista, CA, USA /-O==O------------o==o------------o==o-----------o==o-'
zephyrus@... http://www.prototrains.com