My old 17-20 had about 3" of quill travel. I think the 4" travel came out with the Patriot model. On the quadra lift models the total travel was a combination of the mill head movement plus the quill travel. I found a couple of tricks to get a bit more quill travel- I removed the quill and lengthened the slot a bit, and also cut another tooth in the rack to allow it to drop further- I got abot 3.75" total. You could get more, but then you have so little quill left inside the casting that it would not be stable. Rainman has the best idea- he has locked his quill solid and uses only the mill head travel as the Z axis. On a quadra lift, you could put longer columns and get as much travel as you want.