Geneva Stop Work in a Robert, Gerth & Cie from 1889

AlexanderToerzs · November 24, 2020

Dear all,

my mother gave me a Swiss pocket watch made by Robert, Gerth & Cie in 1889. It belonged to my great-great-grandfather. Wonderful watch - already with a Swiss lever escapement. Unfortunately someone in the past has taken out the the two wheels of the Geneva stop work in the mainspring barrel lid.

The distance between the centers of the wheels are 4 mm. I know that it is highly unlikely to find a scrapper movement with exactly the same dimensions for the maltese cross and the finger. However I found an bought a cardboard box on ebay UK with about 100 antique mainspring barrels. And indeed in one of the barrels I found a stop work with exactly 4 mm center to center.

A fellow named Jules Grossmann from LeLocle in Switzerland wrote a treatise on watchmaking in 1905 called Lessons in Horology. In there he describes the mathematical construction of the Geneva stop work. If you follow his instructions you can very easily make a drawing.

To cut a long story short. All the dimensions fit the wheels I have sourced almost perfectly (give or take a few 1/100th). Now to the problem: The hole in the maltese cross is too small for the seat on the barrel lid. However this can be easily fixed in the lathe. The square hole of the finger wheel (1.3 mm) is too large for the square on the barrel arbour (1.0 mm).

Since I am only an amateur I have absolutely no idea how to go from here. What would a watchmaker proper do?

Thanks and all the best from Hamburg,

Alex

2020_sept_r_g_cie_federhaus_federhausbruecke.bmp

Tudor · November 24, 2020

Perhaps make a square sleeve?

From appropriate material square stock, get the OD so it press fits into the existing square hole (or expand the wheel hole to fit).

Dress the top and bottom to match the old wheel profile (files) and then drill a hole on center that fits within the finished square. So, in your case I'd drill around .90mm and then shape it up with files.

JohnR725 · November 24, 2020

1 hour ago, AlexanderToerzs said:

What would a watchmaker proper do?

it really isn't so much what the watchmaker would do? Typically watchmakers don't want to deal with the stop work so they just take one of the pieces off. The watch will work just fine without the stop works.

It really becomes what does the customer want? If it is explained to the customer the cost X dollars to the service the watch but if you want to stop works restored we will have to manufacture new components and it's going to cost this much more my guess is most customers will say just service the watch so it will run. Most people don't want to pay for restoration work especially if it's not absolutely necessary.

as your the customer and you want it fixed no matter what the cost I would recommend getting a book

https://www.amazon.com/Watchmaking-George-Daniels/dp/0856677043

while the title indicates the book is for making a watch it's a lot more than that. Like looking at my copy there's a section on how to make square holes. Then there's several pages on how to make a stop works mechanism. then just a lot of good information on making parts which are going to need if you want to restore your stop works mechanism.

rodabod · November 24, 2020

I would check if it would work satisfactorily with the oversized square hole.

Or, do what many have done (and has been done here) and remove the stop work entirely.

AlexanderToerzs · November 25, 2020

Dear all,

Thank you for your help. I'll start out checking if it works with the oversized hole, if not I'll follow Tudor's advice. If I can't make a satisfactory job out of that I'll leave it as is and still have a runner but with out stop work.

All the best Alex

Pip · January 3, 2021

HNY to you @AlexanderToerzs!

Can I enquire how you are getting on with this? I am facing a similar situation in that I am restoring a pocket watch (Constantin Mathey from around the 1880's I think) that also has a missing geneva stop works. My mission is to find one or manufacture one (gulp!). To add to my fun I also need the barrel arbor so will have to make that too, again unless I can find one.

So in looking for one, is the important measurement the distance between the two centres? I will have to get my vernier out and look at that.

Thanks,

Phil

AlexanderToerzs · January 3, 2021

Hi Phil,

What a coincidence. I just made a cup of tea to take a break from fileing the square hole in the finger wheel. I followed Tudor's advice step by step. 1. Filling the original square with square material. 2. Centre it on the wax chuck and drilling a new centre hole on the lathe. 3. Punching a new square with a home made square punch in the staking tool. This serves just as guide. 3. Fileing the square to size.

This sounds easy in writing. However since I'm only a beginner / amateur I'm at my third attempt presently and learning. The good news: when you screw up you just punch out your attempt and start all over again.

To your question: yes, the wheel distance is most important since it determins the complete geometry of the gears. Find a pdf copy of Grossmann (Lessons in Horology, 1907) on the net. There he constructs the complete stop work starting from the distance of the centres. If you have CAD software you can make a drawing like I did above. Scaling it to centre distance of your mainspring barrel you can easily see all other dimensions like wheel diameters.

