This week was the 3rd of our intermediate exams. The Geartrain.
Up to this point we’re only concerned with everything from the barrel to the escape wheel (so not the pallets/balance assembly).
The exam itself involved working once again with the ETA 6498. We were each given a brand new movement that had faults introduced to it by the instructor (each watch had the same faults). First up was to assess the movement condition plus the condition of the supplied dial, hands and case.
Then the exam proper started. Careful disassembly of the movement revealed bent 3rd & 4th wheels, displaced jewels in the train bridge and a burred hole in the barrel cap. Crack on!
First up, straighten the wheels. This is done by holding the wheel in a Trupoise tool to assess its shape and pushing with peg wood to remove any bend. I have to say, the result was very good. I managed to get both wheels spot on. It’s worth noting that industry pressures would now probably require a bent wheel to simply be replaced on a modern watch but that may not be an option for a vintage piece with limited parts supply. Wheel trueing is a handy skill to have.
Next up, now I’m working with true wheels, it’s time to set the end shakes of the wheels. Horia tool this time to push the train bridge jewels into their correct position. For the purpose of the exam, we start at the escape wheel and adjust to give 0.02mm of endshake. Then it’s on to the 4th wheel, 3rd wheel and centre wheel to give 0.03, 0.04 and 0.05mm respectively. Again, I’m not at all bad at this bit so I was pleased with the result.
That’s the first key stage done, replace the damaged barrel cap and throw the lot in the cleaner. Time for a coffee.
Reassembly is then just a repeat of the process we’ve practiced a hundred times. Correct oiling of the keyless works and gear train, proper tightening of screws, etc
Movement reassembled, it needs the dial and hands on. In itself this isn’t difficult, it just requires care to avoid marking any components and to ensure the hands are precisely positioned. Black dials and shiny, polished hands show every mark and speck of dust!!
Casing up has always been a bit of an issue for me, not least because we don’t work in a true clean room. The number of times I’ve pushed a bezel and crystal on to spot a rogue speck of dust laughing at me from the dial! Things seemed to go ok this time (unless I missed something!) so then it was just a case of trimming the winding stem to length and fitting the crown.
Although it’s not controlled in this exam, good practice dictates regulating the watch so it’s on to the timing machine. Good numbers show I can’t have done a bad job!
On with the case back, pressure test, final polish and then wind and set to time before handing it in. Job done
Just the minor issue of getting it marked now…..