One of the more underestimated and less considered practices of the watchmakers, both for the difficulty of a precise true and for the time required, is the bushing of the oval-shaped holes on the plate and on the barrel bridge in correspondance with the pivots of the centre wheel and the barrel arbor.

Indeed the pivots of the wheels and the barrel arbor are made of steel and by friction tend to wear and ovalize the brass holes in which they rotate.

In the first picture is shown the common half-moon dig of the beating of the barrel arbor which doesn’t rotate anymore along his axis in an oval-shaped hole, so that wears also the set of the barrel arbor.

Several methods have been adopted by watchmakers for decades in order to solve this trouble:

• One consists of punching the edge of the hole in correspondance with the ovalization in order to push inward some matter.This practice produces various negative effects: firstly the section of the metal in correspondance with the punching is clearly thinner than the original depth and doesn’t guarantee a long-living; furthermore there’s no precision in the alignment of the punched hole and the upper one.Moreover this procedure results aesthetically crude.
• Another method lies in boring (enlarging) the oval-shaped hole, without keeping the hole in a certain true, also when assembling a brass bushing.This method, compared to the first one, enables to obtain the advantages of an equal depth of the metal everywhereand to result aesthetically agreeable.Unfortunately it doesn’t solve the main trouble of keeping precisely the alignment of the holes in which the arbor rotates.

Usually those practices, as a result of a low-quality work, have caused further damage to plates and bridges and barrels which in the best cases do not rotate along the axis (in the worst wear upward or downward) and do not spread constantly the force with consequent effects of low amplitude and irregular gear.

Rolex for years supplied bushings for plates and bridges replaceable after a calibrated drilling and centred with the axis of the original holes, in order to guarantee a constant release af the force.

Here are depicted the mechanical principles that allows us to consider effective the method we adopt:Considering the worn out hole (in the enlarged picture 1), having no certain reference neither of the original axis of the hole now damaged by ovalization, nor of that on the bridge, ovalized too, we assembled a new bridge Rolex and did directly the true on the hole of the same piece.

Dismantling the barrel bridge without keeping the plate away from the mandrel [attezione: non hai mai detto di avercela montata sopra!] so that rotating it it is possible to notice immediately that the hole of the barrel is worn.In order to work out the problem of the correct true of the bridge and the plate, we have turned on the lathe, using a tool created on purpose (photo 5,6,7), the holes of the plate and the bridge, then rounding it off with a calibrated reamer to obtain the right gauge.

The gauge choosen allows to get a correct interference when mounting the bushing inserted by snapping into the hole.

To regain coaxiality we adopted a fixed position (that desumed with the new bridge), making sure of the coaxiality of the setting holes of the barrel arbor and of the right distance and, consequently, the correct gear with the centre wheel.

The same praxis has been retaken in order to regain the holes axis of the cente wheel, making reference to the ruby of the centre wheel set on the bridge.

Once turned and bored each hole, one can proceed burring the holes and assembling the bushings (photo 8).

Finally the watch has been washed in order to remove debris and dirt, then lubricated getting all damaged elements replaced, and tested with the chronocomparator for checking the precision of the work done.