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Endeavor

Pocket-watch hand repair ....

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Thought it may be worth to share;

I received a pretty beaten up, none-running 1890-1900 cylinder-escapement pocket-watch. It had all sorts of problems, a list too long to go into details.

245740099_Pocketwatch.thumb.jpg.38bdfa6a28cda4714eb3e53af5722607.jpg

Among those problems was a bend/broken minute hand. It inevitably broke off when trying to straighten it. The center-hole diameter of the minute-hand was 0.5mm and the length was 15mm. The hour-hand had a hole diameter of 2.0mm and the length was 10mm. Searching the internet to find an identical set proofed futile. The watch is a heirloom so originality was a priority.

The hands turned out the be made of bronze, a copper-tin alloy. Therefor it made sense to attempt soldering but the part that had to be soldered had a thickness of only 0.3mm.

Both parts had to be fixed in place with a sort of clamp capable to fixing both parts, being heat resistant and "none-sticking". A soldering iron, even with the smallest tip, would be far too big for the job and to avoid touching the parts, I choose to use a hot-air gun used in electronics for soldering SMD-components to a circuit-board. A few test were made which tin to use and at which temperatures. 300 degrees C with tin used in electronics seemed to work fast and made the tin to flow nicely. I used a soldering flux-paste.

The clamp consisted of two metal rails, slightly diverting from each other to give many clamping options, bolted on a plate of gypsum.

Clamp-1.jpg.78dce6094a997250fa42b231bb9a202c.jpg

Pulling over a #1000 grid sand paper, I made two 45 degrees chamfered edges  on either end of both parts;

Before.jpg.90d35b94f906621d29bc4c9387eae07e.jpg

The two parts were clamped in;

Clamp-2.jpg.1c3d76aed0ee5b53eb16bdb2595ce0c3.jpg

Applied some soldering flux, heated it all up to 300 deg.C and applied a tiny bit of tin. Once cooled down, I removed some excess tin with a small diamond file.

Here a picture of the back side of the minute-hand;

After-1.jpg.bbf84536fe9b0034f58d6fbe3cb38d13.jpg

And here the front; the tin didn't flow further away from the soldered joint or around the edges :)

After-2.jpg.c27f6f082324fd6efa03db14eef1d2eb.jpg

Most likely not the strongest repair in the world, but when not touched it should be strong enough to do the job. On the picture the hand color looks black, but that's due to the lighting. In reality the hand hasn't lost any of its shiny patina at the front ......

Anyway, I thought to share this repair as one of the many different possibilities ;)

 

 

 

Edited by Endeavor

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Nice. Let me share a little tip.

Solder paste.

Specifically "Mechanic" branded Chinese solder paste from ebay.

This stuff is used for SMD soldering, particularly small runs and SMD rework, and comes in leaded and unleaded. I would suggest the leaded version is better, as it is easier to use, but obviously, don't go eating it, and wash your hands after use.

https://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=mechanic+solder+paste&_sop=15

If you buy from ebay, make sure you are buying the solder paste, and not just the flux with the same brand name.

The paste has a built in flux, and consists of micro-beads of solder. The advantage of using this, over solder wire, is that you can be very precise, in the amount you use, and the location you put it in. It makes soldering tiny electronic components much simpler, and would probably have been ideal for this job.

 

Edited by AndyHull

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This repair operation (and the excellent result), set me wondering if the job could be done more simply.

I have a theory that maybe the engineers here may be able to expand on or alternatively say it's a no go. Supposing a plate of brass or copper 25mm x 15mm was attached to say a hardwood base with a +ve and -ve running to a throwaway battery would that plate heat up uniformly? If so you would simply place the broken parts in situ, face down, with a piece of solder covering the fracture. As the plate heats up and so the broken parts, the solder would melt into the required place. 

I know it requires thought, such as ensuring you don't solder the hand to the plate, but in essence could it work?

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2 hours ago, eezy said:

This repair operation (and the excellent result), set me wondering if the job could be done more simply.

I have a theory that maybe the engineers here may be able to expand on or alternatively say it's a no go. Supposing a plate of brass or copper 25mm x 15mm was attached to say a hardwood base with a +ve and -ve running to a throwaway battery would that plate heat up uniformly? If so you would simply place the broken parts in situ, face down, with a piece of solder covering the fracture. As the plate heats up and so the broken parts, the solder would melt into the required place. 

I know it requires thought, such as ensuring you don't solder the hand to the plate, but in essence could it work?

How do you control the current? How much current do you need to heat up a strip of 15mm very well conducting material to over 200 degrees C? Where do yo get all that current from; a welding machine?

How do you control the heat? How do you measure the heat?

All sounds not so eezy ........;)

Edited by Endeavor

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20 minutes ago, Endeavor said:

How do you control the current? How much current do you need to heat up a strip of 15mm very well conducting material to over 200 degrees C? Where do yo get all that current from; a welding machine?

How do you control the heat? How do you measure the heat?

All sounds not so eezy ........;)

I have not got the answers, just a theory, but I'm sure an engineer would have solutions. Just a question of whether it's viable.

I'm sure it wouldn't need much current. Cross a couple of wires on a torch battery and they are soon glowing. Just thinking outside the box. The idea came from something we used to do years ago, repairing cracks in truck fuel tanks. A jump lead from the truck batt +ve terminal which had a carbon rod scavenged from a torch battery on the other end to heat up the job and brazing rod.

Controllability is the issue

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There are any number of options if you want to spend the money.

Surface mount rework stations, soldering hot plates, hot air guns, gas soldering guns, infra-red soldering lamps, ultrasonic bonding, friction welding, spot welding....

All have the pluses and minuses. However I like to keep things simple, so a soldering iron or hot air gun, and fine gauge solder with flux, or solder paste with flux sound like the simplest solution, particularly for a one off like this.

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9 hours ago, yankeedog said:

What about the above mentioned paste and a non stick frying pan.Heat until solder flows and allow to cool.

This poses another question - how to sneak out with one of Mrs eezy's  best frying pans without her noticing. :)

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