Fixing a worn pivot hole

Lower quality watches cut costs by reducing the number of jewels in a movement. A 17 jewel movement is considered fully jeweled, 15 jewels are still quite high quality but it is all downhill from there.

7 jewel movements wre common, especially pre-1960s and were regarded as everyday watches for everyone which were still of decent quality as pallet fork and balance were properly jewelled. Anything less than 7 jewels would never function properly but these types of movements, especially one jewel ones were common in the 1930s to 1950s as extremely cheap, mass produced watches truly for the masses.

Jewels, made of synthetic ruby (or garnet and even glass in some cases for cost-cutting reasons) are extremely hard and flat thus providing a perfect material for bearings. Watch wheel pivots are made of hardened steel so the jewel will never wear out and with proper maintenance the pivots will also stay in good shape for a long time.

 There is a problem with unjewweled pivot holes. Watch plates are made of brass, most often plated with nickle, rhodium or some other metal. This means that unjewelled pivot holes are softer than the hardened steel pivots that ride inside them so eventually, and especially with older natural oils the pivot hole would stretch, become larger and go out of round.

There are two ways to fix this situation, either by closing the hole with a staking set or by completely cutting out the hole and inserting a friction-fit hard brass bushing. This is generally expected to be manufactured by the watchmaker so not every pivot size and bushing diameter combination are readily available to purchase. Such manufacturing requires a lathe.

In this post I'll show the repair of a worn pivot hole using a staking set, a smoothing broach and a reamer.

 

The pivot clearly cannot turn properly in the hole and sometimes rests at an angle. Other than causing increased friction at the pivot, the wheels will suffer from increased friction due to unoptimal meshing between the teeth of the wheel and the next wheel's pinion leaves. The whel here would barely rotate when blown at with a hand blower even if no other wheels were installed.

Always, always mark the hole. Update: round off the hole with a broach before proceeding! If not done this can cause the hole to wander just enough to cause the teeth to bind in the pinion.

Two rounded punches need to be used. A flat punch/stake can be used to support the hole from the bottom instead of a rounded punch but I find that doing this does not close the hole evenly vertically, with the bottom being wider than the top.

 

Tap tap tap.

The hole after closing with the staking set. A new inner ridge has formed where the hole closed. This also makes the hole round but there's a limit to how far gone a hole can be rounded with this method.

Checking the fit; pivot barely fits now.

Smoothing broach.

 

After broaching the pivot fits with just the right amount of play.

The hole from the top, nice and round. Broaching the hole causes a small burr to form on the edge so it needs to be deburred as otherwise oil would get stuck around the burr instead of flowing around the pivot. Due to the holes being so small (around 0.24mm in this case) a reamer needs to be used for deburring.

Seitz jewelling tool 106 reamer and reaming handle, perfect for the job.

 

The pivot in the hole; doesn't look like much but that's the point: if somethng would be noticed it means that something is wrong. Should look like a normal pivot in a normal hole.

 Both top and bottom holes will probably need this treatment and here we can see the difference fixing one or both holes makes. The first video is with the top hole fixed, an improvement surely but it is obvious that there's extra fiction.

With both fixed and a little 9010 oil in the top hole. The difference is massive and will help the watch run better. This has to be repeated for all unjeweled pivots which is a time consuming, exact task. Not difficult to be sure but there's quite some checking and re-checking. A fairly expensive repair due to the time involved and extremly specific skills required.