Does Z travel make sense as a number?

[Clive S]

Wait... could the same thing not be achieved by introducing a thicker spoil plate to move the work closer to the spindle?

Yes of course. But you might want a small vice etc. What are you trying to achieve?

[Maurizio]

Nothing! Just exploring the interplay between variables that determine the 'true' z cutting depth (which for me means depth of pocket cut from top surface) as a prelude to building my own cnc :)

Edit: just for clarity my first post wasn't proposing no z travel, but more musing over the need for it to be combined with cutter length and table to gantry clearance to assess whether it meets your requirements. e.g. a cnc with a z travel of 100mm and a table to gantry height of 100mm could not cut 100mm narrow pockets, it would need a table to gantry height of 200mm and a cutter of 100mm. The flipside to this, as pointed out by Clive and molliemilo1 is that other operations would benefit from a z travel that goes all the way to the table.

Ohh, I guess it could with multiple cutter changes (a 50mm, then a 100mm), but you'd have to start and finish the cut within the pocket...