By the way: Wilhelm Schulz (Der Uhrmacher am Werktisch, 1941) writes, that it is a bad idea to run a watch with missing stop work without the finger wheel. The square that usually holds the finger wheel would most certainly drill itsself into the lower barrel arbour pivot hole and thus completely ruining it. If I can't manage to alter my stop work wheels I will make a simple washer to serve as dummy spacer.

Making a new set of wheels is completely out of my league. Although George Daniels (Watchmaking 1981) describes it completely as JohnR pointed out above.

All the best from Hamburg and good luck,

Alex

Pip · January 3, 2021

5 hours ago, AlexanderToerzs said:

Hi Phil,

What a coincidence. I just made a cup of tea to take a break from fileing the square hole in the finger wheel. I followed Tudor's advice step by step. 1. Filling the original square with square material. 2. Centre it on the wax chuck and drilling a new centre hole on the lathe. 3. Punching a new square with a home made square punch in the staking tool. This serves just as guide. 3. Fileing the square to size.

This sounds easy in writing. However since I'm only a beginner / amateur I'm at my third attempt presently and learning. The good news: when you screw up you just punch out your attempt and start all over again.

To your question: yes, the wheel distance is most important since it determins the complete geometry of the gears. Find a pdf copy of Grossmann (Lessons in Horology, 1907) on the net. There he constructs the complete stop work starting from the distance of the centres. If you have CAD software you can make a drawing like I did above. Scaling it to centre distance of your mainspring barrel you can easily see all other dimensions like wheel diameters.

By the way: Wilhelm Schulz (Der Uhrmacher am Werktisch, 1941) writes, that it is a bad idea to run a watch with missing stop work without the finger wheel. The square that usually holds the finger wheel would most certainly drill itsself into the lower barrel arbour pivot hole and thus completely ruining it. If I can't manage to alter my stop work wheels I will make a simple washer to serve as dummy spacer.

Making a new set of wheels is completely out of my league. Although George Daniels (Watchmaking 1981) describes it completely as JohnR pointed out above.

All the best from Hamburg and good luck,

Alex

Thanks Alex, that is good information and gives me a good place to start from. I will get started in the next few days and record my progress and update where I can. Although I'm on here a lot less now that unfortunately the updated site doesn't work with Tapatalk.

Edited January 3, 2021 by Pip

Poljot · January 3, 2021

I've never seen such design until I recently bought H. Moser pocket watch (1890s? or 1900?)

4mm distance also.

AlexanderToerzs · January 3, 2021

Congratulations Poljot to your Moser. They made lovely watches in Petersburg. Although I'm not an expert the Geneva stop work was quite popular before Guillaume invented Invar steel somewhen in the 1890s. An Invar mainspring has a much more uniform power distribution then the old blue steel springs. Hence there is no need to limit the mainspring action to the four middle turns as the stop work does.

Greetings from Hamburg,

Alex

p.s. reassembleing is a bit tricky. First hold the barrel arbour in a vice. Then allign the maltese cross in start position. Then give the barrel half a turn. That's the end of the power reserve you don't want. Then put in the finger wheel. You are now able to wind the watch 4 turns. Plus the one unused half turn from the beginning makes four and a half. Stoping about two turns to two and a half turns before the end of the spring. All depending of course on how many windings your spring is capable of.

Poljot · January 4, 2021

Thanks. Yes, it's a very nice looking and well made watch in deed. Too bad there is virtually zero info (catalogue, parts list, etc) available. I had to measure the barrel and arbour and calculate the mainspring dimensions to order replacement. I wish there was a parts list to verify my calculations against what was initially installed.

My second Moser watch was "modified" - there is no Geneva Stop Work anymore as the driving finger is broken (not sure if it was done by someone intentionally or not), and the Maltese cross is missing. But other than that - the watch is in excellent condition after I cleaned it. Now waiting for two mainsprings from UK to see how both will work. This could be another 6 weeks of waiting for the parcel these days.

AlexanderToerzs · January 10, 2021

Dear all,

here is a bit of an update. The sourced Maltese cross unfortunately does not work. It doesn't match the seat on the mainspring barrel cover. Fortunately everything else worked and I put in the finger wheel as as the appropriate spacer so I could wind the watch. The old barrel hook was torn out also. I replaced that with one that I filed from the thread of an old winding stem. Didn't take any pictures though. Here is the workflow to reduce the size of the finger wheel pretty much following Tudor's advice.

This is actually my third try. I fixed the new steel square with a spot of Loctite to give it a bit of extra grip. I lost my first "collar" somewhere in a wave of shellac when reheated.