I am a BT from an Ashkenaz family that practiced conservative Judaism. I have tied Tefillin according to the Chabad custom most of my life because that’s where I became inspired to use Tefillin each day. Now I attend an Ashkenaz shul and bought new Ashkenaz style Tefillin but I have had a difficult time adapting. The Ashkenaz way seems to allow for the Tefillin to loosen and slide a lot more easier than the Chabad way which wraps a shin on the arm and keeps it in place. I try to tie it very tight but it always seems to loosen. Any advice?
It is interesting that this is happening to you, but if you find that the teffilin are becoming loose and moving from thier proper place, you can wrap the strap once over the side of the tefillin in order to keep it in its place.
If this doesn’t work and you still have a problem let me know.
Mishna Berura 27-32.