Balancing the Balance Wheel

One of my favorite tools is used to adjust the weight of a balance wheel to assure that it is not heavier on one side than another.  This called poising, and it is done whenever the staff is replaced, or anything else is done that might change the balance - or if it just isn't right to begin with.

Poising is done, in part, with a poising vise.

The poising vise has jaws of clean, polished ruby, both very hard and smooth.  It also features a built in bubble level to level the tool on the bench (although a separate level is generally more accurate).  Two of it's legs are adjustable.

The idea is to set the balance assembly, without the hairspring, resting on the edges of the jaws on its pivots only, and then adjust the weights of the balance so that it will sit idle on any position.

If the balance turns and settles with one particular side down, then that side is too heavy.  On the heavy side, a selected timing screw is removed and a very small amount of material removed from the underside of the screw head with a tool called an under-cuter.  The process is repeated until the balance is even.