1920s Silver Cased Swiss Watch help required

[steve1811uk]

Hi, I am looking for some help with a recent eBay acquisition. It's what I believe to be a 1920s watch. Brand is Medana.

Help needed:

Watch movement: I don't know the manufacturer or type. It is marked with a 'J' and has a cylindrical escapement. Diameter is 27.96mm which is 12 and 3/8 ligne.

Mainspring: Does it look set? Barrel inner diameter is 11.2mm. Spring height 1.7mm and thickeness 0.16mm. How do I find a suitable replacement, assuming it is set as I don't know the length without bending it into a straight length.

Curb pin: There's only one. Would this be positioned on the outside or inside of the outer turn of the hairspring? It needs replacing anyway as it is really rough and is also loose, possibly too short (looks like a bad repair). Going to try and make a replacement with brass wire. Hole that it goes into is 0.45mm. Would there be an easier way to solve this?

Hairspring: It's coned and the final turn needs a tweak but I should be able to solve that.

Glass: 27.85mm diameter domed with a knife edge profile. Dome height is 2.8mm external. Any idea which series of glass I should be looking at here?

Thanks in advance for any help received. Steve.

[mikepilk]

Don't know what the "J" signifies, Do you have a pic of the keyless work - it will help to ID it in BestFit.

The mainspring is set. As it will need replacing, there's no problems straightening it to measure.

The hairspring needs quite a bit of tweaking - good luck with that !

[jdm]

6 hours ago, mikepilk said:

The mainspring is set. As it will need replacing, there's no problems straightening it to measure.

That is never necessary. The formula for MS (or any other regular spiral) length is accurate https://www.engineeringtoolbox.com/spiral-length-d_2191.html

Applied to watchmaking

http://theindex.nawcc.org/CalcMainspringLength.php

So you can keep the original part in case no replacement is available after all, future reference, or just out of respect to for non-destructive science. 

 

Edited June 2, 2022 by jdm

[mikepilk]

14 minutes ago, jdm said:

So you can keep the original part in case no replacement is available after all, futur reference,or just out of respect to for non-destructive science. 

 

But I like breaking things ! 

[steve1811uk]

1 hour ago, mikepilk said:

Don't know what the "J" signifies, Do you have a pic of the keyless work - it will help to ID it in BestFit.

The mainspring is set. As it will need replacing, there's no problems straightening it to measure.

The hairspring needs quite a bit of tweaking - good luck with that !

Thanks, will try and get a pic of the keyless works. Hairspring isn't too bad. The really rough part is the bit further on from where it was pinned.

15 minutes ago, steve1811uk said:

Thanks, will try and get a pic of the keyless works. Hairspring isn't too bad. The really rough part is the bit further on from where it was pinned.

Barrel arbor was 3.7mm diameter. Picture of keyless attached. Hope this helps.

[Nucejoe]

 Hi steve,

 Before spending money on mainspring and other parts,  I would test if the oscilator runs without putting up a stiff fight. Build your oscilator, install the escapement and gear train without the barrel and  turn a gear of the train to see if oscilator runs  with normal amount of persuasion, in case it desn't cooperate, it might take a lot of work to get it to run. 

Good luck pal.

 

 

[steve1811uk]

3 hours ago, Nucejoe said:

 Hi steve,

 Before spending money on mainspring and other parts,  I would test if the oscilator runs without putting up a stiff fight. Build your oscilator, install the escapement and gear train without the barrel and  turn a gear of the train to see if oscilator runs  with normal amount of persuasion, in case it desn't cooperate, it might take a lot of work to get it to run. 

Good luck pal.

 

 

Pretty sure it will run. Before disassembly it would run for about 5 seconds and stop and upon inspection it had a lot of issues.

Hairspring badly coned and tilted, rubbing against balance arms 

Very dirty movement.

Second hand pinion badly bent (straightened now)

Dial loose (missing one dial screw).

Set mainspring?

Lots of dried oil.

I think I will try and get it running with the original spring first and take it from there. I've tackled the hairspring already, pretty flat now. Pinning it back is going to be a challenge as the stud is fixed. Probably need to fit the hairspring to the balance and then pin it. I will also need to make and fit a curb pin. I think as there is only one curb pin then it should bear against the outside of the outer coil, but I am no expert regarding that.

[JGrainger]

On 6/2/2022 at 8:32 PM, steve1811uk said:oil.I will also need to make and fit a curb pin. I think as there is only one curb pin then it should bear against the outside of the outer coil, but I am no expert regarding that.

There should be another pin - it looks like the remains of a brass pin may be in the regulator.. I’ve not fitted a new pin but would guess it pushes in, possibly with a slight taper, from the side which the remaining pin protrudes from, then is lightly riveted on the other side to hold in place.

[steve1811uk]

17 hours ago, JonathanGrainger said:

There should be another pin - it looks like the remains of a brass pin may be in the regulator.. I’ve not fitted a new pin but would guess it pushes in, possibly with a slight taper, from the side which the remaining pin protrudes from, then is lightly riveted on the other side to hold in place.

Hi, There's only one hole in the regulator arm so I am guessing it only ever had one pin. Up to now, my best guess is to fit a new brass pin in place of the old one which tbh wasn't fitted too well and was very fat. That one was extremely loose and just pulled out with tweezers. I will then widen out the outer turn so the new curb pin can fit inside of the final turn, just resting on the curb pin. Unless anyone has a better idea or more experience with low cost (1 jewel) cylindrical movement. Steve.

[JGrainger]

On 6/4/2022 at 3:54 PM, steve1811uk said:

Hi, There's only one hole in the regulator arm so I am guessing it only ever had one pin. Up to now, my best guess is to fit a new brass pin in place of the old one which tbh wasn't fitted too well and was very fat. That one was extremely loose and just pulled out with tweezers. I will then widen out the outer turn so the new curb pin can fit inside of the final turn, just resting on the curb pin. Unless anyone has a better idea or more experience with low cost (1 jewel) cylindrical movement. Steve.

It's just dawned on me, occasionally cylinder watches have a single wire which is bent back on it's self to give the effect of having 2 pins, forming a "U".

I just a had a flashback to disassembling one - having to unhook the regulator due to that arrangement.

[steve1811uk]

7 hours ago, JonathanGrainger said:

It's just dawned on me, occasionally cylinder watches have a single wire which is bent back on it's self to give the effect of having 2 pins, forming a "U".

I just a had a flashback to disassembling one - having to unhook the regulator due to that arrangement.

Thanks Jonathan, I think that's going to be an interesting task making that with my rudimentary tool set. Fingers crossed.