When doing metric threads on most machines made or imported into the US, you DON'T disengage the lead screw between passes, and you don't use the thread dial. The reason has to do with the lead screw pitch and the odd number of gear teeth required to make it all work with metric threads. Oops, my bad
The usual technique is to engage the half-nuts, make your pass, STOP and REVERSE the lathe to back up the carriage WITHOUT disengaging the half-nuts, THEN make your next pass. It's the one thing that makes cutting metric threads a little touchier than standard threads. And the rather high minimum speed of your lathe makes it even more difficult, because you have to guess how far the carriage is going to coast after you shut off the power.
And reading all this, you'd think I knew what I was doing
. NOT! I've learned just enough to be dangerous, and to know how little I've learned. Hope this is some help. Later.