11-06-2013, 09:12 PM
Well, I had some spare time today, so I retrieved one of the 'demics' from the box in the loft. This is a small, rather ugly mantel lock made by 'Prescott' which I was only keeping because I've never seen another of this make. I think it must be 'foreign' as I'd never heard of this manufacturer until I acquired the clock.
This clock has one of the expensive 'Junghans' German movements fitted, operating from a 'C' sized cell. This movement has a small mainspring which is wound up by flipping a dumbell shaped lever round a quarter-of-a-turn. The mainspring then operates a normal hairspring/balance wheel arrangement for 10-15 minutes. A moving contact on the dumbell shaped lever touches a fixed contact and the solenoid is activated which flips up the lever and the process repeats. A fixed resistor limits the current through the solenoid.
The clock had been dropped at some time with the battery fitted so there was plenty wrong with it. I removed the movement a while ago to assess it, but put it all into storage until a replacement movement could be found. I recently acquired another, non-working movement so it seemed like a good idea to make good one from the pair.
The damage to the dropped clock movement included a broken battery holder, a broken pivot on one end of the hairspring wheel and a coil with the armature floating instead of being hinged. The other movement had a cracked perspex cover and broken mainspring.
Firstly, I exchanged both movement cases (battery holders) and perspex covers. I then dismantled both movements and exchanged balance wheels and the corresponding jeweled bearings. The mechanical part of this movement is no bigger than a pocket watch so don't take it apart if you've no experience with small watch parts. This is by far the most difficult movement I have had to service as it is of 'layered' construction and everything falls out only after the final screw is removed. I exchanged solenoids and the only task remaining was to change over the mainsprings. This done, I then realised that a special tool is required to wind up the mainspring to remove all the slack. I think this needs to be wound up, such that there is just sufficient power to still (just) operate the balance wheel when the contacts close to flip up the lever. Too much tension, and the solenoid will not be able to flip up the lever against the power of the spring.
Unfortunately, I will have to make up a tool to fit the two slots in the adjusting mechanism on the back of the movement.
For now, I'll just post some pictures of what I've done so far with the rest to follow.
If anyone remembers the car Haynes manuals and those 'cuss marks' for difficulty level, this one I would rate at four out of five 'cuss marks' so it's not really a good movement for beginners to play with.
Pic 1 shows the battery holder, perspex cover and solenoid assembly.
Pic 2 shows the dismantled movement and broken mainspring.
Pic 3 shows the smaller parts of the balance wheel assembly.
Pic 4 shows the backplate into which the vsrious wheels fit.
I'll post further progress as I complete the clock.
This clock has one of the expensive 'Junghans' German movements fitted, operating from a 'C' sized cell. This movement has a small mainspring which is wound up by flipping a dumbell shaped lever round a quarter-of-a-turn. The mainspring then operates a normal hairspring/balance wheel arrangement for 10-15 minutes. A moving contact on the dumbell shaped lever touches a fixed contact and the solenoid is activated which flips up the lever and the process repeats. A fixed resistor limits the current through the solenoid.
The clock had been dropped at some time with the battery fitted so there was plenty wrong with it. I removed the movement a while ago to assess it, but put it all into storage until a replacement movement could be found. I recently acquired another, non-working movement so it seemed like a good idea to make good one from the pair.
The damage to the dropped clock movement included a broken battery holder, a broken pivot on one end of the hairspring wheel and a coil with the armature floating instead of being hinged. The other movement had a cracked perspex cover and broken mainspring.
Firstly, I exchanged both movement cases (battery holders) and perspex covers. I then dismantled both movements and exchanged balance wheels and the corresponding jeweled bearings. The mechanical part of this movement is no bigger than a pocket watch so don't take it apart if you've no experience with small watch parts. This is by far the most difficult movement I have had to service as it is of 'layered' construction and everything falls out only after the final screw is removed. I exchanged solenoids and the only task remaining was to change over the mainsprings. This done, I then realised that a special tool is required to wind up the mainspring to remove all the slack. I think this needs to be wound up, such that there is just sufficient power to still (just) operate the balance wheel when the contacts close to flip up the lever. Too much tension, and the solenoid will not be able to flip up the lever against the power of the spring.
Unfortunately, I will have to make up a tool to fit the two slots in the adjusting mechanism on the back of the movement.
For now, I'll just post some pictures of what I've done so far with the rest to follow.
If anyone remembers the car Haynes manuals and those 'cuss marks' for difficulty level, this one I would rate at four out of five 'cuss marks' so it's not really a good movement for beginners to play with.
Pic 1 shows the battery holder, perspex cover and solenoid assembly.
Pic 2 shows the dismantled movement and broken mainspring.
Pic 3 shows the smaller parts of the balance wheel assembly.
Pic 4 shows the backplate into which the vsrious wheels fit.
I'll post further progress as I complete the clock.
