A concentric hole needs to be drilled down the length of the arbor. Concentricity is key here, any eccentricity will cause the arbor to 'wobble' and depthing to vary considerably as the wheels turn.
This process is completed in the 8mm watchmakers lathe, using a self-made piece of kit unique to our workshop and often using very brittle tungsten carbide drills as the arbors are made of hardened carbon steel.
At this point the excess material is parted off in the lathe and the pivot filed and burnished to the correct dimensions.
Burnishing polishes and work hardens the surface causing a longer lasting and low friction pivot.
What is Re-pivoting?
Re-pivoting an arbor is an added cost to any clock service which requires it, So I thought it sensible to explain process and to identify the reasons for the additional cost and expertise needed.
Image one is a perfect example of a worn pivot. usually, worn pivots are filed and burnished but in this case too fine a pivot would be left for reliable running of the clock.
So I snapped the pivot off and ground it back to the original shoulder. this is where it gets tricky.
A piece of blued steel is made to the correct diameter to be a firm press fit in the hole. Too large and the arbor will split and be rendered useless. Too small and the new pivot will not hold.
Provided the process has been carried out accurately so far, an oversize but concentric pivot is now in place.
Here is an example of a work in progress on a far smaller scale. This pivot has been drilled at 0.3mm and is ready for the rest of the process to be completed. This is a small clock pivot but some watchmakers are capable of accurately re-pivoting watch arbors!
The job is infinitely harder as the work gets smaller. consequently it takes longer to complete and costs more to do so.
The moral of the story is regular maintenance!