Hi Steve,
It’s common to have to close the collet a little bit. The dimension of the new staff may have been a tiny bit undersized. The best way to close it would be with one of the tools that Bergeon offers but they are incredibly expensive. I do it on my staking set and it only takes a minute. You can use a concave punch (tapered inside) and a flat stump. You would need to remove the hairspring collet from the staff and place it on the stump in your staking set and then choose a punch that just reaches the full diameter of the collet. This part is critical because if it is too large it may make contact with the hairspring and distort or damage it (it can’t touch the hairspring!). You can then tap it lightly and check the fit repeating the process until you’re happy with it. Also if the hairspring isn’t pinned at the center of the collet then put the punch on the side of the collet furthest from hairspring.
Hope this helps Steve,
Bob
