Not all folks do it this way, but I've always ground a very shallow groove in the outer race of the bearing with a Dremel and cutoff disk... lightly dragging a finger on the backside to keep it from spinning up to damaging speeds. I then use a "mandrel" (a drill bit shank) about 2/3 the OD of my bearing to wind my loops around... about 1-1/4 to 1-1/2 turns and I usually leave a little tail/handle, which makes it easy to slightly spring open the loops to go around the bearing race. The loops spring back a bit when removed from the mandrel but, when fitted around the bearing, it "snaps"/settles and holds in the shallow groove in the outer race simply by its own spring pressure. I have some pictures in
this post that show the basic procedure.
Some folks have had problems with the grooving procedure above and have used super glue, flanged bearings, etc... with some success.
More recently I've used a 3d printed "keeper" that surrounds the bearing with a close fit... and the needle has a simple 90 deg bend in it...
Keepers have been made for 8mm and 10mm OD bearings... the most common sizes used, I believe. Post some pictures and give some details of your cutter and we'll do what we can to help.
This discussion should also probably belong in a different thread... feel free to use my needle cutter thread, or start your own.
-- David