I will have a go at the analysis tomorrow evening and report back...approximately what distance do you expect between the tool tip and the bottom of the gantry?

Quote Originally Posted by wilfy View Post
am i reading this right that mounting on steel box section is a no no?? if so how big of a problem are we talking here?
Yes, mounting on opposite sides of steel box section is a no-no since the distance between those sides when the steel is manufactured has a much greater tolerance than for aluminium. This means that there is a high probability of the dimension being sufficiently even for the bearings to run smoothly upon the rails. Profile rails especially tolerate very little misalignment, so it is important to ensure they are mounted accurately to avoid premature failure due high stress.