Hi Dave,
during the retrofit of my TongIl TNV40 (witch is still not finished), i came also to the
probing / toollength question.
i am trying to explain, how i want to "handle" this, just to give you (maybe) some ideas.
some basic's of the TongIl
-BT40 spindle toolclamp spring loaded and pneumitc tool release
-16 place umbrella toolchanger
i got to the question 16 places, but i have more than 16 Tools?

so i created Screen and script functionality to use the full range of Mach Tooltable,
according to the 16 place TC. means i created a Little database (well it is a Textfile) to
create a relationship between Tools (Mach tooltable) and TC places.
so now i can "book in" a tool to TC place and M6 handles to get the tool from the right
TC place. that gave me the "range" of the full Mach tooltable.
next question BT40 spindle, but i have a lot of SK40 Tools?

they are principly the same, exept the pick and place height of Z-axis, and a different look pin (lenght).
look pin's are avaliable, so no Problem, but the different pick/place , ok added this Information also
to my "extrenal" datebase some Scripting, done.
next question was how to handle the tool lenght?

out of your thread i "grabbed" the idea of the tool lenght setter.
so some material laying around ,some Screen work, some VB Scripting later
the tool setter was finished , toollenght is stored automatcly in the Mach tooltable.
next question surface probing?

i digged out a 3d touch probe (chineese) witch i buyed years ago, did some testing,
tolerance 0.01-0.02mm good enough for what i do.
again some Screen work, some Scripting and it does what i Need.
after all this i recogized, i don't Need a touchplate (or sensor, witch i use on an older machine) to
get the tool lenght.
i write this only to give you some more idea's,
if you want to take some, the coding is no Problem.
Thomas