Originally Posted by
TXFred
When you reversed, did you back the cross slide off by a turn or two? If not, then the threading insert was dragging on the reverse pass. Since the lead screw has backlash, this will mess up the thread.
That's my best guess, after looking at the saw tooth profile of your thread.
I would not worry about the thread pitch yet. It's probably OK, but since the thread got screwed up, it looks like it's off. On your next attempt, check the thread pitch after your first threading pass. It should be obvious if it's right or not. in fact, at that point it's actually easier to see than later on when the thread is cut deeply, especially if you mark the work with a sharpie before you begin. Silver on black is very easy to see.
Frederic