I tie a ton of wet flies size 6 & 8 that requires floss bodies. I use two strands of Daville floss. Once the floss is tied in you need to lift the two strands at the 12 O'clock position and stroke the two floss strands together at the same time. You will see that the two strands become as if one. Next you as you start making the first wrap you will need to continually stroke the two strands. You will do this until the first wrap has been completed. From there on keep uniform tension on the floss and give it a stroke or two with each turn. You will dee the floss lay down nicely as well as still acting as one nice single piece that was really two. A Rotary vise can not give you the same affect as using your hands. The key with using floss is to use uniform tension and not to over pull so tight or under pull. It only takes a little practice and this will be a non issue moving forward. Last part, make sure you hands are washed before using floss or the oils from your hand will come off and discolor the floss. Also smoothe down and rough spots on your fingers with an emery board to help from fraying the floss. Again I repeat that your hands are the best tool for applying floss and not a rotary vise or floss bobbin.

Andy B