"To adjust the tension on the Swiss there is a machined nut at the rear of the head, it allows a wide range of tension on the rotary shaft. The drawback of this is that is comes loose during use, I find myself frequently adjusting tension if using the rotary feature. Again, I have contacted the manufacturer to see if this is functioning properly."
Sorry for commenting such an old post
I have fought with the very same problem with my vise #764.
The only working solution I found is the plumbers tape. I recommend to give it a go, that loosening nut can make one nut