Depthing tool

 Depthing tools are used to make sure that the distance between pivot holes is correct and is useful when either making a movement or when working on unjewelled pivot holes, or barrel arbor holes.

These tools were manufactured in large quantities during the late 19th and early 20th century but not anymore because our modern technology allows us to calculate every detail of a watch movement. Still an invaluable tool when working on old movements with unjewelled holes or when manually making a movement scratch.

Operation is pretty straight forward. Both wheels are inserted in the runners and made to mesh at the correct height.

 Here we can see the result of a third wheel and a center seconds pinion being too close to eachother - the teeth are stuck.

 

 

Screw at the bottom is then adjusted and the wheels turned until the meshing of the teeth and pinion are just right. This is based on feel and experience, both of which I lack but it is possible to get the hang of it and get decent results in a short time.

 

 

 

 

Once the correct distance is found the movement can either be marked or the pivot holes checked. The tool needs to be completely perpendicular to the plate for this measurement to be correct.

 

 Here we can see that the holes are too close together; the left hole's center is ever so slightly to the left of the pointed tip of the tool's runner. This caused the wheels to bind and happened because the holes were not broached before being closed with a staking set.

It was possible to move the right hole by gently broaching one side causing it to become a little eggshaped and then broaching and finally closing with the staking set. A time-consuming and difficult operation because everything needs to be just right and a few hundreds of a millimeter make a huge difference. This is also something that cannot be done very often as a lot of material is lost during deburring so it will decrease the time before the hole needs to be bushed, probably by quite a lot.