When dealing with linear brushing, I have found the easiest way to maintain a straight "BRUSH" is to hold the bracelet or watch in your hand, put the brushing material on the work surface and secure it in place (Tape, clamp, whatever).
Then in ONE MOVEMENT brush the item by pulling it straight towards yourself.
One, LONG, STRAIGHT as possible, movement.
Take the bracelet off the clasp and do each side independently.
Also do the Clasp Independently.
I rebrushed this old 70's seiko bracelet this way.
