I was going get finnished calibrating my OX today. But when I came to the z-axis I ran into problems. When I drive the z-axis up, it just sag down to my base again. What I have on there is a Makita 700W router fasten with a litle wooden jig. Nothing especially heavy. The wheels are also pretty tight. I use a nema 17 there. Is that the problem? What shall I do?