I'm on step 6, at 3:40 in the video. My belt is looped through the belt clip exactly as shown, and I have a good 4-5 inches of belt looped back on its self with all teeth meshing. As I tighten, the teeth just slip, over and over and over.
I've tried to tighten the belt maybe 15 times now, spent well over half an hour on it. If I get to the "loose guitar string" stage everything seems fine, until I slide the X carriage back and forth once and the teeth start slipping until the belt is way too loose.
My assembly is identical to what's depicted in the video, I've reviewed the steps multiple times, and everything looks perfect. Teeth just don't want to hold.
Is it a bad belt? Are the teeth worn down from so many failed attempts?
I'm no stranger to this type of assembly, but so far this has been quite unpleasant.