Not sure exactly what you mean but some people have it so the collet of the spindle, without any tool in it, comes right down to the bed. In my case the largest cutter I'm using is 50mm long so the distance from the end of my collet to the tool tip will be about 70mm. Then I will be using sacrificial boards on top of the bed and in some cases a small vacuum clamp on top of the bed, then my stock might be up to 50mm thick, maybe more, so the spindle has to rise above all that with a 50mm cutter in the collet. Mine is working out to have a 190mm travel on the Z axis.