Opening clock mainspring barrel

[HectorLooi]

 

This is the going barrel from a Forestville mantel clock. It is a bit strange. It has a couple of cogs attached to the arbor that doesn't seem to do anything. 

I am trying to get the barrel cover open. I've tried turning the cover anticlockwise but it seems stuck. I've sprayed WD40 and tried it again but nothing budges.

Any suggestions? ?

[wls1971]

The cogs on top of the barrel are Known as stop work or Geneva stop works they allow the mainspring to be wound only so far they are designed to utilise the mainsprings optimum range of power delivery to the movement the spring can neither wind up or unwind fully thus eliminating the springs highest or lowest torque and evening out power delivery throughout the week.The stop works always rely on a certain amount of pre tension being put on the spring during fitting I can tell looking at yours there is non

Quite a few manufactures started using bayonet fitting great wheels on mainspring barrels instead of end caps do you have a photo of the other end of the barrel ? I would say it should twist apart try putting slight upward pressure on the barrel and slight downward pressure on the wheel as you twist.

Do you have a full picture of the movement it may help identify it because Forestville used a lot of European imported movements, from France, Germany and England.

[HectorLooi]

I'm familiar with Geneva stopworks. I've seen them on pocketwatch mainsprings. But this doesn't seem to be a Geneva stopwork because it doesn't have the missing cutout on one of the wheels. Besides, Geneva stopworks only allow about 300° rotation of the arbor. This would not be sufficient for a 8 day movement. 

I didn't take a photo of the movement as package was obviously dropped during transport and the foot of the casing was broken off. The movement was partially pulled off the mountings. I took the movement apart to check for damage but it appears to be ok as it was still ticking away.

The movement is German made and it says "Suevia Sidelfingen".

 

[oldhippy]

There are different types of Geneva stop works, this type is most common and the main thing it is for, it prevents the arbor from becoming detached from the spring. First thing is to remove the fitting from the arbor. Put the key winding arbor into your bench vice, if it is a smooth jaw its fine if not you need plates to cover the jaws because you do not want to mark the arbor, turn the barrel with you hand as if you are winding it and remove the pars that are over the arbor, when removed slowly let the spring unwind through your hand until all the power is off. Then do this.   The wheel green arrow is detachable by moving it away from the red arrow part.

[HectorLooi]

I managed to open the barrel. There wasn't any power in the spring so that confirms that it isn't a Geneva stopworks. Or it's one that isn't working properly.

 

[oldhippy]

That's because this part is damaged its bent or it might not have been fitted properly. It is a Geneva stopwork. 

[HectorLooi]

Ok. If that's the case, then with only 1 turn of the mainspring, the power reserve would probably last only 1 day.

Is there any harm in not having a properly working Geneva stopwork, other than erratic time keeping?

Should I try doing a tooth repair or cut a new wheel?

[oldhippy]

If you are able to cut a new wheel then do so. I always believe parts are there for a reason. Its also good practice to have the clock working in its original condition.  

[HectorLooi]

I've been studying the mechanism of this stopwork and found it devilishly ingenious. There is one extra long cog on the smaller wheel and the bigger wheel has one groove that is shorter. So the arbor can be wound almost 8 complete revolutions before the long cog would contact the short groove and come to a stop.

I think I'll try straightening the bent tooth and braze another piece of brass on top of it to reinforce and stop it from bending again.

Thanks again OldHippy. Your guidance is most helpful.

[oldhippy]

Congratulations you have worked out how a Geneva stopwork works. 

[HectorLooi]

I've straightened the crooked cog on the Geneva work. But as expected, it formed a slight crack, which I filled up with solder. I'll reinforce the cracked tooth with a piece of brass later.

[oldhippy]

That will do fine. Its always better if you can save the original.  

[nickelsilver]

When you put it all back together, wind some power on the spring before putting the center stop piece in, then put it in the "stop" position (stop for unwinding). 1/2 turn is a general rule; what you really want to do is wind the spring fully without the stopworks to see how many turns of wind the spring develops. Typically this is about 6 or 7, but some clocks can be more or less. Very old clocks I see here often develop about 5 turns, and have stopworks that permit about 3-1/2, some modern ones from this area (Le Castel for example) do about 15 full turns of wind. You want to set up the stopworks so that you are using the middle part of the spring, so if you get 8 turns with that stopwork, and the spring develops 9 turns without, 1/2 turn of pre-wind is good, actually slightly less than more if you see things don't want to line up at 1/2.

 

Stopworks help use the most even part of the mainspring's power, but also keep a lot of stress off of the hook and end of spring where it attaches to the barrel.

[oldhippy]

Here you go all the info you need about the Geneva Stopwork.

 

[HectorLooi]

I spent the afternoon reinforcing the  cracked tooth. I roughed out a piece of brass, then soldered it with solder paste. The hand filed and polished it.

[oldhippy]

Its probably stronger now then it has ever been. The brass and steel in these types of English & German clocks are not that hard that is why you find normally loads of re-bushing and pivots worn. There are a few exceptions in the better types of movements. 

[watchweasol]

A tidy job Hector, as Old Hippy says probably stronger than before. 

[rodabod]

I always take it easy when approaching the end of winding to avoid unnecessary strain. That includes fusee stop arms as you can literally rip them off the main plate if you wind too hard. 
 

The same applies to releasing the pressure of the winding key, each time you wind. It’s not necessary to suddenly release the key and hit the train and click spring with all of that force at once. 

[HectorLooi]

After removing the cover, the teeth of the great wheel are no longer on the barrel. The smooth barrel tends to slip when I'm trying to wind the spring.

I tried tightening a hose clamp to the barrel. This gives me a better grip, but even through thick gloves, it really hurts the hand. Is there a better way to hold the barrel?

[HectorLooi]

And another thing I noticed, there are a lot of small cracks emanating from the stress points on the lip of the barrel. Is this common? And is there any danger of the entire barrel falling apart?

[oldhippy]

First of all what type of mainspring winder do you have?

Those stress cracks need to be soldered. 

[HectorLooi]

I'm using a Webster winder.

[nickelsilver]

I don't think solder will help with those cracks. Making a close fitting brass hoop that fits the barrel around them and gets soldered on will, as long as it clears the pinion that mates to the gear that bayonets on the barrel. It can be quite thin and work.

 

[oldhippy]

Wear a thick pair of gloves when removing springs. This is the type of winder I have. 

 

If you put a hoop around you will only be able to fit it so far, the cracks show where the wheel fits. That is why I suggested solder. In an ideal world a new barrel should be made.   

[HectorLooi]

I have one of those English pattern winders too. But it looks rather fragile next to a Webster. 

I think I'll wrap a few rounds of copper wire around the barrel then flow solder under it.